Abstract:
An alloy steel having the capability of retaining high hardness at elevated temperature for a prolonged time is suitable for use as a high speed tool steel. The alloy steel comprises in % by weight: 0.7-1.4 C; less than 1 Mn; less than 0.04 P; up to 0.7 Si; 3-6 Cr; 4-12 Mo; less than 0.5 Co; 0.5-2.25 V; 1-7 W; up to 1.25 Al; at least one of 0.04-2.5 Nb; 0.025-2.5 Zr; 0.08-4.75 Ta and 0.005-0.7 Ti; balance substantially Fe. The alloy may also have an S content of 0.036-0.300; Mn of 0.30-1.35 and may optionally be treated when in a liquid state with up to 0.05 of Mg or Ca.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of earlier filed U.S. Provisional Patent Application Ser. No. 60/059,143, filed Sep. 17, 1997, entitled “Cobalt Free High Speed Steels”. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the art of metallurgy and, more particularly, to high speed tool steels. 
     High speed steels are composite materials that contain a variety of alloy carbide particles in an iron base plus, depending on the heat treatment, various atomic arrangements of iron carbon in the form of austenitic, ferritic, bainltic and martensitic structures. Various carbide forming elements such as, for example, chromium, molybdenum, tungsten and vanadium, are constituents of high speeds. Infrequently, niobium and titanium are used as additional carbide forming elements. These above enumerated elements are found combined as carbides as the result of ledeburitic and eutectoid reactions as the molten alloy solidifies and transformation as the temperature drops. Silicon is normally present and higher levels may be added to the alloy to increase attainable hardness. 
     Because of the high temperatures produced during machining more difficult materials, the retention of the critical cutting surfaces is related to the hardness of the tool. The ability of the tool to retain its hardness is assessed by the hardness of the tool at elevated temperatures. Retention of the hardness can be measured by testing the steel at a given temperature or heating the steel for a prolonged time at a given temperature then measuring the steel&#39;s retention of hardness at room temperature when the tool cools down. The present invention improves the hot hardness properties of high speed steel without the use of cobalt or very high tungsten and/or molybdenum combinations. Cobalt is not only expensive but its supply is irregular and the use of very high tungsten and molybdenum combinations produce steels that are difficult to hot work without utilizing costly powder metallurgy methods. 
     The present invention provides a family of high speed steel compositions that have the capability of achieving high hardness upon proper hardening and retaining a significant portion of that property at temperatures commonly encountered by cutting tools such as drills, taps and reamers. These steels are also useful in operations that require high hardness at more moderate to room temperature operations such as punches and thread forming tools. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an alloy steel having the capability of retaining high hardness at elevated temperature for a prolonged time. The alloy steel is suitable for use as a high speed tool steel and broadly comprises in % by weight: 0.7-1.4 C; less than 1 Mn; less than 0.04 P; up to 0.7 Si; 3-6 Cr; 4-12 Mo; less than 0.5 Co; 0.5-2.25 V; 1-7 W; up to 1.25 Al; at least one of 0.04-2.5 Nb; 0.25-2.5 Zr; 0.08-4.75 Ta; and at least one of 0.005-0.7 Ti; 0.025-1.4 Zr; balance Fe. The alloy may also have an S content of 0.036-0.300; and Mn of 0.30-1.35 and may optionally be treated when in a liquid state with up to 0.05 of Mg or Ca. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a high speed steel similar to the popular types such as AISI M-2 with the hot hardness properties similar to AISI M-42. Since the hardness and other physical properties of high speed steels are related to their heat treatment, carbide size, distribution and composition, the theoretical phases of high speed steels were examined through the calculations of Thermo Calc® (a registered tradermark of Thermo-Calc AB) a software program that utilizes known thermodynamic values of the constituent elements to predict phase formation. Initially, a fractionated factorial experiment was designed based on the concept that small, primary, MC carbides would resist softening. As AISI M-2 high speed was chosen as a base, the carbon, tungsten, vanadium and molybdenum levels were varied with the addition of varying amounts of niobium and aluminum The niobium was added to combine with the carbon as a source of carbides stable at high temperatures. Whilst the aluminum was added as a means of improving the hot hardness of the alloy since it retards softening, it was also added since it enhances the stability of the ferrite and modifies the morphology of niobium carbide particles. The modification of the niobium carbide morphology is affected by aluminum because it reduces the activity of carbon in the melt and in the austenite. If the niobium combines to form carbides in the form of M 6 C, these will be large blocky particles. Large blocky particles are less desirable than smaller fine particles which are type formed when the niobium forms M 2 C type carbides. The use of aluminum to improve hot hardness properties of high speed steels and M-2 grade in particular has been used in the past, particularly at concentrations around one weight percentage. Aluminum, however, reduces the solidus temperature substantially and thus causes difficulties in heat treating because it limits the ability to use very high austenitizing temperatures for maximum hardening response. Aluminum also increases the carbide content that precipitates during secondary hardening brought out by tempering at intermediate temperatures. Heat treated hardness is also improved by the addition of aluminum since it decreases the amount of retained austenite. Aluminum is critical in the present invention and preferably added up to 1.25 wt. %. Smaller amounts of aluminum, in the range of 0.025 to 0.25, are effective in obtaining the desired properties. 
     Although silicon also increases temper hardness, it also drastically lowers hardening temperatures as the liquidus and solidus temperatures. Silicon can replace tungsten, molybdenum and vanadium in the matrix and raise the solubility of carbon in the matrix. These changes cause a higher quenched hardness, but this effect decreases in the presence of nitrogen. Nitrogen is typically present in high speed tool steels in concentrations of 0.01 to 0.08%. Nitrogen raises the tempered hardness and it causes the primary, MC carbides, to be globular in shape. 
     Niobium readily forms carbide particles. These particles form as the metal solidifies in the form, MC, that is noted as good for wear resistance. Niobium decreases the solubility of carbon in austenite and the lower carbon content of the austenite matrix results in higher martensite transformation start temperature. These higher martensite start temperatures favor less retained austenite. The addition of niobium and consequent formation of niobium carbide particles result in higher hardening temperatures. The formation of niobium carbide particles is favored, as measured by the free energy at elevated temperatures, over the formation of other common carbide compounds such as vanadium, molybdenum, tungsten and chromium carbides. 
     An experiment was designed to examine the effects of variations of six elements, carbon, tungsten, niobium, vanadium, aluminum and molybdenum on a high speed steel of the composition of AISI M-2 steel. Chromium was set for an aim of 3.75 wt. %, silicon at 0.35%, manganese at 0.32%, phosphorus at 0.015% maximum, sulphur at 0.005%, nickel at 0.16% with no additions of cobalt or titanium. A series of trail ingots based on a fractionated factorial was melted in a 100 pound vacuum induction furnace then cast into round molds which were rolled to bar for evaluation. An additional alloy in the middle of the factorial design composition range was also melted, alloy number 17. The initial heats to be melted had the following aim compositions. 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Factorial Experimental Design: Chemical Composition 
               
             
          
           
               
                   
                   
                   
                   
                   
                 Al 
                   
               
               
                 Heat 
                 C 
                 W 
                 Nb 
                 V 
                 soluble 
                 Mo 
               
