Determination of low levels of retained austenite in low-carbon high-manganese steel using X-ray diffraction

A method involving the decomposition of the X-ray diffraction (XRD) peaks for the single wavelengths K alpha 1 and K alpha 2 was used to quantify the amount of retained austenite at levels lower than 5% in low-carbon high-manganese steels. By applying this method, it was possible to use the two main peaks of austenite ( gamma ) and the two main peaks of ferrite ( alpha ) in the calculations, despite the partial overlapping of the (111) gamma and (110) alpha peaks. The diffraction peaks were modeled with the Pearson VII equation using a nonlinear least-squares optimization technique. This allowed the integrated intensities of the XRD peaks to be calculated using only the K alpha 1 side. The method was used to measure the levels of retained austenite in samples of a metal-inert gas steel welding rod cooled at the rates of 10 degree C/s and 1.6 degree C/s. The accuracy of the method was determined by performing six measurements in different directions in both the longitudinal and the transverse section of the 1.6 degree C/s sample.