JPH0266152A - Surface hardening method for titanium or titanium alloy - Google Patents

Abstract

PURPOSE:To form a thick hardened layer on a Ti surface by diffusing O, N, C, etc., from the Ti surface at a specific temp. to remove the hardened layer of a specific hardness and heating further the surface at a specific temp., then subjecting the Ti to forming. CONSTITUTION:The Ti or Ti alloy is subjected to a 1st time of heating at 1,000 to 1,600 deg.C in the gas of such atmosphere at which the O, N, and C or >=2 kinds of the elements are diffused from the surface thereof or in such molten bath. The above-mentioned molten bath is adequately >=1 kinds of soda lime glass, barium glass, borosilicate glass, and alumina silicate glass of 650 to 950 deg.C softening point, and enamel, etc., of >=750 deg.C calcination temp. The diffusion hardened layer of the interstitial type elements of the O, N and C is formed on the surface of the Ti or Ti alloy in this way. The layer having >=600 Vickers hardness Hv is removed if such layer is generated in this case. The above- mentioned Ti or Ti alloy is in succession subjected to the 2nd time of the heat treatment at 700 to 1,600 deg.C. The alloy is thereafter subjected to the desired forming such as rolling or forging. The diffusion treatment is executed in a short period of time at a high temp., by which the surface hardening of a low cost is executed.

Description

Detailed Description of the Invention (Industrial Application Field) It can be used to manufacture plates and parts that are made of titanium and titanium alloy and require a relatively thick hardened layer of about 0.1 tm or more on the surface of about 500 Hv. The present invention relates to a method for surface hardening titanium or titanium alloys.

(Prior art) Conventional surface hardening methods for titanium and titanium alloys are performed on molded products, and hardening methods include oxygen,
There are interstitial hardening methods such as nitrogen, hardening methods using metals and intermetallic compounds, and hardening methods by dispersing hard powder materials into the titanium matrix.
This is done using ion blating, plasma arc, laser, etc. Among these, oxygen, nitrogen, carbon, or two or more of these elements are heated in an atmospheric gas or cyanide-containing salt molten bath that diffuses from the surface of titanium and titanium alloy to form a hardened layer. This method is relatively low cost and is commonly used in boat fishing.

For example, JP-A-50-60437, JP-A-50
60438, JP 50-98451, JP 5240442, JP 53-120642
No. 53-138936, Japanese Patent Application Laid-Open No. 1983
-146875, JP 58-161771, JP 62-161947, JP 62-2
There is a method described in No. 56956. However, since these methods perform hardening treatment after molding, the treatment temperature is kept at about 900"C or less to ensure the shape and material quality, and it takes a considerable amount of time to form a thick hardened layer. do.

(Problem to be solved by the invention) In conventional technology, surface hardening is performed on the molded product, so the method of heating the entire product to a high temperature using a heating furnace makes it difficult to secure the material and shape. Therefore, it is not possible to raise the temperature to a temperature higher than the β range. On the other hand, it takes a long time to make the cured layer sufficiently thick at temperatures below the β range, resulting in low productivity.

(Means for Solving the Problems) The present invention is a surface hardening method characterized by performing a hardening treatment before forming. That is, oxygen, nitrogen, carbon, or two or more of these elements are titanium and The first heating is performed in an atmosphere of gas or molten bath that diffuses from the surface of the titanium alloy to form a thick, hardened layer in a short time due to the diffusion of interstitial elements, and then it has a hardness of at least a certain level. If a layer unsuitable for processing is generated, this surface hardening method is characterized in that it is removed, followed by second heating and forming processing such as rolling or forging.

Here, the first heating temperature is 1000 to 1600°C, in an atmosphere containing oxygen, nitrogen, and carbon, in a nitriding melt bath such as a salt bath containing cyanide, or in an atmosphere containing oxygen, nitrogen, and carbon, or in a nitriding melt bath such as a salt bath containing cyanide, or in an atmosphere containing oxygen, nitrogen, and carbon, or in a nitriding melt bath such as a salt bath containing cyanide. Perform in an oxidizing molten bath, etc. 1
This is because if the temperature is less than 1,600°C, it takes time to form a hardened layer and productivity is poor, and if it exceeds 1,600°C, the economical efficiency of the furnace becomes extremely poor.

Here, as an example, Fig. 1 shows the heating temperature and 4 suitable for processing.
The relationship between layer thicknesses with 00 to 5008 ν is shown. In this way, by heating at high temperatures, a thick hardened layer can be coated in a short time. In the present invention, processing is performed after hardening treatment.

