焊接热循环及铌对原油储罐用钢粗晶热影响区组织和性能的影响

Effects of simulated thermal cycles and niobium on microstructure and toughness of coarse grain heat-affected zone in HSLA steels

采用热模拟试验研究了Nb对不同焊接热循环时粗晶热影响区组织、性能及转变动力学的影响。试验结果表明,在全部热输入下,不含Nb钢韧度均高于含Nb钢韧性,但大热输入(60～100kJ/cm)时韧性值相差较大,差值最小为60kJ/cm时相差153J,小热输入(40～30kJ/cm)时韧性值相差较小,差值最大为30kJ/cm时相差68J。从不同热输入时膨胀试验分析可知,含Nb钢转变开始温度Ar3比不含Nb钢低约15～30℃,大热输入时固溶Nb抑制铁素体转变,促进粒状贝氏体形成,严重恶化韧性,小热输入时含Nb钢低碳自回火马氏体数量较多,但韧度较好,与以细板条贝氏体组织为主的不含Nb钢相比韧性仅有小幅下降。

The influence of Nb on the coarse grain heat-affected zone(CGHAZ)microstructure,mechanical properties and the transformation kinetics of HSLA steels under different heat inputs,has been investigated.CCHAZ impact toughness of the steel without Nb at all heat inputs is higher than that of the steel containing Nb.When welding with higher heat inputs(60～100 kJ/cm),there exists greater difference of Charpy impact energies between the two steels,and the highest difference is 153 J at 60 kJ/cm.Minor difference is observed at lower heat inputs(40～30 kJ/cm),and the difference is 68 J at 30 kJ/cm.Dilatation studies indicate transformation start temperatures(Ts)of the steel containing Nb are approximately 15～30 ℃ lower than that without Nb at all heat inputs.Under higher heat inputs,Nb in solid solution suppresses ferrite transformation and promotes the formation of granular bainite which has detrimental effect on impact toughness.Under lower heat inputs,higher Charpy impact energy values in the steel containing Nb are relative to the formation of low carbon self-tempered martensite.