JP2002180175A - Sintered alloy excellent in high temperature property and die for hot forming using the alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered alloy which is excellent in high temperature hardness, oxidation resistance and specular properties, also excellent in sinterability, and is particularly suitable to a die for hot forming. SOLUTION: The sintered alloy consists of an alloy with a three phase mixed structure in which a first phase consists of WC, a second phase is a double carbide (nitride) essentially consisting of Ti and W, and bonding phase metal is present as a double carbide (nitride) of a third phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered alloy having excellent sinterability, high-temperature hardness, oxidation resistance and mirror finish, and a hot-forming die using the same.

[0002]

2. Description of the Related Art In recent years, many glass or plastic products such as lenses and substrates for hard desks have been manufactured by hot forming such materials in order to save complicated machining. I have. The material of the mold used for such hot forming is required to have excellent mechanical properties at high temperatures, excellent oxidation resistance, and excellent mirror surface properties. , Ceramics and cemented carbide have been proposed. For example, JP-A-52-4
5613, silicon carbide or silicon nitride,
Japanese Patent Publication No. 62-51211 discloses a tungsten carbide-based cemented carbide containing 3 to 10% by weight of cobalt.

[0003]

However, although ceramics are excellent in oxidation resistance, they are poor in toughness and poor in grindability, so that there is a problem that a long time is required for mirror finishing. Cemented carbides are mainly composed of WC as a hard phase and Co and / or Ni as a binder phase. However, since the binder phase is a metal, the hardness is significantly reduced at a high temperature, and the binder is bonded at room temperature. Since the phase is softer than WC, there is a problem that dents are likely to occur during mirror finishing. As a countermeasure against this, Japanese Patent Application Laid-Open No. 2-120244 discloses a mold for molding an optical element which does not contain a binder phase metal. However, since it does not contain a binder phase metal, it has poor sinterability and often has minute pores in the alloy. And even if the HIP treatment is performed after sintering, it is difficult to completely eliminate the sintering, and there is a problem that the specularity is impaired.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. That is, WC is the first phase, and double carbon (nitride) mainly composed of Ti and W is the second phase.
The phase and binder phase metal are present as a third phase double carbon (nitride) by adjusting the carbon content of the alloy low.
By doing so, the binder phase metal improves sinterability during the sintering process, but in the structure after sintering, double carbon (nitride)
Since the oxides do not form and remain as a metal phase, the resulting alloy has characteristics of being excellent in hardness, strength, oxidation resistance at high temperatures and extremely excellent in mirror finish.

The reason why WC is used as the first phase is that WC has excellent mechanical properties. However, if the average particle size exceeds 2.5 μm, the transverse rupture strength decreases, and if the average particle size is less than 0.4 μm, the WC becomes hard at high temperatures. Tends to decrease. The addition of Ti is for the purpose of improving the high-temperature hardness and oxidation resistance of the double carbon (nitride) containing Ti, and the effect is small when the addition amount is less than 1%,
If it is added in excess of 25%, it becomes difficult to densify during sintering. The addition of Ni and / or Co is for improving the sinterability. When the addition amount is less than 0.5%, the effect is small, and when it exceeds 2%, the third phase double carbon (nitride) and The WC becomes coarse and the strength is significantly reduced. Periodic tables IVa, V other than Ti and W
Substitution with one or more transition metals belonging to groups a and VIa has effects such as further improving the oxidation resistance of the alloy and increasing the hardness. Bondability decreases. It is preferable to replace a part of carbon with nitrogen, because the oxidation resistance of the alloy is further improved.
%, The sinterability decreases. Although the replacement of a part of Ni and / or Co with Fe is effective in improving the sinterability, the oxidation resistance is deteriorated when the replacement amount is large. Therefore, the replacement amount is the total of Ni and / or Co. It is preferable to set the amount to 50% or less.

[0006]

EXAMPLES In order to manufacture the product of the present invention, W is required as an essential composition.
Using C, TiC, W and Ni and / or Co powder,
The carbon content in the mixed powder is blended so as to be lower than the carbon content of the stoichiometric composition determined by the blending ratio of WC and TiC, wet-mixed with a ball mill or an attritor, and dried to a desired shape of about 1 to 5 t / cm. Press molding at ² . next,
After vacuum-sintering the molded body at 1350 to 1500 ° C. for 60 minutes, HI was performed at 1350 ° C. for 60 minutes in 1000 atm of Ar.
P processing is performed, and then processed into a final shape. The reason why the W powder is added here is to adjust the amount of carbon to be lower so that Ni and / or Co form double carbon (nitride). Table 1 shows the composition of the alloy of the present invention and the comparative alloy. The alloy No. of the present invention. Nos. 1 to 4 were obtained by changing the amount of Ti with the binder phase metal being Ni. 5
No. 8 to No. 8 represent a periodic table IVa, Va and VIa other than Ti and W with a part of Ti and W as the binder phase metal being Ni.
Substituted with one or more transition metals belonging to the Nos. 9 to 13 were obtained by substituting a part of carbides with nitrides using Ni as the binder phase metal. No. 14 was obtained by using Co as the binder phase metal. No. 15 was obtained by using Ni and Co as binder phase metals. 16 and 17 are Ni
, Ni and Co partially substituted with Fe, Comparative Alloy No. 1 is a sintered alloy containing no binder phase metal, N
o. Nos. 2 to 4 were samples in which the amount of W powder added was reduced and Ni was present in the metal phase, and Reference numerals 5 and 6 are ordinary cemented carbides for wear-resistant tools that do not contain Ti. The table also shows the carbon content in the alloy after sintering and the average WC particle size.

