JPS61284559A - Surface treatment of titanium material - Google Patents

Abstract

PURPOSE:To improve the mechanical properties of a Ti material having an oxide film by the diffusion and penetration of O2 into the Ti material as well as to give metallic luster to the Ti material by the disappearance of the oxide film by heating the Ti material at a specified temp. in vacuum or in an inert gas. CONSTITUTION:A Ti material having an oxide film formed on the surface by heat treatment is heated at 600-790 deg.C for about 10min in vacuum or in an atmosphere of an inert gas such as Ar. O2 in the oxide film diffuses and penetrates into the Ti material to improve the bendability and mechanical strength of the Ti material. At the same time, the oxide film disappears, forming a surface having metallic luster.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention removes the surface oxidation layer formed on titanium material (pure titanium and titanium alloy) lumps, plate tubes, rods, wires, etc. The present invention relates to a method in which the metallic luster is removed by heating to a temperature range of 790° C., thereby obtaining a metallic luster surface and improving mechanical properties at the same time.

(Prior Art) It is well known that titanium material is a metal that has a strong affinity for oxygen. Therefore, when a titanium hammer is heated in an oxidizing atmosphere such as in the air, an oxide layer is formed on the surface. Generally, industrial products made of titanium are preferred to have a metallic luster without an oxidized layer in terms of appearance. When manufacturing these products, it is common to perform hot working or cold working and then softening annealing.

In order to prevent the formation of these oxide films at this time, heating is performed in vacuum or in an inert gas atmosphere from the beginning (for example, Japanese Patent Publication No. 57-47751). In addition, if an oxide film is formed on the surface by heating in an oxidizing atmosphere such as the air, mechanically grinding or chemically pickling the surface with a solvent is an industrially adopted method. ing.

In order to prevent the formation of an oxidized layer, it is necessary to take great care to prevent oxidation by keeping it in a vacuum or inert gas before heating. The process is complicated and it is not advantageous in terms of cost.

On the other hand, oxygen plays a role in improving the mechanical properties of titanium, such as increasing its mechanical strength.Currently, oxygen content is adjusted during ingot production to adjust the mechanical strength of the final product. There is. In recent years, small-scale manufacturing has become commonplace, and it has traditionally been thought that it was impossible to adjust the strength of ingots after the ingot manufacturing process. Therefore, even for small lots, the ingredients must be adjusted from the melting stage. This resulted in a decrease in yield.

Furthermore, it has been known that when heated in an oxidizing atmosphere, oxygen penetrates into titanium and increases its strength (Titanium/Zirconium Vol. 1.32, No.

1.17), this causes a concentration gradient in the surface layer, and a thick oxide scale is formed on the surface, which is unfavorable in terms of appearance.

(Problem to be solved by the invention) Conventionally, when an oxide film was formed on the surface of titanium, it was removed mechanically or chemically. There are disadvantages in terms of labor and cost due to the addition of one step. Furthermore, removing the surface of a relatively expensive metal such as titanium is not advantageous in terms of yield in industrial production, and is a process that should be avoided as much as possible.

However, mechanical grinding often creates unevenness on the surface, which is not aesthetically pleasing, and even with chemical solvents, different degrees of oxidation and pitting may occur depending on the thickness of the oxide film. It is often very uneven. The conventional method of removing the oxide film as described above has many problems in terms of industrial production, cost, and surface quality.

In addition, titanium materials are made with different mechanical properties depending on the oxygen content. Conventionally, the components have been determined depending on the time of dissolution, and it has been impossible to adjust the components thereafter. Furthermore, as the number of small lots has increased in recent years, yields have been decreasing in industrial production.

(Means for Solving the Problems) The present inventors have discovered a method for simultaneously solving the problems on the surface and mechanical properties. In other words, if an oxide film is formed on the surface of titanium by heat treatment or the like, or if an oxide film is formed in advance as a measure to prevent scratches with the roll during molding, it is heated for 600 minutes in a vacuum or in an inert gas. When heated in a temperature range from ℃ to 790℃, the oxygen in the oxide film on the surface diffuses into the metal, and the oxide film disappears, giving the surface a metallic luster. It has been found that as a result of the transferred oxygen showing a tendency to become homogenized, mechanical properties as well as bending workability are improved.

The method of the present invention will be explained in detail below.

The present invention involves heating a titanium lump, plate, tube, rod, or wire rod that has an oxide film on its surface to a temperature range of 600°C or more and 790°C or less in an inert gas or vacuum. This is a method that eliminates the surface oxidation layer in appearance and provides metallic luster, while at the same time improving mechanical properties.

