JPS5858245A - Hard alloy for impact resistant tool - Google Patents

Abstract

PURPOSE:To obtain a sintered hard alloy for an impact resistant tool with superior impact and wear resistances by sintering a hard phase contg. Mo-W carbide as a principal component with a binding phase of an Fe group metal. CONSTITUTION:Particles of simple hexagonal system (Mo,W)C or a mixture of (Mo,W)C with WC as a hard phase are sintered with 3-60wt% Fe group metal such as Co as a binding phase. The percentages of Mo and W in the hard phase are 5-95% Mo and 95-5% W, and the ratio of (Mo,W)C/WC is adjusted to 0.1-10. The carbide particles as the hard phase are composed of 10-90wt% fine particles having <=1mum size and the balance coarse particles having >=3mum size. When an impact resistant tool such as a metallic header mold is manufactured using the resulting sintered body, the life of the mold is considerably prolonged owing to the superior impact and wear resistances of the sintered body.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on WC-Co, a conventional hard alloy for impact-resistant tools.
It concerns the improvement of alloys.

In general, impact-resistant tools are required not only to have excellent wear resistance, but also to have even higher toughness and impact resistance.

Particularly in cold forging applications, the workpiece is forced to undergo a large amount of unilateral deformation, forcing it to be crimped and rubbed against the original die under high stress levels.'11 This is the key to the lifespan of impact-resistant tools. This is the cause of burn-in. Therefore, reducing the chemical affinity with the workpiece material is an effective means of preventing seizure.

On the other hand, more than half of the lifespan of cemented carbide header dies is due to cracks in the cemented carbide parts, and most of them end up breaking after a much shorter lifespan than the steady lifespan due to wear. In general, as a material for cemented carbide for header molds, in order to prevent breakage, which is the main cause of its safe life, the mean free row of the bonding metal is 5I, which is generally said to suppress crack propagation.
The material is made of coarse carbide with increased toughness. However, if the mean free path of the bonded metal is made too large, it becomes susceptible to plastic deformation, and in a one-piece mold that is subject to high impact, there are cases where the life of the product is shortened due to dimensional defects of the product.

The present inventors have conducted repeated research to eliminate the above-mentioned drawbacks of the cemented carbide used for this Hesogoo mold, etc., and have found a part of W in WC that is known to eliminate the drawbacks of WC-based alloys. As a result of a detailed study of the sintering phenomenon of (M O, W ) C in which MO is substituted, the following knowledge was obtained.

In other words, in (Mo, W)C-based alloys, grain growth of carbides due to Ostwald drying of the melt precipitation reaction type, which is observed in normal WC-based alloys, hardly occurs even when the liquid phase appears, and it is as if diffusion occurs. We have discovered the fact that grain growth is rate-limiting and only slow. Therefore, when powder containing WC and (MO,W)C is sintered, some of the fine (Mo,W)C is dissolved into W due to the dissolution precipitation phenomenon.
It has been found that most of Wc and (Mo, W)C are stable and coexist, although they may precipitate on the surface of C or (MO,W)C. Moreover, by coexisting these particles, the toughness characteristic of WC-based alloys and (Mo
, W) It has been found that it is possible to produce an alloy that combines the melting G resistance characteristic of the base alloy with steel.

Figure 1 shows we-ssvoz%Co alloy (A) and (MOn
, 7 +W 0.3) C-25voZ%WC-55
The results of a comparison of the friction coefficient of vot%Co alloy (B) with 845C material are shown, and the alloy containing (Mo, W)C has a friction coefficient of 40 or less than that of the conventional WC-Co alloy. However, this also shows that by including (Mo , w ) C in the alloy, the welding resistance with steel is significantly improved.

The present inventors have also discovered that plastic deformation resistance can be improved by mixing coarse and fine hard phases. That is, as shown in Figure 2, 0.5, 1Moo, wo3)
C-25vot%61t WC-55vot%CO alloy (C, i1 grain mixed crystal) is 5μ (MoO, 7WO2)C-
25vat%6μV+'C-55vot% Co alloy C
D, the amount of strain for the same stress 4 is smaller compared to (coarse grain only),
Improved plastic deformability. Coarse particles and fine particles herein mean 5 microns or more and 1 micron or less, respectively, and particles with a particle size of 1 to 5 microns reduce the above effect.

In other words, it is thought that the coarse carbides increase the mean free path of the bonded metal to suppress the propagation of cracks, and the fine carbides are uniformly dispersed in the bonded metal to improve compressive strength. This phenomenon is caused by coarse WC grains and fine (M
o, W) 0 grains, coarse grains (Mo, W) 0 grains and fine grains of WCl
'i2, or when at least two or more types of coarse grains and fine grains (MO2W)0 grains with different grain sizes were used, the same effect was obtained in all cases. However, alloys using coarse and fine WC grains showed no significant difference in welding resistance to steel compared to conventional WC-Co alloys.

Coarse and fine grained hard alloys containing MO with strict grain size control are significantly superior in impact resistance and welding resistance compared to conventional impact resistant WC-Co cemented carbide. Based on this knowledge, the present invention was completed.

