JPH06114410A - Manufacture of high chromuim steel seamless tube excellent in quality of inside surface of tube - Google Patents

Abstract

PURPOSE:To reduce the generation of rolling defect and to obtain a high chromium steel seamless tube excellent in the quality of the inside surface of tube by applying water glass or executing aluminum coating on the inside surface of a hollow tube stock. CONSTITUTION:The hollow tube stock is used as a base stock and coated with water glass before heating the base stock. The film of liquid glass excellent in lubricating performance at the time of heating is formed on the whole inside surface of the tube stock. Since the glass film during rolling is always present in the boundary between a tool and a material to be rolled and its lubricating effect is greatly high, friction is drastically reduced, shearing strain added on the inside surface of the material to be rolled is reduced and rolling defect is reduced. And, when the alumimum coating is formed before heating the base stock, alumimum is diffused into the base stock at the time of heating, the chemical structure of the outer layer of the material to be rolled is changed and the structure of the outer layer becomes ferritic single-phase structure excellent in hot workability. Thus, the outer layer is deformed by throughly following additional shearing strain in piercing or elongating rolling and the defects of crack, flaw, etc., are not caused.

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-Cr steel seamless steel pipe which is excellent in the inner surface quality of the pipe with less rolling defects.

[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, the deeper the well is, the more the content of highly corrosive gas is increasing. 13% as a seamless oil well pipe material that can respond to such environmental changes
High Cr steel represented by Cr steel (mainly SUS420) has come to be used. Also, in the boiler for thermal power generation, the application of various ferritic heat-resistant steel pipes based on 9% Cr is increasing due to the needs for high-temperature and high-pressure operation.

The 13Cr steel (SUS420) and 9Cr steel seamless pipes are generally manufactured by a rolling method. However, the rolling method has a problem that rolling flaws and cracks occur on the inner and outer surfaces of the pipe. In particular, the inner surface flaws of the pipe are difficult to care for and cause serious damage. Conventionally, "Materials and Processes" [vol. 2 (1991) -590], targeting SUS420 steel (13% Cr steel), from the viewpoint of δ-ferrite precipitation due to center segregation, the composition, the slab size, and the heating temperature are optimized so that the inner surface defects of the pipe are prevented. Techniques for reducing it have been proposed, but the same 13% Cr
Even with steel, the amount of C is less than that of SUS420. In the case of SUS410 steel in which δ-ferrite precipitates and cracks during hot working, severe internal flaws still occur, and it is always a sufficient measure against high Cr steel. Cannot be

[0004]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides means for preventing defects on the inner surface of a pipe which causes problems of cost and productivity in producing a high Cr steel seamless pipe by the Mannesmann rolling method. Especially.

[0005]

[Means for Solving the Problems] As a result of research and development going back to the mechanism of rolling flaw generation in order to achieve such an object, the present inventors found that the flaws are mainly due to insufficient deformability of the inner surface layer of the material. It was found that this occurs in the stretch rolling in which an excessive shear strain is added. Therefore, from the machining side, it is effective to significantly improve the deformability of the surface layer of the material to reduce the additional shear strain and reduce the flaws.To this end, the friction between the tool and the material to be rolled is greatly reduced. The technology to reduce it is required. As a result of searching various methods for reducing the friction between the surface layer of the material and the tool, it was found that it is effective to apply water glass to the entire inner surface of the material in advance. It was also found that when an aluminum coating is applied to the entire inner surface of the material in advance, the surface layer of the material has a ferrite single phase structure with excellent hot workability. That is, the gist of the present invention is to provide a method for producing a high Cr steel seamless tube, which is manufactured by the Mannesmann rolling method using a hollow shell having water glass coated on the inner surface or an aluminum coating on the inner surface. Is.

The present invention will be described in detail below. It is necessary to use a hollow shell as the material. The reason for this is that water glass or an aluminum coating must be applied to the inner surface of the raw tube before heating the raw tube.

The reason why water glass is applied before heating the material is to form a liquid glass film having excellent lubricating performance on the entire inner surface of the raw tube during heating. The glass film during rolling always exists at the interface between the tool and the material to be rolled, and because it has an extremely high lubrication effect, friction is significantly reduced, and shear strain added to the inner surface of the material to be rolled is also significantly reduced. As a result, rolling flaws are reduced. Further, the glass film in the heating stage has an effect of preventing the decarburization of the inner surface layer and blocking the precipitation of the δ phase which lowers the deformability because it blocks the heating atmosphere from the material surface.

