JPS6335706B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention relates to a Co-Cr-(W-Mo)-C based sintered alloy that has high hardness at high temperatures and has heat and wear resistance and is used as a hot tool. It is. [Conventional technology and its problems] Conventionally, Co-Cr-(W-Mo)-C alloys have a 700
Its high hardness does not decrease up to around 800℃, and it has excellent wear resistance and corrosion resistance at high temperatures, so it is manufactured or coated by casting or overlaying, and is widely used in a variety of applications. ing. On the other hand, production of these alloys by powder metallurgy has also been partially put into practical use. Hot forging molds are a major use of Co-Cr-(W-Mo)-C alloys. In hot forging, the forging temperature tends to increase as the mold material improves, but when the forging temperature reaches 800℃ or higher, Co-Cr
(W-Mo)-C alloys soften and have a short life as molds. Attempts have been made to use WC-Co-based cemented carbide in hot forging dies under these conditions, but even when used in a shrink-fit manner, cracks tend to occur due to thermal shock, resulting in short life. Therefore, at present, there is no suitable mold material made of a sintered alloy that can be used for hot forging at temperatures of 800°C or higher. [Objectives and findings of the invention] The present inventors have conducted various tests and research on materials for hot tools that can be used for a longer period of time even at high temperatures of 800°C or higher. By dispersing nitrides or carbonitrides of one or more metals from group 4a, 5a, and 6a metals in a specific proportion in the -(W-Mo)-C alloy, it is possible to It can improve the hardness and wear resistance of the material, and it can also have much stronger resistance to thermal shock than cemented carbide, so it can be used at high temperatures of over 800℃ It has been found that when used as a hot tool such as a forging die, almost no thermal cracks occur. [Matters Essential to the Structure of the Invention] This invention was invented based on the above-mentioned findings, and includes a nitride or a metal nitride of one or more of group 4a, 5a, and 6a metals as a dispersed phase. Carbonitride, or two or more of the nitrides and/or carbonitrides: 2 to 20%, Co-based alloy as a binder phase: 98 to 80% (weight%), Moreover, the Co-based alloy as a binder phase contains Cr: 15 to 35%, one or both of Mo and W: 5 to 25%, C: 1.0 to 3.0%, and the remainder is Co and unavoidable. This is a super heat-resistant and wear-resistant sintered alloy for hot tools, characterized in that it has a composition (hereinafter, weight %) consisting of impurities. [Components of the invention] () Dispersed phase The dispersed phase is a nitride or carbonitride of one or more metals from group 4a, 5a and 6a metals, or
Two or more types of nitrides and/or carbonitrides, and nitrides or carbonitrides of one or more metals from group 4a, 5a, and 6a metals are nitrides or carbonitrides of a single metal. This refers to both a carbonitride and a composite nitride (solid solution) of two or more metals, or a composite carbonitride, and a nitride in which the dispersed phase is different from the two or more of the nitrides and/or carbonitrides. This means that carbonitrides and/or carbonitrides are mixed in the binder phase. And its content is 2
~20% by weight. If the content is less than 2% by weight, the effect of improving hardness at high temperatures, the wear resistance when used as a hot tool, and the effect of improving thermal shock resistance will be small; on the other hand, if the content exceeds 20% by weight This is because there are many dispersed particles, and the toughness and impact resistance are significantly reduced, making it easy to break when used as a hot tool. Also, it constitutes the dispersed phase of the obtained sintered alloy.
The average particle size of the particles of nitride or carbonitride of one or more metals of groups 4a, 5a and 6a is
The thickness is preferably 3 μm or less. When the particles become coarse and have an average particle diameter of more than 3 μm, the strength of the sintered alloy decreases. Therefore, it is preferably 3μm or less, but 0.5~
2.0 μm is also preferable. () Binding phase The binding phase is a Co-Cr-(W-Mo)-C alloy, and its content is 98 to 80% by weight. If it exceeds 98% by weight, the effect of improving hardness at high temperatures, the wear resistance as a hot tool, and the effect of improving thermal shock resistance will be small;
If it is less than that, the toughness and impact resistance will be significantly reduced, and when used as a hot tool, it will easily break. The reason for limiting the composition of the alloy as the binder phase will be described below. (a) Cr Cr is an important component that improves wear resistance, corrosion resistance, and oxidation resistance in the alloy of this invention, and when this amount is less than 15% by weight,
The high-temperature hardness of the alloy decreases significantly, resulting in a decrease in wear resistance at high temperatures.
It has a short lifespan when used as a hot tool,
Corrosion resistance and oxidation resistance also decrease. On the other hand, 35
