【摘要】 采用热膨胀仪、光学显微镜、扫描电镜和透射电镜等研究了不同Nb含量对X80管线钢环焊接头热影响区中不同位置的显微组织、大角度晶界分布及韧性的影响。结果表明：高Nb钢(0.055%Nb)中较多固溶的Nb降低了γ→α的转变温度，促进了粒状贝氏体形成。0.055%Nb钢中的临界粗晶热影响区(ICCGHAZ)及亚临界粗晶热影响区(SCGHAZ)韧性显著恶化。ICCGHAZ韧性降低的原因是原奥氏体晶界上形成尺寸较大的链状M/A组元所致，而SCGHAZ则是由于有效晶粒尺寸变大、显微组织中大角度晶界数量降低，以及贝氏体板条束边界上尺寸较大的M/A组元所致。较高的合金含量引起的亚稳奥氏体中碳含量升高是导致0.055%Nb试验钢韧性降低的主要原因。更多还原

【Abstract】 Effect of Nb content on microstructure, large angle grain boundary distribution and toughness of X80 pipeline steel girth welded joint in different locations of the heat-affected zone was studied by means of thermal dilatometer, optical microscope, scanning electron microscopy and transmission electron microscopy. The results show that the more solid solution Nb in high Nb steel(0.055% Nb) reduces the transition temperature of γ→α and promotes the formation of granular bainite. The toughness of the critical coarse grain heat-affected zone(ICCGHAZ) and subcritical coarse grain heat-affected zone(SCGHAZ) in the 0.055% Nb steel significantly deteriorates. The decrease in toughness of the ICCGHAZ is due to the formation of chain shape M/A constituent with larger size on the prior austenite grain boundary, while the decrease of the toughness of SCGHAZ is due to the increase in effective grain size, the decrease in the number of large angle grain boundaries in the microstructure and the larger size M/A constituent on the bainite lath boundary. The increase of carbon content in metastable austenite caused by higher alloy content is the main reason for the decrease of toughness of the 0.055% Nb steel.更多还原