Effect of process parameters and heat treatment on the properties of stainless steel CX fabricated by selective laser melting

Highlights: • The process parameters of stainless steel CX fabricated by SLM were optimized. • Effects of various heat treatments on phase transformation and microstructure evolution were discussed. • Excellent mechanical properties of the SLMed stainless steel CX were achieved using the solution aging treatment. -- Abstract: The present work envisages the effects of three heat treatment processes, i.e. solution treatment (ST), aging treatment (AT) and solution aging treatment (ST+AT) on the microstructure and mechanical properties of a new type of martensitic stainless steel CX (SS-CX) alloy formed by selective laser melting (SLM) with Cr and Ni as the main components. The results revealed that the densest parts with a few tiny pores were fabricated at optimized laser process parameters (laser power 340 W, scanning speed 850 mm/s, hatch spacing 0.1 mm). The SS-CX that underwent the SLM process was mainly composed of the martensite and retained austenite, and has a tensile strength of 1058 MPa and an impact toughness of 57.7 J. After ST at 900 °C for 1 h, the micro-segregation disappeared, the retained austenite of the as-built transformed into martensite, Ni and Al dissolved in the matrix to form supersaturated solid solution, and a reduction of the mechanical properties of the SS-CX was observed. When the SS-CX was aged at 530 °C for 3 h (AT), part of the martensite in the as-built recovered to austenite, and the precipitated particles with the mechanical properties strengthened. When the SS-CX was solution-aged at 900 °C for 1 h and then 530 °C for 3 h (ST+AT), the retained austenite of the as-built transformed completely into martensite, and the dissolved elements in the solution treatment precipitated again, forming the precipitation particles composed of β-NiAl. The precipitated particles increased rapidly the tensile strength and the surface hardness of the SS-CX with values of 1683 MPa and 50.4 HRC, respectively, thereby indicating that the SS-CX exhibited a good comprehensive property.