JPS6372420A - Manufacture of beta type titanium alloy wire stock - Google Patents

Abstract

PURPOSE:To obtain wire stocks having good dimensional accuracy and surface quality by heating a beta type titanium alloy at a specific temp. in a vacuum or an inert gas atmosphere, annealing by cooling at a specific speed, again heating the alloy at a specific temp. in the air, and then cold drawing the alloy. CONSTITUTION:As for cold drawing of a beta type titanium alloy, the alloy is heated at a temp. in a temp. range higher than the beta transformation point in a vacuum or an inert gas atmosphere. Then, the alloy is subjected to a solution heat treatment (annealing) by cooling at a speed higher than 1.8 deg.C/min, is subjected to an oxide film forming treatment by heating at a temp. of 600-800 deg.C in the air, and then is cold drawn. Thus, the cold wire drawing without seizure by a die is performed and wire stocks having the good dimensional accuracy and surface quality.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a β-type titanium alloy wire, and in particular to a method for producing a wire with good dimensional accuracy and surface quality. Regarding the method.

Background of Clarity Titanium and titanium alloys have excellent specific strength, corrosion resistance, and heat resistance, and are therefore used in a wide range of applications such as aerospace materials, various chemical plants, and seawater desalination equipment.

As titanium alloys, alpha-deca-beta type titanium alloys such as Ti-6AI-4V alloy have been widely used, but alpha+beta type alloys have poor cold workability and require much of the processing to be done by cutting. Because of this, the yield rate up to the final product is extremely low. Therefore, the use of β-type titanium alloys has been expanding in recent years because they have superior cold workability and high strength compared to α+β-type alloys.

One field of use is wire rods as materials for bolts, spring materials, etc., which take advantage of their excellent cold workability and high strength when subjected to aging treatment. In other words, β-type titanium alloy has excellent cold workability in the β single set after solution treatment, so it is easy to cold draw and draw the wire, and this wire can be used depending on the purpose of use. High strength can be obtained by performing aging heat treatment after forming.

Note that 1. The β-type titanium alloy in this specification refers to the entire metastable β-type titanium alloy that forms a single β-type even at room temperature by rapid cooling from the β region, precipitates the α phase by aging treatment, and has age hardenability. , Ti-15V-3Cr-3S n
-3A 1 alloy, Ti-15Mo -52r -3A
1 alloy, Ti-11,5M.

-6Zr-4,5Sn alloy, Ti-13V-11Cr
An example of this is an alloy such as -3A1 alloy.

U Support Δ Upper 1 Disadvantage In general, titanium materials such as pure titanium have excellent cold workability, and can be cold-drawn and drawn to a high degree of workability.

However, such titanium materials have the disadvantage that they easily seize with tools, and if only a normal lubricant for drawing wire is used, it may seize with drawing dies and wire drawing Even if the wire could be drawn, many large die defects would occur on the surface of the material, resulting in a defective product.

For this reason, the pure titanium material before drawing and wire drawing is generally subjected to heat treatment at 500 to 650° C. in the atmosphere, which serves as both a treatment to generate an oxide film with lubricating properties on the surface and an annealing treatment.

However, in the case of β-type titanium alloys, most of them are heated to 750°C.
Since the β transformation point is nearby, annealing is generally performed at 75
In the temperature range exceeding 0 to 800"C.

It is carried out in vacuum or in an inert gas.

During this annealing, it also serves as a treatment to generate a surface oxide film with lubricating properties, so if heating is performed in the above temperature range in the air, especially in a temperature range exceeding 800°C, the oxide film that is generated may becomes hard and brittle and does not serve as a lubricant. In addition, when atmospheric heating exceeds 800℃ at the same time,
The amount of oxygen absorbed by the β-type titanium alloy increases, and the oxygen-enriched layer with poor workability becomes thick under the oxide film, resulting in a decrease in the workability of the material itself.

Therefore, in the case of a β-type titanium alloy, it is difficult to perform atmospheric heating for both annealing and oxide film formation.

