JP2004169186A - SINTERED TITANIUM-BASED CARBONITRIDE ALLOY CONTAINING Ti, Nb, W, C, N, AND Co FOR SUPERFINISHING WORK AND ITS MANUFACTURING METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered titanium-based carbonitride alloy containing Ti, Nb, W, C, N, and Co used for metal cutting, especially, for a superfinishing turning work. <P>SOLUTION: The alloy contains Ti, 3 to below 9 at% Co, Ni and Fe on impurity levels, 2 to below 4 at% Nb, and 3 to 8 at% W and has a C/(N+C) ratio of 0.50 to 0.75. It requires that the amount of a non-soluble Ti(C, N) core should retain 26 to 37 vol% hard phase and the balance comprising at least one complex carbonitride containing Ti, Nb, and W. This alloy is useful for, especially, superfinishing work of steel and cast iron. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a sintered carbonitride alloy comprising Ti as a main composition and a cobalt binder phase, wherein the alloy is used for milling of tool materials for metal cutting, especially steel. With particularly improved properties. More particularly, the present invention relates to a carbonitride-based hard phase of a particular chemical composition, in which the amount of insoluble Ti (C, N) core is optimal for maximum grinding wear resistance On the other hand, the contents of Co and Nb simultaneously optimize providing the desired toughness and resistance to plastic deformation.

  That is, a titanium-based carbonitride alloy, called a cermet, is produced by powder metallurgy and includes a hard carbonitride phase embedded in a metal binder phase. This hard phase grain has a complex texture with a core that is almost always surrounded by the rim of the other component. In addition to Ti, Group VIa elements, usually both Mo and W, are added to promote wettability between the binder and the hard phase and strengthen the binder phase by solid solution hardening. Group IVa and / or Va elements such as Zr, Hf, V, Nb and Ta are added to all commercially available alloys available today. Elements forming carbonitrides are usually added as carbides, nitrides and / or carbonitrides. The metal binder phase can contain one or more of Ni, Co and Fe.

  Compared to WC-Co based materials, cermets have better chemical stability when contacted with hot steel, even though the cermets are uncoated and have substantially lower strength. This is where cermets are most suitable for finishing operations, which are generally characterized by a limited mechanical load on the cutting edge and a high surface finish requirement for the finished part. And

  Cermets typically include a carbonitride hard phase embedded in a Co and Ni metal binder phase. Cermet is manufactured using powder metallurgy. The powder forming the binder phase and the powder forming the hard phase are mixed, pressed and sintered. The elements forming the carbonitride are added as single or complex carbides, nitrides and / or carbonitrides. Upon sintering, the hard phase partially or completely dissolves in the liquid binder phase. Some such as W dissolve easily, while others such as Ti (C, N) are more stable and can remain partially undissolved at the end of the sintering time. During cooling, the dissolved composition precipitates as a composite layer on the undissolved hard phase particles or as nucleation in the binder phase forming the core-rim structure.

  In recent years, various attempts have been made to control the main properties of cermets in cutting tool applications, mainly toughness, abrasion resistance and composition deformation resistance. In particular, much work has been done on the chemistry of the binder phase and / or the hard phase and the formation of the core-rim structure in the hard phase. In most cases, one or at most two of these three properties can be optimized simultaneously, at the expense of the third property.

  No. 5,308,376 discloses a cermet wherein at least 80 vol.% Of the hard phase constituents have several, preferably at least two, different hard phase types with respect to core and / or rim composition. Core-rim structured particles. Each of these individual hard phase types comprises a total content of hard phase of 10-80%, preferably 20-70% by volume.

  In the Ti-Nb-WCN cermet disclosed in Japanese Patent Application Laid-Open No. 6-248385, 1% by volume or more of a hard phase contains particles without a core, regardless of the chemical composition of the particles.

  The cermet disclosed in EP 872566A coexists particles with different core-rim ratios. When the structure of the titanium-based alloy is observed with a scanning electron microscope, the particles forming the hard phase in the alloy have a black core portion and a peripheral portion that appears in gray around the black core portion. For some particles, at least 30% of the total particle area, called the large core, has a black core occupation area, and some have less than 30% of the total particle area, called the small core, has a black core occupation area. The amount of particles having a large core is 30-80% of the total amount of particles having a core.