That is, in the present invention, the hard phase is a simple hexagonal type (M
o, W) Consisting of a mixture of C or (Mo, W)C and WC, the binder phase is composed of 5 to 60% by weight of iron group metals, and the hard phase is fine grains of 1μ or less and grains of 5μ or more The present invention relates to a hard alloy for impact-resistant tools, which is characterized by a mixture of coarse grains and fine coarse grains.

The ratio of fine and coarse particles in the hard phase of the present invention is such that the fine particles account for 10 to 90% by weight of the entire hard phase, which provides excellent impact resistance and welding resistance〇 (MOX HW 1. , -x) C") The composition is preferably 0.05≦x≦0.95, and X is 0.0
When X is less than 5, the effect of Mo is not recognized, and when X is o, and when it is more than 95, the sinterability is poor and the molybdenum is unstable as a carbide.

Also, regarding the ratio of (Mo, W)C and WC, (Mol
For alloys with W)C/WC of 0.1 or less, no significant difference was observed in friction coefficient from WC alloys, and (Mo, W)C/W
This is because when C is 10 or more, WC diffuses into (Mo, W)C, and an alloy containing WC and (Mo, WJC) is not substantially formed.

In addition, in the alloy of the present invention, the composition ratio of MO and W is (M
ox + W + -x) When displayed as C,
The composition of (Mox, Wl-x)C in the alloy is not necessarily one type, but it is also possible to change the properties by combining two or more types.

It has also been found that, in the alloy of the present invention, the characteristics of the alloy of the present invention are fully satisfied even in alloys containing IVasVa, V[a group metal carbide or nitride, and the head of which is a carbonitride.

At the same time, even if C in (Mo, W)C is replaced with N, OlH, B, etc., the effect is the same. In addition, in order to strengthen the binder phase of the alloy of the present invention, At% BN
Trace amounts of elements such as 0% AgXCr5 P-, Si, and Ca can also be added.

In addition to cold forging tools, which are well known as impact-resistant tools, the alloy of the present invention has also shown its effectiveness in wear-resistant parts such as dies, rolls, shearing tools, sliding parts, can making tools, drills, and mining tools. It is something that can be demonstrated.

Example 1 A mixed powder with a composition ratio of 40% by weight each of C with an average particle size of 5μ (MOo, , wo3) and WC with an average particle size of 0.5μ and 20% by weight of CO powder was milled using a ball mill. The mixture was mixed for 20 hours in an alcohol solvent. After adding 2.0% by weight of paraffin to the mixed powder, it was dried. After stamping the mixed powder, it was heated at 1550°C in vacuum for 1
time, sintered. The properties of the obtained alloy were as follows.

Specific gravity: 11.8 Hardness: 84.5 Transverse rupture strength: 270 Kg/am2 Example 2 An alloy was prepared using the manufacturing method of Example 1 and had the composition shown below. The main physical properties of the alloy are shown in Table 1.

Table 1 Example 5 Alloy 4 and Alloy 9 prepared according to Example 2 were used as five header mold materials together with Alloy 12.15 prepared as a comparative example, and the heads of screws made of 545C type standard force were plasticized. We conducted life tests of various alloys when processed.

The results are shown in Table 2.

Table 2 Appetizer All alloy sides are the same as in Example 2.

Example 4 42.5% by weight of each of (lvLo, , wo, ) C with an average particle size of 6μ and (Moa6, wo2) with an average particle size of 0.5μ was mixed with 15% by weight CO powder. The mixture was mixed for 50 hours in an alcohol solvent using a ball mill. After adding 2.0% by weight of paraffin to the mixed powder, it was dried. After the mixed powder was pressed, it was fired in vacuum at 1400° C. for 1 hour. The properties of the obtained alloy were as follows.

Ratio Weight 12.0 Hardness 88.2 Transverse rupture strength 25 (I Kg7d

[Brief explanation of the drawing]

Figure 1 is a graph comparing the friction coefficients of the conventional cemented carbide (A) and the alloy of the present invention (B), and Figure 2 is a graph comparing the coefficient of friction of the conventional cemented carbide (A) and the alloy of the present invention (B).
Stress-strain curves of C) and comparative alloys (DJ compression test. Representative 1) Representative Akira Ryo Hagiwara -

Claims (1)

[Claims] tIi11! The quality phase is of simple hexagonal type (M(1, W
) C or (Mo, W) A mixture of C and WC, the binder phase is composed of 5 to 60% by weight of iron group metals, and the l1i14 phase consists of fine particles of 1μ or less and 5μ
A hard alloy for use in impact-resistant tools, characterized by a coarse mixed grain of υ■ coarse grains. 2. The composition of (M ox + W, -X) is 00
The hard alloy for impact-resistant tools according to claim 1, where 5≦X≦0.95. The impact-resistant hard alloy according to claim 1 or 2, where 501≦(Mo, W) C/WC≦10. Hard alloy for tools. 4. The hard alloy for impact-resistant tools according to claim 1, wherein the fine-grained hard phase accounts for 10 to 90% by weight of the entire hard phase.