Effect of Heat Treatment on Microstructures and Properties of Wire and Arc Additive-Manufactured Bainite Steel

It is difficult to actively control the thermal cycle in wire and arc additive manufacturing（WAAM）, resulting in uneven microstructures and poor mechanical properties. Therefore, an anisothermal quenching and tempering process for bainite steel deposition is presented herein. The microstructures and properties were analysed and optimised after a series of heat treatments. The results show that the annealed microstructures change from tempered sorbite to lower bainite and tempered martensite after posttreatment, and the anisotropy is evidently weakened. After isothermal quenching at 290 ℃/oil cooling followed by tempering at 280 ℃/air cooling, the WAAM bainite steel shows more homogeneous microstructures and better mechanical properties, with increases in the tensile strength, yield strength, elongation, impact toughness, and hardness, by 39%, 61%, 29%, 17%, and 20%, respectively.