Sumitomo Metal Industries, Inc.

Nippon Steel Corporation

Mitsui Chemicals, Inc.

Nippon Steel Sumitomo Metal Corporation

Akio Yamamoto

Nobuaki Takahashi

Masahiko Hamada

Tomoaki Ikeda

Ken Takata

Hiromi Shigemoto

Kojiro Kan

Tetsuya Fukuba

Izuru Minato

Shigemichi Yamauchi

A high-strength steel sheet having improved HIC resistance and fracture resistance even when it is thick has a chemical composition comprising, in mass %, C: 0.02-0.07%, Si: 0.05-0.50%, Mn: 1.10-1.60%, P: at most 0.015%, S: at most 0.0030%, Nb: 0.005-0.030%, Ti: 0.005-0.020%, Al: 0.005-0.060%, Ca: 0.0005-0.0060%, N: 0.0015-0.0070%, at least one of Cu, Ni, Cr, and Mo in a total of greater than 0.1% to less than 1.5%, and a remainder of Fe and impurities and a steel structure composed of at least 10% by area of bainite and a remainder of ferrite and pearlite. The degree of segregation is less than 1.6 for Nb and less than 1.4 for Mn in the central portion of the thickness of the steel sheet.

High-strength steel sheet having improved resistance to fracture and to HIC

A bent pipe corresponding to at least API X100 grade and having a base metal with high strength and toughness and a weld metal with high toughness is provided. A steel plate prepared by cooling after hot rolling at a cooling rate at the central portion in the plate thickness direction of at most 5&#xb0; C. per second at 700-500&#xb0; C. is formed into a bend mother pipe, which is then heated to 900-1100&#xb0; C. and subjected to bending, then it is cooled to a temperature of at most 300&#xb0; C. at a cooling rate in the central portion of the thickness direction of at least 5&#xb0; C. per second at 700-500&#xb0; C., after which it is tempered at 300-500&#xb0; C.

Method of manufacturing a bent pipe

A high-strength hot bend pipe which has a balance between an excellent strength of at least X70 grade and toughness and which has excellent tensile properties and a weld metal with excellent low temperature toughness is manufactured. A UOE steel pipe having a base metal with a composition of C: 0.03-0.12%, Si: 0.05-0.50%, Mn: 1.4-2.2%, S: at most 0.01%, Al: at most 0.06%, N: at most 0.008%, and a remainder of Fe and impurities, with the carbon equivalent (Ceq) being at most 0.36% and the weld cracking parameter (Pcm) being at most 0.22%, and having a weld metal with a weld cracking parameter (Pcm) of at most 0.28%, a B content of at most 5 ppm, and an O content of at most 280 ppm is heated to a temperature range of 900-1100&#xb0; C. and subjected to bending, and then is immediately cooled to a temperature range of 300&#xb0; C. or lower at a cooling rate of at least 3&#xb0; C./sec, and then is tempered in a temperature range of 300-500&#xb0; C.

Hot bend pipe and a process for its manufacture

A welding method includes performing welding to form a weld metal consisting essentially of, in mass %,  and a remainder of Fe and unavoidable impurities. The amounts of impurities are P: at most 0.03%, S: at most 0.03%, N: at most 0.01%, Ca or Mg: at most 0.005%. The value of Pcm expressed by the following Equation (3) is in the range of 0.23-0.35%, and the time T until the weld metal is cooled to 100&#xb0; C. after welding satisfies the following Equation (1):(seconds)&#x2267;exp(7.0&#xd7;+4.66)&#x2003;&#x2003;Equation (1)/60&#x2003;&#x2003;Equation (2)(mass %)=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B&#x2003;&#x2003;Equation (3)

High strength steel weld having improved resistance to cold cracking and a welding method

The high yield ratio problem intrinsic in high-strength steel pipes is solved and a method of producing a steel pipe, while securing the pipe roundness is provided. A steel pipe produced from a steel plate by forming and welding is subjected to 0.3 to 1.2% of expansion and then to 0.1 to 1.0% of reduction. The steel pipe produced by this method has a structure in which martensite and/or bainite accounts for more than 80% as expressed in terms of area percentage, and has a yield strength of not lower than 551 MPa and a yield ratio of not higher than 93%. The pipe reduction is desirably carried out at a lower work ratio as compared with the pipe expansion.

Method of producing steel pipes, and welded pipes

4-methyl-1-pentene polymer composition

Disclosed is a ferritic stainless steel for forming into bellows having high resistance to stress corrosion cracking, comprising, in terms of wt %, not greater than 0.02% of C, from 0.1 to 1.5% of Si, not greater than 1.0% of Mn, from 11.0 to 22.0% of Cr, from 0.01 to 0.08% of Al, not greater than 0.015% of N, at least one of not greater than 0.6% of Ti and not greater than 1.0% of Nb, whenever necessary, and furthermore, at least one of not greater than 2% of Mn, not greater than 1.5% of Cu and not greater than 1.5% of Ni. This steel has the crystal grain size measured in a section in a direction orthogonal to a rolling direction is not greater than 8.5 in terms of the grain size number, and the crystal grain size measured in a section orthogonal to a section parallel to the rolling direction is not smaller than 5.0 on an average in terms of the grain size number.

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Kashima, Japan

Akio Yamamoto