If the content exceeds % by weight, the toughness will decrease and the tool will be easily damaged when used as a hot tool. Therefore, the Cr content was set at 15 to 35% by weight. (b) Mo and W Mo and W are carbide-forming components in this alloy system and have a remarkable effect on improving the hardness and wear resistance of the alloy at high temperatures. If this amount is less than 5% by weight, the hardness at high temperatures will be low and the wear resistance will be low, while if it is contained more than 25% by weight, the toughness and oxidation resistance of the alloy will decrease. Its content was set at 5 to 25% by weight. (c) C C forms carbides (mainly M ₇ C ₃ , M ₂₃ C ₆ , M ₆ C) with Cr, Mo and W, and improves the hardness and wear resistance of this alloy at high temperatures. It is an ingredient. Therefore, the optimal amount of C is related to the content of Cr and the content of Mo and W, and in a composition with large amounts of Cr, Mo and W,
The optimum amount of C will also be higher. If the amount of C is less than 1.0% by weight, the hardness and wear resistance at a predetermined high temperature cannot be maintained, and conversely, if the content exceeds 3.0% by weight, it will become too hard and will be accompanied by a decrease in toughness. The content of C was set at 1.0 to 3.0% by weight. The reasons for limiting the composition of the Co-based alloy as a binder phase have been described above, but B, which promotes sintering,
Additives such as P, Ca, Mg, Fe, Ni, Mn, Si
It is also within the scope of the present invention to contain unavoidable impurities such as O and O in a total amount of 3% by weight or less when the sintered alloy consisting of the dispersed phase and the binder phase is 100% by weight. [Additional Matters to the Invention] The Co-based alloy powder used as the binder phase-forming component used in the present invention may be prepared by atomizing a molten metal, or may be prepared by atomizing a molten metal, or by using an oxide of Co, an oxide of Cr,
It may also be carried out by co-reduction, in which a powder mixture of Mo and/or W oxides and carbon is reduced by heating in a reducing atmosphere. In addition, commercially available powders of nitrides or carbonitrides of one or more metals of group 4a, 5a, and 6a metals, which are dispersed phase-forming components, can be used, but they must be ground to 3 μm or less in advance. Preferably, it is prepared by: It is preferable to mix the binder phase-forming component and the dispersed phase-forming component by wet mixing using a ball mill or the like, as this provides a better dispersion state in the sintered body than dry mixing. The molding is carried out using a mechanical press or a hydrostatic press, and a suitable molding pressure is 1 to 5 t/cm ² . Sintering is performed in a vacuum with a vacuum degree of 10 ^-4 to 10 ^-1 torr or in a reducing atmosphere with a gas pressure of 30 to 760 torr at temperatures of 1250 to 1250 torr.
This is done by heating at a temperature of 1350° C. for 0.5 to 3 hours, and it can be sintered to a state with almost no pores, with a shrinkage of 13 to 20%. Furthermore, in order to reduce the number of pores and improve reliability, it is desirable to further perform hot isostatic pressure sintering. [Example] Next, the configuration and effects of the present invention will be described in detail by describing Examples and Comparative Examples. In the following examples, all percentages shall mean percentages by weight. Example 1 Co oxide powder, Cr oxide powder, W oxide powder and carbon powder were mixed at 41.4% and 33.6%, respectively.
%, 18.2%, and 6.8%, and heated at 1220℃ in hydrogen with a gas pressure of 760torr.
Co-reduction with hydrogen and carbon is performed by heating for a period of time, resulting in 45.3%Co-32%Cr-20%W-2.7%
A Co-based alloy powder having a composition of C and an average particle size of 2.0 μm as a binder phase forming component was prepared. 15% titanium nitride powder with an average particle size of 0.8 μm;
Co-based alloy powder was blended at a blending ratio of 85% and mixed in alcohol for 48 hours in a ball mill. After drying the resulting mixed slurry, it was placed in hydrogen at a gas pressure of 760 torr at 700℃ for 1 hour. Annealed by heating. To this mixed powder, 1.0% stearic acid was added to the mixed powder, and pressure molding was performed using a hydrostatic press at a pressure of 3t/cm ² at 1300°C.
Sintering was carried out under vacuum (10 ^-2 torr) for 1 hour to obtain a sintered alloy having a density ratio of 99% and having substantially the same composition as the blended composition. The sintered alloy of the present invention had a Vickers hardness of 850 Kg/mm ² at room temperature, 600 Kg/mm 2 at 700°C, and 480 Kg/ ^{mm 2 at} 800°C. For comparison, we measured the Vickers hardness of a sintered alloy with only binder phase forming components without a titanium nitride dispersed phase, and found that it was 700 Kg/mm ² at room temperature, 520 Kg/mm ^{2 at 700°C, and 330 Kg/mm 2 at} 800°C. Ta. In this way, the sintered alloy of the present invention can be used even at high temperatures.
Furthermore, it has high hardness. Next, a test was conducted to make a bevel gear using a hot forging die made of the sintered alloy of the present invention.
The material to be forged was S35C, and the heating temperature was 800℃. The life of the conventional mold made of die steel was 5000 times, whereas the life of the mold made of the sintered alloy of the present invention was 20000 times. In addition, when a mold made of a sintered alloy containing only binder phase forming components without a dispersed phase was used, the number of cycles was 3000. Example 2 54.4% by atomization method using Ar gas
