Metallurgical behavior and interfacial characteristics of GT35/20 steel dissimilar joint welded with CoCrNi medium-entropy alloy filler wire

This study presents an innovative approach using a CoCrNi medium-entropy alloy (MEA) filler wire to join GT35 steel-bonded carbide to 20 steels via tungsten inert gas (TIG) welding. The method addresses interfacial bonding issues caused by the thermal expansion coefficient (CTE) mismatch and the poor wettability of TiC hard phases. Results indicate that backside argon shielding is essential to suppress TiC oxidation and eliminate root porosity. Under adequate protection, the weld metal formed a single face-centered cubic (FCC) solid solution. Microstructural characterization revealed a TiC particle-reinforced gradient transition layer, approximately 476 μm wide, at the GT35 interface. Mechanical property testing indicates that this gradient structure achieves a smooth microhardness transition from the GT35 substrate (∼1199.3 HV 0.3 ) to the weld center (∼205.4 HV 0.3 ). Impact test results demonstrate that the weld metal exhibits superior impact toughness compared to the 20 steel substrate. This study provides new material options and process strategies for high-performance connections between steel and cemented carbide.