Analysis Microstructure of Weld Metal for HQ130+QJ63 High Strength Steel

The microstructure in the weld metals for HQ130+QJ63 high strength steels, which are welded by Ar-CO2 gas shielded metal arc welding, was analyzed by means of microscope and scan electron microscope (SEM). The relative content of different microstructure was evaluated with XQF-2000 micro-image analyzer. The effect of acicular ferrite content on the impact toughness was also studied. The test results indicated that the main microstructure in the weld metals of HQ130+QJ63 high strength steels is acicular ferrite and a few pro-eutectic ferrite on the boundary of original austenite grain. Near the fusion zone there are columnar grains whose direction coefficient (X) is 3.22, but the microstructure in the center of the weld metal is isometric grain, whose direction coefficient X=1. In order to avoid welding crack and improve welding technology the weld heat input should be strictly controlled in 10-16 kJ/cm. Thus, the main microstructure in the weld metals is fine acicular ferrite and the content of pro-eutectic ferrite is limited. The impact toughness in the weld metals of HQ130+QJ63 steels can be ensured and can meet the requirements for application in engineering and machinery.