Q690钢激光-MIG复合焊焊缝耐腐蚀性能研究

Research on Corrosion Resistance of Hybrid Laser-MIG Weld Metal of Q690 Steel

采用焊接效率较高的激光电弧复合焊对Q690钢中厚板(16 mm)进行焊接试验,分析不同激光功率下焊接接头的显微组织和晶粒尺寸的变化,及其开路电位、交流阻抗谱、极化曲线和腐蚀形貌,探讨激光功率对焊缝电化学腐蚀行为的影响规律。结果表明,激光-MIG复合焊焊缝的显微组织由大量针状铁素体和少量侧板条铁素体、粒状贝氏体组成,其中电弧区的针状铁素体、侧板条铁素体含量多于激光区,电弧区的晶粒尺寸比激光区略大;粗晶热影响区显微组织主要由板条马氏体组成。随着激光功率的增加,焊缝中粒状贝氏体含量减少,针状铁素体和侧板条铁素体含量增加。当激光功率从1.5 kW增至2.5 kW时,焊缝的开路电位上升,容抗弧半径增加,极化电阻变大,极化曲线有右移倾向,自腐蚀电流密度下降,耐腐蚀性能提高。但当激光功率增至3.0 kW时,由于组织过于粗大,耐腐蚀性能反而下降。激光功率为2.5 kW时,复合焊焊缝的耐腐蚀性能最佳。

The hybrid laser arc welding with high efficiency were conducted on Q690 medium thick plate.The microstructure transformation and grain size change of the welded joint under different laser powers were analyzed.The open circuit potential,polarization curve,and EIS of the weld metal under different laser powers were tested,and the effect of laser power on the electrochemical corrosion behavior of the hybrid weld metal was obtained.The results showed that the microstructure of the laser-MIG hybrid welding metal was composed of a large amount of acicular ferrite and a small amount of side plate ferrite and granular bainite.The amount of acicular ferrite and side plate ferrite in the arc zone was greater than those in the laser zone,and the grain size in the arc zone was slightly larger than that in the laser zone.The microstructure of the coarse grain heat affected zone was composed of lath martensite.With the increasing of laser power,the content of granular bainite decreased,and the content of acicular ferrite and side plate ferrite increased in the weld metal.When the laser power increased from 1.5 kW to 2.5 kW,the open circuit potential of the weld metal,the diameters of capacitive loops in Nyquist plot and the polarization resistance all increased,the polarization curve tended to shift right,the self-corrosion current density decreased,and the corrosion resistance improved.The weld metal under 2.5 kW laser power showed the best corrosion resistance.