JPS62230406A - Production of seamless metallic pipe - Google Patents

Abstract

PURPOSE:To produce a seamless metallic pipe having a good surface and tough structure by forming a difficult workable metal to a hollow stock by centrifugal casting and hot working the stock to a prescribed size. CONSTITUTION:The compsn. of the difficult workable metal 5a is an alloy, etc., contg. 35% Ni, 20% Cr, and 5% Mo. While a casting mold 10 is rotated by turning rollers 3, the difficult workable metal 5a is poured from a pouring spout 4 into the mold 10. The casting is ended to obtain the hollow stock pipe 5 in the state when the thickness of the hollow stock pipe 5 is formed. The hollow stock pipe 5 is then rolled to a prescribed pipe wall thickness at about 1,300 deg.C hot rolling temp. according to a Mannesmann pipe producing stage of a cross helical roll type. The seamless metallic pipe having the excellent surface characteristics and the tough structure is obtd. from the difficult workable material as well by the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing seamless metal pipes, and particularly to a method suitable for manufacturing seamless pipes from difficult-to-work steel materials.

(Prior art) For example, in seamless metal pipes used as oil country tubular goods, etc., as the oil well environment has become harsher in recent years, in order to cope with this, seamless pipes made of conventional austenitic stainless steel and duplex stainless steel have been replaced. In addition, Ni: 30-60%, Cr: 15-25%, which is even more difficult to process.
MO: Now oil country tubular goods are required to be made from corrosion-resistant materials such as high Ni alloys containing elements such as 3 to 18% MO, and Mannesmann drilling is required for steel and duplex stainless steel with 22 to 25% Cr. However, for ultra-high-speed workability Ni alloys that have high deformation resistance, poor hot workability, and are prone to cracking, round billets, which are the usual seamless pipe manufacturing method, are used as raw material. With the Mannesmann pipe manufacturing method, it was impossible to obtain good quality pipes due to defects that occurred on the inner and outer surfaces of the pipes. In other words, the processing conditions in the Mannesmann drilling method are extremely strict, and as shown in Figure 5, when drilling round billet a, the piercer plug b
The degree of processing at the tip and the degree of tube expansion on the outer surface a' of the tube are large, which causes cracks C to occur at the tip of the piercer plug, as well as flaws d on the outer surface of the tube.

For this reason, hot extrusion methods and the like have conventionally been applied as pipe manufacturing methods for difficult-to-work steel materials.

(Problems to be solved by the invention) However, in the hot extrusion pipe manufacturing method, long pipes (approximately 12
It was difficult to economically obtain tubes m).

Therefore, the purpose of the present invention is to develop ultra-fast processable materials that cannot be manufactured into Mannesmann tubes from round billets, specifically alloys in the range shown in Figure 1 (including Ni+Cr≧50% alloys). The object of the present invention is to provide a method for economically obtaining long seamless pipes having a good surface and a strong rolling diameter from these materials.

(Means for Solving the Problems) In order to solve the above problems and achieve the above objects, the present invention involves forming a difficult-to-work metal into a hollow material using a centrifugal casting method, and then heating it to a predetermined size. It is characterized by inter-rolling. That is, the present invention obtains a hollow material from a difficult-to-process material by a centrifugal casting method, and subjects the obtained hollow material to reduction rolling with a small degree of processing using, for example, a Mannesmann rolling mill, instead of perforation, thereby creating a good surface. The purpose is to manufacture seamless pipes with a strong rolling structure.

(Function) If the hollow material obtained by the centrifugal casting method is used as it is, there will be residual cavities and porosity, and the impact properties will be poor. Furthermore, it is difficult to obtain a thin-walled tube with a tube wall thickness of about 10 mm. For this reason, the hollow material obtained by casting is rolled using a Mannesmann rolling mill, preferably at a reduction ratio of 2.0 or more, to crimp the blowholes and porosity.
A tube having a rolled structure with good impact properties was obtained.

