THICK STEEL SHEET HAVING HIGH STRENGTH AND METHOD FOR PRODUCING SAME

• Main Authors: OKA, MASAHARU, KUMAGAI, TATSUYA, USAMI, AKIRA
• Format: Patent
• Language: English; French; German
• Published: 27.06.2012
• Subjects: ALLOYS; CHEMISTRY; CRANES; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; HAULING; HOISTING; LIFTING; LOAD-ENGAGING ELEMENTS OR DEVICES FOR CRANES, CAPSTANS,WINCHES, OR TACKLES; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; PERFORMING OPERATIONS; TRANSPORTING; TREATMENT OF ALLOYS OR NON-FERROUS METALS

A high-strength steel plate includes the following composition: 0.18 to 0.23 mass% of C; 0.1 to 0.5 mass% of Si; 1.0 to 2.0 mass% of Mn; 0.020 mass% or less of P; 0.010 mass% or less of S; greater than 0.5 mass% and equal to or less than 3.0 mass% of Cu, 0.25 to 2.0 mass% ofNi; 0.003 to 0.10 mass% ofNb; 0.05 to 0.15 mass% of A1; 0.0003 to 0.0030 mass% of B; 0.006 mass% or less of N; and a balance composed of Fe and inevitable impurities. A weld crack sensitivity index Pcm of the high-strength steel plate is calculated by Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5[B], and is 0.39 mass% or less. The A c3 transformation point is equal to or less than 850°C, the percentage value of a martensite structure is equal to or greater than 90%, the yield strength is equal to or greater than 1300 MPa, and the tensile strength is equal to or greater than 1400 MPa and equal to or less than 1650 MPa. If the tensile strength is less than 1550 MPa, the prior austenite grain size number N³ satisfies the formula N³‰¥([TS]-1400)×0.006+7.0, and if the tensile strength is equal to or greater than 1550 MPa, the prior austenite grain size number N³ satisfies the formula N³‰¥([TS]-1550)×0.01+7.9.