Microstructural evolution and mechanical properties of maraging steel by additive manufacturing

Laser powder bed fusion (LPBF) is a revolutionary and innovative technology that provides advanced technical support for the forming of parts with high precision and complex structures. In this work, a new type of Fe-NiMo-Ti-Al-Y cobalt-free maraging steel was successfully fabricated by LPBF. The additive manufacturing parameters and the microstructural evolution of cobalt-free maraging steel under different heat treatment parameters were systematically studied. The results show that the parts without cracks and close to complete density can be fabricated under a wide LPBF process window. The dislocation cell with 500 nm in the printing state makes the material have good plasticity. After post-heat treatment, the preferred orientation of LPBF maraging steel is reduced, but the typical characteristics of molten pool and cellular structure in maraging steel disappeared, which is the result of local composition and microstructure homogenization. The elongation of LPBF maraging steel in solution annealed state is higher than that in as-printed state, which is due to the reduction of dislocation density and grain coarsening. However, after direct aging, due to the formation of nanosized Ni-3(Ti, Mo) precipitates in the matrix, the mechanical properties of the material were effectively enhanced, and the tensile strength increases from similar to 1.1 GPa in as-printed state to similar to 1.6 GPa in aging state. In contrast, the corrosion resistance of as-printed maraging steel is higher and comparable to that of traditional cobalt-containing maraging steel. However, the corrosion resistance of LPBF maraging steel after being aged is reduced, which is due to the existence of precipitates and dislocations. This study provides a theoretical reference for the composition design and strengthening mechanism of LPBF cobalt-free maraging steel.