JPS61243165A - Surface hardening method for titanium and titanium alloy - Google Patents

Abstract

PURPOSE:To form a hard layer having satisfactory adhesion without producing grayish white spots by holding a Ti (alloy) member in a salt bath contg. a cyanide under heating and by cooling the member in the absence of oxygen. CONSTITUTION:Ti or Ti alloy parts are immersed and held in a sodium cyanide- base salt bath melted by heating to carry out carburization, nitriding or oxidation. The Ti parts are taken out of the salt bath, put in a salt water spraying apparatus and cooled by spraying salt water. When the Ti parts are taken out of the salt bath, they may be covered with gaseous Ar so as to isolate the air. By this method, hardened surface films having satisfactory adhesion can be formed. This surface hardening method is advantageously applicable to ornaments such as external parts for a time piece.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is directed to a surface hardening method used for ornaments, particularly watch exteriors.

[Summary of the invention]

When titanium or titanium alloy is immersed in a molten salt bath containing all cyanide compounds to form a black hard surface layer, oxygen is blocked from the time the titanium or titanium alloy is taken out of the bath until it is cooled, resulting in a grayish-white color. ? This is the surface hardening method that was lost.

[Prior Art J] Conventionally, there are various methods for surface hardening titanium or titanium alloys.

Typical methods are nitriding, boriding, and anodic oxidation.The nitriding method produces a yellow hard film, the boriding method produces a stainless steel color, and the anodizing method produces interference colors of red and blue. You can freely select your favorite color tone.

In addition to this, although not a typical technique, a technique has been announced in which titanium or titanium-containing material is immersed in a salt bath containing cyanide to form a hard layer having a black color on the surface. Mr.
B.Finner's 2nd Lecture in Japan DURAtJ
"Improvement of wear resistance of titanium and titanium alloys by the method" published by Nippon Heat Treatment Kogyo Co., Ltd., May 1972 [Problems to be solved by the invention] The above method was originally developed in West Germany for the production of titanium and titanium alloys. This technology was developed to add wear resistance to engine parts.

That is, a method has been used in which the above-mentioned parts are immersed in a cyanide-containing salt bath at around 800° C. for 1 to 2 hours and then cooled with water.

Although this method also yields a hard layer with a blackish brown color, it cannot be used as is for decorative purposes due to insufficient color tone, color unevenness, and adhesion.

The color is dark brown, not the deep black that is required for decorative purposes. Also, if you look closely, you will notice that there are linear grayish-white spots on the surface, which seriously detracts from its aesthetic appearance.

If you just lightly rub the surface with a cloth, black powder will adhere to the cloth, indicating poor adhesion.

[Means to solve the problem The present invention solves these problems.

In other words, the titanium alloy member is heated and held in a salt bath containing cyanide, then pulled up, and immediately cooled by spraying salt water, or cooled in an argon atmosphere, etc. The required characteristics could be satisfied by one or a combination of two or more of the methods described above.

According to this treatment, the maximum hardness is Hv800, and the hardened layer depth is 1
A hardened layer of about 0.0511 was obtained, and the increase in hardness is said to be mainly due to carbonitriding.

The figure shows the relative distribution of carbon and oxygen content with respect to depth from the surface. Carbon is more diffused inside than oxygen, and since this corresponds to the hardness, it can be concluded that the hardness is due to the diffusion of carbon into the titanium. Since oxygen is hardly diffused only on the outermost surface of Fi, it can be considered that it is not involved in hardness. (However, nitrogen was not analyzed.) TlO2, which is a combination of oxygen and titanium, is known as a white pigment, and TiO is known as titanium black.・This T10. 0IJ of titanium black in salt bath during salt bath treatment
It is thought that this TiO is generated by receiving Ot-, and when this TiO is pulled up from the salt bath and encounters oxygen during cooling, it changes to gray-white TlO2.

That is, in the present invention, if the object to be treated is removed from the salt bath after the salt bath treatment and is exposed to oxygen while it is being cooled down to room temperature, it will change to gray-white TlO2. The decisive factor is to cut it.

With the conventional water cooling method, the color was blackish-brown and grayish-white spots appeared.When the parts were removed from the salt bath, they were covered in molten salt and air was blocked for the time being. It is thought that this is due to the incompleteness and the rapid vaporization of water around the component due to water cooling, resulting in bubbles that adhered to the surface of the component and remained as spots.

〔Example〕

The cooling method of the present invention will be explained below using examples.

[Example-1] Salt containing soda cyanide as the main component was heated and melted to 80%
The titanium exterior parts were immersed in the liquid at 0°C.
Carburized, nitrided, and oxidized.

``Subsequently, the exterior parts were taken out of the salt bath and immediately placed in a salt water injection device, where salt water was sprayed and cooled.

As a result of observing this exterior part, it was found that the color tone was deep deep black, there were no grayish white spots, and the adhesion was also good.

[Example-2] Carbonitriding oxidation treatment was performed in the same manner as in Example 1, and then the product was rapidly cooled in a bath with agitating flow maintained at 300°C containing nitrite (sodium nitrite) as the main component. .

The results were as good as in Example 1.

In addition, when taking it out from the salt bath, be careful not to expose it to air.
When covered with argon gas, even better quality exterior parts were obtained.

〔Effect of the invention〕

As explained in the above example, conventional salt bath treatment was unsuitable for decorative items, but by using the cooling method of the present invention, it is possible to exhibit excellent properties as a watch exterior part. Became.

[Brief explanation of drawings]

The figure shows the characteristic X-ray scanning profile of the carbonized layer and oxidized layer on the titanium surface. that's all

Claims (2)

[Claims] (1) In a surface hardening method in which titanium or a titanium alloy is immersed in a molten salt bath containing a cyanide compound to form a black hard layer on the surface of the material, the process from the time it is pulled out of the molten salt bath until the time it is cooled is A surface hardening method for titanium and titanium alloys that is characterized by blocking oxygen during the process. (2) The method for surface hardening titanium and titanium alloys according to claim 1, wherein the method for blocking oxygen is one or a combination of two or more of the following. (a) Liquid cooling method: salt water cooling, ice water cooling, molten salt cooling, water-added molten salt cooling, oil cooling, water cooling (b) Gas cooling method: argon cooling, helium cooling, nitrogen cooling, hydrogen cooling, (c) liquid injection cooling Law water, salt water, water with salt dissolved, oil