On the other hand, as a manufacturing technology for wire rods, there are methods that use roller dies or groove rolling instead of drawing wire drawing.
In wire drawing by these methods, the dimensional accuracy of the manufactured wire is poor, and particularly good roundness cannot be obtained, so that it cannot be used as a product as it is.

Therefore, when such a roller die or groove rolling is used, drawing wire drawing is more or less required as a subsequent process.

Due to this situation, there has hitherto been no effective method for drawing and drawing β-type titanium alloys.

In view of the above circumstances, the present invention has been developed to make it possible to cold-draw and wire-draw β-type titanium alloys without causing seizure with dies, and to produce wire rods with good dimensional accuracy and surface quality. Provides a manufacturing method.

That is, in the present invention, when cold drawing a β-type titanium alloy, the alloy is heated in a vacuum or in an inert gas atmosphere to a temperature range equal to or higher than the β transformation point, and then heated at 1.8°C/
A β-type titanium alloy characterized by performing solution treatment (annealing) by cooling at a rate of at least min. The present invention relates to a method for manufacturing wire rods.

The titanium alloy material that is the object of the present invention is a β-type titanium alloy that has excellent cold workability.

Titanium alloy products generally start with an ingot breakdown process in order to destroy the cast structure of the cast ingot and obtain an intermediate material suitable for subsequent processes. Ingot breakdown is performed by blooming or forging an ingot. Next, the manufactured billet is processed into a wire for cold wire drawing through a rolling process of hot rolling to a predetermined size and a descaling process such as pickling and peeling.

This strand is used as a raw material and subjected to cold wire drawing according to the product dimensions, and finally heat treatment such as annealing (solution treatment) or aging treatment is performed according to the use of the product.

The main process of the present invention is a process of cold drawing the descaled hot-rolled wire by drawing, and the processed layer in the previous process is not a requirement of the present invention. Any process can be used. Furthermore, it is not at all prohibited to perform roller die or groove rolling in the cold wire drawing process.When such a processing method is used, the cold wire drawing process of the present invention is finally applied in order to improve the dimensional accuracy. Perform wire drawing.

As mentioned above, in the conventional cold drawing wire drawing of pure titanium materials, the wire is annealed by heating it in a temperature range of 500 to 650°C, and an oxide film with lubricating properties is generated on the surface. After the treatment, a lubricant for wire drawing was applied on top of the treatment.

However, in the case of β-type titanium alloys, most of them are 750
Since the β-transformation point is near the β-transformation point, in order to obtain a β-single set with excellent cold workability, it is necessary to
It is necessary to heat it to a temperature of 0°C or higher.

However, temperatures above 750-800℃, especially 800℃
When atmospheric heating is performed in a temperature range exceeding 'C, the oxide film formed on the surface of the wire becomes hard and brittle, and has no lubricating performance.

Therefore, in the case of β-type titanium alloys, it is necessary to distinguish between annealing and a treatment for forming an oxide film with lubricating properties. Annealing (solution treatment) is performed by heating and holding the wire rod in a temperature range above the β transformation point in vacuum or in an inert gas for 5 to 60 minutes, and then cooling at a rate of 1.8° C./min or more. The reason why annealing is performed in vacuum or in an inert gas is to prevent surface oxidation.

The reason why the heating time was set to 5 to 60 minutes is that annealing is not sufficient if the heating time is 5 minutes or less, and the reason why the heating time is set to 60 minutes or less is that heating for more than 60 minutes causes coarsening of the β grains. This is because the ductility of the material decreases.

The cooling rate was set to 1.8/min or higher.

This is because if the cooling rate is less than 1.8° C./min, precipitation of α phase may occur during cooling of the material, which may reduce cold workability.

Through such treatment, a single set of β strands without an oxide film can be obtained.

However, the above-mentioned treatment may be replaced by a treatment in which a solution treatment is performed in the atmosphere, and then an oxide film and an oxygen-enriched layer on the surface are removed by peeling, centerless treatment, or the like.

The wire rod annealed in this way was heated in the atmosphere for 600 minutes.
Heat at a temperature of ~800"C for 5 minutes to 1 hour.

Cool at a rate faster than air cooling to form an oxide film on the surface.

