17-4PH stainless steel with excellent strength–elongation combination developed via material extrusion additive manufacturing

Abstract

The current study intended to manufacture 17-4PH stainless steel using material extrusion additive manufacturing (MEAM) process and to control the microstructure and mechanical properties of the steel through heat treatment. The as sintered MEAM 17-4PH steel was densely manufactured with a 97% or more sintered density and few inter-layer defects. Microstructure images of the prepared specimen showed an isotropic microstructure, and the matrix was mainly composed of lath martensite. After heat treatment (a standard H900 condition), no phase change was observed in the matrix of the specimen, and the dislocation density slightly increased. In the case of nano-sized particles, 16.38 nm 3R structure Cu-rich precipitates (CRP) and some NbC were present in the as sintered steel. A high fraction of BCC structure CRP of size 3.51 nm and NbC of size about 88 nm precipitated in the post-heat-treated specimen. Tensile test of the specimen before the heat treatment (as sintered) showed the best mechanical properties among the MEAM 17-4PH steels reported so far. After the heat treatment, tensile strength, yield strength, and elongation even increased to 1.35 GPa, 1.11 GPa, and 7.8%, respectively. This study also aimed to suggest a method for controlling the properties of the MEAM-built 17-4PH stainless steel to improve its mechanical properties based on its microstructures change and the difference in strengthening mechanisms.