A Comparative Study on Microstructure, Mechanical Properties and Corrosion Resistance of M390 and 304 with Different Welding Methods

Tungsten argon arc welding (TIG), cold metal transfer (CMT) welding and flash butt welding (FBW) are used to join M390 and 304. The mechanical properties of M390 and 304 welded joints with different welding methods were compared by tensile and microhardness experiments. The microstructure evolution and phase changes of TIG, CMT and FBW welded joints were compared and analyzed by scanning electron microscope (SEM) and x-ray diffraction. The grain size of weld metal (WM) and M390 heat-affected zone of three types of welded joints were measured by Image J software. Corrosion resistance of three types of weld joints was characterized by electrochemical corrosion tests, and the microstructure of post-corrosion test specimens was characterized by SEM and EDS. The results show that three types of welded joints without cracks and voids can be obtained between dissimilar metals M390 and 304. The microstructure of TIG weld metal is composed of martensite and the carbides M7C3 and M23C6 due to higher heat input during TIG welding processes. Because extensive C, Cr and Ni element diffusion occurs during FBW welding due to low heat input, the microstructure of the weld metal is composed of martensite and austenite matrix and carbides of M7C3 and M23C6. The filling of nickel-based alloys during CMT welding processes make the microstructure include austenite and (Al, Ni, Ti) carbide. The tensile strength and elongation of CMT welded joint can reach 501 MPa and 21.8%, the corrosion current density is 4 mA cm(-2), and the corrosion voltage is - 21 mV, which is the best mechanical properties among the three types of welded joints. The welded joints with the three welding methods are all fractured at WM position.