HIGH BURRING PROPERTY HOT ROLLED STEEL SHEET HAVING EXCELLENT LOW CYCLE FATIGUE STRENGTH AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide a high burring property hot rolled steel sheet having excellent low cycle fatigue strength and to provide a production method by which the steel sheet can inexpensively and stably be produced.;SOLUTION: This high burring property hot rolled steel sheet having excellent low cycle fatigue strength is composed of steel having a composition containing 0.01 to 0.2% C, 0.01 to 2% Si, 0.05 to 3% Mn, ≤0.1% P and ≤0.01% S, containing Al and N by ≤0.2% Al and 0.001 to 0.1% N also so as to satisfy 0.52Al/N≤10, further containing one or more kinds selected from Cr, Mo and V by ≤2.5% Cr, ≤1% Mo and ≤0.1% V also so as to satisfy (Cr+3.5Mo+39V)≥0.1, and the balance Fe with inevitable impurities, whose microstructure with the maximum volume ratio is composed of bainite or of the composite one of ferrite and bainite, and the area ratio of a cell structure in the dislocated structure observed after a fatigue test is ≤50%. In the method for producing the above steel sheet, the steel having the above components is subjected to hot finish rolling so as to be finished at the Ar3 transformation point or higher, is thereafter cooled at a cooling rate of ≥20°C/s and is coiled at a coiling temperature in the temperature range of 450 to 650°C.;COPYRIGHT: (C)2002,JPO