直接淬火研制800MPa级低焊接裂纹敏感性高强钢厚板

800MPa grade heavy plates with low susceptibility to welding crack produced by direct quenching

采用低碳微合金成分体系和直接淬火工艺,研制了屈服强度超过800MPa,抗拉强度超过950MPa,-40℃冲击功超过90J且焊接裂纹敏感性指数Pcm小于0.2%的40mm低焊接裂纹敏感性厚板。厚板的微观组织为厚度小于1μm贝氏体铁素体板条和沿板条界面分布的M/A组元,贝氏体板条内部有亚板条。随着终冷温度的降低,贝氏体铁素体板条变细。不同终冷温度钢板的贝氏体板条内部均存在高密度位错。试验用钢的贝氏体形核长大过程可以用扩散机制较好的解释。

A kind of low carbon micro-alloyed heavy plates with thickness 40mm and low susceptibility to welding crack was produced by direct quenching process. Yield strength,tensile strength and charpy V-notch impact energy at - 40℃ of the heavy plates are higher than 800MPa, 905MPa and 90J, respectively. The microstrueture of the heavy plates consists of bainitic ferrite laths with thickness less than 1μm and M/A constituent distributed at bainitic ferrite lath boundaries. Bainitic ferrite laths composed by sub-plates become thinner with the finish cooling temperature decreasing. High density dislocations are observed in the bainitic ferrite laths of experimental steel plates produced at different finish cooling temperatures. The bainite nucleation and growth process in the experimental steel can be explained reasonably by diffusion mechanism.