One example where this invention can be effectively applied is when softening annealing is performed after hot or cold working (for example, hot rolling or cold rolling). However, if the heat treatment temperature in vacuum or inert gas is made too high, problems arise in terms of mechanical properties. In other words, when the temperature exceeds 790°C, the crystal grains of the titanium material become coarse, resulting in roughness on the surface during bending and forming processes, as well as a decrease in tensile strength and elongation.
Similarly, it does not cause surface cracks during bending, etc., and is therefore undesirable as a material.

Further, if the temperature is lower than 600°C, it takes a considerable amount of time to obtain a metallic lustrous surface, and it is difficult to recrystallize during softening annealing, making it impossible to obtain a good material. For example, Figure 1 shows a pure titanium material that has been heated in advance at 750°C for 2 minutes in the air to form an oxide film on its surface, and then heated in vacuum at different temperatures and times to improve its surface appearance. The results of the investigation are shown below.

A metallic luster is obtained in the shaded area in FIG.

FIG. 2 is a diagram showing the relationship between the heating temperature in a vacuum of a titanium material whose surface has been oxidized in advance, the surface state crystal grain size, and the surface roughness state in a bending test. The surface oxidation was performed in advance at 750° C. for 2 minutes in the air, and the heating retention time in vacuum was 2 minutes.

In terms of material quality, as shown in Figure 2, when the temperature exceeds 790°C, the crystal grains become coarse and the surface becomes rough during bending, and tensile strength and elongation tend to decrease. Cracks may occur.

Note that the suitable conditions for showing metallic luster vary depending on the degree of the initial oxide film.
The temperature range is 790°C, which is defined as the high temperature side or the long time side. It should be noted that titanium alloys containing elements that do not have much effect on the deformation characteristics of pure titanium (for example, Ti-0
, 2% Pd alloy Na), similar effects are observed.

(Example) (1) The following two heat treatments were performed using a pure t-7 JIS Class 2 material and a cold rolled 1 material with a plate thickness of 0 to 3 mm. One was heated at 700° C. for 10 minutes in the air to form an oxide film on the surface, and then heated at 780° C. for 10 minutes in Ar gas. The other parts were heated at 700°C for 10 minutes in a vacuum, and then Ar was continued without forming an oxide film on the surface.
Heating was performed at 780° C. for 10 minutes in gas.

As a result, the external appearance of both surfaces showed a metallic luster with no oxide film. In addition, the mechanical strength of the former was approximately 5% higher than that of the latter, and even after bending, no cracking occurred and there was almost no roughening of the surface.

(2) A hot-rolled sheet made of pure titanium JI 82 has a thick oxide scale on its surface, which is removed by
As a result of heating at a constant temperature of 50 minutes at °C, the appearance showed a metallic luster with no oxide film. The effect of improving mechanical strength was also observed.

(Effects of the Invention) The present invention provides a metallic luster surface by heating a titanium material having a surface oxide film in a temperature range of 600°C to 790°C in a vacuum or in an inert gas, and at the same time shows a metallic luster surface. The aim is to improve all the physical properties of the robot.

This invention can be applied industrially, such as when annealing a plate or strain relief annealing after forming a pipe, in which the surface oxide film is completely formed from the beginning, or even if it is not formed. During annealing, when inserting the entire material into a vacuum or Ar atmosphere heating annealing furnace, even if the surface comes into contact with the atmosphere during the initial heating stage and becomes slightly oxidized, the material may be subsequently placed in a vacuum or inert gas. When heated, a surface with a metallic luster can be obtained.

On the other hand, in the conventional process after melting, it was not possible to adjust the components, but after heating in an oxidizing atmosphere in advance, heating in vacuum or inert gas allows oxygen on the surface to diffuse into the interior. In addition, it improves mechanical strength, improves elongation, and improves bending workability. Traditionally, small-lot production has resulted in lower yields, but
By the method of the present invention, the surface exhibits metallic luster and the mechanical properties can be adjusted, which is highly effective in industrial production.

[Brief explanation of drawings]

Figure 1 is a diagram showing the condition range for the formation of an oxide film on pure titanium material and metallic luster, and Figure 2 is a diagram showing the retention heating time in vacuum and the surface and material quality of titanium material (0C).

Claims (1)

[Claims] A method of heating a titanium material having a surface oxide film to a temperature range of 600°C to 790°C in vacuum or in an inert gas to eliminate the oxide film and at the same time improve mechanical properties. Characteristic surface treatment method for titanium materials.