Heat treatment routes and strengthening mechanism of H13 steel hybrid components produced by forging and additive manufacturing

Abstract

Compared with traditional forging or additive manufacturing, the hybrid manufacturing that combines forging and wire-arc directed energy deposition (WA-DED) can better balance manufacturing efficiency, cost, and flexibility. Two heat treatment process routes were designed for the hybrid manufactured H13 steel components: (i) WA-DED directly on a forged H13 substrate, followed by quenching and double tempering (WQT); (ii) first quenching the H13 substrate, then performing WA-DED on the quenched substrate, and finally double tempering (QWT). The effects of two routes on the microstructure evolution were evaluated, and the strengthening mechanism of different zones with martensite was investigated, thereby revealing the fundamental reasons for the differences in mechanical properties of different zones. The results show that both routes produced inhomogeneous microstructures, leading to differentiated mechanical properties in different zones of the samples. The differences in yield strength of different zones with martensite mainly arise from differences in martensite size, carbides distribution and size, and dislocation density. The precipitation strengthening effect was the most critical factor that affected the yield strength. QWT shows better comprehensive tensile properties than WQT. Furthermore, experimental and simulated high-resolution transmission electron microscopy images show that the extra diffraction spots observed in the martensite twins are attributed to the secondary diffraction and rotating moiré effects caused by the overlap of the martensite matrix and twins rather than from the ω phase. This work provides a new perspective on the heat treatment routes of hybrid manufactured H13 steel and provides theoretical guidance for further optimization of the heat treatment process.