超低碳超高强X120管线钢焊接热影响区粗晶区的组织转变

Microstructure transformation of coarse-grained region in heat-affected zone during welding of ultra-low carbon ultra-high strength pipeline steel

采用热模拟试验方法分析了超低碳超高强X120管线钢焊接热影响区粗晶区的组织转变.粗晶区连续转变曲线(SH-CCT)表明,在较宽的冷却速度范围内(0.8～25℃/s),X120管线钢粗晶区组织为贝氏体;当冷却速度小于0.8℃/s和大于25℃/s时,分别有少量准多边形铁素体和少量马氏体形成.热模拟焊接热输入在12～25 kJ/cm的范围时,粗晶区组织为贝氏体;硬度(276～297 HV 0.2)与室温冲击吸收功(208～225 J)稳定.结果表明,X120管线钢可适用较大范围热输入的焊接,这主要与超低碳设计有关.

The microstructure transformation of coarse-grained region in heat-affected zone(CG-HAZ) during welding of an ultra-high strength X120 pipeline steel was investigated with thermal simulation.Simulated HAZ continuous cooling transformation(SH-CCT) curves showed that the bainitic microstructure was obtained in CG-HAZ in a wide cooling rate range(0.8-25 ℃/s).Besides bainite,a small proportion of quasi polygongal ferrite formed in CG-HAZ when the cooling rate was lower than 0.8℃/s whereas a small proportion of martensite formed when the cooling rate was higher than 25 ℃/s.Bainite was obtained in the CG-HAZ when the welding heat input was in the range of 12-25 kJ/cm.The Vickers hardness of CG-HAZ(276-297 HV0.2) and the impact toughness at room temperature(208-225 J) was stable.Simulated results indicated that the X120 pipeline steel was suitable for welding with wide heat inputs,which was attributed to the ultra-low carbon design.