Effect of Tempering Temperature on the Microstructural Evolution and Properties of 800 MPa Grade Low-Carbon Bainite-Deposited Metals

The effects of carbides at prior austenite grain boundaries (PAGBs) and reversed austenite (RA) in the interdendritic zone (IDZ) on the impact toughness were investigated systematically for an 800 MPa grade low-carbon bainite-deposited metal. The results showed that M 3 C, M 2 C, and RA were generated in the deposited metals during the tempering process. In particular, the number and size of M 3 C precipitates generated on PAGBs increased when the temperature reached 570 °C, and coarse M 3 C precipitates on PAGBs became sites of crack initiation during the fracture process, which resulted in severe loss of toughness. In addition, a large amount of film-like RA was observed between laths in the IDZ when the tempering temperature reached 610 °C due to enrichment of alloying elements (Ni and Mn) in the IDZ. Austenite coordinated deformation and impeded crack propagation during the fracture process, and the microstructure of deposited metals tempered at 610 °C had typical layered structure. Therefore, the toughness of the deposited metals was restored due to the decrease in intergranular fracture and increase in the resistance of the microstructure to crack propagation when the tempering temperature reached 610 °C.