[0007]

[Table 1]

The structural constituent phases, transverse rupture strength, hardness, oxidation resistance (increase in oxidation) of the alloys of the present invention and comparative alloys having the compositions shown in Table 1, and the push pins for molds (outer diameter 30
mm), and the results of examining the change in surface roughness of the push pin pressing surface are shown in Table 2. The hardness was measured by micro Vickers hardness (load 1 kgf), and the oxidation weight increase test was performed by heating a test piece of 10 × 10 × 5 mm in the air at 800 ° C. for 30 minutes in the air after surface finishing.
It was calculated from the change in weight. The glass lens forming test was performed as follows. First, the flint-based optical glass is made into a spherical shape and placed in a cavity of a cemented carbide mold. Next, heat molding is performed in a vacuum or nitrogen atmosphere. The conditions were as follows: the temperature was raised at 10 K / min, heated to 600 ° C., and maintained at a molding pressure of 10 kgf / cm ² for 5 minutes.
Cool down to 00 ° C at 5K / min, then 20K / mi
Cool at a rate of n or more and open to the atmosphere at 300 ° C. The above molding was repeated up to 100 times,
The surface roughness of the push pin pressing surface after molding 100 times and 100 times was measured.

The alloy of the present invention is superior in the surface roughness before the test as compared with the comparative alloy 1 and has a low transverse rupture strength as compared with the comparative alloys 2 to 6, but has a high hardness at high temperature (600 ° C.). In addition, it can be seen that the oxidation increase is small and the oxidation resistance is excellent. Also,
Since the surface roughness of the push pin pressing surface of the alloy of the present invention in the glass forming test is not significantly deteriorated and hard to be worn as compared with that of the comparative alloy, it is understood that it is extremely excellent as a die material for hot press forming.

[0010]

[Table 2]

[0011]

As described above, the sintered alloy according to the present invention is excellent in high-temperature hardness and oxidation resistance, hardly worn out even in a practical test as a hot-forming die, and has an industrial value. Is high.

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Claims (6)

[Claims] 1. (a) In mass ratio (hereinafter the same), W: 6
3 to 93%, Ti: 1 to 25%, C: 5 to 10%, Ni
And / or Co: 0.5-2% and a composition consisting of unavoidable impurities, and (b) the first phase is tungsten carbide having an average particle size of 0.4-2.5 μm, and the second phase is Ti
A sintered alloy, characterized by having a three-phase mixed structure of a double carbide of W and W, and the third phase is a double carbide containing Ni and / or Co. 2. In the composition of (a) of claim 1, one of transition metals belonging to groups IVa, Va and VIa of the periodic table excluding Ti and W accounts for 10% or less of the total amount of Ti and W. 3. A three-phase which is substituted by one or more kinds and wherein the second phase is one or two or more double carbides of Ti, W and the transition metal in the structure of claim 1 (b). A sintered alloy with a mixed structure. 3. The composition according to claim 1, wherein not more than 20% of carbon is substituted with nitrogen.
(B), a sintered alloy having a three-phase mixed structure in which the second phase is a double carbonitride of Ti and W, and the third phase is a double carbonitride containing Ni and / or Co. . 4. A transition metal belonging to Group IVa, Va and VIa of the Periodic Table excluding Ti and W in which Ti and W account for 10% or less of the total amount of the composition of (a) of claim 1. Wherein at least 20% or less of the carbon is replaced by nitrogen, and wherein the second phase comprises Ti, W and the transition metal in the structure of claim 1 (b). And a sintered alloy having a three-phase mixed structure in which the third phase is a double carbonitride containing Ni and / or Co. 5. The sintered alloy composition according to claim 1, wherein Ni and / or Co are substituted with Fe for 50% or less of the total amount thereof, and the third phase of the microstructure is A sintered alloy having a three-phase mixed structure that is a double carbide or double carbonitride containing Ni and / or Co and Fe. 6. A hot forming mold using the sintered alloy according to claim 1.