The water glass applied to the inner surface of the blank is a commercially available sodium silicate solution (Na ₂ O: 18% equivalent, Si
O ₂ : containing 36% equivalent) may be appropriately diluted with water before use. The application method may be a simple method such as a spray method.

Before heating the material, aluminum (Al)
The reason for forming the coating is to obtain the following action of Al during heating. That is, when Al is diffused into the material during heating, the chemical composition of the surface layer of the material to be rolled changes, and the structure of the surface layer that undergoes the most severe shear strain becomes a ferrite single-phase structure with excellent hot workability. For this reason, the surface layer is well deformed following additional shear strain in perforation or stretch rolling, and as a result, defects such as cracks and scratches are not caused. Furthermore, since this effect extends not only to the piercing and stretching rolling stages but also to the downstream rolling processes such as plug mill rolling, it is possible to prevent the occurrence or growth of flaws in the downstream processes. Further, the application of the Al coating before heating also has the effect of preventing the decarburization of the inner surface layer and thus preventing the precipitation of the δ phase, which causes the deterioration of the deformability. Further, since the ferrite single-phase alloy layer formed on the inner surface layer also has a lubricating effect of reducing seizure with the tool, the additional shear strain is reduced and the tool is less likely to melt. As a combined effect of the above, defects are less likely to occur.

According to the present invention as described above, it is possible to manufacture a high Cr steel seamless pipe having a good pipe inner surface quality by the Mannesmann rolling method without causing rolling defects.
Next, the present invention will be further described based on examples.

[0011]

【Example】

(Example 1) Test rolling was performed by the Mannesmann rolling method. As shown in Table 1 for the components of the test material, three types of high Cr steels A to C were used. A is SUS410 equivalent steel, B is S
US420 equivalent steel, C is 9% C developed for boiler
r steel. These alloy steels produced in an air melting furnace were cast into hollow shells with a diameter of 256mm x t65mm x 5.5m by centrifugal casting, the inner surface of the shell was shot blasted, and water glass was applied to the inner surface ( The present invention: No. 2 in Table 2.
1 to 3) and those not applied (comparative example; No. 4 to 4 in Table 2)
6) was used as the test material. The water glass used was a commercially available sodium silicate solution (Na ₂ O: 18% equivalent, SiO ₂ : 36).
1 part by weight diluted with 1 part by weight of water was used. The application was by a spray method.

Table 2 shows the evaluation results obtained by visually observing the inner surface of the pipe after cutting the rolled material. As is clear from Table 2
No. According to the present invention of 1 to 3, good tube outer surface quality can be obtained. On the other hand, Comparative Example No. Nos. 4 to 6 had many defects and cracks.

[0013]

[Table 1]

[0014]

[Table 2]

(Example 2) Test rolling was performed by the Mannesmann rolling method. The components of the test material are as shown in Table 1,
Three types of high Cr steels A to C were used. The inner surface of the hollow shell tested in Example 1 was shot blasted, and the inner surface was sprayed with Al (the present invention; No. 1 to No. 1 in Table 3).
3) and those not applied (Comparative example; Nos. 4 to 6 in Table 3) were used as test materials. The test results are shown in Table 3 after being evaluated by visually observing the inner surface of the pipe after cutting the rolled material. As is clear from Table 3, No. According to the present invention of 1 to 3, good tube outer surface quality can be obtained. On the other hand, Comparative Example No. Nos. 4 to 6 had many defects and cracks.

[0016]

[Table 3]

[0017]

As described above, according to the present invention, the inner surface of the high Cr steel seamless steel pipe manufactured by the Mannesmann rolling method has no flaws on the inner surface thereof, and has an extremely good inner surface quality. A product that is extremely advantageous in terms of cost can be provided.

Claims (1)

[Claims] 1. A method for producing a high Cr steel seamless pipe, characterized by using a hollow shell having an inner surface coated with water glass or an aluminum coating on the inner surface, and manufactured by the Mannesmann rolling method. .