Process for producing seamless steel pipe made of high-chromium high-nickel alloy steel

Abstract

A raw material to be rolled made of a high-chromium high-nickel alloy steel containing, in terms of mass%, 20-30% chromium, 30-50% nickel, and at least one of molybdenum and tungsten, the amount of the latter two being 1.5% or more in terms of Mo+0.5W, is subjected to oblique piercing rolling under the conditions of a roll-gouge peripheral speed of 2.3 m / sec or higher after the raw material to be rolled is heated under the conditions satisfying the following relationship (1). Thus, the inner surface can be prevented from developing a rash through melting and plug life can be prolonged. T=1575-4.45OEf-104.7OE-ln(th / r0)} (1) T means the heating temperature ( DEG C), Vf means the roll-gouge peripheral speed (m / sec), r0 means the radius of the inlet-side raw billet (mm), and th means the wall thickness of the raw pipe after piercing (mm).

Description

technical field [0001] The invention relates to a piercing and rolling method of a high Cr-high Ni base alloy steel slab using a skewed roll piercer. Background technique [0002] In the manufacture of seamless steel pipes, Mannesmann mandrel seamless pipe rolling method, Mannesmann automatic pipe rolling method, Mannesmann A Assel mill rolling method and other methods. The manufacturing method of the above-mentioned seamless pipe by the Mannesmann method is to use a mandrel type seamless pipe rolling mill, an automatic A rolling mill such as a pipe rolling mill expands the obtained hollow billet to reduce the wall thickness, and then uses a stretching and shrinking mill, a sizing mill and other reducing machines to reduce the outer diameter and process a finished steel pipe. [0003] Various inventions are disclosed about the manufacturing method of a seamless steel pipe. [0004] For example, Patent Document 1 discloses an invention in which a billet of high-Cr alloy st...

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Problems solved by technology

[0010] Regarding the above-mentioned problems, there is neither description nor suggestion in Patent Document 1, which deals with 12% Cr steel pipes, and Patent Document 2, which deals with steel pipes equivalent to SUJ-2. Literature that mentions the unique problems of seamless steel tubes made of high Cr-high Ni-based alloy steel containing Mo

In addition, in order to solve the above-mentioned problems of seamless steel pipes, there is no reference to determining an appropriate slab heating temperature based on the relationship between the peripheral speed of the roll and the degree of wall thickness processing.

[0011] Therefore, in order to solve the above-mentioned problem of molten inner surface spots occurring during the production of the Mo-containing high-Cr-high-Ni-based alloy seamless steel pipe, the present inventors investigated the relationship between the heating temperature and the peripheral speed of the roll. Detailed research, but only adjusting the relationship between the above two, can not completely prevent the occurrence of Mo melting-like inner surface marks

On the other hand, if the rolling speed is reduced, heat generation during processing can be suppressed, but there are problems such as prolonged rolling time and extremely shortened plug life due to an increase in deformation resistance of the rolled material.

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