               
                   
               
               
                 1 
                 .85 
                 1.60 
                 .10 
                 .90 
                 none 
                 5.00 
               
               
                 2 
                 1.18 
                 1.60 
                 .10 
                 .90 
                 1.00 
                 5.00 
               
               
                 3 
                 .85 
                 6.00 
                 .10 
                 .90 
                 1.00 
                 10.50 
               
               
                 4 
                 1.18 
                 6.00 
                 .10 
                 .90 
                 none 
                 5.00 
               
               
                 5 
                 .85 
                 1.60 
                 1.60 
                 .90 
                 1.00 
                 10.50 
               
               
                 6 
                 1.18 
                 1.60 
                 1.60 
                 .90 
                 none 
                 10.50 
               
               
                 7 
                 .85 
                 6.00 
                 1.60 
                 .90 
                 none 
                 5.00 
               
               
                 8 
                 1.18 
                 6.00 
                 1.60 
                 .90 
                 1.00 
                 5.00 
               
               
                 9 
                 .85 
                 1.60 
                 .10 
                 1.80 
                 none 
                 10.50 
               
               
                 10 
                 1.18 
                 1.60 
                 .10 
                 1.80 
                 1.00 
                 10.50 
               
               
                 11 
                 .85 
                 6.00 
                 .10 
                 1.80 
                 1.00 
                 5.00 
               
               
                 12 
                 1.18 
                 6.00 
                 .10 
                 1.80 
                 none 
                 5.00 
               
               
                 13 
                 .85 
                 1.60 
                 1.60 
                 1.80 
                 1.00 
                 5.00 
               
               
                 14 
                 1.18 
                 1.60 
                 1.60 
                 1.80 
                 none 
                 5.00 
               
               
                 15 
                 .85 
                 6.00 
                 1.60 
                 1.80 
                 none 
                 10.50 
               
               
                 16 
                 1.18 
                 6.00 
                 1.60 
                 1.80 
                 1.00 
                 10.50 
               
               
                 17 
                 1.02 
                 3.80 
                 .85 
                 1.35 
                  .50 
                 7.75 
               
               
                   
               
             
          
         
       
     
     The proposed alloys were examined for predicted equilibrium phases and transformations from the liquid state via Thermo Calc®. 
     Theoretic Predio Phases and Critical Temperatures Thermo Calc® of Initial Factorial Experiment 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Theoretical Prediction Phases and Critical Temperatures from Thermo Calc ® 
               
               
                 of Initial Factorial Experiment 
               
             
          
           
               
                   
                   
                   
                 Anstenite 
                   
                   
                   
                   
                   
               
               
                   
                 Liquidus 
                 Solidus 
                 to Ferrite 
                 % 
               
               
                 Alloy 
                 ° F. 
                 ° F. 
                 ° F. 
                 Ferrite 
                 M 23 C 6   
                 M 6 C 
                 M 2 C 
                 MC 
               
               
                   
               
               
                  1 
                 2588 
                 2243 
                 1514- 
                 84 
                 10.1% 
                 4.8% 
                 — 
                 1.0% 
               
               
                   
                   
                   
                 1473 
               
               
                  2 
                 2582 
                 2142 
                 1764- 
                 77.4 
                 17.5 
                 3.3 
                 — 
                 1.9 
               
               
                   
                   
                   
                 1554 
               
               
                  3 
                 2594 
                 2269 
                 2060- 
                 72.9 
                 5.8 
                 20.85 
                 — 
                 .35 
               
               
                   
                   
                   
                 1688 
               
               
                  4 
                 2531 
                 2206 
                 1497- 
                 74 
                 13.6 
                 9.2 
                   1.6% 
                 1.7 
               
               
                   
                   
                   
                 1444 
               
               
                  5 
                 2586 
                 2305 
                 2305- 
                 78.2 
                 3.6 
                 15.9 
                 — 
                 2.4 
               
               
                   
                   
                   
                 1643 
               
               
                  6 
                 2518 
                 2285 
                 1534- 
                 74 
                 9.3 
                 13.6 
                 — 
                 3.0 
               
               
                   
                   
                   
                 1487 
               
               
                  7 
                 2565 
                 2359 
                 1540- 
                 81.6 
                 3.1 
                 12.2 
                 — 
                 3.1 
               
               
                   
                   
                   
                 incomplete 
               
               
                  8 
                 2603 
                 2243 
                 1883- 
                 77.1 
                 8.6 
                 10.5 
                 — 
                 3.8 
               
               
                   
                   
                   
                 1472 
               
               
                  9 
                 inc. 
                 2338 
                 1631- 
                 78.6 
                 3.9 
                 15.6 
                 — 
                 2.0 
               
               
                   
                   
                   
                 1523 
               
               
                 10 
                 2552 
                 2269 
                 2240- 
                 76.3 
                 6.7 
                 13.4 
                 — 
                 3.6 
               
               
                   
                   
                   
                 1634 
               
               
                 11 
                 inc. 
                 2271 
                 2265- 
                 79.7 
                 5.2 
                 12.8 
                 — 
                 2.2 
               
               
                   
                   
                   
                 1660 
               
               
                 12 
                 2522 
                 2109 
                 1472- 
                 68.0 
                 17.4 
                 12.4 
                 — 
                 — 
               
               
                   
                   
                   
                 1373 
               
               
                 13 
                 2612 
                 2140 
                 no 
                 85.4 
                 3.4 
                 7.2 
                 — 
                 4.1 
               
               
                   
                   
                   
                 anstenite 
                 delta 
               
               
                 14 
                 2526 
                 2274 
                 1552- 
                 81.5 
                 8.7 
                 4.8 
                 — 
                 4.8? 
               
               
                   
                   
                   
                 1489 
               
               
                 15 
                 2543 
                 2348 
                 2337- 
                 73.8 
                 0 
                 22.1 
                 — 
                 4.0 
               
               
                   
                   
                   
                 1763 
               
               
                 16 
                 2533 
                 2241 
                 no 
                 73.1 
                 0 
                 14.2 
                 12.5  
                 0 
               
               
                   
                   
                   
                 anstenite 
               
               
                 17 
                 2562 
                 2233 
                 1746- 
                 81.2 
                 .6 
                 5.5 
                 12.7  
                 0 
               
               
                   
                   
                   
                 1575 
               
               
                 M42* 
                 2512 
                 2212 
                 1572- 
                 77.4 
                 9.4 
                 11.2 
                   0 
                 2.4 
               
               
                   
                   
                   
                 1532 
               
               
                 M42 
                 2508 
                 2212 
                 1592- 
                 80.6 
                 3.7 
                 5.8 
                 8.3 
                 1.5 
               
               
                   
                   
                   
                 1555 
               
               
                 M-2 
                 inc. 
                 2284 
                 1526- 
                 79.2 
                 6.7 
                 12.1 
                 — 
                 1.9 
               
               
                   
                   
                   
                 1472 
               
               
                 M2 + 
                   
                 2063 
                 no 
                 77.6 
                 8.9 
                 10.6 
                 — 
                 3.0 
               
               
                 1% Al 
                   
                   
                 gamma 
                 delta 
               
               
                   
               
               
                 *no nitrogen  
               
             
          
         
       
     
     The ingots were rolled to approximately 1.25×4″ flats. Samples were cut from wrought bars from each trial heat. These pieces were then austenitized at a range of temperatures from 2125-2175° F. Rockwell “C” hardness, “HRC”, was measured after quenching from the austenitizing temperature then again following each two hour tempered cycle. The pieces were austenitized at three or more different temperatures set in the range 2125-2175° F. then tempered over a range of temperatures from 932-1067° F. 
     Chemical Composition and Heat Treat Response of Initial Melts 
     
       
         
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 Maximum 
                 Austenitize 
                 Temper 
               
               
                   
                   
                   
                   
                   
                 Al 
                   
                 Hardness 
                 Temperature 
                 Temperature 
               
               
                 Melt 
                 C 
                 W 
                 V 
                 Mo 
                 soluble 
                 Nb 
                 HRC 
                 ° F. 
                 ° F. 
               