  The cermet disclosed in U.S. Pat. No. 6,004,371 has a variety of microstructural constituents, i.e., the core of the remnant whose metallic chemical composition is determined by the raw material powder, formed during sintering. A tungsten-rich core, an outer rim containing intermediate tungsten inclusions formed during sintering, and a binder phase of a solid solution of at least titanium and tungsten in cobalt. The toughness and abrasion resistance are changed by adding WC, (Ti, W) C, and / or (Ti, W) (C, N) when changing the amount as a raw material.

  U.S. Pat. No. 3,994,692 discloses a cermet chemical composition having a hard phase consisting of Ti, W and Nb in a Co binder phase. The technical properties of these alloys as disclosed in this patent do not look good.

  A significant improvement over the above disclosure is shown in U.S. Patent No. 6,344,170. By optimizing the chemical composition and sintering time in the Ti-Ta-WCN-Co system, improved toughness and resistance to plastic deformation have been achieved. Two factors utilized to optimize toughness and resistance to plastic deformation are the Ta and Co contents. The use of a pure Co-based binder is a great advantage over mixed Co-Ni-based binders in terms of toughness behavior due to differences in solid solution hardening between Co and Ni. However, there is no teaching to optimize grinding wear resistance at the same time as the other two performance factors. However, the resistance to grinding wear has not been optimized, which is almost always required in milling operations, while the resistance to plastic deformation is usually not as important as in turning applications.

U.S. Pat. No. 5,308,376 JP-A-6-248385 European Patent 872566A U.S. Patent No. 6,004,371 U.S. Pat. No. 3,994,692 U.S. Patent No. 6,344,170 European Patent No. 10522297A US Patent No. 5,314,65

  An object of the present invention is to solve the above and other problems.

  Further, it is an object of the present invention to provide a cermet material that has substantially improved wear resistance and maintains the same level of state of the art cermet while maintaining toughness and resistance to plastic deformation. It is.

  It has been found that it is possible to design and manufacture materials that have substantially improved wear resistance while maintaining the same level of state of the art cermets. This was achieved by processing a Ti-Nb-WCN-Co alloy.

  In the Ti-Nb-WCN-Co system, a set of limitations has been found to give the intended optimal properties for a given application. More specifically, the abrasive wear resistance is maximized for a given level of toughness and resistance to plastic deformation by optimizing the amount of insoluble Ti (C, N) core. The amount of insoluble Ti (C, N) core can vary independently of other factors such as Nb and binder content. Therefore, it has become possible to optimize all three main cutting performance criteria simultaneously. For example, three are toughness, resistance to grinding wear and resistance to plastic deformation.

FIG. 1 shows the microstructure of the alloy according to the invention observed by a back reflection method in a scanning electron microscope;
A represents an insoluble Ti (C, N) -core,
B represents the composite carbonitride layer possibly surrounding the A-core, and C represents the Co binder phase.

  In one aspect, the present invention provides a titanium-based carbonitride alloy that is particularly useful for milling operations. This alloy consists of Ti-Nb-WCN and Co. When observed by back-scattering with a scanning electron microscope, this structure is composed of a black core A of Ti (C, N) and sometimes a gray composite carbonitride surrounding the A core, as depicted in FIG. It consists of the material layer B and an almost white Co binder phase.

  In accordance with the present invention, the abrasive wear resistance is optimized for a given level of toughness and resistance to composition deformation by optimizing the amount of insoluble Ti (C, N) -core (A). Can be A large amount of undissolved core is advantageous for grinding wear resistance. However, the maximum amount of these cores is limited by the requirement of sufficient toughness for a particular application, as toughness is reduced with higher levels of non-dissolving core. Thus, the amount is such that the hard phase is 26-37 vol%, preferably 27-35 vol%, most preferably 28-32 vol%, and the balance being one or more composite carbide layers containing Ti, Nb and W. And should be maintained.

The chemical composition of Ti (C + N) is more strictly defined as TiC _X N _1-X . The elemental ratio X of C / (C + N) in these cores should be between 0.46 and 0.70, preferably between 0.52 and 0.64, most preferably between 0.55 and 0.61. .

  The overall C / (C + N) ratio in this sintered alloy should be between 0.50 and 0.70.

