Study on Hardness and Microstructure of 304L Stainless Steel by Selective Laser Melting

Selective laser melting（SLM） austenitic stainless steel has higher hardness than its traditional rolled counterparts, which was closely related to its unique microstructure. The nano-indentation measurement was applied to investigate the hardness evolution in three kinds of samples, including as-built and heat-treated SLM, and the traditional rolled 304L austenitic stainless steels. Combining with the microstructure characterization of the materials, a rapid method for evaluating the yield strength of the materials by hardness was developed. Dislocation strengthening, fine grain strengthening and dispersion strengthening are the three main factors affecting the hardness of SLM 304L. The results show that high density dislocations, precipitates and fine grain size jointly cause the highest hardness of 304L stainless steel as-built SLM. The dislocation density and grain size are the two main material strengthening factors.