               
                   
               
             
             
               
                 645 
                 .82 
                 1.58 
                 .87 
                 5.27 
                 .024 
                 .13 
                 66.8 
                 2120 
                  999 
               
               
                 647 
               
               
                 653 
                 1.03 
                 1.55 
                 .87 
                 5.30 
                 1.07 
                 .10 
                 63.1 
                 2120 
                 1067 
               
               
                 656 
                 .92 
                 1.71 
                 .93 
                 10.70 
                 1.18 
                 1.69 
                 58.2 
                 2145 
                  932 
               
               
                 677 
                 1.19 
                 1.71 
                 .89 
                 10.71 
                 .031 
                 1.72 
                 66.0 
                 2145 
                 1067 
               
               
                 657 
                 1.20 
                 1.81 
                 .90 
                 10.97 
                 .086 
                 1.66 
                 65.9 
                 2120 
                  999 
               
               
                 673 
                 .87 
                 6.08 
                 .85 
                 5.28 
                 .034 
                 1.61 
                 65.0 
                 2145 
                  999 
               
               
                 646 
                 .75 
                 5.60 
                 .78 
                 4.85 
                 .193 
                 1.59 
                 64.1 
                 2145 
                  999 
               
               
                 648 
               
               
                 674 
                 1.18 
                 6.10 
                 .83 
                 5.27 
                 .033 
                 .10 
                 65.9 
                 2120 
                 1067 
               
               
                 658 
                 1.22 
                 6.58 
                 .88 
                 5.30 
                 .105 
                 1.55 
                 65.9 
                 2145 
                 1067 
               
               
                 662 
                 .86 
                 1.69 
                 1.71 
                 5.10 
                 .82 
                 1.55 
                 63.0 
                 2145 
                  932 
               
               
                 678 
                 1.17 
                 1.68 
                 1.68 
                 5.27 
                 .026 
                 1.69 
                 64.4 
                 2145 
                  999 
               
               
                 663 
                 1.19 
                 1.72 
                 1.55 
                 5.18 
                 .82 
                 1.51 
                 66.3 
                 2120 
                  999 
               
               
                 651 
                 .77 
                 1.88 
                 1.88 
                 11.69 
                 .029 
                 .16 
                 63.5 
                 2145 
                  999 
               
               
                 660A 
                 1.14 
                 1.72 
                 1.60 
                 10.95 
                 .90 
                 .096 
                 66.6 
                 2120 
                  999 
               
               
                 659 
                   
                   
                   
                   
                   
                   
                 66.5 
                 2145 
                  999 
               
               
                 661 
                 .86 
                 6.14 
                 1.73 
                 5.34 
                 .85 
                 .10 
                 66.6 
                 2145 
                  999 
               
               
                 660B 
                   
                   
                   
                   
                   
                   
                 65.2 
                 2145 
                  932 
               
               
                 675 
                 1.23 
                 6.25 
                 1.69 
                 5.30 
                 .035 
                 .10 
                 67.4 
                 2145 
                 1067 
               
               
                 650 
                 1.12 
                 6.00 
                 1.50 
                 5.20 
                 .112 
                 .11 
                 66.9 
                 2145 
                 1067 
               
               
                 654 
                 .95 
                 6.31 
                 .82 
                 11.02 
                 1.24 
                 .11 
                 65.0 
                 2145 
                  932 
               
               
                 676 
                 .87 
                 6.11 
                 1.72 
                 10.72 
                 .060 
                 1.60 
                 56.3 
                 2145 
                  999 
               
               
                 652 
                 .75 
                 8.28 
                 1.63 
                 10.98 
                 .174 
                 2.01 
                 24.2 
                 2145 
                 1067 
               
               
                 665 
                 1.03 
                 3.86 
                 1.22 
                 8.03 
                 .41 
                 .90 
                 66.5 
                 2145 
                  999 
               
               
                   
               
             
          
         
       
     
     Heat Treat Response with 2175° F. Austenitize Temperature and 932° F. Temper 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Hardness - HRC 
                   
                 Hardness - HRC 
               
               
                   
                 Melt 
                 after 3 Tempers 
                 Melt 
                 after 3 Tempers 
               
               
                   
                   
               
             
             
               
                   
                 645 
                 64.9 
                 657 
                 65.9 
               
               
                   
                 650 
                 66.1 
                 658 
                 65.5 
               
               
                   
                 654 
                 65.1 
                 663 
                 66.4 
               
               
                   
                 660 
                 66.6 
                 665 
                 66.1 
               
               
                   
                 661 
                 64.4 
                 673 
                 64.3 
               
               
                   
                 674 
                 60.5 
                 677 
                 65.1 
               
               
                   
                 675 
                 66.0 
               
               
                   
                   
               
             
          
         
       
     
     A comparison of the heat treat response with the theoretical phase composition predicted by Thermo Calc® did not show a positive correlation of hardness with M 2 C particles. Wrought samples from the most promising heats plus a sample of AISI M-42 high speed were quenched and tempered, then aged at elevated temperatures, then air cooled to room temperature to determine their retained hardness. 
     Percentage Retained Hardness—HRC of Selected Melts 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 32 hours 
                 32 hours 
                 32 + 176 
                 32 hours 
                 32 + 163 
               
               
                   
                 at 
                 at 
                 hours at 
                 at 
                 hours at 
               
               
                 Melt 
                 700 °F. 
                 1000 °F. 
                 1000 °F. 
                 1100 °F. 
                 1100 °F. 
               