  The average crystal grain size A of the non-solid solution core should be 0.1 to 2 µm, and the average crystal grain size of the hard phase including the non-solid solution core should be 0.5 to 3 µm.

  The content of Nb and Co should be chosen appropriately to give the desired properties for the envisaged application.

  Since the super-finishing operation requires mild high toughness, a high requirement for resistance to plastic deformation and a high requirement for resistance to grinding and abrasion are set. This combination is best achieved with an Nb content of 2 to <4 at%, preferably 3 to <4 at%, and a Co content of 3 to <9 at%, preferably 5 to <9 at%. The content of W should be between 3 and 8 at%, preferably less than 4 at%, to avoid unacceptably high porosity levels.

  For cutting operations that require significant wear resistance, it may be advantageous to coat the bodies of the present invention with a thin wear-resistant coating using PVD, CVD, MTCVD or similar techniques. Either the coatings and coating techniques used today for WC-Co based materials or cermets, of course, the choice of coatings will affect plastic deformation and the toughness of the material, although the choice of coatings will also affect the inserts so that they can be applied directly. It should be noted that the chemical composition is determined.

In another aspect of the present invention, there is provided a method of making a sintered titanium-based carbonitride alloy, wherein the powder of the hard component of TiC _X N _1-X is such that X is between 0.46 and 0.70, preferably 0. 0.52 to 0.64, most preferably 0.55 to 0.61, NbC and WC are mixed with Co powder in a chemical composition as defined above, and pressed into a body of desired shape. You. Sintering _is 1.5-2 hours at a temperature of 1,370 to 1,500 ° C. in a N 2 -CO-Ar atmosphere, preferably using the technique described in EP 1052297A embodiment. In order to obtain the desired amount of insoluble Ti (C, N) core, the amount of Ti (C, N) powder should be 50-70 wt%, its particle size should be 1-3 μm, and sintered The temperature and the sintering time need to be selected appropriately. It is within the skill of the art to determine experimentally the conditions necessary to obtain the desired microstructure according to this specification.

Example 1
A nominal chemical composition (at%) of 39.4 Ti, 3.9 W, 3.7 Nb, and 6.2 Co, with a C / (N + C) ratio of 0.82 (alloy A) The powder mixture of
61.2 wt-% TiC _0.58 N _0.42 with a particle size of 1.43 μm,
10.0 wt-% NbC with a particle size of 1.75 μm,
19.3 wt-% WC with a particle size of 1.25 μm, and 9.5 wt-% Co,
Was prepared by a wet mixing method.

The powder was spray dried and pressed into inserts of TNMG160408-PF. This green body is dewaxed in H _{2 and} sintered in N ₂ —CO—Ar at 1480 ° C. for 1.5 hours according to EP-A-1052297, after which the grinding and the conventional blade treatment are carried out. Continued. Polished cross sections of the inserts were prepared by standard metallurgical techniques and characterized using a scanning electron microscope. FIG. 1 shows a scanning electron micrograph of this cross section observed by the backscattering method. As shown in FIG. 1, the black particles (A) are insoluble Ti (C, N) cores and the light gray areas (C) are the binder phase. The remaining gray particles (B) are portions of the hard phase composed of carbonitride containing Ti, Nb and W. Using image analysis, the amount of insoluble Ti (C, N) core A was determined by the hard phase being 29.4 vol%.

Example 2 (comparative example)
A prior art insert of chemical composition (Alloy B) was manufactured and characterized as described in Example 1. The chemical composition (at%) of Alloy B is 39,4 Ti, C / (N + C) of 0.38, W of 3.9, Ta of 3.7, Co of 6.2. The features were performed in the same manner as shown in Example 1. Using image analysis, the amount of insoluble Ti (C, N) core A was determined by the hard phase being 36.2 vol%.

Example 3
A cutting test on a workpiece requiring a cutting tool having high toughness was performed using the following cutting data. That is,
Work material: SS2234
V = 210 m / min, f = 0.25 mm / rotation, d. o. c. = 0.5mm, with coolant,
Results Number of pieces that passed the failure (5 cutting edges tested)
Number of cutting blades
1 2 3 4 5
Alloy A 185 172 210 176 194
Alloy B 160 84 120 145 98

Example 4
Abrasion resistance tests of alloys A and B with longitudinal turning were performed using the following cutting data. That is,
Work material: Ovako, 825B
V = 250 m / min, f = 0.15 mm / rotation, d. o. c. = 1mm, with coolant
The tool life standard is vb> 0.3 mm.
Tool life in minutes (average of 3 cutting edges)
Alloy A: 32
Alloy B: 31
From Examples 3 and 4, the alloys produced according to the present invention have significantly improved toughness compared to prior art materials which have exhibited comparable wear resistance.