Here, a layer having a hardness of more than a certain level and unsuitable for processing is a layer having a Vickers hardness of 600 Hv or more,
This was determined by examining the hardness at which cracks occur during hot working. In addition, as a method to avoid unnecessary formation of layers inappropriate for processing, it is also possible to include an appropriate amount of oxygen in argon gas or to perform the process in a cyanide salt bath, but from the viewpoint of economical and non-pollution problems, glass It is recommended to use a molten bath such as

Here, as a molten bath of glass etc., the softening point is 650 to 95.
Soda lime glass, barium glass, borosilicate glass, aluminosilicate glass having a firing temperature of 0°C, enamel having a firing temperature of 750°C or higher, or a mixture of two or more of these are preferred. This is because glass with a softening point of less than 650°C will produce a layer unsuitable for processing, such as scale, due to heating as in the air, and a glass with a softening point of less than 950''C will not form a sufficient oxygen solid solution layer. In addition, if the firing temperature is lower than 750° C., a layer unsuitable for processing such as scale will similarly occur.The above contents are shown in Table 11 and Table 2.

Table 1 Table 2 It was confirmed that by cooling with water after heating the molten bath, the glass and enamel could be easily removed, the structure was uniform, and the toughness was increased.

Next, a second heating for processing is performed.

Here, the second heating temperature is 700 to 1600"
It is C. As shown in Figure 2, even if the layer is less than 600 Hv at room temperature, which softens at high temperatures below 700°C, it is harder than the base material titanium, making it difficult to process at strain rates of 0.1 to 100/sec, and cracking occurs. Because it does. 160 again
This is because if the temperature exceeds 0° C., the economical efficiency of the furnace deteriorates significantly.

(Example 1) A titanium plate of 50 mm t, such as a JIS type 2 phase, was heated and oxidized in the atmosphere at 1200° C. for 17 hours, shot, and then 0.3 mm thick on one side with a solvent. As a result, the surface hardness was approximately 480 Hv. After reheating this plate to 920"C, it was rolled to 5 mm t and air-cooled. The hardness distribution of this plate is shown in Figure 3. From Figure 1, it can be seen that
The thickness of the cured layer with 0-50 old 1v is about 211ffI
l, and the thickness becomes 1/10 due to processing, so 0,2
It should be a hardened layer of mm, but in Figure 3 it is 0,4 mm.
mm. This is because the thickness of the hardened layer has increased due to grain refinement due to processing, and the hardened layer is not processed unevenly.

(Example 2) A 25φ titanium rod of JIS 3 types, etc. was placed in a borosilicate glass (trademark Pyrex) melting bath in a 1300” CX 4
After holding H, cooled with water and removed the glass, the length was 13nv.
It was cut into ++ and forged at high speed to a length of 5 mm. Table 3 shows the pre-processing heating temperature and the presence/absence and shape of cracks. FIG. 4 shows the state of hardened layer formation in a product forged at 900°C.

Table 3 (Effects of the Invention) In the present invention, since the interstitial hardening treatment by diffusion of oxygen, nitrogen, etc. is performed before the molding process, it is possible to use high temperatures that pose a problem in securing the shape, and therefore the diffusion treatment can be performed in a short time. It is possible to obtain a thick hardened layer in the process, and since the surface is molded with a Vickers hardness of less than 600 Hv, which softens at high temperatures, there are no problems such as cracking, and the above hardening process is performed using only a heating furnace. It has many advantages, such as low cost and the ability to adjust the structure by rapid cooling or heat treatment after processing.

[Brief explanation of the drawing]

Figure 1 shows the relationship between heating temperature and hardened layer thickness of 400 to 500 Hv, Figure 2 shows the relationship between temperature and Vickers hardness, and Figure 3 shows the depth from the plate surface and Pinkers hardness. FIG. 4 is a diagram showing the hardening distribution in the cross section of the disk component. Fig. 1 100゜OO 1;'00 /300 Temperature (°C) (Murotama) 1 house (C) <my+t) Radial force direction length Fig. Plate surface force/depth (Chikum) Procedure amendment 2 tI: (Shihansho (=[J November 12, 1963

Claims (2)

[Claims] (1) The first heating is carried out in a gas or molten bath in an atmosphere where oxygen, nitrogen, carbon, or two or more of these elements diffuse from the surface of titanium and titanium alloy.
After forming a hardened layer by diffusion of interstitial elements such as oxygen, nitrogen, and carbon at 00°C to 1600°C, if a layer with a Vickers hardness of 600Hv or more is generated, it is removed, and then, Second heating to 700℃~160℃
A method for surface hardening titanium or titanium alloy, which is carried out at 0° C. and is characterized by performing forming processes such as rolling and forging. (2) The molten bath is soda lime glass, barium glass, borosilicate glass, aluminosilicate glass with a softening point of 650°C to 950°C, or a firing temperature of 750°C.
The surface hardening method according to claim 1, which is the above enamel or a mixture of two or more thereof.