               
                   
               
             
             
               
                 650 
                 89 
                 101 
                 99 
                 81 
                 75 
               
               
                 660B 
                 89 
                 98 
                 94 
                 83 
                 66 
               
               
                 661 
                 92 
                 97 
                 95 
                 86 
                 72 
               
               
                 675 
                 86 
                 98 
                 94 
                 84 
                 66 
               
               
                 663 
                 90 
                 100 
                 92 
                 76 
                 69 
               
               
                 665 
                 90 
                 97 
                 93 
                 78 
                 71 
               
               
                 666 M-42 
                 90 
                 97 
                 90 
                 78 
                 67 
               
               
                   
               
             
          
         
       
     
     Examination of samples from cast ingots on a scanning electron microscope revealed the presence of dark spots in the core of some of the niobium carbide particles. EDS examination of these niobium carbides showed the dark spots were titanium. Titanium had not been included in the original factorial in order to keep the number of variables limited. It is well known that titanium acts as a nucleation agent for niobium carbide particles. The formation of titanium carbide is more favored as measured by free energy than niobium carbide at elevated temperatures. Additionally, titanium carbide has the same crystal structure as niobium carbide which allows the particles to be coherent to each other. 
     The original ingots were examined for titanium content which was picked up apparently as a contaminant from some of the raw materials used to make up the trial ingots. 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Titanium Levels in Initial Melts 
               
             
          
           
               
                   
                 Heat 
                 Titanium 
                 Heat 
                 Titanium 
                 Heat 
                 Titanium 
               
               
                   
                   
               
               
                   
                 645 
                 .010% 
                 654B 
                 .027% 
                 663 
                 .014% 
               
               
                   
                 646 
                 .023 
                 655A 
                 .023 
                 664 
                 .018 
               
               
                   
                 647 
                 .010 
                 656 
                 .022 
                 665 
                 .012 
               
               
                   
                 648 
                 .023 
                 657 
                 .004 
                 666 
                 .008 
               
               
                   
                 649 
                 .020 
                 658 
                 .005 
                 673 
                 .011 
               
               
                   
                 650 
                 .020 
                 659 
                 .002 
                 674 
                 .007 
               
               
                   
                 651 
                 .020 
                 660 
                 .003 
                 675 
                 .007 
               
               
                   
                 652 
                 .021 
                 661 
                 .012 
                 676 
                 .013 
               
               
                   
                 653A 
                 .011 
                 662 
                 .014 
                 677 
                 .015 
               
               
                   
                   
                   
                   
                   
                 678 
                 .012 
               
               
                   
                   
               
             
          
         
       
     
     A second set of melts were made involving a factorial around the heats with good hardenability and high retained hardness, heats 650, 660, 661 and 675, using different levels of aluminum and titanium. These heats are basically AISI M-2 with a low niobium content modified with varying amounts of aluminum and titanium. Two additional high niobium heats were melted because of the promising results on the initial melts of 663 and 665. Heat 663 is basically AISI M-1 with 1.5% niobium plus aluminum. 
     The 5″ round ingots were pressed to 2.25″ squares which were then rolled to 0.520″ round bars. Samples were tested for composition and heat treat response. 
     Chemical Composition of Second Factorial Experimental Design Melts 
     
       
         
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                   
                   
                 Al 
                   
                   
                   
                   
               
               
                 Melt 
                 C 
                 W 
                 V 
                 Mo 
                 soluble 
                 Nb 
                 Ti 
                 Si 
                 Cr 
               
               
                   
               
             
             
               
                 505 
                 1.11 
                 6.37 
                 1.74 
                 5.12 
                 .023 
                 .11 
                 .005 
                 .39 
                 3.83 
               
               
                 511 
                 1.11 
                 6.25 
                 1.66 
                 5.03 
                 .033 
                 .10 
                 .030 
                 .40 
                 3.79 
               
               
                 513 
                 1.12 
                 6.20 
                 1.73 
                 5.08 
                 .094 
                 .10 
                 .005 
                 .42 
                 3.95 
               
               
                 509 
                 1.16 
                 6.53 
                 1.75 
                 5.27 
                 .093 
                 .11 
                 .025 
                 .40 
                 3.78 
               
               
                 507 
                 1.12 
                 6.24 
                 1.74 
                 5.08 
                 .102 
                 .11 
                 .040 
                 .40 
                 3.79 
               
               
                 514 
                 1.07 
                 6.22 
                 1.59 
                 5.06 
                 .730 
                  .059 
                 .026 
                 .39 
                 3.77 
               
               
                 1043  
                 1.00 
                 5.53 
                  .82 
                 7.00 
                 .139 
                 .31 
                 .033 
                 .40 
                 3.86 
               
               
                 1044  
                 1.03 
                 2.05 
                  .92 
                 9.05 
                 .149 
                 .99 
                 .029 
                 .37 
                 3.83 
               
               
                   
               
             
          
         
       
     
     Samples from each melt were hardened in salt then tempered in air with two hours for each cycle. 
     Heat Treat Response of Second Factorial Melts Hardness HRC 
     
       
         
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Austenitizing 
                   
                 977F 
                 977F 
                 1043F 
                 1043F 
                 1112F 
                 1112F 
               
               
                   
                 Temperature 
                 As 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
               
               
                 Heat 
                 ° F. 
                 Quenched 
                 2 + 2 
                 2 + 2 + 2 
                 2 + 2 
                 2 + 2 + 2 
                 2 + 2 
                 2 + 2 + 2 
               
               
                   
               
             
             
               
                 505 
                 2140 
                 63.77 
                 66.9 
                 66.5 
                 65.2 
                 65.8 
                 64.8 
                 63.9 
               
               
                   
                 2170 
                 62.78 
                 67.3 
                 67.2 
                 64.2 
                 66.5 
                 65.0 
                 64.6 
               
               
                   
                 2200 
                 62.98 
                 66.8 
                 67.3 
                 65.0 
                 67.0 
                 65.2 
                 65.1 
               
               
                 507 
                 2140 
                 63.9  
                 66.2 
                 66.6 
                 65.2 
                 66.7 
                 64.2 
                 63.4 
               
               
                   
                 2170 
                 62.9  
                 67.1 
                 67.2 
                 66.2 
                 66.8 
                 65.4 
                 64.6 
               
               
                   
                 2200 
                 63.00 
                 67.3 
                 67.7 
                 65.0 
                 66.9 
                 65.7 
                 65.3 
               
               
                 509 
                 2140 
                 62.4  
                 67.0 
                 67.0 
                 64.3 
                 66.6 
                 65.5 
                 64.5 
               
               
                   
                 2170 
                 61.6  
                 67.3 
                 67.5 
                 64.0 
                 66.4 
                 65.7 
                 65.3 
               
               
                   
                 2200 
                 61.9  
                 67.6 
                 67.7 
                 64.3 
                 — 
                 65.8 
                 65.7 
               
               
                 511 
                 2140 
                 63.3  
                 66.5 
                 66.4 
                 64.0 
                 66.2 
                 63.8 
                 63.3 
               
               
                   
                 2170 
                 63.3  
                 66.4 
                 66.3 
                 65.0 
                 66.6 
                 65.1 
                 64.3 
               
               
                   
                 2200 
                 62.37 
                 67.3 
                 67.7 
                 65.0 
                 66.1 
                 65.5 
                 64.8 
               
               
                 513 
                 2140 
                 63.7  
                 62.8 
                 64.7 
                 66.5 
                 65.5 
                 65.0 
                 63.7 
               
               
                   
                 2170 
                 63.6  
                 67.1 
                 67.2 
                 64.8 
                 66.7 
                 65.4 
                 64.8 
               
               
                   
                 2200 
                 62.38 
                 67.3 
                 67.5 
                 67.2 
                 67.2 
                 64.7 
                 64.6 
               
               
                 514 
                 2140 
                 63.6  
                 66.4 
                 66.9 
                 65.1 
                 66.5 
                 64.0 
                 63.0 
               
