Comparison on Microstructure and Mechanical Properties of QStE420 Steel Produced by Conventional Hot Rolling and Compact Strip Production

The microstructure, mechanical properties, and strengthening mechanisms of QStE420 steel produced by the conventional hot rolling process and the compact strip production (CSP) process were systematically studied. The results revealed that the conventional hot‐rolled steel featured a coarse‐grained (5.52 ± 0.54 μm) ferrite–lamellar pearlite microstructure, whereas the CSP process facilitated the formation of a fine‐grained (4.34 ± 0.36 μm) ferrite–flocculent pearlite microstructure through the synergistic effects of rapid cooling and heavy reduction rolling. Compared with the conventional hot rolling process, the CSP process results in fewer precipitates during the rolling stage, but generates a greater number of finer precipitates during the coiling stage. The synergistic effect of the grain refinement strengthening and precipitation strengthening increases the yield strength of the steel from 455 to 497 MPa and the tensile strength from 526 to 556 MPa. Moreover, owing to the characteristics of fine grains and a greater number of grain boundaries, steel produced by the CSP process exhibits a higher strain‐rate sensitivity ( m‐ value) at low strains. In contrast, the steel produced by the conventional hot rolling process maintains a higher dislocation accumulation rate at high strains, consequently exhibiting a larger m‐ value and better ductility.