Kawasaki Steel Corporation

Pacific Steel Mfg. Co., Ltd.

Taro Kanayama

Akira Yorifuji

Takaaki Toyooka

Osamu Furukimi

Yuji Hashimoto

Takatoshi Okabe

Saiji Matsuoka

Masahiko Morita

Motoaki Itadani

Takaaki Hira

Nobuki Tanaka

Masanori Nishimori

Yuichiro Sato

Masaharu Kita

Ken Shimamoto

Shoitsu Seo

Toshiaki Kasuya

Satoshi Matsuoka

The steel pipe has a structure composed mainly of ferrite or ferrite plus pearlite or ferrite plus cementite. The steel pipe is characterized by grain size not greater than 3 &mgr;m, preferably not greater than 1 &mgr;m, elongation greater than 20%, tensile strength (TS:MPa) and elongation (E1:%) whose product is greater than 10000, and percent ductile fracture greater than 95%, preferably 100%, measured by Charpy impact test on an actual pipe at &minus;100&deg; C. The structure is characterized by C: 0.005-0.03%, Si: 0.01-3.0%, Mn: 0.01-2.0%, and Al: 0.001-0.10% on a weight basis, and is composed of ferrite or ferrite and a secondary phase, with ferrite grains being not greater than 3 &mgr;m and the secondary phase having an areal ratio not more than 30%. A steel pipe stock having the above-mentioned composition is heated at a temperature of (Ac,&plus;50&deg; C.) to 400&deg; C. and subsequently reduced at a rolling temperature of (Ac,&plus;50&deg; C.) to 400&deg; C. such that the cumulative reduction of diameter is greater than 20%. The reducing is preferably performed such that at least one of rolling passes reduces the diameter by more than 6% per pass. The steel pipe will have high ductility and high strength and will be superior in toughness and stress corrosion cracking resistance, if the content of C, Si, Mn, and other alloying elements is limited low and reducing is performed at the temperature specified above. The resulting steel pipe has good fatigue resistance and is suitable for use as line pipe.

Steel pipe having high ductility and high strength and process for production thereof

A steel pipe containing fine ferrite crystal grains, which has excellent toughness and ductility and good ductility-strength balance as well as superior collision impact resistance, and a method for producing the same are provided. A steel pipe containing super-fine crystal grains can be produced by heating a base steel pipe having ferrite grains with an average crystal diameter of di (&mgr;m), in which C, Si, Mn and Al are limited within proper ranges, and if necessary, Cu, Ni, Cr and Mo, or Nb, Ti, V, B, etc. are further added, at not higher than the Ac,transformation point, and applying reducing at an average rolling temperature of &thgr;m (&deg;C.) and a total reduction ration Tred (%) within s temperature range of from 400 to Ac,transformation point, with di, &thgr;m and Tred being in a relation satisfying a prescribed equation.

Ultrafine-grain steel pipe and process for manufacturing the same

This invention provide a plug and a mandrel bar for use in rolling a seamless steel pipe of which life can be substantially improved more than that of the prior art under a severe condition of use always exposed to a high temperature and high load. The entire plug or the mandrel bar or at least the surface layer of the extremity end and the work section of it is made of ceramics. In addition, this invention provides a method for manufacturing a seamless steel pipe using such a plug or mandrel bar as described above.

Plug and mandrel bar for seamless steel pipe rolling operation for manufacturing seamless steel pipe

A lubricant is provided for use in hot working such as cross-roll rolling of a seamless steel pipe. It effectively reduces the friction coefficient between the working tools and the material under the hot work, thus extending the lives of the tools. The lubricant contains: (A) from about 10 to about 60 wt % of alkali silicate; (B) from about 1 to about 20 wt % of silane coupling agent; (C) from about 0.1 to about 5.0 wt % of at least one kind of alkali compound selected from a group consisting of an alkali hydroxide, an alkali carbonate, an alkali borate and an alkali salt of mineral acid; and (D) from about 30 to about 70 wt % of water. Alternatively, the lubricant contains: (A) from about 10 to about 60 wt % of alkali silicate; (B) from about 1 to about 20 wt % of silane coupling agent; (C) from about 0.1 to about 5.0 wt % of at least one kind of alkali compound selected from a group consisting of an alkali hydroxide, an alkali carbonate, an alkali borate and an alkali salt of mineral acid; (D) from about 5 to about 50 wt % of water; (E) from about 10 to about 60 wt % of iron oxide; and (F) from about 0.1 to about 5.0 wt % of at least one additive selected from a group consisting of a dispersant and a thickening agent.

Lubricant for use in hot work

A forged roll for rolling a seamless steel pipe, having excellent biting properties and wear resistance, and manufacturing method. The forged roll comprises a high carbon alloy cast steel comprising about 1.10-1.85 wt % carbon, about 0.3-1.2 wt % silicon, about 0.4-1.5 wt % manganese, about 0.5-2.0 wt % nickel, about 0.5-2.0 wt % chromium and iron. Heat treatment for spheroidal carbide formation is performed so that the spheroidal carbide covers about 35-55% of the area of the roll metallurgical structure.

Forged roll for rolling a seamless steel pipe and manufacturing method

A forged roll for rolling a seamless steel pipe, having excellent biting properties and wear resistance. The forged roll includes a high carbon alloy cast steel comprising about 1.10-1.85 wt % carbon, about 0.3-1.2 wt % silicon, about 0.4-1.5 wt % manganese, about 0.5-2.0 wt % nickel, about 0.5-2.0 wt % chromium and iron. Heat treatment for spheroidal carbide formation is performed so that the spheroidal carbide covers about 35-55% of the area of the roll metallurgical structure.

Forged roll for rolling a seamless steel pipe

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Aichi, Japan

Taro Kanayama