An X-ray diffraction method has been developed for quantitative determination of retained austenite in the production line of cold-rolled type SUS 301 metastable austenitic stainless steel sheets. A new unit of diffractometer designed for application in the mill is equipped with an X-ray source of Cr Kα and three separate scintillation detectors and is provided with mechanisms of lateral movement along the transverse direction of strip and rotation around an axis vertical to the strip surface. Intensities of {211} martensite reflection, {110} austenite reflection, and background are measured separately by the three detectors.
Measurements were carried out by scanning of a coil, cold rolled in a reversing mill, during uncoiling operation in a slitting line. Diffraction intensities of austenite phase were weaker in the top and tail ends than in the middle part of the coil. Variation of the diffraction intensities throughout the whole coil length is well correlated with a conceptional distribution of retained austenite which can be deduced from the nickel equivalent and rolling temperature of the tested material. This findings suggest applicability of the present method in the production line, even though the effect of textures is not corrected.
The new X-ray diffractometer unit is proved to be successfully employed in the production mill as a practical means for prediction of inhomogeneity of material properties in the stainless steel strip for use of springs by monitoring the relative amount of austenite and martensite.