JPH0547285B2 - - Google Patents

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. [Prior Art] 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 roll a solid billet heated to a predetermined temperature into a piercing rolling machine (Piercer).
The hollow tube is made into a hollow tube by drilling, and this tube is stretched by a stretching mill such as an elongator, mandrel mill, or plug mill, and then its shape is corrected by a forming rolling mill such as a sizer or reducer to form a seamless tube of specified dimensions. Incline rolling method (Mannesmann method) for obtaining pipes,
It is broadly divided into pressing methods, which use a blank pipe that has been previously perforated by a perforation press or mechanical processing, and extrude it using a press to obtain a seamless pipe of a predetermined size. 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 production of pure titanium seamless pipe, which is a difficult-to-process material, the raw pipe after perforation Defects such as blemishes and cracks may occur on the surface, and these may remain on the product surface, leading to deterioration of product quality. Therefore, in the production of pure titanium seamless pipes, the Eugene-Ségiurnet method, which is a type of pressing method, has been commonly used. The pipe-making billet used in the Eugene Sejourne process is rough 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. Methods that have made it possible to manufacture pure titanium seamless pipes by the inclined rolling method are disclosed, for example, in Japanese Patent Application No. 167593/1983 filed by the applicant of the present application;
It has been proposed in Titanium Alloys vol.1 (1982), etc. The former was proposed for a two-roll type inclined roll piercer, and the latter for a three-roll type inclined roll piercer. In addition to the above-mentioned inclined roll piercer, as a piercer used in the inclined rolling method, 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 Caliber roll. [Problems 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. Therefore, the material is subjected to extremely severe deformation during piercing, resulting in deformation of the material. If this ability is insufficient, problems such as cracks and other defects will occur on the tube 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 pure titanium is to be perforated by piercing rolling, the billet for making the pipe must be endowed with sufficient deformability. However, conventionally,
At present, nothing has been clarified regarding the manufacturing method of this billet for drilling. 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 enables seamless production of pure titanium by the inclined rolling method, regardless of the type of piercer. [Means for Solving the Problems] 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 have found that it is extremely important to control the processing ratio of the ingot (ingot) 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 properties such as the deformability of the surface of the drilling billet, and if the surface temperature is not well controlled, severe shear deformation occurs on the billet surface during inclined rolling, resulting in external deformation. It was found that cracks were generated from the surface. The present invention has been made based on the above basic knowledge, and the gist thereof is to pierce and roll a solid billet to make a hollow pipe, which is then stretched and formed into a pure titanium seamless pipe. In the method for producing a pure titanium joint, the billet is produced by forging and/or rolling an ingot at a surface temperature range of 500 to 1100°C and with an area reduction ratio of 2 or more. This is a method of manufacturing a billet for tubeless use. [Function] In the present invention, a pure titanium billet is processed under predetermined processing conditions, is supplied to a piercer in a state with improved deformability, and is pierced and 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 cracks 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 surface of the billet after machining, and cutting or the like will be required to remove them, resulting in a significant decrease in yield. Example 1 Three types of billet materials with square cross-sections with side lengths of 75 mm, 90 mm, and 115 mm are cut from the center of a rod-shaped ingot equivalent to ASTM Gr-3, and each of these is cut to a diameter of 70 mm under the conditions shown in Table 1. 18 types of round forged materials with different processing conditions were obtained by forging into round bar shapes.
Three 250mm round billets were collected and
After being maintained at a temperature of 1100° C. for 3 hours, the material was fed to an inclined roll piercer equipped with two barrel-shaped rolls, and a perforation test was performed under conditions of a perforation ratio (ratio of length before and after perforation) of 2.1. Dimensions after drilling are outer diameter 72
mm, inner diameter 53.4mm, length 525mm. Table 1 also shows the processing ratio (forging ratio) and surface temperature at the end of forging (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 drilling test. For evaluation of defects, after descaling the perforated material,