               
                   
                 2170 
                 62.9  
                 67.1 
                 67.2 
                 65.2 
                 66.6 
                 65.4 
                 64.4 
               
               
                   
                 2200 
                 62.96 
                 67.2 
                 67.5 
                 65.5 
                 66.8 
                 65.8 
                 63.0 
               
               
                 1043  
                 2100 
                 62.46 
                 66.15 
                 63.88 
                 63.5 
                 65.9 
                 64.0 
                 63.6 
               
               
                   
                 2140 
                 61.58 
                 66.7 
                 66.9 
                 63.4 
                 65.7 
                 64.8 
                 65.6 
               
               
                   
                 2170 
                 60.52 
                 66.5 
                 67.1 
                 62.3 
                 65.0 
                 66.6 
                 66.3 
               
               
                   
                 2200 
                 59.38 
                 66.57 
                 66.8 
                 63.8 
                 65.0 
                 65.7 
                 65.6 
               
               
                 1044  
                 2100 
                 64.9  
                 65.6 
                 66.0 
                 65.1 
                 66.2 
                 63.3 
                 62.7 
               
               
                   
                 2140 
                 64.3  
                 66.3 
                 66.3 
                 65.5 
                 66.4 
                 64.1 
                 63.8 
               
               
                   
                 2170 
                 63.48 
                 67.1 
                 66.9 
                 65.4 
                 66.9 
                 64.6 
                 64.0 
               
               
                   
                 2200 
                 62.7  
                 67.0 
                 66.8 
                 66.1 
                 66.9 
                 63.5 
                 62.4 
               
               
                   
               
             
          
         
       
     
     Other bar samples were hardened and tempered then given aging treatments to measure resistance to softening in service. 
     Aging Trials: Percent Retained Hardness HRC 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Hardness 
                   
               
               
                   
                 Quench &amp; 
                 Retained after 
               
               
                   
                 Tempered 
                 1024 hours  
                 Hardness Retained after 
               
               
                 Melt 
                 Hardness - HRC 
                 at 991 °F. 
                 1024 hours at 1101 °F. 
               
               
                   
               
             
             
               
                  505 
                 66.57 
                 92.53% 
                 62.64% 
               
               
                  507 
                 66.62 
                 91.71 
                 62.29 
               
               
                  509 
                 66.80 
                 92.07 
                 62.72 
               
               
                  511 
                 66.55 
                 92.41 
                 62.81 
               
               
                  513 
                 66.47 
                 92.07 
                 62.28 
               
               
                  514 
                 66.61 
                 92.93 
                 62.15 
               
               
                 1043 
                 66.66 
                 92.86 
                 64.35 
               
               
                 1044 
                 66.56 
                 90.29 
                 63.40 
               
               
                 A0333 
                 66.50 
                 89.32% 
                 64.96% 
               
               
                 M-42 
               
               
                   
               
             
          
         
       
     
     Additional samples from these melts were hardened and tempered before being tested at elevated temperatures for hot hardness. 
     Hot Hardness Second Factorial Melts 
     Hardness—HRC and Percent of Initial Hardness Retained 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Room 
                 900° F. 
                 1000° F. 
                 1100° F. 
                 1200° F. 
               
               
                   
                 Temperature 
                 HRC 
                 HRC 
                 HRC 
                 HRC 
               
               
                 Melt 
                 HRC 
                 % 
                 % 
                 % 
                 % 
               
               
                   
               
             
             
               
                 505 
                 65.8 
                 58.8 
                 56.0 
                 52.6 
                 43.9 
               
               
                   
                   
                 89.4 
                 85.1 
                 79.9 
                 66.7 
               
               
                 507 
                 65.6 
                 57.5 
                 55.5 
                 51.3 
                 41.5 
               
               
                   
                   
                 87.7 
                 84.6 
                 78.2 
                 63.3 
               
               
                 509 
                 65.1 
                 56.0 
                 56.5 
                 53.6 
                 43.9 
               
               
                   
                   
                 86.0 
                 86.8 
                 82.3 
                 67.3 
               
               
                 511 
                 65.9 
                 57.5 
                 55.3 
                 52.1 
                 42.2 
               
               
                   
                   
                 87.3 
                 83.9 
                 79.1 
                 64.0 
               
               
                 513 
                 67.4 
                 53.4 
                 56.4 
                 52.8 
                 44.3 
               
               
                   
                   
                 86.6 
                 83.7 
                 78.3 
                 65.7 
               
               
                 514 
                 66.5 
                 58.2 
                 56.1 
                 52.8 
                 43.9 
               
               
                   
                   
                 87.5 
                 84.4 
                 79.4 
                 66.0 
               
               
                 1043  
                 66.6 
                 57.9 
                 55.2 
                 52.3 
                 43.2 
               
               
                   
                   
                 86.9 
                 82.9 
                 78.5 
                 64.9 
               
               
                 1044  
                 67.0 
                 58.3 
                 56.7 
                 53.9 
                 43.5 
               
               
                   
                   
                 87.0 
                 84.6 
                 80.4 
                 64.9 
               
               
                 A0333 
                 67.0 
                 59.0 
                 57.6 
                 54.7 
                 45.2 
               
               
                 M-42 
                   
                 88.1 
                 86.0 
                 81.6 
                 67.5 
               
               
                   
               
             
          
         
       
     
     Longitudinal and transverse sections of annealed samples were examined using an optical microscope and 100× and 400×. The low niobium heats with higher titanium levels showed a tendency toward thicker banding of the carbides. The highest aluminum heat, 507, showed much larger carbides with heavy banding. Therefore, a larger heat based on the 509 analysis was scheduled. A semi-production heat of high niobium was based on the results of 1043 melt. However, based on relating of high aluminum levels with larger carbides in the annealed condition, the aluminum aim was lowered. 
     Chemical Composition Weight Percent Initial Semi-Production Heats 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 Chemical Composition Weight Percent 
               
               
                 Initial Semi-Production Heats 
               
             
          
           
               
                   
                 C 
                 W 
                 Si 
                 V 
                 Cr 
                 Mn 
                 Co 
               
               
                   
                   
               
             
          
           
               
                 aim low 
                 1.08 
                 6.25 
                 .39 
                 1.75 
                 3.80 
                 .32 
                 DNA 
               
               
                 niobium 
               
               
                 actual 
                 1.07 
                 6.34 
                 .40 
                 1.80 
                 3.92 
                 .41 
                 .28 
               
               
                 G3643 
               
               
                 aim high 
                 1.08 
                 4.50 
                 .32 
                 1.00 
                 3.80 
                 .32 
                 DNA 
               
               
                 niobium 
               
               
                 actual 
                 1.07 
                 4.74 
                 .34 
                 1.03 
                 3.95 
                 .38 
                 .19 
               
               
                 G3644 
               
               
                   
               
             
          
           
               
                   
                   
                 Al 
                   
                   
                   
                   
                   
               
               
                   
                 Mo 
                 soluble 
                 Nb 
                 Ti 
                 N 
                 S 
                 P 
               
               
                   
                   
               
             
          
