Effect of welding parameters on microstructure and properties of welded joints of large-thickness 316L/Q370qE clad plates

The 316L/Q370qE stainless steel clad plates with a thickness of （3+32） mm are studied by using X-groove welding process. The effects of welding current on the microstructure and properties of the welded joints of clad plate are analyzed by means of optical microscopy， scanning electron microscopy， transmission electron microscopy， energy dispersive spectroscopy. The results show that the weld metal microstructure of the stainless steel cladding layer and transition layer is austenite and skeletal δ ferrite. The microstructure of carbon steel weld metal is proeutectoid ferrite， acicular ferrite， and ferrite side-plate. And a fine-grained bainite is formed in the area adjacent to the stainless steel transition layer. As the welding current increases， the content of δ ferrite in the weld metal of stainless steel decreases and its shape becomes more irregular. The microstructure in the local weld metal of the carbon steel coarsens. There is extensive mutual diffusion of elements in the interface between the weld metal of transition layer and carbon steel. At the same time， the microstructure in the heat-affected zone of the stainless steel and carbon steel coarsens. However， the change in the original layered interface of the clad plate is not obvious. The tensile fractures of the welded joints of clad plate with different currents all occur in the heat-affected zone. When the current is 230 A， the tensile properties are the best， and the tensile strength and elongation reach 557 MPa and 23.9%， respectively. The low-temperature impact absorption energy of both the carbon steel weld metal and fusion zone near the stainless steel cladding layer is about 20 J lower than that at the position keeping away from the stainless steel cladding layer. The impact energy difference in the heat-affected zone at the two positions is more significant. The change of welding current in the range of 210-280 A has little influence on the intergranular corrosion performance of stainless steel cladding layer. Therefore， when using 230 A and 30-31 V parameters to weld the stainless steel transition layer and cladding layer， the impact performance difference of the weld metal of carbon steel on both sides of the X-groove is the smallest， and the tensile properties of the welded joint of clad plate are the best.