Research on microstructure and properties for welded joint of the yield strength700 MPa grade HSLA

According to the design principles of equal strong matching,the high strength low alloy steel sheet which the yield strength is700MPa grade were welded by Gas metal arc welding. The microstructure and mechanical properties of welded joints were studied by observation of microstructure and mechanical properties measured. The test results show that the microstructure of the coarse grain zone in the heat affected zone was equiaxed ferrite and granular bainite. The microstructure of welded zone was based on acicular ferrite,a little of proeutectoid ferrite and bainite. The hardness of welded zone was equaled to base metal. The Impact energy was 38 J at- 40 ℃.The tensile strength of welded joint can reach the 97. 1% of the base metal,the crack position was located the coarse grain zone of heat affected zone. The fracture morphology of the crack source zone were dimple and Cleavage step. The welded joints had high strength and toughness by equal strong matching welding,it has excellent comprehensive mechanical properties.