(Specific Examples of the Invention) The present invention will be described in more detail below with reference to the drawings.

FIG. 2 is an explanatory diagram showing a specific example for obtaining a hollow material. The mold 10 is composed of a cylindrical mold member (hollow cylinder) 1 and end mold members 2 that are fitted at both ends of the cylindrical mold member (hollow cylinder) and form the mold 10 together with the mold member 1. The mold 10 configured in this manner is placed on the turning roller 3.

The turning roller 3 supports the mold 10 and is rotated about its axis by a motor (not shown), thereby rotating the mold 10 in the circumferential direction.

While rotating this mold lO, one end mold member 2
Difficult-to-process molten metal 5 is poured from pouring gutter 4 through opening 2a of
Inject a into the mold 10. At the stage when the target thickness of the hollow material tube 5 is formed, the casting is finished and the hollow material tube 5 is obtained.

The hollow material tube 5 obtained in this manner contains cavities and porosity and has poor impact properties. Therefore, this hollow material tube 5 is hot-rolled by Mannesmann plug mill method, Eugene Sedzierne method, etc. to compress the blowholes and porosity and improve the impact properties.

In the Mannesmann plug mill method, as shown in FIGS. 3 and 4, an inclined roll Mannesmann rolling mill 20, a plug mill 30, etc. are used. 21.31 is a rolling roll, and 22.32 is a plug.

The reduction ratio is set to about 2.0 or more. The hot rolling temperature is 1
The temperature is about 200 to 1300°C.

(Example) Three types of alloys shown in Table 1 were centrifugally cast to a diameter of 280 mm
It was cast into a 75 mm t x 4 m j+ hollow cylinder.

A hollow cylindrical material was obtained by pouring molten steel while rotating in the circumferential direction at a circumferential speed of 11,000 rpm.

However, when any alloy is used as a cast) illumination, its toughness, that is, the absorbed energy in the 2 mV Notch Charpy impact test, is extremely poor even at +20°C, which is a problem for harsh applications such as oil country tubular goods. It was something.

The above-mentioned hollow cylindrical material was rolled at a hot rolling temperature of about 1290°C to several types of pipe wall thickness shown in Table 1 according to the inclined roll type Mannesmann pipe making process. The absorbed energy in the Charpy impact test was such that a sheet with a plate thickness rolling ratio of 2.0 or more had good toughness, and the structure was a rolled structure, and the porosity during casting was also compressed. Note that the pressure generation on the inner surface of the tube was also good without any problems up to the plate thickness rolling ratio of 5.0.

(Effect of the invention) As is clear from the above, according to the present invention,
A long seamless pipe with excellent surface properties and a tough rolling structure can be obtained economically from materials that can be processed at ultra-high speeds.

[Brief explanation of drawings]

Figure 1 shows the area of the alloy targeted by the present invention, Figure 2
The figure is an explanatory diagram showing a hollow material manufacturing method by centrifugal casting of difficult-to-process materials, Figures 3 and 4 are explanatory diagrams showing a Mannesmann rolling mill and a plug mill used for hot rolling, respectively, and Figure 5 is a round billet. FIG. 3 is an explanatory diagram showing the bottom of the inner and outer surfaces of the tube that is generated when Mannesmann drilling is performed from the tube. lO... Mold, l... Cylindrical mold member, 2... End mold member, 3... Turning roller, 4... Pouring gutter, 5... Hollow material, 5a... Difficult to process molten metal,
20...Mannesmann rolling mill, 30...Plug mill, 21°31...Rolling roll, '#! #, 32
"・Plug, a...Round billet, b...Piercer plug, C...Crack, d...Flaw. Figure 1 Cr-eq = Cr+Mo+1.5SL+0.5N
bFigure 2Figure 3

Claims (1)

[Claims] (1) A method for manufacturing a seamless metal pipe, which comprises forming a difficult-to-work metal into a hollow material by centrifugal casting, and then hot rolling it into a predetermined size.