A Co-based alloy powder as a binder phase forming component having a composition of Co-30%Cr-13%W-0.5%Fe-2.1%C and an average particle size of 3.5 μm was prepared, and the Co-based alloy powder had an average particle size of 1.0 μm. TiC _0.5 N _0.5 powder, Co-based alloy 85%,
TiC _0.5 N _0.5 Added at a blending ratio of 15%,
Wet mixing was performed for 72 hours using a vibratory mill with carbide balls. Dry this mixture at 650℃
It was annealed in hydrogen at a gas pressure of 760 torr for 1 hour.
This powder was molded using a hydrostatic press at a pressure of 3t/ ^cm2 , and then molded in hydrogen at a gas pressure of 760 torr at 1290°C.
After sintering for 1.5 hours, a sintered alloy with a density ratio of 97% was obtained. This sintered alloy was subjected to hot isostatic pressing at 1250°C and 1000 atm for 1 hour to obtain a sintered alloy of the present invention having a density ratio of approximately 100% and a composition substantially the same as the blended composition. The sintered alloy of the present invention had a Vickers hardness of 750 Kg/mm ² at room temperature, 560 Kg/mm 2 at 700°C, and 470 Kg/ ^{mm 2} at 800°C. On the other hand, the Vickers hardness of a sintered alloy containing only binder phase forming components without TiC _0.5 N _0.5 is 640 Kg/mm ² at room temperature, 480 Kg/mm ² at 700°C, and 310 Kg/mm ² at 800°C. The effect of improving hardness was clearly seen. Next, a test was conducted to make an arm using a hot forging die made of the sintered alloy of the present invention. The material to be forged was S45C, and the heating temperature was 830℃. While the lifespan of conventional die steel molds is 4000 times,
The life of the mold made of the sintered alloy of the present invention was 25,000 times. In addition, when a mold made of a sintered alloy containing only binder phase forming components without a dispersed phase was used, the number of cycles was 3000. Example 3 Co-reduction method using Co oxide powder, Cr oxide powder, W oxide powder, Mo oxide powder, and carbon powder produced bonds having various binder phase compositions shown in Table 1. Co-based alloy powder (average particle size: 2.0 μm) as a phase-forming component was prepared. Next, dispersed phase forming components having various dispersed phase compositions listed in Table 1 were added to the various Co-based alloy powders described above.
Each was added to the content shown in Table 1, mixed in alcohol for 24 hours using a ball mill,
Pressure forming is performed using a hydrostatic press at a pressure of 3t/ ^cm2 , sintered at 1300℃ for 1 hour in a vacuum (degree of vacuum 10 ^-2 torr), and then hot-sintered for 1 hour at 1250℃ and 1000 atm. Isostatic pressing was performed to obtain sintered alloys Nos. 1 to 22 of the present invention and comparative sintered alloys Nos. 1 to 8 having the sintered alloy compositions shown in Table 1. The conventional sintered alloy refers to a sintered alloy containing only a binder phase and no dispersed phase, and was produced in the same manner except that no dispersed phase forming component was added. The Vickers hardness at 800° C. and the transverse rupture strength at room temperature were measured for the sintered alloy of the present invention, the comparative sintered alloy, and the conventional sintered alloy, and the results are shown in Table 1. Further, a test was conducted in which disk-shaped test pieces were made using hot forging dies made of the sintered alloy of the present invention, a comparative sintered alloy, and a conventional sintered alloy. The material to be forged is S45C,
The heating temperature was 850°C. The life of the mold at this time was measured and shown in Table 1. This life is expressed as the number of times hot forging can be performed before the amount of wear on the die becomes large and burrs occur. When the sintered alloys of the present invention were used, the molds withstood long-life hot forging work without breaking, whereas comparative sintered alloys Nos. 1, 3, 5, and 7 and the conventional sintered alloys The mold life of the alloys was short, and mold cracks occurred in comparative sintered alloys No. 2, 4, 6, and 8 due to lack of toughness.

【table】

[Overall effect of the invention]

The super heat-resistant and wear-resistant sintered alloy of this invention maintains its hardness at high temperatures of 800°C or higher, has excellent thermal shock resistance, and has good transverse rupture strength, so it can be used as a hot tool, especially at temperatures of 800°C or higher. It is a useful material that can be used as a hot forging mold at forging temperatures, and has a much longer life than conventional sintered alloys, and can be used for a longer period of time than conventional die steel.

Claims (1)

[Scope of Claims] 1. A nitride or carbonitride of one or more metals from group 4a, 5a and 6a metals, or two or more of the nitrides and/or carbonitrides as a dispersed phase:
Cr: 15-20%, Co-based alloy as a binder phase: 98-80% (by weight), and the Co-based alloy as a binder phase contains Cr: 15-35%, Mo and It is characterized in that it contains one or two of W: 5 to 25%, C: 1.0 to 3.0%, and the remainder consists of Co and inevitable impurities (hereinafter referred to as weight %). Super heat-resistant and wear-resistant sintering alloy for hot tools.