Example 5
An alloy C having the same nominal composition as the alloy A was produced and was characterized by the same conditions except that the sintering temperature was 1510 ° C. Using image analysis, the amount of insoluble Ti (C, N) core A was determined to be 25.0 vol% hard phase.

Example 6
Wear testing of alloys A and C with longitudinal turning was performed using the following cutting data. That is,
Work material: Ovako, 825B
V = 250 m / min, f = 0.15 mm / rotation, d. o. c. = 1mm, with coolant
The tool life standard is vb> 0.3 mm.
Tool life in minutes (average of 3 cutting edges)
Alloy A: 32
Alloy B: 36

Example 7
The plastic deformation resistance of alloys A and C was determined in a test consisting of facing towards the center of the tubular blank under the following cutting conditions:
Work: SS2541
V = change between 500-700 m / min, f = 0.3 mm / rotation, d. o. c. = 1mm, with coolant
The following results show the cutting speed at m / min when the cutting edge is plastically deformed (average of three cutting edges).
A: 600
B: 550

Example 8
A cutting test on a workpiece requiring a cutting tool having high toughness was performed using the following cutting data. That is,
Work material: SS2234
V = 240 m / min, f = 0.25 mm / rotation, d. o. c. = 0.5mm, with coolant,
Results Number of pieces that passed the failure (5 cutting edges tested)
Number of cutting blades
1 2 3 4 5
Alloy A 185 172 210 176 194
Alloy C 189 169 205 183 187
From these results, it was concluded that no significant difference in toughness from Alloys A and B was observed.
It is clear from Examples 6 to 8 that the alloys produced according to the invention have better cutting properties than the comparative materials.

FIG. 1 shows the microstructure of the alloy according to the invention.

Explanation of reference numerals

A: insoluble Ti (C, N) core B: gray particles, hard phase C: light gray area, binder phase

Claims (6)

A titanium-based carbonitride alloy containing Ti, Nb, W, C, N, and Co for superfinishing containing a hard phase containing an insoluble Ti (C, N) core,
Ti, 3 to <9 at% Co, impurity levels of Ni and Fe, 2 to <4 at% Nb, 3 to 8 at% W, and 0.50 to 0.75 C / (N + C) Containing C and N having a ratio,
The amount of insoluble Ti (C, N) core is 26 to 37 vol% of the hard phase, and the balance is one or more double carbonitride phases;
A titanium-based carbonitride alloy containing Ti, Nb, W, C, N and Co for superfinishing operations.   The alloy according to claim 1, wherein the alloy contains 5 to <9 at% Co.   The alloy of claim 1 wherein said alloy contains 3 to <4 at% Nb.   The alloy of claim 1 wherein said alloy contains 3-4 at% W.   The alloy according to claim 1, wherein the amount of the non-dissolved Ti (C, N) core is 27 to 35 vol% of the hard phase, and the balance is one or more double carbonitride phases. . After X has the desired chemical composition by mixing NbC and WC with Co powder in the powder of hard phase of _TiC X _{N 1-X} is the value of 0.46 to 0 · 70, pressurizing the body of a desired shape by 1.5-2 hours sintered at a temperature range of 1,370-1,500 ° C. in after pressure molding _N 2 -CO-Ar atmosphere containing undissolved Ti (C, N) hard phase comprising a core A method for producing a sintered titanium-based carbonitride alloy containing Ti, Nb, W, C, N and Co for superfinishing operations,
To obtain the desired amount of insoluble Ti (C, N) core, the amount of Ti (C, N) powder is 50-70 wt% of the powder mixture,
The particle size is 1 to 3 μm, and
The sintering temperature and sintering time are selected so that the insoluble Ti (C, N) core is 26 to 37 vol% of the hard phase.
A method for producing a sintered titanium-based carbonitride alloy, comprising:

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