Mechanical properties and microstructural characterization of selective laser melted 17-4 PH stainless steel

• Published in: Rapid prototyping journal 2017-03, Vol.23 (2), p.280-294
• Main Authors: Mahmoudi, Mohamad, Elwany, Alaa, Yadollahi, Aref, Thompson, Scott M, Bian, Linkan, Shamsaei, Nima
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Alloys; Corrosion resistance; Grain size; Lasers; Manufacturers; Mechanical properties; Morphology; Nitrogen; Precipitation hardening; Scanning electron microscopy; Stainless steel; Studies
• ISSN: 1355-2546; 1758-7670
• DOI: 10.1108/RPJ-12-2015-0192

Purpose The purpose of this paper is to understand the effect of four different factors: building orientation, heat treatment (solution annealing and aging), thermal history and process parameters on the mechanical properties and microstructural features of 17-4 precipitation hardening (PH) stainless steel (SS) parts produced using selective laser melting (SLM). Design/methodology/approach Various sets of test samples were built on a ProX 100™ SLM system under argon environment. Characterization studies were conducted using mechanical tensile and compression test, microhardness test, optical microscopy, X-ray diffraction and scanning electron microscopy. Findings Results indicate that building orientation has a direct effect on the mechanical properties of SLM parts, as vertically built samples exhibit lower yield and tensile strengths and elongation to failure. Post-SLM heat treatment proved to have positive effects on part strength and hardness, but it resulted in reduced ductility. Longer inter-layer time intervals between the melting of successive layers allow for higher austenite content because of lower cooling rates, thus decreasing material hardness. On the other hand, tensile properties such as elongation to failure, yield strength and tensile strength were not significantly affected by the change in inter-layer time intervals. Similar to other AM processes, SLM process parameters were shown to be instrumental in achieving desirable part properties. It is shown that without careful setting of process parameters, parts with defects (porosity and unmelted powder particles) can be produced. Originality/value Although the manufacturing of 17-4 PH SS using SLM has been investigated in the literature, the paper provides the first comprehensive study on the effect of different factors on mechanical properties and microstructure of SLM 17-4 PH. Optimizing process parameters and using heat treatment are shown to improve the properties of the part.