Effect of Welding Process on Fatigue Property of FH420 Steel

The 80 mm-thick FH420 steel used in test was welded by carbon dioxide gas shielded welding （ heat input ： 7 kJ / cm ）， single （ heat input ： 24 kJ / cm ） and double submerged arc welding （ heat input ： 38 kJ / cm ） to form three kinds of welded joints. The microstructure morphology observation and hardness test of the base metal， heat affected zone and weld seam at 1 / 4 thickness were carried out， and the high cycle fatigue test under different stress levels was carried out. The results show that with the increase of heat input， the size of pearlite and ferrite in the fine-grained heat-affected zone increases， the content of granular bainite in the coarse-grained heat-affected zone decreases and the content of ferrite increases， the content of acicular ferrite in the weld zone decreases and the content of proeutectoid ferrite increases. The fatigue results and fracture analysis show that the fatigue properties of the three steels are not significantly correlated with the microstructure evolution caused by welding heat input. Since the failure position is mostly located in the base metal， the fatigue S-N curves of the three joints are close. The incomplete fusion defect of carbon dioxide gas shielded welding under lower stress may become the fatigue crack initiation point， resulting in a decrease in the fatigue performance of the joints.