JPS6031896B2 - Hard alloys containing MO - Google Patents

Description

[Detailed Description of the Invention] Tungsten, which is used in cemented carbide, exists in only a small amount on the earth, so it is an expensive metal, and its price has soared in recent years as a so-called strategic material.

Therefore, it has become important to replace tungsten in cemented carbide with pond materials. One solution is to use cemented carbide tools or titanium-based cermet tools. However, these tools have poor toughness and cannot replace cemented carbide in many cases. Therefore, it has been investigated whether tungsten carbide in cemented carbide can be replaced with molybdenum carbide. The present invention relates to the latter.

Tungsten carbide (MC) to molybdenum carbide (MoC)
There has been little consideration in the past to replace it with .

The reason for this is that molybdenum carbide does not stably exist as MoC at room temperature, but exists as Mo2C.
Mo2C has a room temperature hardness (bits) of 1800 to 150.
There is only 0k9' secret. This is about 2/3 of WC's 2400k9/fence. Furthermore, MoC is not often used as an additive in cemented carbide raw materials. This is Mo
When 2C is added, the carbide grain size of the cemented carbide becomes fine, and acicular crystals of Mo2C grow, reducing the alloy strength. However, when molybdenum carbide forms a solid melt with tungsten carbide, it becomes stable as a monocarbide having a simple hexagonal crystal structure.

If this solid carbide of tungsten and molybdenum consisting of (Mo,W)C is used as a raw material for cemented carbide, the carbide will have the same hardness as WC, and WC will harden in MoC, resulting in M
This is a very favorable result as it prevents oC from decomposing into Mo2C and carbon. Therefore, if a stable carbide of (Mo,W)C can be easily produced, it is considered possible to replace tungsten with molybdenum. In order to make this more concrete, development of a stable manufacturing method for (Mo, W)C is also underway. (Unexamined Japanese Patent Publication No. 51-146306) However, even if the (Mo.W)C powder obtained by this method is used as a raw material for a (Mo.W)C-Co alloy as a substitute for WC, MoC is not stable in the alloy. In many cases, Mo2C is precipitated. The present inventors conducted a detailed study on why Mo2C precipitates when a solid solution of MoC and WC is used as a raw material for cemented carbide.

As a result, the mechanism of the burning streaks in the (Mo.W)C-Co alloy was considered to be as follows. In the cooling process, WC and M are added to Co.
The dissolved elements of oC do not precipitate at the same temperature.

When only WC precipitates at the liquidus line of WC-Co of 1320°C, only Mo and C remain in the Co binder phase.

MoC becomes stable until 118,000, but remains unchanged)
When cooled, it decomposes into Mo2C and C. Therefore, even if the amount of carbon is close to the stoichiometric amount, cooling occurs as Mo2C and carbon coexist. In such an alloy, the precipitates can be dispersed by rapid cooling treatment in order to prevent the agglomeration of precipitated free carbon and Mo2C.

However, although such a method can provide a sufficient cooling effect since the heat capacity of a small-sized alloy is 4 mm, it is difficult to apply it to a large-sized cemented carbide having a large heat capacity. However, when the present inventors analyzed the binder phase of the precipitated alloy of acicular Mo2C by X-ray diffraction, the lattice constant of the binder phase was completely unchanged from that of the pure metal, indicating that the binder phase was not alloyed. It was discovered that the binder phase was not tarnished, and that if the precipitated acicular Mo2C could be dispersed in granular form, it would be possible to prototype an alloy with sufficient strength.

The present inventors have conducted various studies on the relationship between the alloy carbon content and the rutting property of cemented carbide made from (Mo.W)C as a raw material, and have found the following.

When the carbon content of the alloy was less than the theoretical carbon content, molybdenum-tungsten double carbide was precipitated as needle-like crystals. (Fig. 2) However, in the case of an alloy containing a certain amount of impurity elements such as Fe, it was found that double carbides do not form needle-shaped crystals but precipitate as fine granular precipitates.

