Analysis of the amount of retained austenite in the structure of steel rolls for sheet rolling

The amount of residual austenite in martensitic roll steels is an important technological parameter of heat treatment, which affects the performance properties of the rolls. But determining its amount in roll steels is a complex and not fully solved scientific and technical problem. The aim of the work was to comparatively analyze the amount of residual austenite in the structure of alloy steel rolls by X-ray diffraction, ultrasonic methods and metallography analysis. However, the qualitative difference of microstructures in the content of the light phase - austenite, confirms the results of X-ray diffraction analysis. No correlation was found between the austenite content in the samples and their hardness. It was found that the X-ray method, based on the comparison of the intensities of the α- and γ-phase lines of iron, overestimates the value of the amount of residual austenite in some samples of roll steels. The results of the analysis of residual austenite by ultrasound rate showed better convergence. The amounts of residual austenite, calculated on the sample of stainless steel (100% γ-Fe), had reduced values (2.6-4.5%). The most accurate results on the amount of residual austenite gave the use of the established regression dependence with the selected standard (2.7-7.8%). This dependence is obtained at the speed of sound in austenite ~ 4000 m / s. It is determined that the application of the ultrasonic method allows to determine the content of residual austenite in the samples of roll steels quite quickly and accurately.