Microstructural evolution and high strain rate compressive behavior of as-built and heat-treated additively manufactured maraging steels

Maraging steel is ultra-high-strength steel with low carbon content hardened by secondary precipitation during aging treatments. Additive manufacturing is an advanced technique for fabricating near net-shaped components from a powder or wire feedstock. In the present study, maraging 300 samples were additively manufactured using laser powder bed fusion (LPBF) and were subjected to dynamic impacts. Using a Split Hopkinson Pressure Bar apparatus, compressive loads were applied at strain rates ranging between 1500 s-1 and 4000 s-1 for the asbuilt and 150 s-1 to 1930 s-1 for the heat-treated LPBF-maraging steel samples. Scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were used to analyze the microstructure and texture evolution during the dynamic impact loadings. While as-built LPBF-maraging steel samples fractured when impacted at a strain rate of 3500 s-1, aged LPBF-maraging steel samples fractured when loaded at a strain rate of 1930 s- 1. The microstructural analysis of the as-built samples revealed the formation of adiabatic shear bands as a result of heat accumulation in strain rates of 1500 s-1, 2000 s-1, and 3200 s- 1. In addition, adiabatic shear bands were detected at the strain rate of 890 s-1 in the aged maraging steel samples as well. Finally, a constitutive model was developed to understand better the high strain rate behavior of LPBF-maraging steel samples. For both as-built and heat treat conditions, the Chang-Asaro hardening model showed good agreement with experimental results.