Weldability of Low Carbon Bainite High-Strength Steel Q690CFD

CO2 gas shielded arc welding was utilized to weld low carbon bainite high-strength steel Q690CFD with flux-cored welding wire and solid core welding wire.The cold cracking susceptibility of the steel was evaluated through Y-groove crack susceptibility test and maximum hardness test in the heat affect zone.The toughness in the weld coarse grain zone with the steel cooling from 800℃ to 500℃ (t8/5) was investigated through impact test.The welding usability was evaluated by means of optical microscopy,tensile testing machine,hardness testing machine and impact testing machine.The results show that the steel plate had harden quenching tendency without preheated at 14℃.The toughness of the microstructure in the coarse grain zone decreased significantly after the t8/5 was longer than 40 s.The steel could avoid the cracking as the flux-cored weld wire preheating at 80℃ (25 mm) and 100℃ (30 mm) or solid core weld wire without preheating.The microstructure in the coarse grain zone was composed of lath matensite and few bainite,and the welded joint had good properties.There was no obvious effect of the stress relief heat treatment after welding at 500℃ for 2 h on tensile properties of the heat affect zone and the substrate.