STEEL SHEET, MEMBER, METHOD FOR PRODUCING SAID STEEL SHEET, AND METHOD FOR PRODUCING SAID MEMBER

• Main Authors: ASAKAWA Taiyo, YOSHIOKA Shimpei, KANEKO Shinjiro
• Format: Patent
• Language: English; French; Japanese
• Published: 02.02.2023
• Subjects: ALLOYS; CHEMICAL SURFACE TREATMENT; CHEMISTRY; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DIFFUSION TREATMENT OF METALLIC MATERIAL; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; TREATMENT OF ALLOYS OR NON-FERROUS METALS

Provided are a steel sheet having high strength and excellent delayed fracture resistance, and a method for producing the same.　The steel sheet contains, in terms of mass%, 0.15-0.45% C, no more than 1.5% Si, more than 1.7% Mn, no more than 0.03% P, less than 0.0040% S, no more than 0.20% sol Al, no more than 0.005% N, 0.0015-0.0100% B, and a total of 0.005-0.080% Nb and/or Ti, the remainder comprising Fe and unavoidable impurities, the area ratio of martensite with respect to the structure overall being 95-100%, the prior γ grain diameter being less than 11.2 µm, and the number density A of precipitates having an equivalent circle diameter of 500 nm or greater satisfying the expression: A (number/mm2) ≤ 8.5×105 × [B]. L'invention fournit une tôle d'acier de solidité élevée et d'une excellente résistance à la rupture différée, et fournit également un procédé de fabrication de cette tôle d'acier.　Cette tôle d'acier comprend, en% en masse, ０,１５ à ０,４５％ de C, １,５％ ou moins de Si, plus de １,７％ de Mn, ０,０３％ ou moins de P, moins de ０,００４０％ de S, ０,２０％ ou moins de ｓｏｌ．Ａｌ, ０,００５％ ou moins de N, ０,００１５ à ０,０１００％ de B, et ０,００５ à ０,０８０％ au total de Nb et/ou Ti, le reste étant constitué de Fe et des impuretés inévitables. Le rapport surfacique d'une martensite pour l'ensemble de sa structure est compris entre ９５ et １００％. La taille de grains γ antérieur est inférieure à １１,2μｍ. La densité en nombre (A) de précipités de diamètre de cercle équivalent supérieur ou égal à ５００ｎｍ, satisfait la formule Ａ（nombre de précipités／ｍｍ２）≦　８,５×１０５×［Ｂ］. 高強度であり、優れた耐遅れ破壊特性を有する鋼板およびその製造方法の提供。　質量％で、Ｃ：０．１５～０．４５％、Ｓｉ：１．５％以下、Ｍｎ：１．７％超、Ｐ：０．０３％以下、Ｓ：０．００４０％未満、ｓｏｌ．Ａｌ：０．２０％以下、Ｎ：０．００５％以下、Ｂ：０．００１５～０．０１００％、ＮｂとＴｉのうち一種以上を合計で０．００５～０．０８０％を含有し、残部がＦｅおよび不可避的不純物からなり、マルテンサイトの組織全体に対する面積率が９５～１００％であり、旧γ粒径が１１．２μｍ未満であり、円相当径５００ｎｍ以上の析出物の数密度Ａが式：Ａ（個／ｍｍ２）≦　８．５×１０５×［Ｂ］を満たす。