Effect of Secondary Welding Thermal Cycles on Microstructure and Toughness of Over-heated Zone of Ultrahigh Strength Steel

In this paper,thermal simulation technique is adopted to investigate the microstructure and toughness of over-heated zone of 900MPa yield strength steel exposed secondary thermal cycle.The results show that the toughness of the steel after the thermal cycles decreased,specially at the temperature of 850℃.It may be caused by the small grains distributed continuously on the border of grain which led to disability of border.