Effect of interlayer temperature on microstructure evolution and mechanical performance of wire arc additive manufactured 300 M steel

Abstract The 300 M steel straight wall parts (SWPs) are fabricated by wire arc additive manufacturing based on cold metal transfer technology. The effects of interlayer temperature on microstructure evolution and mechanical performance in the different regions of the SWPs are investigated. The results show that the surface waviness of the SWP first decreases and then increases with the increase of interlayer temperature, and the lowest surface waviness is controlled in 0.47 mm at the interlayer temperature of 200 °C. In the top region, the microstructure mainly consists of untempered martensite and slightly changes with the increase of interlayer temperature. In the middle and bottom regions, the microstructure is mainly composed of tempered martensite as the interlayer temperature is 100 or 200 °C. However, when the interlayer temperature is increased above 400 °C, the needle-like bainite and feather-like bainite are gradually formed due to the slow cooling rate and long dwell time in the bainite transformation zone. The microhardness and ultimate tensile strength in the top region are significantly higher than those in the middle and bottom regions, which are attributed to the enhanced solid solution strengthening effect of untempered martensite. The tensile fracture morphology is transformed from the quasi-cleavage fracture mode to the ductile mode with the increase of interlayer temperature or the decrease of distance from the substrate.