Titanium based carbonitride alloy with controlled structure

Abstract: According to the invention there now exists a sintered titanium based carbonitride alloy containing hard constituents with core-rim structure based on, besides Ti and W and/or Mo, one or more of the metals Zr, Hf, V, Nb, Ta or Cr in 5-30 weight% binder phase based on Co and/or Ni with simultaneously increased wear resistance and toughness. The alloy is characterized in that at least 70 %, preferably at least 80 %, of said hard constituents has four different types of cores with the following contents of Ti and W in weight% of the total metal content: 1-5 W and 90-95 Ti(1A), 15-25 W and 65-85 Ti(1B), 50-75 W and 20-40 Ti(1C) as well as 20-30 W and 30-60 Ti(2A), whereby the share of each type amounts to at least 5 %.

Description: The present invention relates to a sintered carbonitride alloy with titanium as main component which simultaneously has obtained improved toughness behaviour and increased wear resistance and resistance against plastic deformation. Classic cemented carbide, ie based on tungsten carbide (WC) and cobalt (Co) as binder phase has in the last few years met an increased competition from titanium based hard materials, usually called cermets. In the beginning these alloys were used only for extreme finishing due to their extraordinary wear resistance at high cutting temperatures. This property depends primarily upon the good chemical stability of these titanium alloys. The toughness behaviour and the resistance against plastic deformation were not satisfactory however, and therefore the area of application was relatively limited. Development has, however, proceeded and the area of application for titanium based hard material has been considerably enlarged. The toughness behaviour and the resistance to plastic deformation has been considerably improved. This has been done, however, by partly sacrificing the wear resistance. Besides titanium the other metals from groups IVa, Va and VIa, ie Zr, Hf, V, Nb, Ta, Cr, Mo and/or W are normally used as hard constituent formers generally as carbides, nitrides and/or carbonitrides. The grain size of the hard constituents is generally <1 µm. As binder phase nowadays often both cobalt and nickel are used. The amount of binder phase is generally 3-25 weight%. During sintering the relatively seen less stable hard constituents are dissolved in binder phase and precipitate then as a rim on the more stable hard constituents. A very common structure in alloys in question is therefore hard constituent grains with a core-rim structure. An early patent in this area is U.S. 3,971,656 which comprises Ti-and N-rich cores surrounded by rims rich in Mo, W and C. Through Swedish patent application SE 8902306-3 corresponding to EP-A-406201 is known that at least two different combinations of duplex core-rim-structures in well balanced proportions give optimal properties with regard to wear resistance, toughness behaviour and/or resistance against plastic deformation. Further examples of patents in this area are U.S. 4,904,445, U.S. 4,778,521, U.S. 4,957,548 to mention a few. It has now turned out that if the structure contains cores of several different compositions of tungsten and titanium surrounded by rims with the same composition an increase in toughness without loss of wear resistance and resistance against plastic deformation is obtained. Figure 1 shows the structure of a sintered carbonitride alloy according to the invention in 4000X in which 1A, 1B, 1C and 2A are cores with different electron optical contrast and therefore different composition. According to the present invention there is, thus, now provided a titanium based carbonitride alloy containing hard constituents with core-rim structure. At least 70 %, preferably at least 80 %, of said hard constituents have four different types of cores designated 1A, 1B, 1C and 2A in figure 1 surrounded by rims with the same composition. The amount of each core type amounts to at least 5%, preferably at least 10% of the total amount of hard constituents having a core-rim structure in the alloy. Core type (1A) is built up mainly of titanium, 90-95 weight%, as hard constituent former and contains besides 1-5 weight% W, only small amounts, <3 weight%, of the remaining metallic elements. These cores are relatively large compared to remaining cores and often have a measure around 1 µm and even somewhat longer in their longest dimension. The core types 1B and 1C contain mainly titanium and tungsten as the metallic hard constituent formers and relatively low content of other metallic elements, <5 weight% of each. The content of tungsten and titanium is for type 1B 15-25 weight% resp 65-85 weight% and