HIGH STRENGTH HOT ROLLED STEEL PLATE AND METHOD FOR PRODUCING THE SAME

• Main Authors: KONO OSAMU, TAKAHASHI ATSUSHI, KOBAYASHI YUKIKO, TAKAHASHI YUZO
• Format: Patent
• Language: English; Japanese
• Published: 07.12.2015
• Subjects: ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; TREATMENT OF ALLOYS OR NON-FERROUS METALS

PROBLEM TO BE SOLVED: To provide a high strength steel plate excellent in low temperature toughness and mainly used for an automobile undercarriage member or the like.SOLUTION: Provided is a high strength hot rolled steel sheet having a composition comprising, by mass, 0.030 to 0.100% C, 0.001 to 1.5% Si, 0.5 to 3.0% Mn and 0.03 to 0.20% Ti, in which P is limited to 0.1% or lower, S is limited to 0.005% or lower, Al is limited to 1% or lower and N is limited to 0.010%, and the balance Fe with inevitable impurities, in which the average crystal grain size thereof is 8 μm or lower, the segregation amount of C to large angle crystal boundaries with an orientation angle of 15° or higher is 4 to 15 atoms/mm, the number of TiC precipitates with a sphere equivalent diameter of 3 nm or higher on the large angle crystal boundaries is below 0.01 piece/nm, and the ratio of the crystal grains in which the piece density of TiC precipitates with a sphere equivalent diameter in the crystal grains of 0.8 to 2 nm is 8×10pieces/cmis 10 to 70%. 【課題】主に自動車用足回り部材等に使用される、低温靭性に優れた高張力鋼板を提供する。【解決手段】質量％で、Ｃ：０．０３０〜０．１００％、Ｓｉ：０．００１〜１．５％、Ｍｎ： ０．５〜３．０％、Ｔｉ：０．０３〜０．２０％を含有し、Ｐ：０．１％以下、Ｓ：０．００５％以下、Ａｌ：１％以下、Ｎ：０．０１０％以下に制限し、残部がＦｅおよび不可避的不純物からなる鋼板であって、その平均結晶粒径が８μｍ以下であり、方位差が１５?以上の大角結晶粒界へのＣの偏析量が４〜１５ａｔｏｍｓ／ｎｍ2であり、上記大角結晶粒界上の球相当径３ｎｍ以上のＴｉＣ析出物の個数が０．０１個／ｎｍ2未満であり、結晶粒内の球相当径０．８ｎｍ以上２ｎｍ以下のＴｉＣ析出物の個数密度が８?１０16個／ｃｍ3以上である結晶粒の比率が１０〜７０％であることを特徴とする靭性に優れた高強度熱延鋼板。【選択図】 なし