Patent Publication Number: US-2011056589-A1

Title: Iron-nickle alloy

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an iron-nickel alloy having a low thermal expansion coefficient and special mechanical properties. 
     It is known that iron-based alloys having approximately 36% nickel exhibit low thermal expansion coefficients in the temperature range between 20 and 100° C. These alloys have therefore been used for several decades wherever constant lengths are required, even with changes in temperature, such as for instance in precision instruments, clocks, bimetals, and shadow masks for color televisions and computer monitors. 
     KR 100261678 B1 is an invar alloy wire and a method for producing it. The invar alloy has the following composition (in mass %): 33 to 38% nickel, 0.5 to 1.0% cobalt, 0.01 to 1.3% niobium, 0.5 to 4% molybdenum, 0.2 to 1.5% chromium, 0.05 to 0.35% carbon, 0.1 to 1.2% silicon, 0.1 to 0.9% manganese, max. 0.1% magnesium, max. 0.1% titanium, the remainder being iron; the sum of Mo+Cr being between 1.2 and 5.0%, and the sum of niobium and carbon being between 0.1 and 0.6%. 
     KR 1020000042608 discloses a high-strength invar alloy wire and a method for producing it. The alloy used contains (in mass %): no more than 0.1% nitrogen, 0.01 to 0.2% niobium, 0.3 to 0.4% carbon, 33 to 38% nickel, 0.5 to 4% molybdenum, 0.2 to 1.5% chromium, 0.1 to 1.2% silicon, 0.1 to 0.9% manganese, 1.0 to 10% cobalt, and, as needed, additions of up to 0.1% each Al, Mg, and Ti, with the remainder being iron. 
     Both publications provide method parameters for cold drawing. hot drawing, and annealing within defined temperature ranges. 
    
    
     SUMMARY OF THE INVENTION 
     The object of the inventive subject-matter is to provide a creep-resistant iron-nickel alloy having a low thermal expansion coefficient and special mechanical properties. Moreover, a production process for wire-like components made of this alloy is provided. Finally, it should be possible to employ the material for specific uses, and the alloy should have a low thermal expansion coefficient. 
     This object is attained using an iron-nickel alloy having the following composition, in mass %: 
     C 0.05 to 0.5% 
     Cr 0.2 to 2.0% 
     Ni 33 to 42% 
     Mn &lt;0.1% 
     Si &lt;0.1% 
     Mo 1.5 to 4.0% 
     Nb 0.01 to 0.5% 
     Al 10.1 to 0.8% 
     Mg 0.001 to 0.01% 
     V Max. 0.1% 
     W 0.1 to 1.5% 
     Co Max 2.0% 
     Fe Remainder and process-related impurities. 
     One preferred variant of the inventive iron-nickel alloy is provided as follows (in mass %): 
     C 0.1 to 0.4% 
     Cr 0.5 to 1.5% 
     Ni 34 to 40% 
     Mn &lt;0.08% 
     Si &lt;0.08% 
     Mo &gt;2.0 to &lt;3.5% 
     Nb 0.05 to 0.4% 
     A 10.2 to 0.5% 
     Mg 0.001 to &lt;0.01% 
     V Max. 0.1% 
     W 0.2 to &lt;1.0% 
     Co 0 to 1.0% 
     Fe Remainder and process-related impurities. 
     Another variant is formed by (in mass %): 
     C &gt;0.15 to &lt;0.4% 
     Cr 0.6 to max. 1.2% 
     Ni 35 to 40% 
     Mn &lt;0.08% 
     Si &lt;0.08% 
     Mo &gt;2.0 to &lt;3.0% 
     Nb 0.05 to 0.3% 
     Al &gt;0.1 to &lt;0.5% 
     Mg &gt;0.001 to &lt;0.01% 
     V Max. 0.1% 
     W 0.25 to 1.0% 
     Co 0 to max 0.5% 
     Fe Remainder and process-related impurities. 
     The inventive composition of the alloy is distinguished from the prior art in that the Si and Mn contents are kept as small as possible. It is known that there is a strong relationship between the elements silicon and manganese with respect to the thermal expansion coefficient. On the other hand, these elements are metallurgically necessary in order to ensure adequate processability. This relates in particular to hot shaping to create billets and wire rods. 
     Thus, using the inventive chemical composition, it is possible to use the smallest possible amounts of the elements silicon and manganese, so that the negative effects these elements have on the thermal expansion coefficient can be avoided. At the same time, the alloy is easy to process. For this reason, the sum of Mn+Si should not exceed 0.2% (in mass %). The sum of Mn+Si should be ≦0.1%, where technically feasible. 
     It is of particular advantage when the inventive alloy has a nickel content between 35 and 38 mass %, a chromium content of &gt;0.6 to &lt;1.2 mass %, a molybdenum content between 2.1 and 2.8 mass %, an aluminum content between 0.2 and 0.4 mass %, and a tungsten content of &gt;0.25 to &lt;1.0 mass %. 
     Also, the element zirconium may also be added in contents &gt;0 to &lt;0.2 mass % and/or the element B may be added in contents &gt;0−0.01 mass % of the inventive alloy. B+Zr individually or together improve the hot formability of the alloy. 
     Moreover, it is advantageous when the sum of the elements Mo+W is between 2.0 and 4.0 mass %. 
     Likewise, mechanical properties are improved when the sum of the elements Cr+W is between 1.0 and 2.0 mass %. 
     According to another aspect of the invention, the element W may be substituted for some of the element Mo. 
     It is significant that the alloy elements Mo, W, Cr, and C are available in sufficient quantities and that the ratio of (Mo+W+Cr)/C is selected such that it is possible to achieve a balanced mix of carbide strengthening, mixed crystal hardening, and cold hardening in the final product. An optimum ratio is considered to be in the range between 14 and 15. 
     According to another aspect of the invention, the W:Cr:Mo ratio should be approximately 1:2:5. However, the portion of the aforesaid elements in the inventive alloy must be provided such that the predetermined target value of thermal expansion coefficient is not exceeded. 
     In the temperature range between 20 and 200° C., the inventive alloy has a thermal expansion coefficient of &lt;4×10 −6 /K, especially &lt;3.5×10 −6 /K. 
     Further provided is a method for producing components from the inventive alloy in an arc furnace, an induction furnace, or a vacuum furnace (where necessary with VOD treatment), with subsequent ingot casting, hot rolling (or forging) to create billets and wire rods on wire of a predetermined thickness, and subsequent drawing to create wire-shaped pre-products with a predetermined diameter, with annealing occurring, when necessary, between individual drawing steps. Since the degree of cold strengthening is critical for the usage properties, both with regard to the thermal expansion coefficient and with regard to strength, the wire rod diameter must be adjusted such that adequate cold forming can be performed prior to and after intermediate annealing, which may take place in multiple stages. 
     According to another aspect of the invention, the inventive alloy may be used as wire for power lines, especially as the core wire for power lines. 
     The inventive alloy may moreover be advantageously used for: 
     Lead frames 
     Shaped parts, especially carbon fiber molded parts 
     Components in chip production. 
     For the preferred uses the inventive alloy may be present in the form of sheet, bar, strip, or wire material.