Effect of heat treatment on the crystal structure of deformed samples of chromium–manganese steel

Abstract

Results of studying microstructures and the crystal structure of samples of 35KhGF steel (0.31–0.38 wt % С, 0.17–0.37 wt % Si, 0.95–1.25 wt % Mn, 1.0–1.3 wt % Cr, 0.06–0.12 wt % V, and the remainder was Fe) have been presented. The samples have been selected from hot-rolled pipes subjected to different heat treatments. A study has been carried out in order to explain the choice of the heat-treatment regime based on determining the structure–properties relationship that provides an increase in the corrosion resistance of pipes to the effect of hydrocarbons. Methods of the energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) have been used. In the microstructure of samples, oxide inclusions and discontinuities with sizes of 1–50 μm that presumably consist of the scale were detected. The ferrite grain size and the orientations of crystals were determined; the data on the local mechanical stresses in the Taylor orientation- factor maps were obtained. The grain refinement; the increase in the fraction of the low-angle boundaries; and the decrease in the local mechanical stresses and, therefore, the highest corrosion resistance to the effect of hydrocarbons is achieved by normalizing at 910°С.