for 1C 50-75 weight%, preferably 55-70 weight%, resp 20-40 weight%. The size of these cores is <1 µm. Core type (2A) contains 20-30 weight% tungsten and 30-60 weight%, preferably 35-55 weight%, titanium but considerably higher, in all 25-35 weight%, content of the remaining in the alloy present metallic alloying elements than cores of type 1A-C. The core type 2A has further about the same content of alloying elements, in addition to titanium and tungsten, as the rims and compared to the other here defined core types, however somewhat higher content of heavy elements, which together with the somewhat higher tungsten content is evident from the brighter contrast of the scanning electron microscope micrographs in backscattered electron mode. Core type 2A has the smallest size, is generally about 0.5 µm or less. It is further the most frequent and constitutes about 50% or more of the total number of cores. The share of 1A-cores is lower in the surface than in the inner of the material. The rims round core types 1A-C arise primarily in connection with the cooling after finished sintering and are consequently identical. Measured deviations lie within the error limits. The rims round core type 2A are in addition not at all as developed as those round the other core types, 1A-C. There is, however, no reason to assume that the thin nevertheless rims round core type 2A should have another composition than the rims round core type 1A-C. They have clear epitaxy and round cores have as a result often angular rims. This is contrary to what normally is the case for known titanium based carbonitride alloys. Further core types, in addition to what has been defined above with associated rims, can also be present in the alloy according to the invention up to 30%, preferably up to 20%, of the total number of cores. It has even turned out to be possible to further alloy core types 1B and 1C further with elements from group V, ie vanadium, niobium and tantalum which can give further improvement of the resistance against plastic deformation. This has, however, mainly marginal effects because core type 2A with high tantalum content is so frequent. This improvement of the resistance against plastic deformation has been possible to obtain without serious deterioration of the toughness behaviour. Particularly good properties have been obtained for alloys with the following composition in weight%: WC 10-15, TiC+TiN 50-60, TaC <8, VC <5, Mo 2 C <10 whereby however TaC+VC+Mo 2 C <20 and Co+Ni 5-20, preferably 8-16. A carbonitride alloy according to the invention is manufactured by in itself known powder metallurgical methods milling, pressing and sintering. Powders forming the hard constituents and powders forming binder phase are mixed to a mixture with desired composition. Of this mixture bodies are then pressed and subsequently sintered. The special properties of the alloy according to the invention are obtained by essentially adding all tungsten and nitrogen as (Ti,W) (C,N) with the following composition in weight%: 18-22 % W, 60-65 % Ti, 11.5-12.2 % C and 5.5-6.2 % N. The toughness increasing effect obtained in an alloy according to the present invention now makes it possible that titanium based carbonitride alloys with a wear resistance and a related toughness behaviour, which earlier did that they only could be used for extreme finishing under continuous engagement, nowadays with maintained wear resistance can be used even for intermittent machining and certain copying operations, ie with varying cutting depths. In addition an increase in wear resistance on the rake face (ie the side of the insert on which the metal chip slides) is obtained in the form of an increased resistance against so called crater wear. Example 1 A powder mixture consisting of in, weight%, 13.7 WC, 40.8 TiC, 15.7 TiN, 6.2 TaC, 4.1 VC, 8.2 Mo 2 C, 6.7 Co and 4.6 Ni was manufactured whereby all WC was added as (Ti,W) (C,N) with the composition 20 % W, 62 % Ti, 11.85 % C and 5.85 % N. Of the mixture inserts of type TNMG 160408 QF were pressed which subsequently were sintered in 9 mbar Ar at 1430°C. The structure in these insert is shown in Fig 1 which is a scanning electron microscope micrograph in so called back scattered mode in 4000x magnification. In the figure the following four types of cores with their contrast can be distinguished: Core Type Contrast 1A black 1B grey 1C white 2A light grey The metal content of these cores and in the rims associated with resp core type as well as of the composition of the binder phase have been determined with energy dispersive technique and put together in table 1 below. Due to that core type 2A has considerably thinner and more diffuse rim than the cores of type 