Nisshin Steel Co., Ltd.

Seiichi Isozaki

Naoto Hiramatsu

Kouki Tomimura

Hiroshi Fujimoto

Satoshi Suzuki

Yasutoshi Hideshima

A stainless steel material having compositions which contain on the basis of percent by mass, C from 0.04 to 0.12%, Ni from 0 (including a case of no addition) to 5.0%, Cr from 12.0 to 17.0%, N from 0.0 to 0.10%, Si from 0.2 to 2.0%, Mn at 2.0% or less, Cu from 0.0 to 2.0%, P at 0.06% or less, S at 0.006% or less, with residue being Fe and unavoidable impurities. Further, a parent phase has any one of a single phase structure of ferrite phase or martensite phase and a diploid phase structure of ferrite phase and martensite phase. An end of the base material is melt-welded as a joint to form a pipe. The parent phase is provided with carbide uniformly separated at grain boundaries and within grains, with a dissolved amount of C being 0.03% by mass or less.

High-strength stainless steel pipe

A high-strength, high-toughness martensitic stainless steel sheet has a chemical composition comprising, in mass percent, more than 0.03 to 0.15% of C, 0.2-2.0% of Si, not more than 1.0% of Mn, not more than 0.06% of P, not more than 0.006% of S, 2.0-5.0% of Ni, 14.0-17.0% of Cr, more than 0.03 to 0.10% of N, 0.0010-0.0070% of B, and the balance of Fe and unavoidable impurities and has an A value of not less than &minus;1.8, where A value&equals;30(C&plus;N)&minus;1.5Si&plus;0.5Mn&plus;Ni&minus;1.3Cr&plus;11.8. The suitability of the steel sheet as a gasket material is enhanced by producing it to include not less than 85 vol % of martensite phase and to have a spring bending elastic limit Kb after application of tensile strain of 0.1% of not less than 700 N/mm . Edge cracking during cold rolling is inhibited by conducting cold rolling after subjecting the hot-rolled sheet to 600-800&deg; C.&times;10 hr or less intermediate annealing to impart a steel hardness of not greater than Hv 380.

Method of inhibiting cold-rolled steel sheet edge cracking, and method of producing the steel sheet

A high-strength, high-toughness martensitic stainless steel sheet has a chemical composition comprising, in mass percent, more than 0.03 to 0.15% of C, 0.2-2.0% of Si, not more than 1.0% of Mn, not more than 0.06% of P, not more than 0.006% of S, 2.0-5.0% of Ni, 14.0-17.0% of Cr, more than 0.03 to 0.10% of N, 0.0010-0.0070% of B, and the balance of Fe and unavoidable impurities and has an A value of not less than &minus;1.8, where A value&equals;30(C&plus;N)&minus;1.5Si&plus;0.5Mn&plus;Ni&minus;1.3Cr&plus;11.8. The suitability of the steel sheet as a gasket material is enhanced by producing it to include not less than 85 vol % of martensite phase and to have a spring bending elastic limit Kb after application of tensile strain of 0.1% of not less than 700 N/mm . Edge cracking during cold rolling is inhibited by conducting cold rolling after subjecting the hot-rolled sheet to 600-800 &deg; C.&times;10 hr or less intermediate annealing to impart a steel hardness of not greater than Hv 380.

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Yamaguchi, Japan

Seiichi Isozaki