OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 formed in the rod center (Fig. 4, c). However, the heterogeneous structure obtained during CRF has high thermal stability. The evolution of the microstructure during CRF and subsequent annealing is considered in more detail in earlier works [21, 22]. Fig. 5 shows the Kikuchi line contrast maps (Fig. 5, a1–a2), kernel average misorientation (KAM) maps (Fig. 5, b1–b2), crystal direction maps (Fig. 5, c1–c2), direct (Fig. 5, d1 –d2) and inverse (Fig. 5, e1–e2) pole figures of the material under study after the thermomechanical treatment. It is worth noting that for the center of the rod, the Kikuchi line contrast maps (Fig. 5, a1) and KAM maps (Fig. 5, b1) are of higher quality. 95 % CRF leads to the high КАМ value both in the center and at the edge of the rod (Fig. 5, b1–b2). Moreover, in the subsurface layer (Fig. 5, b2), the КАМ value is higher than that in the rod center (Fig. 5, b1). In addition, the pronounced two-component axial texture <001>/<111> is formed in the rod center (Fig. 5, c1, d1). However, the subsurface layer is characterized by the shear texture B/B ̅(Fig. 5, d2) [24–26]. In addition, according to the crystal direction maps (Fig. 5, c1-c2), a decrease in the volume fraction of grains of both orientations is observed in the cross section of the rod in the direction from the center to the edge. Namely, from the center to the subsurface layer, the fraction of <001>-oriented grains decreases from 38 % to 5 %, with a decrease in the fraction of grains with the <111>-orientation from 50 % to 30 %. Subsequent heat treatment at 600–700 °C improves the quality of the Kikuchi line contrast maps (Fig. 6, a1–a4) and KAM maps (Fig. 6, b1–b4) for all areas. However, of КАМ value remains high throughout the rod cross section with a characteristic increase in the direction from the center to the edge (Fig. 6, b1–b4). Obviously, the highest КАМ value is recorded along the grain boundaries and mechanical twins, while in the body of the grains this indicator is minimal (Fig. 6, b1–b4). In addition, in the subsurface layer, the formation of new small areas with the low КАМ value is observed (Fig. 6, a4 and a4, indicated by white arrows). In the rod center, the two-component axial texture <001>/<111> is preserved a b c d Fig. 4. Fine structure of the center (a, c) and subsurface layer (b, d) of a steel rod subjected to annealing at 600 °C (a, b) and 700 °C (c, d)
RkJQdWJsaXNoZXIy MTk0ODM1