고강도 강판 및 그의 제조 방법

• Main Authors: MATSUDA HIROSHI, ONO YOSHIHIKO, NAKAMURA NOBUYUKI, TANIGUCHI KOICHI, MURAI TAKESHI, YOSHIOKA SHIMPEI, HONDA YUMA
• Format: Patent
• Language: Korean
• Published: 05.04.2021
• Subjects: ALLOYS; CASTING; CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES; 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; PERFORMING OPERATIONS; POWDER METALLURGY; PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OFWROUGHT-IRON OR STEEL; TRANSPORTING; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS

본 발명의 과제는, 인장 강도가 980㎫ 이상에서 우수한 내지연 파괴 특성을 갖는 고강도 강판 및 그의 제조 방법을 제공하는 것이다. 본 발명의 고강도 강판은, 특정의 성분 조성을 갖고, 특정 영역에 있어서의 Mn 편석도가 1.5 이하이고, 특정 영역에 있어서의 P 최대 농도가 0.08질량％ 이하이고, 표면으로부터 판두께 방향으로 100㎛ 이내의 영역에 있어서의, 강판의 압연 방향에 평행한 판두께 단면에서, 특정의 MnS 입자군을 포함하고, 특정의 MnS 입자군이 1㎟당 2.0개 이하이고, 특정의 산화물계 개재물이 1㎟당 8개 이하이고, 상기 산화물계 개재물의 전체 개수 중, 특정의 조성을 갖는 것의 개수 비율이 80％ 이상이고, 강 조직이, 체적 분율로, 마르텐사이트: 30∼95％, 페라이트상: 5∼70％, 베이나이트: 30％ 미만(0％ 포함함), 오스테나이트상: 2.0％ 미만(0％ 포함함)을 갖고, 인장 강도가 980㎫ 이상이다. Objects of the present invention are to provide a high-strength steel sheet having a tensile strength of 980 MPa or greater and having excellent delayed fracture resistance and to provide a method for producing the same.A high-strength steel sheet of the present invention has a specific chemical composition. Furthermore, in the steel sheet, a degree of Mn segregation in a specific region is 1.5 or less; a maximum P concentration in a specific region is 0.08 mass% or less; in a region within 100 µm of a surface in a sheet thickness direction, at least one specific MnS particle group is present, the number of specific MnS particle groups is 2.0 or fewer per 1 mm2, and the number of specific oxide-based inclusions is 8 or fewer per 1 mm2, as viewed in a cross section in the sheet thickness direction and parallel to a rolling direction of the steel sheet; of all of the oxide-based inclusions, oxide-based inclusions having a specific composition are present in a number ratio of 80% or greater; the microstructure includes, in terms of a volume fraction, 30 to 95% martensite, 5 to 70% ferrite phase, less than 30% (and 0% or greater) bainite, and less than 2.0% (and 0% or greater) austenite phase; and a tensile strength is 980 MPa or greater.