           
               
                 aim low 
                 5.10 
                 .095 
                 .10 
                 .025 
                 .0325 
                 .005 
                 .015x 
               
               
                 niobium 
               
               
                 actual 
                 5.17 
                 .032 
                 .10 
                 .024 
                 .0408 
                 .011 
                 .021 
               
               
                 G3643 
               
               
                 aim high 
                 6.87 
                 .095 
                 .50 
                 .025 
                 .0325 
                 .005 
                 .015x 
               
               
                 niobium 
               
               
                 actual 
                 7.44 
                 .047 
                 .30 
                 .025 
                 .0370 
                 .007 
                 .022 
               
               
                 G3644 
               
               
                   
               
             
          
         
       
     
     The initial low niobium heat was set to be 0.06% in carbon below stoichiometric balance with the carbides while the actual heat is 0.09% below balance. The high niobium heat was aimed to be 0.01% deficient in carbon from stoichiometric balance but the final product was 0.04% deficient. Although the molybdenum level in the high niobium heat was above the aim, the molybdenum to tungsten ratio was essentially unchanged. The aim on the soluble aluminum content was missed substantially on both heats, but processing to wrought bar and testing were continued. 
     The ¾ ton ingots were slow cooled then given a subcritical stress relief at 1360° F., then rotary forged to 4.9375″ round comer squares which were further rolled, then machined to a variety of bar sizes from 0.500 to 2.107″ rounds. Hot acid macro examination of the billets from both heats showed excellent freedom from segregation and pattern at all locations from product of both heats. Bar samples were then tested for heat treat response, hot hardness, etc. 
     Optical microscope examination revealed typical primary carbides in large colonies in the as-cast material with the general carbide distribution growing finer as the material was hot worked. However, the primary carbide particles in the high niobium heat, G3644, larger and more squarish in shape. Examination of the material in the hardened and tempered condition showed some of the primary carbides in the heat G3644 at three way grain boundaries. The larger carbide particles in the high niobium heat are attributed to not only the higher niobium content but the relative lower amounts of aluminum and titanium in this heat that are available to nucleate fine particles and minimize their growth. 
     Bar samples of annealed material were hardened in salt, quenched, then tempered in air for two hours for each temper. 
     Heat Treat Response: Melt G3643 Hardness HRC 
     
       
         
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Austenitize 
                 As 
                   
                 1st 
                 2nd 
                 3rd 
                 4th 
               
               
                 Temperature 
                 Quenched 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
               
               
                 ° F. 
                 HRC 
                 ° F. 
                 HRC 
                 HRC 
                 HRC 
                 HRC 
               
               
                   
               
             
             
               
                 2120 
                 64.7 
                  977 
                 64.3 
                 66.0 
                 66.1 
                 66.4 
               
               
                 2140 
                 64.0 
                   
                 64.1 
                 66.0 
                 66.6 
                 66.9 
               
               
                 2200 
                 63.1 
                   
                 63.8 
                 66.0 
                 66.9 
                 67.3 
               
               
                 2240 
                 62.9 
                   
                 64.5 
                 66.6 
                 67.2 
                 68.0 
               
               
                 2180 
                 64.0 
                 1025 
                 — 
                 — 
                 — 
                 66.9 
               
               
                 2120 
                 64.7 
                 1033 
                 65.8 
                 66.2 
                 65.8 
                 65.9 
               
               
                 2140 
                 64.0 
                   
                 66.0 
                 66.4 
                 65.7 
                 66.0 
               
               
                 2160 
                 63.8 
                   
                 65.5 
                 67.0 
                 67.7 
                 67.9 
               
               
                 2200 
                 63.1 
                   
                 66.3 
                 67.0 
                 67.1 
                 67.0 
               
               
                 2240 
                 62.9 
                   
                 66.7 
                 67.4 
                 67.7 
                 67.4 
               
               
                 2120 
                 64.7 
                 1085 
                 65.4 
                 64.6 
                 64.0 
                 63.1 
               
               
                 2140 
                 64.0 
                   
                 65.5 
                 64.7 
                 63.8 
                 63.1 
               
               
                 2160 
                 63.8 
                   
                 65.9 
                 65.5 
                 65.4 
                 65.4 
               
               
                 2200 
                 63.1 
                   
                 65.7 
                 64.6 
                 64.3 
                 63.9 
               
               
                 2240 
                 62.9 
                   
                 66.6 
                 66.6 
                 66.3 
                 66.0 
               
               
                   
               
             
          
         
       
     
     Heat Treat Response: Melt G3644 Hardness HRC 
     
       
         
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Austenitize 
                 AS 
                   
                 1st 
                 2nd 
                 3rd 
                 4th 
               
               
                 Temperature 
                 Quenched 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
               
               
                 ° F. 
                 HRC 
                 ° F. 
                 HRC 
                 HRC 
                 HRC 
                 HRC 
               
               
                   
               
             
             
               
                 2140 
                 62.6 
                  977 
                 63.3 
                 65.2 
                 65.7 
                 66.4 
               
               
                 2180 
                 61.8 
                   
                 63.0 
                 64.5 
                 66.0 
                 66.5 
               
               
                 2200 
                 60.4 
                   
                 61.9 
                 64.7 
                 65.9 
                 66.4 
               
               
                 2220 
                 59.8 
                   
                 62.0 
                 64.7 
                 65.2 
                 66.2 
               
               
                 2220 
                 1025 
                 1025 
                 — 
                 — 
                 — 
                 67.4 
               
               
                 2130 
                 — 
                 1033 
                 65.9 
                 66.3 
                 66.5 
                 — 
               
               
                 2140 
                 62.6 
                   
                 65.9 
                 66.5 
                 67.0 
                 66.8 
               
               
                 2160 
                 61.7 
                   
                 65.6 
                 66.8 
                 67.0 
                 67.1 
               
               
                 2180 
                 61.8 
                   
                 64.2 
                 65.2 
                 64.2 
                 67.1 
               
               
                 2200 
                 60.4 
                   
                 66.4 
                 66.9 
                 66.2 
                 66.5 
               
               
                 2220 
                 59.8 
                   
                 65.1 
                 67.4 
                 68.0 
                 68.2 
               
               
                 2140 
                 62.6 
                 1085 
                 65.6 
                 64.9 
                 64.6 
                 63.8 
               
               
                 2160 
                 61.7 
                   
                 65.8 
                 65.4 
                 64.6 
                 64.1 
               
               
                 2180 
                 61.8 
                   
                 64.2 
                 64.5 
                 64.0 
                 64.0 
               
               
                 2200 
                 60.4 
                   
                 65.4 
                 66.6 
                 66.5 
                 65.8 
               
               
                 2220 
                 59.8 
                   
                 65.5 
                 66.2 
                 66.3 
                 66.0 
               
               
                   
               
             
          
         
       
     
     Bar samples from both heats were quenched and tempered, then aged at elevated temperature, 1128° F., then air cooled to room temperature to determine their retained hardness. 
     Percentage Retained Hardness—HRC of Initial Semi Production Heats Aged at 1128° F. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Austenitization 
                   
                 at 194 
                 % 
                 at 339 
                   
               
               
                   
                 Temperature 
                 initial 
                 hours 
                 Re- 
                 hours 
                 % 
               
               
                 Heat 
                 ° F. 
                 HRC 
                 HRC 
                 tained 
                 HRC 
                 Retained 
               
               
                   
               
             
             
               
                 G3643 
                 2140 
                 66.6  
                 42.1  
                 63.2 
                 39.2 
                 58.9 
               
               
                   
                 2180 
                 66.86 
                 42.62 
                 63.7 
                 40.4 
                 60.4 
               
               
                 G3644 
                 2140 
                 66.5  
                 44.37 
                 66.7 
                 40.7 
                 61.2 
               
               
                   
                 2220 
                 67.39 
                 42.62 
                 63.2 
                 42.2 
                 62.6 
               
               
                   
               
             
          
         
       
     
     Additional samples from these melts were hardened and tempered before being tested at elevated temperatures for hot hardness. 
     Hot Hardness Initial Semi Production Heats 
     Hardness—HRC and Percent of Initial Hardness Retained 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                 Heat 
                 Room 
                 900° F. 
                 1000° F. 
                 1100° F. 
                 1200° F. 
               
