JPS5910429B2 - Surface hardening method for titanium and titanium alloys - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface hardening titanium and titanium alloys.

Titanium and titanium alloys are widely used in chemical plants and aircraft materials due to their excellent corrosion resistance and high specific strength.

In the watch industry, many applications are being considered to take advantage of this feature, but especially on the watch side, bezel
Oxygen Component in Mixed Gas There are great expectations as an exterior material for products such as MHV 275 in Oppm.

When titanium is used as a watch exterior, if the material itself is used, it has no special features other than corrosion resistance and light weight, and is unattractive considering its high cost. Therefore, a method is often used to harden the surface to improve scratch resistance and give it a distinctive character. Although various methods can be considered for surface hardening treatment of titanium, nitriding and oxidation treatments are considered to be the easiest to implement. However, conventional simple nitriding treatment using pure nitrogen did not provide a sufficiently thick hardened layer, making it impractical for use as a watch exterior. Furthermore, although the single wire oxidation treatment produces a hardened layer with sufficient thickness, it is extremely brittle and easily cracks and chips, making it impractical. In order to solve these problems, it is conceivable to carry out nitriding and oxidation simultaneously. Up until now, there have been techniques in which nitriding is performed after oxidizing to perform nitriding and diffusion of the oxidized layer, but this technique has the disadvantage that the process is laborious twice. The present invention is characterized in that a hardened layer with sufficient thickness and toughness is obtained by processing with a mixed gas in which the amount of oxygen in nitrogen is strictly controlled. The invention will be described in detail below with reference to Examples.

Example The influence of the oxygen component on the hardness distribution when pure titanium was heated at 850° C. for 96 hours in a nitrogen-oxygen mixed gas in which the molar component of oxygen was 0 to 10,000 PPM was investigated.

The results are shown in Figure 1. Table 1 summarizes the hardness at a depth of 100μ from the surface, as well as the presence of cracks and chips in the cross section and edges of the polished sample, and determined whether the hardening was tough or brittle. .1- It can be seen from Figure 1 and Table 1 that the more oxygen components there are, the higher the hardness becomes.

However, Table 1 shows that a tough hardened layer has an oxygen component of 100%.
It has been shown that if the amount is up to ppm or more, the cured layer becomes brittle. When used as a watch exterior, especially a watch case, the surface is polished to a mirror finish.

Therefore, the surface is shaved off by 50 to 150 microns, and the real problem is the hardness at a depth of 50 to 150 microns. Furthermore, it is naturally required that the polished surface and edges be free from cracks and chips in terms of appearance quality. From FIG. 1 and Table 1, it is clear that the condition for obtaining a hardened layer with sufficient hardness and toughness is that the oxygen content is in the range of 10 to 100 ppm. That is, if the oxygen content is less than 1 ppm, the hardness will be insufficient, and if it is more than 1000 ppm, the hardened layer will become brittle, and both are judged to be unsuitable for practical use. As described above, the present invention is characterized by successfully obtaining a hardened layer with sufficient thickness and excellent strength by performing hardness treatment using a mixed gas of nitrogen and oxygen whose composition is strictly controlled.

Such hardening treatment of titanium and titanium alloys is unprecedented and appears to be of great industrial significance. It is clear that the object of the present invention is not limited to the exterior of a watch, but has a wide range of applications such as improving the wear resistance of various mechanical parts.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the hardness distribution from the surface of pure titanium when heated at 850° C. for 96 hours in a nitrogen-oxygen mixed gas with an oxygen content of 0 to 10,000 ppm.

Claims (1)

[Claims] 1. A method for surface hardening titanium and titanium alloys, which is characterized by heating in a mixed gas containing 10 to 100 PPM of oxygen and nitrogen at a molar ratio.