Invention Grant
- Patent Title: High-tensile steel plate giving welding heat-affected zone with excellent low-temperature toughness, and process for producing same
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Application No.: US14349209Application Date: 2012-10-01
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Publication No.: US09945015B2Publication Date: 2018-04-17
- Inventor: Masao Yuga , Shigeki Kitsuya , Kenji Hayashi , Minoru Suwa
- Applicant: JFE Steel Corporation
- Applicant Address: JP Tokyo
- Assignee: JFE Steel Corporation
- Current Assignee: JFE Steel Corporation
- Current Assignee Address: JP Tokyo
- Agency: RatnerPrestia
- Priority: JP2011-219307 20111003
- International Application: PCT/JP2012/006269 WO 20121001
- International Announcement: WO2013/051231 WO 20130411
- Main IPC: C22C38/00
- IPC: C22C38/00 ; C22C38/42 ; C21D8/02 ; C22C38/58 ; C22C38/02 ; C22C38/04 ; C22C38/06 ; C22C38/44 ; C22C38/46 ; C22C38/50 ; C22C38/54 ; C21D9/50

Abstract:
A high-tensile steel plate has a chemical composition containing, by mass, specific amounts of C, Mn, Si, P, S, Al, Ni, B, N, one or more elements selected from Cr, Mo, V, Cu, Ti, and Ca as needed, Ceq≤0.80, and a center-segregation zone hardness index HCS satisfying 5.5[C]4/3+15[P]+0.90[Mn]+0.12[Ni]+0.53[Mo]≤2.5. The hardness of a center-segregation zone satisfies HVmax/HVave≤1.35+0.006/C−t/750. A steel having the above-described chemical composition is subjected to hot rolling at a specific slab-heating temperature at a specific rolling reduction ratio, subsequently reheated, cooled at a cooling rate of 0.3° C./s or more until the temperature of a central portion in a plate-thickness direction reaches 350° C. or less, and tempered to a specific temperature range.
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