(Figure 1) As a result of measuring the strength of an alloy in which acicular molybdenum tungsten double carbides were precipitated and an alloy in which granular double carbides were precipitated, it was found that the latter showed a significant improvement in toughness.

It is a well-known fact that alloy strength significantly changes depending on the shape of the precipitates. The former is molybdenum tungsten double carbide with needle-like crystals (crystal structure Mo
2C type), which tends to become a starting point for fracture, resulting in a deterioration in alloy strength. It is thought that the strength of the alloy is improved because stress concentration does not occur, but rather serves to absorb external forces applied to the alloy. Although the details of the reason why this granular crystal molybdenum tungsten double carbide precipitates are unknown, it is thought to be as follows.

In ordinary (MOW)C alloys, needle-shaped molybdenum tungsten double carbides precipitate because W, Mo, and C are dissolved in the binder phase during the cooling process from the liquid phase. This is because the precipitation temperatures are different.

That is, since WC precipitates at a relatively high temperature, only Mo and C remain in the binder phase, and 1180q0
In the following, since MoC decomposes into Mo2C and C, Mo
2C remains as aggregates. However, if a certain amount of impurity element exists in the binder phase, this element becomes the nucleus (M
o・W) 2C is combined and many nuclei of molybdenum tungsten double carbide particles are generated and precipitated before the liquid phase disappears, and Mo and C no longer exist in the binder phase, so the liquid phase disappears at 1180:00. Even in the following cases, needle-like crystals of MoC do not precipitate.

Generally, such multinucleated precipitates precipitate in spherical or granular shapes, but in order to disperse and precipitate molybdenum-tungsten double carbide in the alloy even more finely, it is necessary to rapidly cool it from the leech silk temperature to the liquid phase disappearance temperature. It is also effective by suppressing the precipitation and grain growth of molybdenum-tungsten double carbides. Elements added as impurity elements to the bonding metal include Be, Mg, Ca, B, Si, P, and Mn.
, Fe, Re, or more. Among them, Fe is highly effective because it easily reacts with the elements Mo, W, and C. If the total amount of these exceeds 3% by weight, the molybdenum-tungsten double carbide becomes arms and is not effective in improving strength. In addition, Tj, Zr, Hf, Ta,
Even when Nb is added, it is effective in dispersing and precipitating double carbides. Moreover, if it is less than 0.1% by weight, there is no effect. In addition, the size of molybdenum tungsten double carbide, which is a granular precipitate, is 0.1
〃 to 10 y is good, and the most effective is 1.0 y to 2 y.

The reason for this is that when the precipitate particles become coarse, the alloy strength deteriorates and the hardness decreases, and in the case of fine molybdenum tungsten double carbide, the double carbide (MOW)
This is because since it precipitates at the C interface or the binder phase interface, the interfacial strength decreases, which causes the alloy strength to deteriorate. The carbon content in the alloy ranges from 80% to 99% of the theoretical carbon content.
% is good, but 90 to 98% is particularly effective. The reason for this limitation is exactly the same as the grain limitation for molybdenum tungsten double carbide. Granular or spherical molybdenum-tungsten double carbide gives alloy properties a large change depending on its particle size and distribution state, but also changes greatly depending on the value of the double carbide amount.

The present inventors clarified the following as a result of X-ray diffraction of the alloy. Using CuK2, 40KV, 8 melon hA, F.
S400 ratio's, T. C.O. In X-ray diffraction (20) under $ec conditions, if the line height ratio of the molybdenum tungsten double carbide peak to the (MOW) C peak appearing near 39.4o and 48.4o is between 0.05 and 0.20. The alloy properties were found to have an alloy strength equivalent to or higher than that of the WC-Co alloy. For convenience, molybdenum tungsten double carbide is also written as Mo2C, but even if W, Co, Ni, Fe, N, and 0 are solidly dissolved in this Mo2C, the ratio of metal components to nonmetal components is 2: Even if it fluctuates around 1, the effect of the present invention is not lost.

