X80管线钢焊接粗晶区组织与韧性的研究

Coarse Grain Heat Affect Zone Microstructures and Toughness of X80 Pipeline Steel

X80钢经焊接热模拟后粗晶区组织明显粗化,韧性显著下降.低碳时在粗晶区中的贝氏体铁素体板条间形成的硬而脆的Fe3C是恶化粗晶区韧性的主要原因.超低碳时在粗晶区中形成的马氏体-奥氏体(M-A)组元的含量比低碳时少,M-A组元中残余奥氏体所占的比例大,由于马氏体中偏聚的碳含量低,因而其塑性好,同时因超低碳抑制了Fe3C碳化物的形成而改善了粗晶区的韧性.

X80 pipeline steels produced by thermo-mechanical control process (TMCP)have high strength and high toughness with ultra-fine microstructure. The microstructure becomes coarsening and the toughness becomes worsening at the coarse grain heat affect zone (CG HAZ) after welding simulation. The hard and brittle Fe3C carbide formed between the bainitic ferrite laths in low carbon condition is the main cause of the above phenomenon. The ultra-low carbon content in base metal can improve the CG HAZ toughness through restraining the formation of carbides. Compared with low carbon in base metal, ultra-low carbon content decreases the martensite-austenite constituent (M-A) content and increases the residual austenite (A) content, which improves the toughness of CG HAZ.