JPH0579404B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing seamless pipes made of pure titanium or titanium alloys, and more specifically, a continuous pipe manufacturing method using the Mannesmann pipe manufacturing process consisting of piercing rolling, elongation rolling, and diameter rolling. Regarding. [Prior Art] Titanium is classified into pure titanium and titanium alloys such as α-type and α+β-type. α-type titanium alloys include Ti-0.15Pd, Ti-0.8Ni-0.3Mo, Ti-5Al
-2.5Sn etc. α+β type titanium alloys include Ti-8Al-1Mo-1V, Ti-3Al-2.5V, Ti
−6Al−4V, Ti−6Al−6V−2Sn, Ti−6Al−
There are 2Sn-4Zr-6Mo, Ti-6Al-2Sn-4Zr-2Mo, etc., and Ti-3Al-2.5V is known as an alloy that can be cold worked. In the present invention, titanium is a general term for these. These titanium materials are lightweight and have high corrosion resistance, and their seamless pipes are particularly expected to be applied to chemical plants and aircraft hydraulic piping. Conventionally, such titanium seamless pipes meet the JIS-
As specified in H4630, it is generally manufactured by a combination of hot extrusion and cold drawing. This is because titanium inherently has poor hot workability, and tubes made from titanium are said to be susceptible to shear strain in the circumferential direction. [Problems to be Solved by the Invention] However, the hot extrusion method is less efficient than other hot tube manufacturing methods, and it is difficult to manufacture long tubes. Further, the cold drawing method is also effective in improving dimensional accuracy, etc., but the efficiency is low. Therefore, conventional titanium seamless pipes manufactured by a combination of such methods are inevitably high in cost. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a titanium seamless pipe at low cost and with good quality. [Means for solving the problem] If seamless pipes are to be manufactured efficiently and economically, it is best to apply a continuous seamless pipe production line that includes an inclined roll perforating mill such as Mannesmann Piercer. good. According to this, seamless pipes are manufactured in the following order. First, a heated billet is pierced and rolled using an inclined roll pierce-rolling machine to form a hollow hollow piece. The obtained hollow piece is then elongated and rolled in a mandrel mill or a plug mill to form a hollow shell. If a mandrel mill is used for stretch rolling, the hollow shell is reheated if necessary and then reduced by a stretch reducer. If stretch rolling is performed by a plug mill, the hollow shell is reheated if necessary and then reduced by a sizer. Rolled to a fixed diameter. The present inventors have continued to study the production of titanium seamless pipes on such a continuous seamless pipe production line, and in the process, they have obtained the following findings regarding sizing rolling. As mentioned above, sizing rolling is located at the final step of a continuous seamless pipe line that includes an inclined roll piercing mill. Therefore, this diameter rolling determines the surface texture of the product. Since titanium inherently has poor hot workability and its properties change greatly depending on temperature, there is a concern that the surface quality will deteriorate if the necessary dimensional accuracy is to be ensured through this sizing rolling. If the surface quality deteriorates during size rolling, it directly means a decline in the quality of the product, and even if sufficient quality is ensured through piercing rolling and elongation rolling leading up to size rolling, it will be meaningless. . As a result of repeated experiments on the sizing rolling conditions for titanium hollow shells under these circumstances, the present inventors found that in sizing rolling of hollow shells, it is necessary to specify the hollow shell temperature and outer diameter reduction rate at the entrance side of the sizer. It was discovered that properties and properties comparable to those obtained when seamless titanium pipes were manufactured by a combination of hot extrusion and cold drawing were obtained. The present invention was made based on this knowledge, and it is possible to continuously process seamless pipes made of pure titanium or titanium alloy through the following steps: hot piercing rolling, elongation rolling using a plug mill, and sizing rolling using a sizer. During production, the hollow shell obtained by elongation rolling is rolled to a fixed diameter under conditions of a rolling machine entrance temperature of 550 to 1150 °C and an outer diameter reduction of 3 to 15% without cooling it to 450 °C or higher. This article summarizes the manufacturing method of titanium seamless pipes. [Function] According to the present invention, by specifying the sizing rolling conditions, a high-quality titanium seamless pipe can be obtained through a continuous process of piercing rolling, elongation rolling, and sizing rolling. The applicant has already proposed that the product quality of titanium seamless pipes can be further improved by cooling the stretch-rolled material to 450°C or less, then reheating it and rolling it to a fixed diameter. (Japanese Patent Application No. 63-263650) However, such high quality is often not required depending on the application, and the present invention can adequately meet such cases. Rather, in the present invention, active cooling is not performed between elongation rolling and sizing rolling, so thermoeconomic efficiency is good and tube manufacturing efficiency is high. The continuous pipe manufacturing process of piercing rolling, elongation rolling, and diameter rolling employed in the present invention is one of the typical seamless pipe manufacturing processes when the material is steel, but it is not applied to titanium. This is simply because the properties of titanium and steel are significantly different. For example, in the past, titanium's hot workability was so poor that it was not thought that its hot rolled tubes would satisfy product standards. Under these circumstances, the present inventors conducted research on the characteristics of titanium and conducted various experiments, and finally completed the present invention. For reference, the difference in perception between sizing rolling of steel and sizing rolling of titanium will be explained, as well as common sense ideas regarding sizing rolling of titanium and the results of experimental research by the present inventors. In the case of ordinary steel, it is generally considered that a low temperature at the entrance of the sizer below 650°C is undesirable due to the problem of quality deterioration due to the occurrence of roll edge seizure defects. On the other hand, in the case of titanium, in the temperature range below the β transus (approximately 990°C for titanium alloys), the deformation resistance increases significantly as the