In addition, it is preferable that the binding metal is mainly composed of Ni and/or Co, and accounts for 3 to 5% by weight of the composition.

This is because if it is less than 3% by weight, it is too strong, and if it exceeds 5% by weight, the high temperature characteristics will deteriorate.

In addition, when the ferrous metal becomes a binder phase, Wa, Va, W
It is natural to form a solid solution with group a metals, and AI, Si,
The effects of the present invention are not lost even by adding elements such as Ca and Ag that have a hardness compared to these elements. In addition, a part of the carbide* made of molybdenum tungsten is replaced with Ti,
BI including Zr, m, V, Nb, Ta, Cr, Mo, W
There is no change in the basic relationship even when the type double carbide is substituted.

Note that the same relationship holds true for alloys in which a portion of C in the carbide is replaced with nitrogen and/or oxygen.

In this case, the total amount of oxygen and/or nitrogen is regulated by the following formula in order not to impede the crystallinity of the alloy. W atomic%.

o1 mi (1-Wa, Va, Kawa A group metal atomic %) (Aoi Ungi A-ji temple's Norihiro Kirin charter figure) ≦. 5 (no effect is observed below 0.01).

) Also, from the viewpoint of silk-sintering properties, the nitrogen content must be less than 1 atomic % of the oxygen content or 0.5 atomic % of the total of Wa and Va group atomic %, whichever is greater. is desirable. Finally, the scope of application of the alloy of the present invention will be described.

Since this alloy has rutting resistance and hardness equal to or higher than that of WC-Co alloy, it can be applied as wear-resistant tools such as guide loafs and hot wire rolling rolls, as well as cutting tools. If the surface layer is coated with one or more coating layers made of a highly wear-resistant ceramic layer such as TIC, TIN, N203, etc., the tool will have even greater toughness and wear resistance than a tool coated with a WC-Co alloy. We were able to prototype an excellent cutting tool. Furthermore, it is a well-known fact that at this time, a decarburized layer called a slag phase is formed at the interface between the coat layer and the base layer. The same is true for this alloy, and in order to prevent the decarburization layer from forming arms directly under the coating layer, F. It has been found that when C (free carbon) is present, good results can be obtained without impairing quality. Example 1 Using (Mo7W3)C containing 0.2% Fe as an additive, the composition was changed to (MOW)C-
Weighed 15 wt% Co and the amount of alloy carbon so that the reaction rate (bonded carbon amount/theoretical carbon amount) was 100, 99, 98, 96%, mixed wet in an organic solvent, and then after the dry embossing process. , sintered at 1450 oo in vacuum.

The properties of the obtained alloy are shown in Table 1. Table 1 T. 0: Total carbon content, F. 0: Free carbon content Reaction rate: Bonded carbon content (theoretical carbon content) For comparison, an alloy leg, side, 'q that did not contain the additive Fe was prepared.

The disadvantage of the present invention is that [B-, {C], the plate had Mo2C type double carbide precipitated in granular form, whereas the conventional alloy leg,'
F}, when boiled, Mo2C type double carbides were precipitated in the form of needles. It can be seen that the alloy style [B-, Ni-, plate] of the present invention has higher toughness than the conventional alloys (E}, {F}, {G-).

Note that {OK, {F}, {G) does not include the additive Fe. As described above, in the alloy of the present invention, the alloy strength does not decrease even if the alloy carbon content is lower than the theoretical carbon content. However, in conventional alloys, molybdenum-tungsten double carbides produced due to carbon deficiency precipitate as needle-shaped crystals, resulting in low toughness. FIG. 1 shows a photograph of the structure of the present invention {C}, and FIG. 2 shows a photograph of the conventional alloy 'F'.

