Effect of heat input on microstructural and mechanical properties of high strength low alloy steel block parts fabricated by wire arc additive manufacturing

High strength low alloy (HSLA) steel parts fabricated by wire arc additive manufacturing (WAAM) have great potential applications in many sectors. In this study, three 800 MPa class HSLA steel block parts were fabricated by WAAM with low, middle and high heat inputs (5.3 kJ/cm, 15.3 kJ/cm and 21.0 kJ/cm), and effect of heat input (HI) on microstructural and mechanical properties of these parts were investigated. The results show that the microstructure changes from lath martensite/bainite (M/B) to a mixture of M/B and granular bainite (GB) as the heat input increases from low to middle and the proportion of GB increases with the heat input was further increased. The microhardness of the low HI part is 327Hv and decreases significantly (14.1%) with increasing heat input. The yield strength of the parts shows a significant decrease (23.8%) with increasing heat input. The ultimate tensile strength and low-temperature (−50 °C) impact toughness of the parts decrease markedly with increasing heat input from low to middle, while negligible changes were observed with further improvements in heat input. The fracture elongation is 22.0% and 17.5% for the low to middle and high heat input parts, respectively. A dense and sound part with good comprehensive mechanical properties could be obtained with proper heat input.