440MPa级含铌船体钢焊接粗晶区组织与性能

Microstructures and mechanical properties of CGHAZ in 440 MPa ship hull steel

关键词:  焊接粗晶区  晶粒尺寸  粒状贝氏体  第二相粒子

Key words:  coarse grain heat affected zone  grain size  granular bainite  the second phase particles

摘要:

焊接热模拟试验表明,t_8/5≤40s时,低碳高铌钢焊接粗晶区奥氏体晶粒尺寸低于高碳低铌钢,低温冲击韧性高于高碳低铌钢。焊接粗晶区的组织主要以粒状贝氏体为主,当t_8/5≤40s时,粒状贝氏体主要以长条状存在;当t_8/5 >40s时,粒状贝氏体则主要呈现块状,低碳高铌钢中粒状贝氏体的数量和尺寸远低于高碳低铌钢。Thermo-Calc计算析出平衡曲线表明,高碳低铌钢中第二相粒子的析出主要在1200℃以上,平均尺寸大于120nm。低碳高铌钢中第二相粒子的析出粒子主要分布在1200℃以下,平均尺寸小于50nm。低碳高铌钢中细小的第二相析出物有效阻碍了奥氏体晶粒长大,显著改善了焊接粗晶区的低温韧性。

Abstract:

The results showed that the austenite grain size in low carbon high niobium (LCHN)alloy steel was smaller than that in high carbon low niobium steel (HCLN) by adopting welding heat physical simulation, and the low temperature impact toughness of LCHN steel was higher than that in the HCLN steel when t_8/5 ≤ 40 s.The microstructure of coarse grain heat affected zone (CGHAZ) in experimental steels were predominantly granular bainite, the shape of M-A island exhibited long lath morphology when t_8/5 ≤ 40 s and it shows massive morphology when t_8/5 >40 s.The size and the amount of granular bainite in LCHN steel were much lower than that in HCLN steel.The precipitation equilibrium diagrams of two experimental steels were calculated by using Thermo-Calc software.The second phase particles mainly precipitated in the temperature higher than 1 200℃ and the mean size of particles larger than 120 nm in HCLN steel, but the second phase particles only precipitated in the temperature lower than 1 200℃ and the mean size of particles lower than 50 nm in LCHN.The fine second phase precipitation dispersed in LCHN steel inhibited the growth of prior austenite grain boundary and improved the low temperature impact toughness significantly.