METHOD OF MANUFACTURING THICK STEEL PRODUCT OF HIGH STRENGTH AND HIGH TOUGHNESS HAVING EXCELLENT WELDABILITY AND MINIMAL VARIATION OF STRUCTURE AND PHYSICAL PROPERTIES

摘要

A method of manufacturing a thick steel product of highstrength and high toughness having excellentweldability with minimal variation of materialproperties, comprises heating a steel raw material tothe temperature of Ac3 to 1350°C, hot rolling and thencooling at the cooling rate of 10 °C/sec. or less. Thesteel raw material has the following composition:C: 0.001 - 0.025 wt%;Mn: 1.0 - 3.0 wt%;Ti: 0.005 - -0.20 wt%;Nb: 0.005 - 0.20 wt%;B : 0.0003 - 0.0050 wt%; andAl: 0.01 - 0.100 wt%balance substantially Fe and incidental impurities.The composition has a transformation start temperature(Bs) of 670°C or less. Since the steel productobtained by the method has no variation in physicalproperties regardless of variation in cooling rate, itis possible to supply steel products of high strengthand high toughness which have uniform microstructureand properties along their thickness direction and areexcellent in weldability.