               
                 Austenitize 
                 Temperature 
                 HRC 
                 HRC 
                 HRC 
                 HRC 
               
               
                 Temperature 
                 HRC 
                 % 
                 % 
                 % 
                 % 
               
               
                   
               
             
             
               
                 G3643 
                 66.1 
                 56.5 
                 52.6 
                 47.1 
                 22.7 
               
               
                 2140F 
                   
                 85.5 
                 79.5 
                 71.3 
                 34.3 
               
               
                 G3643 
                 65.8 
                 57.5 
                 53.8 
                 48.1 
                 32.4 
               
               
                 2180F 
                   
                 87.3 
                 81.7 
                 73.1 
                 49.3 
               
               
                 G3644 
                 66.1 
                 56.6 
                 54.5 
                 48.5 
                 32.5 
               
               
                 2130F 
                   
                 85.2 
                 82.4 
                 73.3 
                 49.2 
               
               
                 G3644 
                 67.9 
                 58.7 
                 55.4 
                 51.1 
                 37.2 
               
               
                 2220F 
                   
                 86.5 
                 81.6 
                 75.3 
                 54.8 
               
               
                 M-42 
                 67.3 
                 57.5 
                 55.9 
                 50.1 
                 34.8 
               
               
                 A0333 
                   
                 85.8 
                 83.1 
                 74.4 
                 51.7 
               
               
                 2150F 
               
               
                   
               
             
          
         
       
     
     Because the first set of semi production heats was slightly out of the desired chemical analysis, two additional heats were melted. The low niobium composition was tried again with higher aluminum. The higher niobium type was modified to have lower tungsten with higher molybdenum, niobium and aluminum. In essence, this high niobium heat was designed to mimic some of the alloy balances in AISI M-42. In particular, the ratio of vanadium plus niobium and titanium to the total tungsten and molybdenum is similar to M-42. Likewise, the ratio of molybdenum to molybdenum plus tungsten is the same as M-42. The aimed stoichiometric balance is also similar to M-42 while the total atomic fraction of carbide forming elements is the same. 
     Chemical Composition Weight Percent Second Set Semi-Production Heats 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 C 
                 W 
                 Si 
                 V 
                 Cr 
                 Mn 
                 Co 
               
               
                   
                   
               
             
          
           
               
                 aim low 
                 1.08 
                 6.25 
                 .39 
                 1.75 
                 3.80 
                 .32 
                 DNA 
               
               
                 niobium 
               
               
                 actual 
                 1.06 
                 6.17 
                 .32 
                 1.77 
                 3.91 
                 .56 
                 .26 
               
               
                 G3845 
               
               
                 aim high 
                 1.10 
                 2.00 
                 .32 
                 .90 
                 3.80 
                 .32 
                 DNA 
               
               
                 niobium 
               
               
                 actual 
                 1.10 
                 2.19 
                 .50 
                 1.11 
                 3.82 
                 .41 
                 .12 
               
               
                 G3846 
               
               
                   
               
             
          
           
               
                   
                   
                 Al 
                   
                   
                   
                   
                   
               
               
                   
                 Mo 
                 soluble 
                 Nb 
                 Ti 
                 N 
                 S 
                 P 
               
               
                   
                   
               
             
          
           
               
                 aim low 
                 5.10 
                 .095 
                 .10 
                 .025 
                 .0325 
                 .005 
                 .015x 
               
               
                 niobium 
               
               
                 actual 
                 4.97 
                 .100 
                  .097 
                 .027 
                 .0474 
                 .003 
                 .023 
               
               
                 G3845 
               
               
                 aim high 
                 9.00 
                 .14 
                 .90 
                 .025 
                 .0375 
                 .005 
                 .015x 
               
               
                 niobium 
               
               
                 actual 
                 9.07 
                 .116 
                 .80 
                 .034 
                 .0306 
                 .019 
                 .018 
               
               
                 G3846 
               
               
                   
               
             
          
         
       
     
     The second low niobium heat was set to be 0.06% in carbon below stoichiometric balance required to form known precipitates with alloy carbide formers and the actual heat was close to that aim with a carbon content just 0.08% below balance. The high niobium heat was aimed to be 0.07% deficient in the carbon necessary to meet the need for carbon to form a stoichiometric balance with the alloy carbide formers but the final product was 0.10% deficient. However the carbon necessary to combine with the primary, MC, type carbide formers such as VC, TiC, and NbC was 0.03 % more than in the aim chemistry. 
     The ¾ ton ingots were rotary forged to 4.9375″ round corner squares which were further hot rolled then machined to final bar in sizes from 0.500 to 2.107″ rounds. Hot acid macro examination of the billets from both heats showed excellent freedom from segregation and pattern at all locations from products of both heats. Bar samples were then tested for heat treat response, hot hardness, etc. 
     Bar samples from both heats of annealed material were hardened in salt, quenched, then tempered in air for two hours for each cycle. 
     Heat Treat Response: Melt G3845: Low Niobium Hardness HRC 
     
       
         
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Austenitize 
                 As 
                   
                 1st 
                 2nd 
                 3rd 
                 4th 
               
               
                 Temperature 
                 Quenched 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
               
               
                 ° F. 
                 HRC 
                 ° F. 
                 HRC 
                 HRC 
                 HRC 
                 HRC 
               
               
                   
               
             
             
               
                 2120 
                 64.3 
                  979 
                 64.3 
                 65.4 
                 66.3 
                 66.6 
               
               
                 2140 
                 64.1 
                   
                 64.5 
                 65.6 
                 66.1 
                 66.2 
               
               
                 2160 
                 63.6 
                   
                 64.4 
                 65.8 
                 66.6 
                 66.5 
               
               
                 2200 
                 62.0 
                   
                 63.5 
                 65.2 
                 66.6 
                 66.7 
               
               
                 2240 
                 61.8 
                   
                 63.9 
                 66.1 
                 66.9 
                 67.3 
               
               
                 2250 
                 61.2 
                   
                 64.4 
                 66.0 
                 67.0 
                 67.5 
               
               
                 2120 
                 64.3 
                 1033 
                 66.0 
                 65.7 
                 65.2 
                 65.3 
               