This was done using penetrant testing. The perforation test was conducted with a roll inclination angle of 10°, and those that had no defects observed on the surfaces of all three billets obtained under the same processing conditions were classified as "defects". The defects were determined to be "no defects" and are marked with a circle in Table 1, and the other defects were determined to be "defects" and are also marked with an x. Example 2 Three types of billet materials with square cross sections with side lengths of 80 mm, 95 mm, and 120 mm were cut from the center of the same ingot as in Example 1, and each of these materials was heated under the conditions shown in Table 2. , forged into rod shapes with a square cross section of 65 mm on a side to obtain 18 types of rectangular forged materials with mutually different processing conditions, and from the forged materials with a square cross section of 65 mm on a side and a length of 300 mm.
Three rectangular billets were taken from each sample, held at a temperature of 1100° C. for 3 hours, and then fed to a press roll piercer to perform a piercing test under the condition of a piercing ratio of 1.25. The dimensions after drilling are 77 mm in outer diameter, 40 mm in inner diameter, and 375 mm in length. 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 drilling 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 bar billet materials with diameters of 85 mm, 100 mm, and 130 mm were cut from the center of a bar 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 round bars, and three round billets with the same dimensions as in Example 1 were taken from each of the rolled materials, and these were heated at a temperature of 1100°C. After being held at the bottom for 3 hours, a perforation test was conducted under the same conditions as in Example 1 using an inclined roll piercer. 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 the method of displaying it are exactly the same as in the first and second embodiments. From Tables 1 and 2, when the ingot is forged before drilling, the surface temperature at the end of forging is
When the temperature exceeds 1100℃, defects are observed regardless of the size of the forging ratio and the type of piercer.
Furthermore, when the forging ratio is 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 finishing temperature was less than 500°C, defects occurred regardless of the forging ratio. On the other hand, when the surface temperature at the end of forging is below 1100℃ and above 500℃, and when the forging ratio is 2 or above,
No defects occur regardless of the type of piercer.
It is clear that a blank tube with good surface quality is obtained. In other words, from the results of determining the presence or absence of defects in Tables 1 and 2, forging was performed before drilling under processing conditions such that the forging ratio was 2 or higher and the surface temperature at the end of forging was 1100°C or lower and 500°C or higher. It is clear that by producing a billet in this manner, piercing and rolling of a pure titanium billet can be carried out regardless of the type of piercer. Also, in Table 3, which shows the results when rolling is performed before drilling, as well as in 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, Surface temperature is below 1100℃,
Only when the processing conditions of 500°C or higher are satisfied will there be no defects on the surface of the raw tube after drilling. From the above results, the pure titanium billet before piercing and rolling should be processed under processing conditions such that the processing ratio of the ingot is 2 or more and the surface temperature at the end of processing is below 1100℃ and above 500℃. By this, the deformability of the billet can be increased, and when it is pierced and rolled, a raw pipe with no surface defects can be obtained regardless of the type of piercer applied, and this can be stretched and rolled, It is clear that pure titanium seamless pipes with good quality are obtained.

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〔effect〕

As detailed above, in the method of the present invention, in manufacturing seamless pipes made of pure titanium, which is a difficult-to-process material, the processing ratio of the ingot is 2 or more, the surface temperature at the end of processing is 1100°C or less, and 500°C Because we use a billet that has been pre-processed under processing conditions of ℃ or higher and has improved deformability, we can obtain a raw pipe with no surface defects regardless of the type of piercer, making it possible to manufacture pure titanium seamless pipes. The present invention has excellent effects, such as being able to apply an inclined rolling method to improving pipe manufacturing efficiency and 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 and rolled, wherein the billet is formed by forging an ingot. and/or rolling, the area reduction ratio is 2 in the surface temperature range of 500 to 1100℃.
A method for producing a pure titanium seamless pipe billet, which is produced by adding the above processing.