The influence of post-aging treatment on the microstructure and micromechanical behaviors of additively manufactured maraging steel investigated by in situ high-energy X-ray diffraction

The microstructure evolution and micromechanical behaviors of additively manufactured 18Ni300 maraging steel for both as-printed and aged one were investigated using the in situ high-energy X-ray diffraction (HE-XRD) technique with uniaxial tensile tests. The investigations revealed that the volume fraction of reversed austenite increased as the annealing temperature rose. The maraging steel was strengthened by η-Ni3Ti precipitates, where the aged maraging steel had a higher UTS value of ∼1860 MPa than ∼1135 MPa in the as-printed one, but sacrificed more than half of ductility (from ∼8.6% to ∼4.0%). The austenite in aged steel presents more stability induced by the aging process than that in as-printed counterpart, which has a higher critical martensitic transformation stress of ∼1200 MPa than that of ∼780 MPa in as-printed steel. The austenite grains orientated with [200]//LD yield before the macro-yielding and preferential martensite transformation occurs. This study provides further insight into the intricated micromechanical responses of additively manufactured 18Ni300 maraging steel, enlarging the scope of its adaptation and application.