JPH02108402A - Manufacture of billet for pure titanium seamless tube - Google Patents

Abstract

PURPOSE:To obtain a tube stock with no surface flaw and to improve the tube manufacturing efficiency and yield by working the stock by specifying a working ratio of an ingot and a surface temp. at finish of the working. CONSTITUTION:A solid billet is pierced to be a hollow tube stock and the stock is elongated and form rolled to manufacture a pure titanium seamless tube. In that case, the billet is manufactured by adding working of a reduction ratio of area >=2 to an ingot in a temp. range of 500-1,100 deg.C by forging and/or rolling. Thus, a tube stock with no surface flaw is obtained in spite of the working of a type of piercer, so that a pure titanium seamless tube having good quality is obtained by elongating and form rolling the stock.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a solid billet for manufacturing pure titanium seamless pipes.

[Conventional technology]

Pure titanium seamless pipes have excellent corrosion resistance and light weight, and have been widely used in chemical plants and other fields.

Now, the method for manufacturing seamless pipes is to make a hollow raw pipe by punching a solid billet heated to a predetermined temperature using a piercing rolling mill (piercer), and then use an elongator, mandrel mill, plug mill, etc. to produce a hollow raw pipe. Stretched using a stretching mill, and further,
The shape is corrected using a forming rolling machine such as a sizer or reducer,
An inclined rolling method (Mannesmann method) for obtaining a seamless pipe of a predetermined size, and a pressing method for obtaining a seamless pipe of a predetermined size by extruding a blank pipe that has been previously perforated by a perforation press or mechanical processing using a press. Broadly classified. The slope rolling method has the disadvantage that the billet is forced to undergo severe deformation during the perforation process with a piercer, and when this method is applied to the manufacture of pure titanium seamless pipes, which are difficult to process, the raw pipe after perforation Defects such as rashes and cracks may occur on the surface, and these may remain on the product surface, leading to deterioration of product quality. Therefore, in manufacturing pure titanium seamless pipes,
The Eugene-Séjournet method, which is a type of press method, was traditionally used.
It is used for boat fishing.

The pipe-making billet used in this Eugene-Séjournet method is roughly forged in the β temperature range and finished forged in the α temperature range.

However, when compared to the pressing method, the tilt rolling method has the advantages of high pipe manufacturing efficiency and good yield, and it is necessary to use this method in order to mass produce pure titanium seamless pipes at low cost. Application of inclined rolling method to manufacturing is essential. The method that made it possible to manufacture pure titanium seamless pipes by the inclined rolling method is disclosed in Japanese Patent Application No. 62-1675 by the applicant of the present application, for example.
No. 93, and Titanium Alloys vol.
1 (1982) and others.

The former is a 20-inch type inclined roll piercer, and the latter is a 3-inch roll piercer.
This is a proposal for a 01 type inclined roll piercer. As a piercer used in the inclined rolling method, in addition to the above-mentioned inclined roll piercer, there is a press roll piercer which has a structure in which a billet pressed by a press is perforated by a plug and the outer surface of the billet is formed by a Caliba roll.

[Problem to be solved by the invention]

The above-mentioned piercer basically has a configuration in which the main roll advances the material and presses the plug to make the hole.
The material undergoes extremely severe deformation during drilling, and if the deformability of the material is insufficient, problems such as cracks and other defects will occur on the pipe surface of the product. In order to remove these defects, surface cutting, polishing, etc. are required, resulting in a significant increase in man-hours and costs.

Therefore, if you try to pierce pure titanium by pierce rolling,
The pipe-making billet must have sufficient deformability. However, the current state of the art is that nothing has been clarified regarding the manufacturing method of this perforated billet.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method that makes it possible to manufacture pure titanium seamless pipes by the inclined rolling method, regardless of the type of piercer.

[Means to solve the problem]

When manufacturing pure titanium seamless pipes by the inclined rolling method, the present inventors have determined that in order to prevent defects on the surface of the product pipe, the processing conditions for the billet for perforation are as follows:
We found that it is extremely important to control the processing ratio and the surface temperature at the end of processing. Among these, the surface temperature at the end of processing has an extremely important effect on the properties such as the deformability of the surface of the perforation billet, and if the surface temperature is not well controlled, severe shear deformation will occur on the billet surface during inclined rolling, resulting in extrusion. It was found that cracks were generated from the surface.

The present invention has been made based on the above basic knowledge, and its gist is that a solid billet is pierced and rolled to form a hollow pipe, which is then stretched and formed to form a pure titanium seamless pipe. In the method for producing a pure titanium joint, the billet is produced by processing an ingot by forging and/or rolling at a surface temperature range of 500 to 1100°C and an area reduction ratio of 2 or more. This is a method for manufacturing a billet for tubeless use.

[Effect]

In the present invention, a pure titanium billet is processed under predetermined processing conditions and supplied to a piercer with its deformability improved, and is punch-rolled in the piercer.

In this case, unless the area reduction ratio is 2 or more, the coarse structure inherent in the ingot will not be eliminated, and if this coarse structure remains, defects will occur after drilling.

Next, when the surface temperature at the end of processing exceeds 1100° C., an uncomfortable gas-absorbing hardened layer is formed on the surface due to gas absorption, and since this hardened layer has no deformability, it becomes a starting point for cracking during drilling.

On the other hand, if the surface temperature at the end of machining is less than 500°C, cracks will occur on the billet surface after machining, and cutting or the like will be required to remove them, resulting in an increase in yield (reduction).

