Influence of screw extrusion on the atomic order in constructional steel

The atomic order in low-carbon steel strained by screw extrusion making the microstructure finer and changing the phase ratio in the material is studied by X-ray diffraction analysis. The steel is found to consist of multiscale structural fractions: a finely crystalline (300–600 Å) α-Fe matrix, nanodimensional (180–250 Å) Fe₃C and Fe₃Si or Fe₅Si₃ phases, and a fraction with randomly arranged atoms. A second-order order-disorder phase transition is revealed with order prevailing in the longitudinal (‖) section of the samples and disorder prevailing in their cross (⊥) section. Sets of “extended” and “compressed” planes are found to coexist in the structure for the first time, with extended planes prevailing in the (‖) section and compressed planes prevailing in the (⊥) one.