It can be seen that in the alloy of the present invention, the Mo2C type double carbide exists in the form of particles, whereas in the conventional alloy, it is acicular. Example 2 80 to 90% by weight of carbide having a theoretical bonding carbon content of 5 (Mo7W3)C, 0 to 3 of (Mo7W3)C
1% by weight, 9-10% by weight of Co, Fe, Re, Si
, B, and 0.1 to 0.5% by weight were mixed to prepare an alloy as shown in Example 1.

In the structure of the alloy obtained by this method, carbides of the pond C type (MOW) 2C were uniformly dispersed, as shown in FIG. (MOW)C-(Mo,W) obtained by the following method
) In the case of the 2C alloy, needle-like crystals were precipitated as shown in Fig. 2.
Table 2 shows a comparison of the properties of these alloys. Table 2 In the alloy of the present invention, (MOW)2 due to impurity addition
It was found that the alloy in which C was dispersed had high ballability.

A header for machining a tool for cold casting soft iron was made using the alloy obtained by the above method.

Nails were manufactured using this header. As a life test, a test was conducted until the header die cracked.
As shown in Table 3, the alloy of the present invention could be used 30,000 to 100,000 times, while the conventional alloy could only be used 5,000 times on two sides at most.

Note that Fe showed the best results as a dispersant.

Table 3 Example 3 86% by weight of 5-1 (Mo7W3)C, 2-2 (Mo7W3)C
W3) 5% by weight of 2C, 9% by weight of Co, 0.2% of Fe
The mixture was weighed to give a weight percentage, wet-mixed in an organic solvent, dried and stamped, and then condensed in vacuum at 1450°C.

The transverse rupture strength of the obtained alloy is 260k9/rail, hardness (Hv)
was 1400k9/boiled. 3 from the surface phase of this alloy.
F within 00m. After carburizing to precipitate C (free carbon), a TIC layer, a double layer of TIC, TIN, and a TIC layer are formed.
203 layers of IC and AI were coated. For comparison, a commercially available TIC coated chip of WC alloy was inserted and the following cutting test was conducted. (Model number SUN 43
2) Work material SCM 3 (HB = 280) Cutting speed V = 17 h/min Feed f = 086 ribs/rev Depth of cut d = 1.5 ribs Cutting time 3 min The test results are shown in Table 4. .

Table 4 When the alloy of the present invention is coated, ordinary WC-Co
It can be seen that the performance is equivalent to or better than that of the system.

Note that there is a decarburized layer (
No phase) was observed within 300r directly below the coating layer.
F. C (free carbon) was observed. Example 4 83.9% by weight (Mo7W3)C, 1% by weight (Mo7W3)
3) 2C, 5 wt% TaN, Col wt%, M carved. Phosphorization was achieved at 1320 pm with a blending composition of 1% by weight.

The amount of oxygen in the alloy is 0.01% by weight and the amount of nitrogen is 0.2% by weight, and the amount of oxygen and nitrogen in the alloy and Mo, W, ra
The value in the relational expression of the ratio with metal atoms was 0.02. In addition, the above alloy was tested using (40 kV)
, 8 hA) X-ray diffraction revealed that the Mo2C type (
101) plane peak was detected. In addition, the precipitated Mo2
The C-type precipitated phase was dispersed with a particle size of about 0.5 to 1 French. The transverse rupture strength of this alloy is 220k9/Iso, and the hardness is 89.8
Met. On the other hand, in the alloy containing Mg, the transverse rupture strength is 1
The hardness was 52k9/m2 and 89.4. Example 58
0% by weight (M Takumi W5) C, 1% by weight (M et al. W5) Next, 3
Weight % TIN, 2 weight % TaN, Col 3 weight %, balance 1
Ca, P, and Mn were blended in weight% to 1380
Sintered with oo.

Mo2C type precipitates were detected in each of the above alloys and were dispersed in granular form. Table 5 shows the composition, transverse rupture strength, and hardness of each alloy.

Table 5 Note that if Ca, P, and Mn are not added, the transverse rupture strength is 141
k9/fence, total hardness was 0.

