JPH0579403B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a seamless pipe of Ti or Ti alloy. (Conventional technology) Seamless pipes are generally produced by roll rolling, extrusion,
Items that are manufactured using hot pipe manufacturing methods such as the Erhard method and require high quality due to their material or dimensional accuracy are manufactured using cold pipe manufacturing methods using pipes manufactured using hot pipe manufacturing methods. Ru. In the roll rolling method, a solid billet is hot pierced using an inclined roll rolling mill called a piercer, and then hot rolled to reduce its diameter and thickness using a roll rolling mill such as a plug mill, mandrel mill, Atsel mill, or date shear mill. . In addition, the extrusion method is suitable for manufacturing difficult-to-process materials, and involves inserting a heated hollow billet into a cylinder called a container, inserting a mandrel through the billet, and forming the billet between the mandrel and the die. This is a means for pushing the billet out of the container through the gap. Seamless metal pipes manufactured by this extrusion method are used as products as they are, and are often used as raw materials for cold pipe manufacturing methods such as the pultrusion method and the cold pilger method. Furthermore, the Erhardt method is a method in which a bottomed, bottom-shaped hollow base tube is drilled out of a steel ingot, reheated, a mandrel is inserted inside, and then punched out using a die, and is mainly used for manufacturing large-diameter, thick-walled tubes. used. On the other hand, seamless pipes made of Ti or Ti alloys have excellent corrosion resistance and high specific strength, as is well known, and are therefore often used in aviation applications such as aircraft, chemical industry plants, nuclear power plants, and plants. Furthermore, Ti or Ti alloys inherently have poor hot workability, and the tubes thereof are said to be susceptible to shear strain in the circumferential direction. For this reason, Ti or Ti alloy seamless pipes have traditionally been manufactured by hot extrusion or a combination of hot extrusion and cold drawing as specified in JIS-H4630. . (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, although the cold drawing method is an effective means for improving dimensional accuracy, etc., the production efficiency is low. Therefore, Ti or Ti produced by this method
Alloy seamless pipes are inevitably expensive. By the way, a low-cost method for manufacturing seamless pipes is the roll rolling method, but the problem with the Mannesmann plug mill method, for example, is that Ti or
Ti alloys are prone to seizure, so seizure occurs between the inner surface of the tube and the plug during plug mill rolling.
The plug may be damaged. If the plug is damaged in this way, streaks will occur on the inner surface of the tube, the resistance from the plug will increase, resulting in intermediate clogging, misrolls, etc., and external surface flaws will occur due to intermediate clogging as shown in . A problem will arise. That is, conventionally, it has not been possible to economically produce seamless pipes of Ti or Ti alloys by roll rolling or other highly efficient methods. An object of the present invention is to provide a method for manufacturing a seamless pipe made of Ti or a Ti alloy that can solve the above problems. (Means for Solving the Problems) In order to solve the above problems, the present inventor has made various studies and found that (i) By specifying the reduction amount of the pipe to be manufactured and (ii) the surface temperature of the pipe at the entry side of the plug mill, it is possible to manufacture Ti or Ti alloy seamless pipes efficiently and economically. After learning that it is possible, we completed the present invention. Here, the gist of the present invention is a method for manufacturing seamless pipes of Ti or Ti alloy by two-roll inclined rolling method, which comprises: (i) wall thickness reduction: 0.5 to 2.0 mm (ii) in a plug mill; ) Surface temperature of raw tube at plug mill entry side: 600
Characterized by rolling that satisfies the conditions of ~1150℃
This is a method for manufacturing seamless pipes made of Ti or Ti alloy. In the present invention, the method for manufacturing the hollow tube supplied to the plug mill is not particularly limited, and may be performed, for example, by press piercing or punching press. In addition, in the present invention, "two-roll inclined rolling" includes, for example, the Mannesmann plug mill method,
There is a press piercing mill-plug mill method, etc. (Function) Hereinafter, the present invention will be explained in detail along with the function and effect. In the following description of the present invention, the Mannesmann Pragmill method will be used for convenience of explanation. The Mannesmann plug mill method, which has been used conventionally as a manufacturing method for seamless steel pipes using the inclined rolling method, is a process in which a solid billet is heated to a predetermined temperature in a heating furnace and then perforated using a piercing mill. This is made into a tube, which is then elongated by reducing the wall thickness mainly using an inclined elongation rolling mill, further reduced in wall thickness by a plug mill to form a hollow shell, and then polished and reduced by a reeler and a sizer. This is to obtain predetermined product dimensions. The present invention utilizes such a seamless steel pipe manufacturing process to stretch and roll a Ti or Ti alloy seamless pipe under specific conditions.More specifically, the present invention provides the following methods: By two-roll inclined rolling method
When manufacturing seamless pipes made of Ti or Ti alloy, (i) the wall thickness reduction (reduction amount of the wall thickness) of the raw pipe of the plug mill and (ii) the surface temperature of the raw pipe at the entrance side of the plug mill are determined (i). ) Wall thickness reduction: 0.5 to 2.0mm (ii) Surface temperature of raw tube at plug mill entry side: 600
By specifying the temperature as ~1150°C, the present invention provides a means for economically manufacturing a seamless pipe of Ti or Ti alloy by a roll rolling method or a highly efficient method similar thereto. Therefore, the reasons for the above limitations in the present invention will be explained. (i) Thickness reduction If the thickness is less than 0.5 mm, slips will occur and rolling will become impossible. On the other hand, if it exceeds 20 mm, the reduction amount will be excessive and the plug will be damaged, resulting in streaks on the inner circumferential surface of the pipe, and in the worst case, pit flaws will occur on the outer surface due to clogging during rolling. . Therefore, in the present invention, the wall thickness reduction is limited to 0.5 to 2.0 mm. In other words, it is true that according to the conventional technology, the wall thickness reduction is 1.5 to 6.5 for seamless steel pipes.
It is known to be in the mm range. However, in the case of titanium pipes, as shown in Figure 1, it was discovered for the first time through special research and experiments on titanium by the inventors that the relationship between wall thickness reduction and quality is significantly different from that of steel pipes. Ta. In the figure, the quality on the vertical axis is the internal flaw occurrence rate, which is shown as a general trend in relative evaluation. According to this, the appropriate range for plug mill rolling of titanium tubes in terms of quality and operation is extremely narrow, and due to quality constraints caused by seizure between the inner surface of the tube and the plug, as shown by the shaded area in the figure. , it is necessary to keep it to a maximum of 2.0mm. In other words, in the case of ordinary steel, 3 to 4 mm is optimal when considering surface quality and wall thickness accuracy;
The value mm is not desirable. This is because, for example, the roughness of the inner surface and the spiral inner surface unevenness generated in the elongator in the previous process are not sufficiently removed. However, in the case of titanium, the optimum value is 1.0 to 1.5 mm, and even if the thickness is reduced compared to ordinary steel, the above-mentioned problems do not occur and sufficiently good quality can be ensured. (ii) If the entrance temperature is less than 600°C, deformability will decrease, deformation resistance will increase, and biting defects will occur frequently. On the other hand, if the temperature exceeds 1150°C, the mechanical properties (elongation) of the product will decrease due to coarsening of crystal grains.
Therefore, the inlet temperature is limited to 600-1150°C. Here, the present inventors have discovered that there is a temperature range in which plug mill rolling of titanium tubes is possible, starting from a low temperature of 600° C. on the surface of the raw tube at the entrance side of the plug mill. That is, for example, in the case of titanium, as shown in FIGS. 2 and 3, at temperatures below the β transus (approximately 990°C), as the temperature decreases,
The torsion value decreased significantly and the deformation resistance increased,
Deformability deteriorates rapidly. Therefore, 600℃
Until now, it was common knowledge that it could not be deformed at all at such low temperatures. In addition, even in the case of ordinary steel, the higher the base pipe temperature is, the better, in order to prevent damage to the plug and the occurrence of streak-like flaws on its inner surface.
It was common sense to avoid rolling at temperatures above 900°C. However, in the case of the present invention, despite the aforementioned deterioration of deformation characteristics at temperatures below the β transus, plug mill rolling from a low temperature range of approximately 600°C in combination with wall thickness reduction of 0.5 to 2.0 mm improves quality and quality. We obtained the completely unexpected finding that both aspects of operation can be improved. The method according to the present invention satisfies the above two conditions, and all other operations and conditions are based on the conventional Mannesmann-Pragmill method as described above. For example, Table 1 shows tubes made of Ti or Ti alloy,
The conditions for manufacturing a pipe made of ordinary steel (carbon content 0.2% by weight) using the Mannesmann plug mill method are shown below. In other words, in the present invention, although the rolling load in the plug mill is reduced, this is compensated for by increasing the wall thickness reduction in the elongator, so there is no problem with the dimensions of the product tube. .