Naturally, the heating time varies depending on the heating temperature; heating is performed for a long time on the low temperature side, and short time on the high temperature side. The oxide film produced here has good lubrication performance and good adhesion to the base material.

Here, the heating temperature is set to 800° C. or less, but as mentioned above, the oxide film produced by atmospheric heating in a temperature range exceeding 800° C. is hard and brittle, and therefore does not serve as a lubricating film. Further, when heated in the atmosphere above 800° C., the oxygen-enriched layer formed in the matrix under the oxide film becomes thicker, and the workability of the wire rod itself deteriorates.

On the other hand, the heating temperature was 600°C or higher.
Precipitation of α phase occurs in the temperature range below.

This is because the workability of the material may decrease, and
This is because an oxide film having good lubrication performance cannot be obtained.

The reason why the heating time was set from 5 minutes to 1 hour was because an oxide film with good lubrication performance could not be obtained if the heating time was less than 5 minutes, and the reason why the heating time was set to 1 hour or less was because heating for more than 1 hour This is because, if this is done, the oxygen-enriched layer of the matrix becomes thicker, the workability of the material decreases, and at the same time, the lubricating performance of the generated oxide film decreases. The reason why the cooling rate was set to be higher than air cooling was due to the same reason as during annealing. As the heating furnace for this treatment, either a continuous furnace or a batch furnace can be used. In addition, the heating method may be an electric furnace or a heating furnace fueled by heavy oil, propane, etc., and since the base pressure differs depending on the furnace used, the temperature and time must be adjusted for each furnace. Bye.

For example, a resin-based lubricant or the like is applied to the surface of the β-type titanium alloy strand treated in this manner, and cold drawing is performed.

The wire rod after wire drawing is descaled by pickling, and then subjected to solution treatment, solution aging treatment, etc., depending on the requirements of the final product.

We have established a cold drawing wire drawing technology for β-type titanium alloy, which has been increasingly used in recent years, and have made it possible to manufacture wire rods with good dimensional accuracy and surface quality.

As one of the β-type titanium alloys for comparison, a hot-rolled wire rod of Ti-15V-3Cr-3Sn-3A1 alloy having a chemical composition shown in Table 1 and having a diameter of 12 mφ was manufactured. Next, the oxide film and oxygen-enriched layer of this wire were removed by peeling, and the wire was drawn with a roller die to obtain a diameter of 4.5 mm.
Using Iφ wire as a test material, a wire rod with a diameter of 2.8 nnφ was prototyped.

The results of trial production of this wire rod are shown in Table 2 together with comparative examples. Second
In the solution treatment (*1) shown in Table 1, a three-room vacuum heating furnace was used, and after heating in vacuum, Ar gas cooling was performed in a cooling chamber. In addition, the oxide film treatment (*2) was performed using a batch type electric heating furnace.

Circularity (x3) indicates the difference between the maximum and minimum diameters in a circular cross section of a wire.

As shown in Table 2, in the cold drawing method of the present invention, it was possible to draw wire from 4.5+nmφ to 2.8Iφ. When oxide film treatment is performed by heating in the atmosphere at 550°C after vacuum solution treatment, breakage occurs in the 2nd or 3rd pass in both cases, and die scratches appear on the surface of the wire. It was observed.

On the other hand, wire drawn by roller dies and groove rolling can be drawn up to 2.8Iφ, but the roundness is significantly worse than that drawn by drawing, and roll flaws may remain. shown. From the above, it can be seen that the method of the present invention is highly effective in obtaining wire rods with excellent dimensional accuracy and surface quality.

Table 1 Chemical composition of sample material (wt%) Margin below

Claims (1)

[Claims] When cold-drawing a β-type titanium alloy, the alloy is heated in a vacuum or in an inert gas atmosphere to a temperature range equal to or higher than the β transformation point, and then cooled at a rate of 1.8°C/min or higher. A method for manufacturing a β-type titanium alloy wire, which comprises solution treatment (annealing) at 600 to 800° C., followed by oxide film formation treatment by heating in the air at 600 to 800° C., followed by cold drawing and wire drawing.