Quantitative analysis of retained austenite in laser melted martensitic stainless steel

Abstract

An AISI 420 martensitic stainless steel, 0.6 mm thick was melted with a 4.4 Kw continuous wave Nd: Yag laser in order to induce a certain proportion of retained austenite in a matrix. The volume percentage of the retained austenite in the melted-surface layer was investigated by irradiating the surface at different processing conditions. Typically, the sample was melted at different nominal laser beam powers (P), beam scanning speeds (v), and shielding gases, at constant beam diameter (d). The objective of this study was to determine if X-ray diffraction (XRD) was sufficient for quantifying the volume percentage of retained austenite. After a preliminary qualitative analysis, a Rietveld full pattern refinement program was used to quantify the volume percentage of the retained austenite in the melted-surface layer. The results show that the volume fraction of retained austenite in laser melted layer increased with decreasing energy density, when laser melting was carried out in an inert atmosphere.