Example 6 Road. 4% by weight (Mo7W3)C, 1.5% by weight (Mo7
W3) A header die was made by creating an alloy of 2C, 0.1% by weight Fe, Co and Ni in a 2:1 ratio of 30% by weight.

Compared to the conventional WC-25 wt% Co alloy, the lifespan was more than four times longer.

[Brief explanation of the drawing]

FIG. 1 shows a micrograph of the structure of the (Mo7W3)C alloy of the present invention, and FIG. 2 shows a conventional alloy at a magnification of 150 needles. The granular gray precipitates in FIG. 1 are molybdenum tungsten post carbides, and the black acicular precipitates seen in FIG. 2 are Mo2C. FIG. 3 shows the X-ray diffraction pattern of the alloy of the present invention. Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1 At least two of the hard phases are composed of double carbides of Mo and W, and among the double carbides of Mo and W, those with a simple hexagonal crystal structure are 80% of the hard phase. ~
Accounting for 99.5%, (MoW)_2C type is 0
．． The carbide is granular to spherical with a diameter of 0.1 to 10μ, and 3 to 50% by weight of the binder phase is one or more of Ni or Co and 0.1 to 20% by weight. 3
Weight% Be, Mg, Ca, B, Si, P, Mn, Fe
, Re, or more. 2 Among the hard phases, at least two types are composed of double carbides of Mo and W, and among the double carbides of Mo and W, those with a simple hexagonal crystal structure are 80 to 80% of the hard phase.
Accounting for 99.5%, (MoW)_2C type is 0
．． 5 to 20% by weight, and the double carbide has a thickness of 0.1 to 10μ
It has the following granular or spherical shape, and some of the carbon in the carbide is replaced with nitrogen and/or oxygen, and the amount is 0.
01≦(1-(W atomic %)/((Mo+W) atomic %))
((Acid atomic% + Nitrogen atomic%) / ((Mo+W) atomic%
))≦0.5, and 3 to 50% by weight of the binder phase is N
i or Co and 0.1 to 3% by weight of Be, Mg, Ca, B, Si, P, Mn, Fe, R
Mo characterized by consisting of one or two or more of e.
Hard alloys including. 3 At least two of the hard phases are composed of double carbides of Mo and W, and among the double carbides of Mo and W, those with a simple hexagonal crystal structure are 80 to 80% of the hard phase.
Part of the hexagonal type is replaced by a B1 type hard compound containing metals from groups VIIa, Va, and VIa of the periodic table, and the (MoW)_2C type is 0.
．． 5 to 20% by weight, and the double carbide has a thickness of 0.1 to 10μ
It has the following granular or spherical shape, and 3 to 50% by weight of the binder phase is one or more of Ni or Co, and 0.1
~3% by weight of Be, Mg, Ca, B, Si, P, Mn,
A hard alloy containing Mo, characterized by being composed of one or more of Fe and Re. 4 At least two of the hard phases are composed of double carbides of Mo and W, and among the double carbides of Mo and W, those with a simple hexagonal crystal structure are 80 to 80% of the hard phase.
Part of the hexagonal type is replaced by a B1 type hard compound containing metals from groups VIIa, Va, and VIa of the periodic table, and the (MoW)_2C type is 0.
．． 5 to 20% by weight, and the double carbide has a thickness of 0.1 to 10μ
It has the following granular or spherical shape, and a part of the carbon in the hard phase is replaced with nitrogen and/or oxygen, and the amount is 0.01≦(
1-(W atomic %)/(IVa, Va, VIa group metal atomic %)
) ((oxygen atom% + nitrogen atom%)/(IVa, Va, VIa
group metal atom%))≦0.5, and 3 to 50% by weight
The binder phase is one or more of Ni or Co, and 0
．． 1-3% by weight of Be, Mg, Ca, B, Si, P, M
A hard alloy containing Mo, characterized by being composed of one or more of n, Fe, and Re.