JPH04111906A - Production of high-ni alloy seamless pipe having excellent quality of outside surface of pipe - Google Patents

Abstract

PURPOSE:To produce the high-Ni alloy seamless pipe having the good outside surface quantity of the pipe without generating rolling flaws by using a round billet or square bloom of the high-Ni alloy formed with an aluminum film on the surface and forming the pipe by a Mannesmann rolling method. CONSTITUTION:The melt of the high-Ni alloy smelted in an ordinary melting furnace, such as electric furnace or converter, is formed to the round billet or square bloom of a generally used shape by a continuous casting method or blooming method and thereafter, the surface thereof is coated with the aluminum film by an arbitrary method, such as plating method or thermal spraying method. The round billet or the like is thereafter heated to a high temp. and is made into the pipe product by the Mannesmann rolling method in which the billet or the like is made into a thick hollow blank pipe by a Mannesmann piercer and is finished by rolling pipe polishing machine and sizing mills, and further, by a reducing mill after reheating as necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a high Ni alloy seamless pipe that is free from rolling defects and has excellent pipe outer surface quality.

(Prior Art) In the energy development industry such as oil and gas, the environment of the oil and gas fields targeted for development has become increasingly harsh in recent years. That is, as wells become deeper, the content of highly corrosive gases such as H2S and CO2 increases.

High Ni alloys containing 20% or more of Ni have come to be used as seamless oil country tubular materials that can cope with such environmental changes, and the demand for them is increasing year by year.

High Ni alloy seamless pipes are usually manufactured by hot extrusion using the Eugene method, but since such alloys have high deformation resistance, the hot extrusion method has limitations on product size due to limitations in extrusion force, and furthermore, the rolling method Since the production efficiency is low compared to other methods, attempts are being made to manufacture by rolling method. However, when using the rolling method, there is a problem that rolling defects occur not only inside the tube but also on the outside surface of the tube.

There is a Mannesmann rolling method for producing rolling tubes of this type of alloy, and the following techniques have been proposed in the past. In other words, ■As seen in Japanese Patent Publication No. 2-7389, a technique of reducing the contents of S and P, which are harmful to hot workability, and adding Ca, REM, B, etc. ■ [Tetsu to Hagane J
As seen in '89-3354 (198[i)], there is a technique for preventing cracks by controlling the heating temperature, processing temperature and degree of processing of a rolled material within a specific range.

(Problems to be Solved by the Invention) However, (2) is a technique that is applicable only to plate rolling. In other words, cracks during hot working depend on the temperature of the abrasive to be pressed, as described in the technique (2), but in plate rolling, the rolled material cracks at the edge where the temperature drops the most (edge of the plate). Since the pipe is not large in proportion to the total product, this part can be made into a product with some care.

On the other hand, the part where the temperature decreases the most during pipe rolling is not only the end of the pipe but also the outer surface, and if cracks or flaws occur in this part, the pipe may not retain its shape and cannot be used as a product. Regarding (■), although the necessary technical conditions are presented to prevent cracks, this technology alone cannot eliminate rolling defects, which are smaller in scale than cracks but degrade product quality. do not have.

In other words, when producing high-Ni alloy tubes using the rolling method, the occurrence of rolling defects is unavoidable, and grinding is required to remove them, resulting in a decrease in yield and productivity that leads to high manufacturing costs, and is still expensive at present. Ni alloy seamless pipes are hardly manufactured by the rolling method, and the current situation is that they rely mostly on temperature control or hot pressing, which is easy and produces fewer defects. but,
As mentioned above, the hot pressing method has the disadvantages of lower productivity than the rolling method and large size restrictions for the product tube.

The present invention uses the Mannesmann rolling method to manufacture high-Ni alloy seamless pipes instead of the hot extrusion method, which has many restrictions. The purpose is to provide a manufacturing method.