[Table] In this way, according to the present invention, Ti or Ti
When manufacturing seamless alloy pipes using the Mannesmann plug mill method, streaks occur on the inner surface of the tube, the resistance from the plug increases, resulting in intermediate clogging and misrolling, and the intermediate clogging causes defects on the outer surface as shown in . It has become possible to solve the problem of this occurring. Further, the present invention will be described in detail along with examples thereof, but these are merely illustrative of the present invention and are not intended to limit the present invention. Example A solid billet of Ti or Ti alloy whose composition is shown in Table 2 was processed by the Mannesmann plug mill method by variously changing the wall thickness reduction in the plug mill and the surface temperature conditions on the entrance side of the plug mill.
Seamless pipes made of Ti or Ti alloy were manufactured. The conditions and results of this test are summarized in Table 3.

【table】

[Table] (Note) * outside the scope of the present invention As is clear from Table 3, according to the present invention,
Seamless pipes made of Ti or Ti alloys could be economically manufactured using a roll rolling method or a similar highly efficient method. (Effects of the Invention) As detailed above, according to the present invention, it has become possible to economically produce a seamless pipe of Ti or Ti alloy by a roll rolling method or a highly efficient method similar thereto. The practical significance of the present invention having such effects is extremely significant.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the correlation between wall thickness reduction and quality for titanium pipes and ordinary steel pipes. FIG. 2 is a graph showing the relationship between temperature and twist value of Ti-6Al-4V alloy. FIG. 3 is a graph similarly showing the relationship between temperature and deformation resistance of the Ti-6Al-4V alloy.

Claims (1)

[Claims] 1. A method for manufacturing a seamless pipe of Ti or Ti alloy by a two-roll inclined rolling method, which comprises: (i) wall thickness reduction: 0.5 to 2.0 mm; (ii) at the entrance side of the plug mill; Base tube surface temperature: 600
Characterized by rolling that satisfies the conditions of ~1150℃
A method for manufacturing seamless pipes of Ti or Ti alloy.