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

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.