JPH05277515A - Manufacture of high ni alloy seamless tube excellent in inside quality of tube - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for a high Ni alloy seamless tube excellent in the quality of the inside surface of a tube prevented from generation of rolling flaws. CONSTITUTION:A hollow tube stock is used as base stock and before the tube stock is heated, an aluminum film is formed on the inside surface of the hollow tube stock, then, the tube stock is manufactured by the normal Mannesmann rolling method into a tube. In this way, since an alloy layer excellent in hot workability is formed on the inside surface of the tube stock, the inside flaws of the tube are greatly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high Ni alloy seamless pipe which has few defects such as rolling flaws and is excellent in the inner surface quality of the pipe.

[0002]

2. Description of the Related Art In the energy development industries such as oil and gas, the environment of oil and gas fields to be developed has become severe in recent years. That is, it becomes deep well and H ₂
The content of highly corrosive gases such as S and CO ₂ is increasing. As a seamless oil well tubular material capable of coping with such environmental changes, high Ni alloys containing 20% or more of Ni have come to be used, and the demand thereof is increasing year by year.

The high Ni alloy seamless pipe is usually manufactured by hot extrusion of the Eugene system. However, since such alloy has a high deformation resistance, the product size is restricted by the extrusion force in the hot pressing method. Since the production efficiency is lower than that of the rolling method, manufacturing by the rolling method is being attempted.
However, when the rolling method is used, there is a problem that severe rolling flaws occur on both the inner surface and the outer surface of the pipe. In particular, the inner surface defects of pipes are difficult to care for, so that they are seriously damaged.

[0004] As a technique which has been proposed in the past with regard to pipe production by mannesmann rolling of this type of alloy,
As described in "Iron and Steel"'89 -S354 (1986), a method of controlling cracking by controlling the heating temperature, working temperature and working degree of the material to be rolled within a specific range can be mentioned. However, although this technique provides necessary conditions for preventing cracks, this alone does not eliminate rolling defects that are smaller than "cracks" but reduce product quality.

That is, in the production of high Ni alloy pipes by the rolling method, rolling defects are unavoidable, and grinding is indispensable to remove them, leading to a decrease in yield and productivity leading to higher manufacturing costs. At present, almost no production of high-Ni alloy seamless pipes is performed by the rolling method, and the hot pressing method is the only method that can easily control the temperature and has few flaws. However, as described above, the hot pressing method has a problem that the productivity is lower than that of the rolling method and that the size limitation of the product pipe is large.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned conventional problems, and provides a Mannesmann rolling method by providing a means for reducing rolling flaws, in particular, pipe inner surface flaws which cause serious damage. It is an object of the present invention to provide a method for producing a high Ni alloy seamless pipe by the method.

[0007]

[Means for Solving the Problems] The inventors of the present invention conducted research and development back to the mechanism of rolling flaw generation in order to achieve such an object. It was found that the damage in the surface layer due to lack of deformability was one of the causes. Therefore, in order to prevent the destruction of the surface layer in the pipe, it is necessary to improve the deformability of the material surface layer, and for this purpose, it was found that it is effective to form an Al layer on the surface of the material in advance. The present invention is based on such knowledge, and the gist thereof is to use a hollow shell having an aluminum coating formed on the inner surface of the shell,
This is a method for producing a high Ni alloy seamless tube produced by the Mannesmann rolling method.

The present invention will be described in detail below. First, a hollow shell must be used as the material. The reason for this is that it is necessary to form an Al film on the inner surface of the base pipe before heating the base pipe. The reason why the Al coating is applied to the inner surface of the blank before heating the material is to obtain the following effect of the Al coating during heating. That is, due to the diffusion of Al into the material during heating, the chemical composition of the surface layer of the rolled material changes, and the microstructure of the surface layer that undergoes the most severe shearing strain changes to a ferrite single phase, resulting in hot deformability. 1
Improve to the level of 3% Cr steel. For this reason, the surface layer is well deformed by following the additional shear strain in perforation or stretch rolling, and as a result, defects such as microcracks and flaws are not caused. This result extends not only to the piercing and stretching rolling stages but also to the downstream rolling processes such as plug mill rolling, so that the growth of flaws can be prevented.

[0009]

EXAMPLES The present invention will be further described based on examples.
Test rolling was performed by the Mannesmann rolling method. The components of the test material are shown in Table 1. High Ni alloys of A and B2 steel grades were used. 250mm × 250 of these alloys tapped by VIM
A hollow shell having a diameter of 245 mm x t75 mm x 5.5 m was formed by forming a bloom having a mm cross section, and then machining and welding it. In this embodiment, the hollow shell is produced by bloom machining, but it may be formed by centrifugal casting. Further, although the Al film is formed by thermal spraying in this embodiment, a method such as plating may be used. After the rolled material was cut and pickled, the inner surface of the pipe was visually observed, and further, the flaw depth was determined by grinder partial grinding and evaluated. The results are shown in Table 2.

[0010]

[Table 1]

[0011]

[Table 2]

As is clear from Table 2, No. According to the present inventions 1 and 2, it is possible to obtain a relatively good tube inner surface quality. On the other hand, Comparative Example No. In Nos. 3 and 4, rolling defects frequently occurred.

[0013]

According to the present invention as described above, it is possible to manufacture a high Ni alloy seamless pipe having a good pipe inner surface quality by significantly reducing rolling defects by the Mannesmann rolling method. Further, the effect of the present invention extends to an austenitic stainless steel that has a smaller amount of Ni and is easily processed.

Claims (1)

[Claims] 1. A method for producing a high Ni alloy seamless tube, which comprises producing a tube by a Mannesmann rolling method using a hollow shell having an aluminum coating formed on its inner surface.