Heat treatment induced microstructural evolution, oxidation behavior and tribological properties of Fe-12Cr-9Ni-2Al steel (CX steel) prepared using selective laser melting

A novel type of martensitic precipitation hardening stainless steel, Fe-12Cr-9Ni-2Al steel (CX steel), was successfully fabricated via selective laser melting (SLM) technology. The influence of the heat treatment regime on the surface microstructure, high-temperature oxidation resistance and tribological properties of the SLM Fe-12Cr-9Ni-2Al steel was studied. A series of vacuum heat treatment methods including austenitizing treatment and tempering treatment were determined by means of a differential scanning calorimetry (DSC) method. Reverted austenite (γ-Fe phase) would be induced by tempering treatment to generate along the martensite (α′-Fe phase) grain boundaries. During a 400 °C high-temperature oxidation experiment, a loose oxide layer consisted of Al2O3, Cr2O3 and Fe3O4 was formed on its surface. A high-temperature oxidation process model was put forward to illustrate this phenomenon. After austenitizing-tempering treatment, massive nano-NiAl precipitates enhanced the hardness of the SLM CX steel from 356 ± 14.3 HV0.2 in the as-built state to 527 ± 5.2 HV0.2 in the austenitizing-tempering treated state. Correspondingly, the coefficient of friction (COF) and wear rate of the SLM Fe-12Cr-9Ni-2Al steel samples decreased from 0.58 and 16.1 ± 3.1 × 10−5 mm3/(N·m) in the as-built state to 0.49 and 8.1 ± 3.3 × 10−5 mm3/(N·m) in the austenitizing-tempering treated state, respectively.