PRODUCTION OF HOT ROLLED HIGH STRENGTH STEEL PLATE EXCELLENT IN FATIGUE STRENGTH AND FATIGUE CRACK PROPAGATION RESISTANCE

摘要

PURPOSE:To obtain a hot rolled high strength steel plate excellent in fatigue crack propagation resistance as well as in fatigue strength by using a steel containing specific weight percentages of components and performing heat treatment under specific conditions. CONSTITUTION:A steel having a composition consisting of 0.03-0.15% C, 0.10-1.5% Si, 0.10-2.0% Mn, 0.01-0.10% Al, 0.03-0.15% P, and the balance Fe with inevitable impurities is finish-rolled at 780-900 deg.C. Subsequently, the resulting plate is cooled down to 680-720 deg.C at a rate of =40 deg.C/sec, air-cooled for 2-8sec, cooled at a rate of =40 deg.C/sec, and coiled at =500 deg.C. By this method, the final structure where ferrite grain size and the volume fraction of secondary phase (martensite and/or bainite and/or retained austenite) are controlled to 5-25mum and 10-30%, respectively, can be obtained.