JPS5814502B2 - High temperature oxidation treatment method for heavy alloys - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving the high temperature oxidation resistance in the atmosphere of a heavy alloy (90 weight tungsten residue iron and nickel or 90 weight titanium tungsten residue copper and nickel).

Heavy alloys have a high density of approximately 179/cm3, and have better machinability than tungsten, so they can be used particularly in small-volume applications such as gyro/compass rotors, instrument crank counterweights, and nuclear power materials. It is used in parts that require high weight.

In addition, the sintered body made of (tungsten-30chromium)-5 silicon has excellent high-temperature oxidation resistance, and
It has the disadvantage that it does not deteriorate even at high temperatures of 200°C and is difficult to machine.

In order to improve the drawbacks of this (tungsten-30 chromium)-5 silicon sintered body, the present invention involves the simultaneous diffusion of chromium and silicon into a heavy alloy with good machinability. -5 It improves oxidation resistance at high temperatures by forming a phase similar to the composition of silicon.

Therefore, the heavy alloy treated according to the present invention has excellent high-temperature oxidation resistance, and is therefore effective as a die-casting tool, and can prevent oxidative wear and corrosion caused by molten metal.

It is also effective as a component at other high temperatures.

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 Tungsten powder with an average particle size of 1.5 μm was weighed at a weight ratio of 9
0%, 3 μm carbonyl nickel powder, 7% and 3 μm carbonyl iron powder were wet mixed in a 3 tibor mill for 48 hours, and after drying, 1% by weight of paraffin was added as a lubricant.

The mixed powder was compression molded under a pressure of ltan/cm2, heat treated in hydrogen at 800°C for 1 hour to completely remove paraffin, and then sintered in hydrogen at 1430°C for 1 hour.

The sintered body was surface ground to a surface roughness of Ra=5 μm, and chromium and silicon were diffused by a powder diffusion method.

The diffusion powder is -250 mesh chromium powder in weight ratio of 60 parts, -300 mesh silicon powder in 20 parts, and -150 mesh alumina powder as sintering inhibitor in 2 parts.
After mixing 0%, add 0.5% ammonium chloride as a diffusion promoter.
% was added and mixed.

The sintered heavy alloy sample was embedded in a diffusion powder placed in a graphite crucible, and heated at 120° C. in a vacuum (10 −3 Torr).
It was heated at 0° C. for 4 hours to diffuse chromium and silicon.

Table 1 shows the results of an oxidation test conducted in the atmosphere on the diffusion-treated and untreated specimens.

W with chromium and silicon diffused compared to the untreated one
-7Ni-3Fe heavy alloy showed very good results in terms of oxidation resistance at high temperatures.

Next, Table 2 shows the results of the corrosion test against inorganic acids.

Compared to untreated specimens, those in which chromium and silicon were diffused showed superior corrosion resistance, especially against hydrochloric acid and sulfuric acid.

Actual example 2 Tungsten powder with an average particle size of 1.5 μm is 9 in weight ratio
0 part, 3 μm carbonyl nickel powder in 6 parts, and 4 μm copper powder in 4 parts were wet mixed in a ball mill for 48 hours and dried, and then mixed with W-6N in the same manner as in Example 1.
An i-4Cu heavy alloy was manufactured and subjected to chromium and silicon diffusion treatment.

As a result of measuring the obtained sample, the high temperature oxidation resistance after diffusion treatment was found to be higher than that of W-7Ni-3F in Example 1.
The results were as good as those related to the e-alloy.

Table 4 shows the results of the corrosion test in an inorganic acid solution.

In Table 4, the corrosion resistance in nitric acid solution is particularly improved.

Claims (1)

[Claims] 1. High-temperature resistance of a heavy alloy with improved high-temperature oxidation resistance in the atmosphere by simultaneously diffusing chromium and silicon into a heavy alloy (90 weight titanium ungsten, remaining iron and nickel, or 90 weight tungsten, remaining copper and nickel). Oxidation treatment method.