Dynamic tensile mechanical properties of 18Ni350 maraging steel fabricated by wire arc additive manufacturing

The dynamic tensile mechanical properties of 18Ni350 maraging steel (M350) fabricated by wire arc additive manufacturing (WAAM) was investigated by the split Hopkinson tensile bar (SHTB) and microstructural analysis. The results show that the yield stress (YS) of M350 samples, both in as-built and heat-treated state, increases firstly and then decreases with increasing strain rate. The YS of the as-built sample reaches the maximum value of 2195MPa at 1230s-1, and that increases to 3395MPa after heat treatment, due to the precipitation of intermetallic. Compared with the sample in the horizonal direction, the sample in the vertical direction exhibits a higher dynamic strength, due to the preferred growth of columnar crystal along the vertical direction during WAAM process. Under dynamic load, the retained austenite transformed into martensite and the oxide inclusions are cracked, resulting in a heterogeneous fracture morphology. Based on those results the hardening model and the anisotropic model of the strain rate sensitive material fabricated by WAAM were established. The results can provide a guidance for the reliability evaluation of maraging steel fabricated by WAAM under dynamic load conditions.