JPH05317922A - Manufacture of two phase stainless seamless steel tube excellent in intratube quality - Google Patents

Abstract

PURPOSE:To obtain a two phase stainless seamless steel tube less in internal surface rolled flaw by giving an aluminum sprayed deposited film on the internal surface of a tube stock before it is heated, then, rolling it through the Mannesman rolling method. CONSTITUTION:A hollow tube stock as a blank is formed by the centrifugal casting method and so forth. Before it is heated for rolling, the internal surface of the tube stock is shotblasted and melt-sprayed with aluminum, then, the tube stock is heated and formed by the Mannesman rolling method into a tube. Since the aluminum film on the internal surface of the tube stock is diffused into the internal part of steel in a heating stage and an alloyed layer of single phase excellent in workability is formed, generation of inside flaws by rolling in an elongator and a downstream mill is prevented.

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 two-phase stainless seamless steel pipe having a smooth inner pipe surface and less rolling defects and excellent inner pipe quality.

[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. High alloy steel typified by duplex stainless steel has been used as a material for seamless oil well pipes or line pipes that can cope with such environmental changes, and the demand for it is increasing year by year. ..

Duplex stainless seamless steel pipes are usually manufactured by hot extrusion of the Eugene system, plug mill system, or so-called Mannesmann rolling of the mandrel mill system.
In the hot extrusion, the size of the product is limited due to the limitation of the extrusion force, and the production capacity is lower than that of the rolling method. Therefore, the production by the rolling method is becoming popular. However, in the case of the rolling method, there is a problem that rolling flaws occur on the inner surface of the tube as well as the outer surface of the tube. In particular, from the viewpoint of corrosion resistance, the higher the amount of alloys such as Cr, Mo and Ni to be added, the more serious the problem of rolling flaws becomes.

The following techniques have heretofore been known as measures for preventing rolling defects of this type. (1) As seen in Japanese Patent Publication No. 1-19465, Ca, REM, Al, etc. that reduce the amounts of S and O in steel that are harmful to hot workability and indirectly affect the reduction of S and O amounts. A technology that ensures good hot workability by adding a certain amount of steel to steel. (2) As seen in JP-A-1-228603,
A technology that obtains good inner and outer surface quality by specifying the billet heating temperature and controlling the operating conditions of the piercing and rolling mill to a specific range. (3) As disclosed in Japanese Patent Laid-Open No. 63-115606, a technique in which a hollow portion of a hollow shell is filled with a lubricant, steel plates are applied to both end faces of the opening to weld and close them, and then rolled.

However, (1) is not very effective in a downstream rolling mill in which the material temperature is lowered and the ductility of the material is necessarily lowered, and (2) is not effective in the occurrence and growth of flaws after piercing and rolling. Cannot be prevented,
Regarding (3), it is not practical because the high productivity cannot be expected because the pretreatment of the raw tube is complicated. That is,
When manufacturing a duplex stainless seamless steel pipe by the Mannesmann rolling method, the problem of rolling flaws is unavoidable. Therefore, the maintenance of flaws by grinding is indispensable, leading to problems such as low productivity and high cost. Is the reality.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent rolling flaws which cause problems of cost and productivity in manufacturing a duplex stainless steel pipe by the Mannesmann rolling method from the above problems. To do.

[0007]

[Means for Solving the Problems] The inventors of the present invention conducted research and development back to the mechanism of generation of rolling flaws (inner surface of pipe) in order to achieve such an object, and found that the inner flaws caused excessive shear deformation. It was found that it propagates along the α / γ boundary and grows in the downstream mill (plug mill or reeler mill) that occurs in the elongator added to the tube and the material temperature decreases. Furthermore, in order to prevent this, it was found that it is effective to perform rolling by using a hollow shell that can be coated with an aluminum film on the inner surface of the shell before heating. That is, the gist of the present invention is a method for producing a two-phase stainless seamless steel pipe, which is produced by the Mannesmann rolling method using a hollow shell having an aluminum coating formed on its inner surface.

The present invention will be described in detail below. First, the material for pipe manufacturing (element pipe) used in the present invention must be hollow. This is because it is necessary to previously form an aluminum film on the inner surface of the hollow shell before heating the shell.

In the present invention, the reason for forming the aluminum film on the inner surface of the hollow shell before heating is to obtain the following action.

(1) Aluminum formed as a film on the inner surface of the hollow shell diffuses into the interior of the duplex stainless steel during the heating step to form an α-single phase alloy layer having good workability on the inner surface of the shell. For this reason, inner surface defects are generated during rolling in the elongator and the downstream mill, making it difficult to grow. (2) This alloy layer prevents direct contact between the base steel and the tool to prevent seizure, and as a result, reduces the processing strain of the surface layer of the raw pipe during elongator rolling, so that internal flaws are less likely to occur.

[0011]

EXAMPLES Next, the present invention will be further described with reference to examples. Test rolling was performed by the Mannesmann rolling method. The composition of the sample steel is two steel types A and B in Table 1, both of which are SUS32.
9J2 equivalent steel. Both steels produced in an air melting furnace were formed into a hollow shell of φ256mm x t65mm x 5.5m by a centrifugal casting method, and the inner surface of the shell was shot blasted and further sprayed with aluminum (the present invention; No. 2 in Table 2
1, 2) and those not applied (comparative example; No. 3, in Table 2)
4) was used as the test material. The rolled material was cut and pickled, and then the inner surface of the tube was evaluated by visual observation. The results are also shown in Table 2. As is clear from Table 2, No. According to the present inventions 1 and 2, it is possible to obtain a good pipe inner surface quality. On the other hand, Comparative Example No. In Nos. 3 and 4, rolling flaws occur.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

As described above, according to the present invention, a two-phase stainless seamless steel pipe having a good pipe inner surface quality can be manufactured by the Mannesmann rolling method without causing rolling defects that are harmful to productivity and cost. it can. Further, the effect of the present invention is that the direct contact between the base metal and the tool is prevented and seizure hardly occurs, so that the tool life is secondarily improved.

Claims (1)

[Claims] 1. A method for producing a two-phase stainless seamless steel pipe, characterized in that a hollow shell having an aluminum coating formed on its inner surface is used to produce the steel by the Mannesmann rolling method.