Kawasaki Steel Corporation

Jfe Steel Corporation

Masanori Nishimori

Takaaki Toyooka

Akira Yorifuji

Motoaki Itadani

Takatoshi Okabe

Yuji Hashimoto

Nobuki Tanaka

Yoshikazu Kawabata

Masatoshi Aratani

Osamu Furukimi

Saiji Matsuoka

Masahiko Morita

Takaaki Hira

Taro Kanayama

Koji Sugano

Toshio Ohnishi

Kingo Sawada

Masahiro Kagawa

Masao Shoji

Yoshnori Sugie

Yasue Koyama

A steel pipe is produced by a method including performing diameter-reducing rolling on a steel pipe in a temperature range of from 600&#xb0; C. to Acwith a reduction in diameter of not less than 30%, preferably after heating the steel pipe to temperatures of not lower than Acthe steel pipe being produced by seam-welding strip steel, or a method further including the step of performing heat treatment of holding the rolled steel pipe in a temperature range of from 600&#xb0; C. to 900&#xb0; C. for a time of 1 second or longer during cooling subsequent to the diameter-reducing rolling or by reheating the rolled steel pipe after the cooling.

High-workability steel pipe and method of producing same

A steel tube having a composition which contains: 0.05 to 0.30% of C; 1.8 to 4.0% of Mn; Si; and Al is subjected to a diameter-reducing rolling process in which the total diameter-reduction rate is no less than 20% and the temperature at which the diameter-reducing rolling process is finished is no higher than 800&#xb0; C., whereby a structure constituted of martensite and/or bainite or further of ferrite is obtained as a transformation product from the deformed &#x3b3;. As a result, a steel tube having tensile strength of 1000 MPa or more and excellent three-point-bending property can be obtained. The composition of the steel tube of the present invention may further include at least one type of element selected from the group consisting of Cu, Ni, Cr and Mo, or at least one type of element selected from the group consisting of Nb, V, Ti and B, or at least of one type selected from the group consisting of REM and Ca.

Steel pipe for use in reinforcement of automobile and method for production thereof

The invention provides a high-carbon steel pipe having superior cold workability and induction hardenability, and a method of producing the steel pipe. The method comprises the steps of heating or soaking a base steel pipe having a composition containing C: 0.3 to 0.8%, Si: not more than 2%, and Mn: not more than 3%, and then carrying out reducing rolling on the base steel pipe at least in the temperature range of (Ac , transformation point &minus;50&deg; C.) to Ac , transformation point with an accumulated reduction in diameter of not less than 30%. A structure in which the grain size of cementite is not greater than 1.0 &mgr;m is obtained, thus resulting in improved cold workability and induction hardenability.

High carbon steel pipe excellent in cold formability and high frequency hardenability and method for producing the same

A method and apparatus for smoothing a thick walled portion of a steel pipe produced by pressure-welding two opposite longitudinal edges of an open pipe with a squeeze roll after being subjected to induction heating. Outer and inner reduction rollers pressure sandwiches the thick walled portion from the outer and inner surfaces of the pipe, a support supports the inner reduction roller to be rotatable and containing a water passage for cooling water, a connecting rod connects the support device to a coupler and contains a further water passage for feeding cooling water to the water passage, and an anchor holds the connecting rod. In the method of producing steel pipes two opposite longitudinal edges of the open pipe are preformed before being subjected to the induction heating and thereafter a thick walled portion is smoothed by the above-described.

Method for smoothing steel pipe seam portion

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

A method and apparatus for smoothing a thick walled portion of a steel pipe produced by pressure-welding two opposite longitudinal edges of an open pipe with a squeeze roll after being subjected to induction heating. Outer and inner reduction rollers pressure sandwiches the thick walled portion from the outer and inner surfaces of the pipe, a support supports the inner reduction roller to be rotatable and containing a water passage for cooling water, a connecting rod connects the support device to a coupler and contains a further water passage for feeding cooling water to the water passage, and an anchor holds the connecting rod. In the a method of producing steel pipes two opposite longitudinal edges of the open pipe are preformed before being subjected to the induction heating and thereafter a thick walled portion is smoothed by the above-described apparatus.

Apparatus and method for smoothing a welded seam of steel pipe

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Handa, Japan

Masanori Nishimori