               
                 2140 
                 64.1 
                   
                 66.0 
                 63.8 
                 65.5 
                 65.1 
               
               
                 2160 
                 63.6 
                   
                 66.1 
                 66.1 
                 66.7 
                 65.7 
               
               
                 2180 
                 63.2 
                   
                 65.5 
                 66.0 
                 65.7 
                 — 
               
               
                 2200 
                 62.0 
                   
                 66.3 
                 67.0 
                 65.9 
                 66.7 
               
               
                 2240 
                 61.8 
                   
                 66.6 
                 67.3 
                 67.5 
                 67.6 
               
               
                 2250 
                 61.2 
                   
                 66.8 
                 67.7 
                 67.6 
                 67.6 
               
               
                 2200 
                 62.0 
                 1060 
                 66.2 
                 66.1 
                 66.0 
                 65.9 
               
               
                 2240 
                 61.8 
                   
                 66.3 
                 66.3 
                 56.9 
                 66.0 
               
               
                 2250 
                 61.2 
                   
                 66.4 
                 66.6 
                 66.6 
                 66.3 
               
               
                 2120 
                 64.3 
                 1085 
                 65.0 
                 63.8 
                 63.2 
                 63.0 
               
               
                 2140 
                 64.1 
                   
                 65.1 
                 64.0 
                 63.7 
                 63.2 
               
               
                 2160 
                 63.6 
                   
                 65.4 
                 64.5 
                 64.1 
                 63.9 
               
               
                 2200 
                 62.0 
                   
                 65.9 
                 65.4 
                 65.5 
                 64.7 
               
               
                 2240 
                 61.8 
                   
                 66.2 
                 66.0 
                 65.9 
                 65.6 
               
               
                 2250 
                 61.2 
                   
                 66.7 
                 66.6 
                 66.3 
                 66.1 
               
               
                 2200 
                 62.0 
                 1099 
                 66.7 
                 65.0 
                 64.5 
                 64.4 
               
               
                 2250 
                 61.2 
                   
                 66.5 
                 65.9 
                 65.6 
                 65.2 
               
               
                   
               
             
          
         
       
     
     Heat Treat Response: Melt G3846 High Niobium Hardness HRC 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                 Austenitize 
                 AS 
                   
                 1st 
                 2nd 
                 3rd 
               
               
                 Temperature 
                 Quenched 
                 Temper 
                 Temper 
                 Temper 
                 Temper 
               
               
                 ° F. 
                 HRC 
                 ° F. 
                 HRC 
                 HRC 
                 HRC 
               
               
                   
               
             
             
               
                 2120 
                 64.4 
                  979 
                 64.3 
                 65.2 
                 64.5 
               
               
                 2140 
                 64.3 
                   
                 63.9 
                 64.0 
                 64.1 
               
               
                 2160 
                 65.2 
                   
                 65.0 
                 65.6 
                 65.6 
               
               
                 2180 
                 63.6 
                   
                 63.8 
                 64.4 
                 65.1 
               
               
                 2200 
                 64.4 
                   
                 65.1 
                 65.9 
                 65.7 
               
               
                 2220 
                 64.2 
                   
                 65.2 
                 66.1 
                 67.1 
               
               
                 2240 
                 64.1 
                   
                 65.5 
                 66.2 
                 66.5 
               
               
                 2260 
                 63.3 
                   
                 64.9 
                 64.8 
                 65.0 
               
               
                 2120 
                 63.5 
                 1033 
                 62.0 
                 62.0 
                 61.1 
               
               
                 2140 
                 65.0 
                   
                 64.8 
                 64.8 
                 64.2 
               
               
                 2160 
                 65.2 
                   
                 64.8 
                 64.8 
                 64.4 
               
               
                 2180 
                 64.5 
                   
                 65.1 
                 65.1 
                 65.1 
               
               
                 2200 
                 64.7 
                   
                 65.2 
                 65.2 
                 65.0 
               
               
                 2220 
                 64.1 
                   
                 65.7 
                 65.7 
                 65.9 
               
               
                 2240 
                 64.1 
                   
                 65.9 
                 65.9 
                 65.7 
               
               
                 2260 
                 63.3 
                   
                 66.1 
                 66.1 
                 66.0 
               
               
                 2120 
                 64.0 
                 1085 
                 — 
                 57.4 
                 53.2 
               
               
                 2140 
                 65.0 
                   
                 63.4 
                 63.1 
                 62.6 
               
               
                 2160 
                 64.9 
                   
                 63.4 
                 63.5 
                 63.2 
               
               
                 2180 
                 64.7 
                   
                 63.4 
                 63.7 
                 63.0 
               
               
                 2200 
                 64.4 
                   
                 63.9 
                 64.0 
                 63.3 
               
               
                 2220 
                 64.1 
                   
                 64.5 
                 64.2 
                 63.5 
               
               
                 2240 
                 63.5 
                   
                 64.2 
                 64.0 
                 63.6 
               
               
                 2260 
                 64.2 
                   
                 64.1 
                 64.2 
                 63.3 
               
               
                   
               
             
          
         
       
     
     Bar samples from heat G2845 were hardened and tempered and given aging treatments to measure resistance to softening in cutting operations. 
     Bar samples from heat G3845 were hardened and tempered and given aging treatments to measure resistance to softening in cutting operations. 
     Percentage Retained Hardness—HRC of G3845 Low Niobium Heat Aged at 1128° F. 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                 Austenitization 
                   
                 at 164 
                   
                 at 335 
                   
               
               
                 Temperature 
                 initial 
                 hours 
                 % 
                 hours 
                 % 
               
               
                 °F. 
                 HRC 
                 HRC 
                 Retained 
                 HRC 
                 Retained 
               
               
                   
               
             
             
               
                 2180 
                 65.7 
                 41.1 
                 62.6 
                 27.47 
                 41.8 
               
               
                 2240 
                 66.8 
                 43.1 
                 64.5 
                 30.74 
                 46.0 
               
               
                   
               
             
          
         
       
     
     Additional samples from heat G3845 were hardened and tempered then tested at elevated temperatures for hot hardness. 
     Hot Hardness G3845 Low Niobium Heat Hardness—HRC and Percent of Initial Hardness Retained 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Room 
                 900° F. 
                 1000° F. 
                 1100° F. 
                 1200° F. 
               
               
                 Austenitize 
                 Temperature 
                 HRC 
                 HRC 
                 HRC 
                 HRC 
               
               
                 Temperature 
                 HRC 
                 % 
                 % 
                 % 
                 % 
               
               
                   
               
             
             
               
                 2180 
                 66.0 
                 57.0 
                 52.3 
                 48.8 
                 35.5 
               
               
                   
                   
                 86.4 
                 79.2 
                 73.9 
                 53.8 
               
               
                 2240 
                 66.8 
                 57.6 
                 56.4 
                 51.1 
                 38.9 
               
               
                   
                   
                 86.2 
                 84.4 
                 76.5 
                 58.2 
               
               
                   
               
             
          
         
       
     
     While several embodiments have been shown and described, it should be recognized that other variations and/or modifications not described herein are possible without departing from the spirit and scope of the present invention.