Comparative Study of Wire Arc Additive Manufactured and Wrought Ultrahigh-Strength Steels: Flow Behavior and Microstructure Evolution

The combination of wire arc additive manufacturing (WAAM) technology with traditional manufacturing process provides a promising method for fabricating the large and complex parts with the advantages of high performance, time-saving, low cost and high material utilization. In order to acquire the optimal hybrid manufacturing process, the comparative study of flow behaviors and microstructure evolution of wrought and WAAMed ultrahigh-strength (UHS) steels is carried out under the temperatures of 920–1160 ^oC and strain rates of 0.01–10 s^ - 1 . The results show that the coarse prior austenite columnar grains and carbides in the initial microstructure of the WAAMed UHS steel contribute to the higher flow stress and slower dynamic recrystallization (DRX) kinetics during hot deformation as compared to the wrought UHS steel. The hot activation energy under the peak stress of the wrought and WAAMed UHS steels is estimated to be 332.3 kJ/mol and 374.1 kJ/mol, respectively. On the basis of the hot processing maps, the common optimal processing window for WAAMed and wrought UHS steels is determined as the temperatures of 1060–1160 ^oC and strain rates of 0.08–0.66 s^ - 1 . Under these deformation parameters, the microstructures of WAAMed and wrought UHS steels consist of fine DRXed grains, and the DRX behaviors are both dominated by the discontinuous DRX and continuous DRX mechanisms. Graphical Abstract