temperature drops, so common sense suggests that the sizer entrance temperature should be high. It is necessary to raise the temperature considerably higher than the lower limit temperature of ordinary steel. However, according to the experimental research conducted by the present inventors, it was possible to perform rolling at a temperature range of 550°C, which is lower than the lower limit temperature of ordinary steel. Regarding the outer diameter reduction ratio, a sizer is usually composed of 5 to 7 stands, and in this case, it is thought that for ordinary steel, it should be kept to 12% or less from the viewpoint of outer diameter accuracy and roll edge seizure. . On the other hand, in the case of titanium, by analogy with the above-mentioned characteristics, it is common sense to reduce the outer diameter at least as much as ordinary steel. However, according to the experimental research conducted by the present inventors, it has been found that sizer constant diameter rolling with good surface quality and dimensional accuracy is possible even under a large outer diameter reduction ratio of up to 15%. As described above, there is a large difference in perception between sizing rolling of steel and sizing rolling of titanium, and the present invention was completed based on new knowledge that overturns this perception. The reason for limiting the rolling conditions in the present invention is as follows. The properties of titanium change greatly depending on the temperature, especially when it is rolled to a fixed diameter at a sizer entry temperature of less than 550℃.
Since the deformability is reduced, defects such as burrs, streaks, edge marks, and holes occur due to roll seizure, and in some cases, rolling itself becomes impossible. Furthermore, in titanium alloys, when the α/β phase is deformed due to the difference in deformability between the two, vacancies called voids are generated. On the other hand, when rolling is performed at a sizer entrance temperature of over 1150°C, coarse acicular crystals are produced by cooling after rolling. These needles have low deformability and reduce the mechanical properties of the product. Therefore, the hollow shell temperature at the input side of the sizer is 550 to 1150°C. Regarding the outer diameter reduction rate, if this is less than 3%,
The purpose of sizing rolling cannot be achieved and the dimensional accuracy of the product deteriorates. On the other hand, if it exceeds 15%, external flaws such as streaks and edge marks will occur due to roll seizure, and the surface quality of the product will deteriorate. Therefore, the outer diameter reduction ratio in constant diameter rolling is set to 3 to 15%. [Example] Examples of the present invention will be described below. Made of industrially pure titanium (JIS-H4630-Type 3) with the composition shown in Table 1, outer diameter 173 mm, length
A 2040mm solid billet is rolled using a two-roll inclined piercing rolling mill (piercer) at a temperature of 990 to 1250℃ at the entrance of the rolling mill.
A hollow tube with an outer diameter of 178 mm, a wall thickness of 40 mm, and a length of 2,710 mm was made into a hollow tube.
880~1200℃, outer diameter 190mm, wall thickness 19.5mm, length 4500
The dimensions were adjusted to a mm hollow piece. Subsequently, the obtained hollow piece was stretched and rolled in a plug mill at a rolling machine entrance temperature of 600 to 1150°C.
It is a hollow shell with an outer diameter of 183 mm, a wall thickness of 15 mm, and a length of 5940 mm. The stretching ratio at this time was 1.3. Next, the obtained hollow shells were reheated to various temperatures without forced cooling below 450° C., and then rolled to a fixed diameter using a 2-roll, 7-stand sizer while changing the outside diameter reduction ratio. Table 3 shows the results of investigating the properties of the pure titanium seamless pipe after diameter rolling and the room temperature characteristics after annealing at 750°C for 1 hour. For reference, Table 3 shows the JIS-H4630-3 standard values for the same grade products manufactured by a combination of hot extrusion and cold drawing. In No. 1, due to the low temperature at the entrance of the sizer, flaws occurred on the surface of the seamless pipe, and the product value was lost even before mechanical properties were discussed. In No. 6, the temperature at the entrance of the sizer was too high, so although the surface quality was good, the elongation deteriorated significantly. In No. 8, although the sizer inlet temperature was appropriate, the required dimensional accuracy could not be ensured due to an insufficient reduction rate of the outside diameter. In No. 10, the outer diameter reduction ratio was excessive, resulting in surface flaws and loss of product value. In contrast to the above comparative examples, Nos. 2 to 2, which are examples of the present invention,
Samples Nos. 5, 7, and 9 had good surface properties, and their mechanical properties all satisfied the standard values for a combination of hot extrusion and cold drawing. Next, Ti-6Al- having the composition shown in Table 3
The same test as above was conducted for 4V alloy.
The results are shown in Table 4. As is clear from Table 4, the present invention is also effective for manufacturing titanium alloy hollow shells. As described above, in the present invention, by specifying the sizing rolling conditions, a titanium seamless tube can be manufactured with good quality through a continuous process of piercing rolling, elongation rolling, and sizing rolling. Note that the tube after being rolled to a fixed diameter may be subjected to a surface finishing process by cutting, if necessary.

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[Table] *Outside the scope of the present invention

【table】

【table】

[Table] *Outside the scope of the present invention [Effects of the present invention] The method for producing a titanium seamless pipe of the present invention includes the following steps when producing a titanium seamless pipe through a continuous pipe-making process of piercing rolling, elongation rolling, and diameter rolling. Suppresses quality deterioration during diameter rolling and gives superior quality to hot-rolled products. Therefore, it is highly effective in reducing the manufacturing cost of titanium seamless pipes.

Claims (1)

[Claims] 1 Hot piercing rolling of a seamless pipe made of pure titanium or titanium alloy, elongation rolling with a plug mill,
When manufacturing continuously through each step of sizing rolling with a sizer, the hollow shell obtained by elongation rolling is maintained at a temperature at the entrance of the rolling machine of 550 to 1150°C and an outer diameter reduction rate without cooling to 450°C or higher. 1. A method for producing seamless titanium pipe, characterized by rolling to a fixed diameter under conditions of 3 to 15%.