JPS58171562A - Treatment of heavy alloy to enhance oxidation resistance at high temperature - Google Patents

Abstract

PURPOSE:To enhance the oxidation resistance of a heavy alloy such as W-7Ni- 3Fe at high temp. in the air and to increase the surface hardness by simultaneously diffusing Cr and Si in the alloy and carrying out nitriding. CONSTITUTION:Fine W powder is mixed with fine powder of carbonyl nickel and carbonyl iron or carbonyl copper, and the mixture is molded and sintered to obtain a sintered body of a heavy alloy consisting of 90wt% W and the balance Ni and Fe or Cu. The sintered body is planed to about 5mum Ra surface roughness, and Cr and Si are diffused by a powder diffusion method. Powder for the diffusion consists essentially of about 60% Cr powder, about 20% Si powder, about 20% Al2O3 powder and about 0.5% NH4Cl, and it is diffused at about 1,200 deg.C in vacuum. The sintered body is then heated at about 1,100 deg.C for about 2hr in a flow of gaseous N2 contg. gaseous NH3 to nitride the surface.

Description

Detailed Description of the Invention The present invention improves the high temperature oxidation resistance of heavy alloys (90% by weight tungsten residual iron and nickel or 90iii% tungsten residual copper and nickel) in the atmosphere and also increases the surface hardness of the single heavy alloy. Regarding how to increase.

Heavy alloys have a high density of about 179/c-, and are easier to machine than tungsten, so they are used for counters and counters in rotors of gyro compasses and instrument cranks.
Weights, materials for nuclear power, etc.

It is especially used in parts that require small volume and high weight. Further, a sintered body made of (tungsten-30chromium)-5 silicon has extremely high temperature oxidation resistance and does not oxidize even in the atmosphere at a high temperature of 1200°C, but has the disadvantage that mechanical IJDT properties are difficult. The present invention aims to improve all the drawbacks of this (tungsten-30chromium)-5 silicon sintered body by simultaneously diffusing chromium and silicon into a heavy alloy with good machinability.

A phase with a composition similar to that of (tungsten-30 chromium)-s silicon is completely formed on the surface, and then a complete nitriding treatment is performed to form highly hard materials such as silicon nitride (Si, N4J) and chromium nitride (CrN). It has complete wear resistance due to precipitation hardening.In addition to the above-mentioned advantages, the heavy alloy treated according to the method of the present invention also has the characteristic sound of poor wettability with cast iron and aluminum-based alloys. The treated heavy alloy according to the present invention is effective as a die-casting tool because it has excellent high-temperature oxidation resistance, excellent wear resistance, and poor wettability with cast iron and aluminum-based alloys. Yes, oxidation wear due to molten metal,
Erosion can be completely prevented. It is effective as a part used in high temperature and wear parts. The reason why high temperature oxidation resistance increases due to the diffusion of chromium and silicon into heavy alloys is that a dense oxide film of chromium and silicon is formed, which prevents further oxidation, and at the same time improves corrosion resistance against acidic solutions. Also increases.

Therefore, it is also used for decorative parts that have a heavy feel.

This will be explained in detail below using examples.

Example 1 Total weight ratio of tungsten powder with an average particle size of 1.5 μm is 9
0%, 3μm carbonyl/nickel powder mixed with 7% and 3μm carbonyl/iron powder T-3% in a ball mill for 48 hours? After drying, paraffin was added in an amount of 1% by total weight as a lubricant.

The mixed powder was compression molded under a pressure of 1 m/e+d, heat treated in hydrogen at 800°C for 1 hour to completely remove all paraffin, and then sintered in hydrogen at 1450°C for 1 hour. The sintered body undergoes complete magic grinding to achieve a surface roughness of 9.
It was finished to -5 μm and diffused using the chromium and silicon whole powder dispersibility. The diffusion powder was mixed with 1250 mesh chromium powder (60% by weight), -300 mesh silicon powder (20%), and 1150 mesh alumina powder (20%) as a sintering inhibitor, and then as a diffusion promoter. Anthene chloride (05%) was added and mixed.

The sintered heavy alloy sample was immersed in a diffusion powder placed in an all-graphite crucible and heated for 12 hours in a vacuum (10-3 Torr).
After heating at 00°C for 4 hours to completely diffuse chromium and silicon, in a nitrogen gas stream containing ammonia gas, 1
The entire surface was nitrided by heating at 100° C. for 2 hours.

Table 1 shows the results of an oxidation test conducted in the atmosphere on the specimens that were subjected to chromium and silicon diffusion treatment and those that were not treated.

Table 1 Compared to that without oxidation weight increase treatment, W with chromium and silicon fully diffused
-7Ni -3Fe heavy alloy has very good results in terms of oxidation resistance at high temperatures? Indicated. Next, the results of the corrosion test against inorganic acids are shown in Table 2. Corrosion test results Temperature: 20°C Compared to the untreated one, the one in which chromium and silicon were fully diffused was particularly resistant to hydrochloric acid and sulfuric acid. All exhibited excellent corrosion resistance.

Table 3 shows the results of measuring the surface hardness of the samples which were completely nitrided after the diffusion treatment.

Table 3 Hardness measurement results (Hv, 100 #J After the diffusion treatment, the hardness of the surface of the specimens that were completely nitrided increased due to the formation of nitrides.

Next, melted cast iron and aluminum alloy (JIS: AC4
In order to examine the wettability for B), the wetting angle was measured. The angle was 120° for cast iron and 135° for aluminum alloy. This indicates that it has poor wettability and is suitable for die casting molds.

Example 2 Tungsten powder with an average particle size of 15 μm at a weight ratio of 7 to 90
%, 6 μm carbonyl nickel powder total 6% and 4
A total of 4% of μm copper powder was mixed in a ball mill for 48 hours and dried, and then W 6Ni was mixed in the same manner as in Example 1.
-4Cu heavy alloy is manufactured, and after chromium and silicon diffusion treatment,
All nitriding treatments were performed. As a result of measurements on the obtained sample, the high-temperature oxidation resistance after the chromium and silicon diffusion treatment was as good as that for the W7Ni-3p'e alloy in Example 1. The complete results of the corrosion test in an inorganic acid solution are shown in Table 4.

Table 4 Corrosion test results Table 4 shows that the corrosion resistance in nitric acid solution was particularly improved.
Ru.

After the diffusion treatment, the surface hardness of the sample was nitrided in the same manner as in Example 1. As shown in Table 5, the hardness was improved.

Furthermore, the wettability of cast iron and aluminum alloy for this sample showed all the same results as in Example 1.

Claims (1)

[Claims] /, Heavy alloy (90% by weight tungsten, remaining iron and nickel or 90iii% tungsten, remaining copper and nickel) after all simultaneous diffusion of chromium and silicon,
A high-temperature oxidation-resistant treatment method for heavy alloys, which is characterized by performing nitriding treatment to improve high-temperature oxidation resistance in the atmosphere and also increase surface hardness.