Effects of milling time and temperature on phase evolution of AISI 316 stainless steel powder and subsequent sintering

In this study, effects of milling conditions on mechanical and microstructural properties of AISI 316 stainless steel powder were examined. Milling process was performed at ambient and cryogenic (−100 to −90°C) temperatures for 1-12 h. The cryogenic tests were performed using liquid nitrogen without direct contact to the main powder. In order to investigate the effect of milling parameters on final properties of sintered samples, hot pressing was performed on selected as-milled powders at 1150 °C for 1 h under 65 MPa pressure. XRD analysis on as-milled powders confirmed the phase transformation of austenite (γ) to α' martensite in all samples. It was also evident from quantitative measurements carried out by Rietveld refinement method that the α' weight fraction was a function of time and temperature. Based on this method, for all phases, crystallite size reduced to nanometer regime. Microstructural analysis for all samples was carried out by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) that confirmed Rietveld analysis results. For as-sintered samples, relative density and Vickers hardness measurement were also performed to assess the physical and mechanical properties.