Effect of heat treatment on microstructure and mechanical properties of Fe?Cr?Ni?Co?Mo maraging stainless steel produced by selective laser melting

In the present work, a Fe?11Cr?9Ni?6Co?3Mo (wt.%) maraging stainless steel was successfully fabricated by selective laser melting (SLM). The SLM process parameters were optimized and the influence of heat treatment on microstructure and mechanical properties of the SLMed Fe?11Cr?9Ni?6Co?3Mo samples was systematically explored. The results show that the optimized laser volume energy density with the relative density ?99.5% for the SLMed samples is 83.33?200 J/mm3. For SLMed samples, the phase analysis reveals predominantly martensite with some retained austenite, and the microstructure is characterized by the prior austenite grains and fine martensite laths. After subsequent heat treatments (solution + cryogenic cooling + aging), the microstructure results in the formation of nanosized CrMoC carbide precipitates, uniformly dispersed in the martensite laths and retained/reverted austenite. Compared with the SLMed samples, the microhardness and tensile strengths are significantly improved after subsequent heat treatments. The effects of heat treatment parameters (solution temperature, aging temperature and aging time) on mechanical properties primarily depend on the size and fraction of carbide precipitates as well as the content of retained/reverted austenite. The microhardness of 439?444 HV, yield strength of 1325?1355 MPa and ultimate strength of 1365?1374 MPa are obtained with the optimal heat treatment regime (solution treatment at 750?850 ?C for 1 h + cryogenic cooling at -73 ?C for 2 h + aging treatment at 450 ?C for 7 h).