Magnetic and X-ray diffraction measurements for the determination of retained austenite in TRIP steels

The accurate determination of the volume fraction of retained austenite is of great importance for the optimization of transformation induced plasticity (TRIP) steels. In this work, two aluminium-containing TRIP steels are studied by means of magnetization and X-ray diffraction (XRD) measurements. By fitting the field dependence of the approach to saturation in the magnetization curves, the saturation magnetization is determined, which is linearly related to the volume fraction of retained austenite. Moreover, information with respect to the microstructure can be obtained from the fitting parameters and the demagnetizing factor for the magnetization curve. The volume fractions obtained from the magnetization measurements are compared with data from XRD measurements. A discussion of the data suggests that magnetization measurements lead to more reliable results and a more sensitive detection of the retained austenite than XRD measurements.