[Example 1] Three types of billet materials having a square cross section with negative side lengths of 75+u, 90tsuru, and 115n+ were cut from the center of a rod-shaped ingot equivalent to ASTM Gr-3, and each of these was cut out as shown in Table 1. 18 types of round forged materials with different processing conditions were obtained by forging into round bars with a diameter of 70 mm under different conditions, and three round billets each with a diameter of 10 mm and a length of 250 mm were made from the forged materials. It was collected and held at a temperature of 1100°C for 3 hours, then fed to an inclined roll piercer equipped with two barrel-shaped rolls, and the perforation ratio (ratio of length before and after perforation) was 2.
．． A perforation test was conducted under the following conditions. The dimensions after drilling are 72 mm in outer diameter and 53.4 m in inner diameter.

It is 525 dragons long. Table 1 also shows the working ratio (forging ratio) of each billet, the surface temperature at the end of forging (finishing temperature), and the presence or absence of defects on the surface of the raw tube obtained as a result of the drilling test. Defects were evaluated by penetrant testing after descaling the perforated material.

The drilling test was conducted with a roll inclination angle of 10°.
If no defects were observed on the surface of any of the raw tubes manufactured from each of the three billets obtained under the same processing conditions, the tubes were determined to have no defects and were marked with an ○ in Table 1. Other items are determined to have defects and are marked with an x mark.

[Example 2] From the center of the same ingot as in Example 1, three types of billet materials with a square cross section with -side lengths of 80 mm, 95 mm, and 12 (hm) were cut out, and each of these was cut into a second billet material.
After heating under the conditions shown in the table, forging into rods having a square cross section of 65 mm on the side to obtain 18 types of rectangular forged materials with mutually different processing conditions. Three rectangular billets each having a length of 300 mm were taken, and after being held at a temperature of 1100°C for 3 hours, they were fed to a press roll piercer and perforated at a perforation ratio of 1.25. We conducted a test. Dimensions after drilling are outer diameter 7
7mm, inner diameter 40mm, length 375cm. Table 2 also shows the processing ratio and finishing temperature for each billet, as well as the presence or absence of defects on the surface of the raw tube obtained as a result of the piercing test.

The determination of the presence or absence of a defect and the method of displaying it are exactly the same as in the first embodiment.

[Example 3] Three types of round rod-shaped billet materials with diameters of 85 mm, 100+n, and 130 mm were cut from the center of a rod-shaped ingot equivalent to ASTM Gr-1, and each of these was heated under the conditions shown in Table 3. 18 types of round rolled materials with different processing conditions were obtained by rolling into a 70 mm round bar shape, three round billets each having the same dimensions as in Example 1 were collected from the rolled materials, and heated at 1100°C. After being kept at a temperature of 3 hours,
A perforation test was conducted using an inclined roll piercer under the same conditions as in Example 1. Table 3 also shows the processing ratio (rolling ratio) and finishing temperature of each billet, as well as the presence or absence of defects on the surface of the raw tube obtained as a result of the piercing test. The determination of the presence or absence of a defect and its display method are as described in Example 1 and Example 2.
It is exactly the same.

From Tables 1 and 2, when the ingot is forged before drilling, if the surface temperature at the end of forging exceeds 1',00°C, regardless of the size of the forging ratio and the type of piercer, The occurrence of defects was observed, and the forging ratio was 1.5.
It is clear that the same defects are observed regardless of the final surface temperature and the type of piercer.

Even when the processing end temperature was less than 500°C, defects occurred regardless of the size of the forging ratio.

On the other hand, when the surface temperature at the end of forging is 1100°C or lower and 500°C or higher, and the forging ratio is 2 or higher, the raw pipe has no defects and has good surface quality regardless of the type of piercer. It is clear that this can be achieved. That is, from the determination results of the presence or absence of defects in Tables 1 and 2, the forging ratio is 2 or more, the surface temperature at the end of forging is 1100°C or less, and 5.
It is clear that by producing a billet by forging an ingot before piercing under processing conditions of 00° C. or higher, piercing and rolling of a pure titanium billet can be performed regardless of the type of piercer.

Also, in Table 3, which shows the results when rolling is performed before drilling, similar to Tables 1 and 2, which show the results when forging is performed, the rolling ratio is 2 or more, and after the completion of rolling, Only when the processing conditions such that the surface temperature is 1100° C. or lower and 500° C. or higher are satisfied, defects will not occur on the surface of the raw pipe after drilling.

From the above results, it can be concluded that the processing ratio of the ingot is 2 or more, and the surface temperature at the end of processing is 1.
By processing the billet under processing conditions of 100°C or lower and 500°C or higher, the deformability of the billet can be increased, and when the billet is pierced and rolled, there will be no surface defects regardless of the type of piercer applied. It is clear that a pure titanium seamless pipe of good quality can be obtained by elongating and forming-rolling a raw pipe without any cracks.

(Leaving space below) Table 1 [Effects] As detailed above, in the method of the present invention, when manufacturing seamless pipes made of pure titanium, which is a difficult-to-process material, the processing ratio of the ingot is 2 or more. Since we use a billet that has been processed in advance under processing conditions where the surface temperature at the end of processing is below 1100℃ and above 500℃ and has improved deformability, there will be no surface defects regardless of the type of piercer. The present invention has excellent effects, such as obtaining a blank pipe, applying the inclined rolling method to the production of seamless pure titanium pipes, improving pipe manufacturing efficiency, and improving yield.

Claims (1)

[Scope of Claims] 1. A method for producing a pure titanium seamless pipe by piercing and rolling a solid billet to obtain a hollow pipe, which is then stretched and formed to form a seamless pipe, wherein the billet is made of an ingot. 1. A method for producing a pure titanium seamless billet, which is produced by forging and/or rolling at a surface temperature range of 500 to 1100° C. with an area reduction ratio of 2 or more.