Effect of Austenitizing Temperature on Microstructures and Mechanical Properties of Si-Mn Hot-Rolled Plate After Quenching and Partitioning Treatment

The production of quenching and partitioning (Q&P) steel using hot-rolled steel instead of cold-rolled steel can significantly reduce the manufacturing process time and cost. However, the initial microstructures of hot-rolled and cold-rolled steels are different, which affect the microstructures and mechanical properties of Q&P steel. Because most studies used Q&P steel prepared from cold-rolled steel, the microstructures and mechanical properties of Q&P steel prepared from hot-rolled steel are unclear. This study examines the microstructures and mechanical properties of Q&P Si-Mn steel prepared from hot-rolled steel as a function of the austenitizing temperature. The results showed that the ferrite in the Q&P Si-Mn steel produced from the hot-rolled steel had lath-type and blocky-type morphologies. The observed ferrite morphology could influence the morphology of the adjacent retained austenite. The lathtype and blocky-type ferrite surrounding the retained austenite was mainly observed as the thin lath and blocky types, respectively. The ferrite and retained austenite contents decreased with increasing austenitizing temperature. In addition, the corresponding yield and tensile strengths increased gradually with a concomitant decrease in elongation and the product of strength and elongation. When the austenitizing temperature was 810oC, the product of strength and elongation of the Q&P Si-Mn steels produced from hot-rolled steel reached 28.36 GPa center dot%, which was approximately 36% higher than that of Q&P980 produced industrially from cold-rolled steel. The higher product of strength and elongation of Q&P Si-Mn steel produced from hot-rolled steel may be related to the different morphologies of ferrite, which might control the morphology and stability of the adjacent retained austenite. These experimental results could provide a theoretical basis for preparing Q&P steel from hot-rolled steel instead of cold-rolled steel.