Study On Microstructure And Mechanical Properties Of Direct-Quenched Medium Carbon Steel

Compared with conventional quenched and tempered process, Direct quenching eliminated off-line reheating and quenching, reduced processing costs and shortened process, in addition, DQ process increase hardenability ,weldability, and mechanical balance by reducing alloy elements.Most of studies on direct-quenched steel were concentrated on high temperature tempered steel, excellent strength and toughness balance was obtained due to more strong secondary hardening after direct quenching and high temperature tempering, but there are few research on low temperature tempered steel .In the thesis, Effect of different direct-quenching processes on microstructure and mechanical properties was studied with 22SiMn2TiB steel, which was produced by converter continuous casting ,and compared with those of reheating and quenching process, the possibility of improving strength and toughness and the direct quenching mechanism were explored.Tested steel plates was heated to 1250 ℃ for 60min,and finish rolled at 900℃ or 750℃ and direct quenched .followed by tempering at 200℃ for 120min, i. e.,recrystal1ization-control led direct-quenched(RCR&DQ-T)and controlled-rolled direct-quenched (CR&DQ-T) conditions, respectively. As for conventional reheat quenching process(RQ&T), the plate was air cooled to room temperature after finish rolled at 980℃, and reheated to 920 °C for 30min, followed by quenching and tempering.The strength , hardness and toughness of the tested steel after direct quenching were obviously higher than those of RQ&T, but the plasticity was approximate. The strength and hardness generally increased in the following order: RQ&T