Development of Direct Hot-Rolled Ultralow-Carbon Pre-peritectic Ferrite-Bainite Dual-Phase Steel for a Compact Slab Production Plant

The current work developed a direct hot-rolled ultralow-carbon ferritic-bainitic dual-phase “FBDP” steel with high ductility values in accordance with a compact slab production CSP plant. Four ultralow-carbon alloys with chemical compositions of 0.045% C, 0.28 Si%, 0.91% Mn and different Cr weight contents of 0.59, 1, 1.56 and 2% were determined within the pre-peritectic region from phase diagrams plotted by Thermo-Calc 2020. These alloys were melted and cast into blocks, and then, a certain thermomechanical schedule was applied using the actual data obtained from the log files of a CSP plant. The cooling schedule was designed with the aid of CCT and TTT curves plotted by JMat Pro. The results show that hot-rolled FBDP steel contains a substantial amount of bainite from 10 to 28% and negligible martensite. The increase in Cr led to an increase in the bainite volume fraction and an increase in the yield strength and tensile strength, while the elongation decreased slightly. The strain hardening exponent (n-value) reached values ranging from 0.28 to 0.36, while a value of 0.18 was found in the literature for martensitic DP steel. Stroke-force curves plotted from the Erichsen test achieved high Erichsen index values from 14 to 18 mm.