1A-C no reliable analysis has been obtained. There is, however, no reason to believe that the rims round core type 2A should have another composition than the rims round core type 1A-C. Type of structure-elements Compositions in weight% of the total metal content(averages) Ti V Co Ni Mo Ta W Core, 1A 92.2 0.3 0.6 0.4 1.5 2.0 3.3 Core, 1B 75.6 0.9 0.5 0.3 2.4 3.0 17.6 Core, 1C 29.2 1.0 0.6 0.2 2.0 2.6 64.4 Core, 2A 46.6 5.5 2.1 1.2 11.5 9.7 23.4 Rim, 1A 59.0 3.5 0.7 0.5 9.2 9.2 18.0 Rim, 1B 57.5 3.9 1.0 0.6 8.7 9.3 19.0 Rim, 1C 57.9 3.7 1.7 1.0 7.9 8.8 19.1 Rim, 2A can not be analyzed, too thin Binder phase 5.7 2.6 43.2 27.5 8.1 2.5 10.4 From table 1 is evident that the rims round core types 1A-C are as identical as one can desire, ie the deviations lie within the error limits, why they are to be regarded as if they have one and same composition. This agrees well with the content of titanium as well as of heavy elements. From table 1 is further evident that core type 1A mainly contains titanium as metallic element and that types 1B and 1C have different Ti- and W-content, but remaining metallic elements are the same. Core type 2A contains considerably more of remaining metallic elements than the three other core types. That the rims contain somewhat more tungsten than core type 1B, but less than type 2A, depends on how the average composition of the actual carbonitride alloy has been chosen and is consequently not characteristic for the invention as such. Example 2 Two different commercially available titanium based carbonitride alloys one of a wear resistant type and intended for finishing and the other of a tougher type intended also for intermittent machining and copying operations, were compared with an alloy according to example 1. The same insert type was used, namely TNMG 160408 QF. The edge radius was the same for all inserts. The wear resistance was tested in a facing operation of tubes SS 2234. The tube diameter was D o = 95 mm and D i = 50 mm. Cutting data: Speed = 400 m/min Feed = 0.15 mm/rev Cutting depth = 0.5 mm The following result was obtained expressed as relative life to the same degree of flank wear, V B , alternatively failure: Relative life to V B failure According to the invention 1.0 1.1 Wear resistant grade 1.0 1.0 Tough grade 0.4 0.6 Toughness was tested in an intermittent turning operation in SS 2244-05. The following cutting data were used: Speed = 110 m/min Feed = 0.10 mm/rev Cutting depth = 1.5 mm Result expressed in percent victories compared to the reference which was the wear resistant grade: % victories According to the invention 90 Tough grade 93 Wear resistant grade(reference) 50 The example shows that an alloy according to the invention has the same toughness as the tough grade and simultaneously the same wear resistance as the wear resistant one.

Claims: Sintered titanium-based carbonitride alloy containing hard constituents with core-rim structure based on, besides Ti and W, one or more of the metals Zr, Hf, V, Nb, Ta, Mo or Cr in 5-30 weight% binder phase based on Co and/or Ni, characterized in, that at least 70 weight% of said hard constituents have four different types of cores with the following contents of Ti and W in weight% of the total metal content in each hard constituent, respectively: 1-5 W and 90-95 Ti(1A); 15-25 W and 65-85 Ti(1B); 50-75 W and 20-40 Ti(1C); 20-30 W and 30-60 Ti(2A), whereby the share of each type amounts to at least 5 % of the total amount of hard constituents having a core-rim structure in the alloy and the cores being surrounded by rims having the same composition. Titanium based carbonitride alloy according to the preceding claim, characterized in, that the core type 2A has a size <0.5 µm and that the share amounts to at least 50 %. Titanium based carbonitride alloy according to any of the preceding claims, characterized in, that the composition is in weight%: WC 10-15, TiC+TiN 50-60, TaC <8, VC <5, Mo 2 C <10 whereby, however, TaC+VC+Mo 2 C <20 and Co+Ni 5-20. Method of manufacturing a sintered titanium-based carbonitride alloy according to claim 1, containing hard constituents with core-rim structure based on, besides Ti and W and/or Mo, one or more of the metals Zr, Hf, V, Nb, Ta or Cr in 5-30 weight% binder phase based on Co and/or Ni with powder-metallurgical methods such as milling, pressing and sintering, characterized in, that all the tungsten is added as (Ti,W) (C,N) with the following composition: 18-22 % W, 60-65 % Ti, 11.5-12.2 % C and 5.5-6.2 % N.

Inventors: HULTMAN LARS, OSKARSSON ROLF, WEINL GEROLD, HULTMAN, LARS, OSKARSSON, ROLF, WEINL, GEROLD
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1993
Main classification: C22C29
IPC codes: C22C1, B23P15, B23B27, C22C29