铌对船板钢大热输入焊接热影响区组织与韧性的影响

Effect of Nb on Microstructure and Toughness of Heat Affected Zone of Shipbuilding Steel under High Heat Input Welding

采用控轧控冷工艺(TMCP)生产含铌(质量分数0.025%)和无铌两种DH36级船板钢,并进行150 kJ·cm^(-1)大热输入气电立焊,研究了焊接接头热影响区的组织与韧性。结果表明:铌元素的添加可推迟铁素体和珠光体相变,促进粒状贝氏体和贝氏体铁素体生成,导致含铌钢热影响区粗晶区中的晶界铁素体含量较少,粒状贝氏体和贝氏体铁素体含量较多,细晶区中的铁素体和珠光体析出缓慢。无铌钢焊接接头各区域的组织与韧性良好,-20℃冲击功单值均在102 J以上,远高于船级社规范要求;含铌钢焊接接头熔合线处-20℃冲击功出现单值低于24 J的情况,不满足船级社规范要求,其他区域-20℃冲击功单值均在143 J以上。铌的添加对DH36级船板钢大热输入焊接接头的韧性不利。

Two DH36 shipbuilding steels,containing 0.025 wt%Nb and Nb-free,were produced by a controlled rolling and controlled cooling(TMCP)process,and then welded by 150 kJ·cm^(-1) high heat input gas electric vertical welding.The microstructure and toughness of heat-affected zones of welded joints were studied.The results show that the addition of Nb could delay the transformation of ferrite and pearlite,and promote the formation of granular bainite and bainite ferrite,leading to less grain boundary ferrite and more granular bainite and bainite ferrite in the coarse-grained zone,and the slow precipitation of ferrite and pearlite in the fine-grained zone of the heat-affected zone of the Nb-bearing steel.The microstructure and toughness in different locations of the welded joints of Nb-free steel were good,and every single value of impact energy at-20℃was above 102 J,which was far higher than the requirements of classification society.The Nb-bearing steel welded joint had single values of impact energy at-20℃lower than 24 J,which did not meet the requirements of classification society,but every single value of impact energy at-20℃in other locations was above 143 J.The addition of Nb was detrimental to the toughness of the welded joints of DH36 shipbuilding steel with high heat inputs.