(Means for Solving the Problems) As a result of conducting research and development tracing back to the mechanism by which rolling scratches occur, the present inventors found that rolling scratches occur starting from surface defects in the material, and the temperature of the rolled material decreases. We obtained the knowledge that it grows in the downstream mill (after the elongation mill). Therefore, in order to prevent this, it is important to properly control the rolling conditions in the downstream mill where the temperature of the material to be rolled decreases, but it is also important to prevent surface defects in the material to be rolled in the upstream mill (perforation or elongation mill). It turns out that minimizing it is more important. Furthermore, as a result of searching for various techniques to overcome this problem, the present invention has been made based on the following:
It has been found that it is effective to form an A1 layer on the material/surface in advance.

That is, the present invention was completed based on such knowledge, and its gist is to manufacture the product by the Mannesmann rolling method using a round billet or square bloom of a high Ni alloy with an aluminum coating formed on the surface. This is a method for manufacturing a high Ni alloy seamless pipe.

The present invention will be explained in detail below.

After forming high-Ni alloy melt produced in a regular melting furnace such as an electric furnace or a converter into a round billet or square bloom in a generally used shape by continuous casting or blooming, the surface An aluminum film is coated by any method such as plating or thermal spraying. After that, the round billets are heated to high temperature and made into thick-walled hollow tubes using a Mannesmann drilling machine.
It is made into pipe products through the Mannesmann rolling method, which involves rolling, polishing and shaping, and if necessary, reheating and finishing with a reducing mill.

In the pipe manufacturing process of the Mannesmann rolling method, the aluminum coating coated on the surface of the round billet or square bloom exhibits the following effects. In other words, (1) the aluminum in the coating during heating diffuses into the high N1 alloy material, changing the chemical composition of the surface layer of the rolled material;
As a result, the hot deformability of the surface layer is improved to the same level as that of 13% Cr steel, so the surface layer is deformed to better follow the added shear strain during drilling or elongation rolling, resulting in the prevention of microcracks and scratches. Does not cause defects. This effect is not limited to the perforation and elongation rolling stages, but also extends to downstream rolling processes such as plug mill rolling, so that it is possible to prevent the growth of scratches.

■Also, AN formed on the surface layer by diffusion of aluminum.
The 203-based scale effectively prevents metal-to-metal contact between the tool and the rolled material and prevents seizure, which dramatically reduces shoe marks and jump scratches.

(2) Furthermore, since the scale mainly composed of Ag2O formed on the surface layer has low heat conductivity, the reduction in hot deformability immediately below the surface layer due to temperature drop is suppressed, and as a result, the occurrence of defects such as microcracks and scratches can be suppressed.

The high Ni alloy seamless pipe produced by the method of the present invention as described above does not cause seizure damage to tools and has excellent pipe external surface quality without rolling defects.

(Example) Next, the present invention will be further explained based on examples.

Test rolling was performed using the Mannesmann rolling method.

The composition of the sample is as shown in Table 1.
J alloy was used. These alloys tapped at VIM are
It was formed into a bloom with a cross section of 15 x 215 mm, and its surface was subjected to AΩ thermal spraying to obtain a rolling material.

In this embodiment, the A and Q coatings were formed by thermal spraying, but they may also be formed by plating or other methods. A material that was not subjected to Aρ thermal spraying treatment was used as a comparative example. The test results were evaluated by visually observing the outer surface of the tube after pickling the rolled material, and the results are shown in Table 2.

Table 1 Chemical composition (wt %) of 6t, H Table 2 Test results As is clear from Table 2, according to the present invention of <No. 1.2, good tube outer surface quality can be obtained.

On the other hand, Comparative Example No. 3.4 had many scratches.

(Effects of the Invention) As described above, according to the present invention, a high N1 alloy seamless pipe with good quality on the outside surface of the pipe can be manufactured by the Mannesmann rolling method without causing rolling defects. Furthermore, the effects of the present invention extend to austenitic stainless steel, which has a lower Ni content and is easier to process. Further, according to the present invention, direct contact between the base metal and the tool can be prevented by the Aρ alloy layer and the scale mainly composed of AΩ203, so that seizing damage to the tool can also be prevented, which is of great industrial value.

Claims (1)

[Claims] A method for producing a seamless pipe of a high Ni alloy with excellent external surface quality, characterized in that the pipe is produced by the Mannesmann rolling method using a round billet or square bloom of a high Ni alloy on which an aluminum coating is formed on the surface.