The method of manufacturing a thick steel article having a high strength and high toughness and excellent weldability and minimum variation of the structural and physical properties

摘要

A method of manufacturing a thick steel product of high strength and high toughness having excellent weldability with minimal variation of material properties, comprises heating a steel raw material to the temperature of Ac.sub.3 to 1350° C., hot rolling and then cooling at the cooling rate of 10° C./sec. or less. The steel raw material has the following composition:PPC: 0.001-0.25 wt %; PP Mn: 1.0-3.0 wt %;PPTi: 0.005-0.20 wt %; PPNb: 0.005-0.20 wt %;P PB: 0.0003- 0.0050 wt %; andPPAl: 0.01-0.100 wt %PP balance substantially Fe and incidental impurities. The composition has a transformation start temperature (Bs) of 670° C. or less. Since the steel product obtained by the method has no variation in physical properties regardless of variation in cooling rate, it is possible to supply steel products of high strength and high toughness which have uniform microstructure and properties along their thickness direction and are excellent in weldability.