Abstract: The influences of different rolling and cooling processes along with reheating quenching and tempering treatment on the microstructures， mechanical properties and reheating austenization progress of a low alloy quenched and tempered high strength steel were investigated. The results showed that the controlled rolling process increases the prior austenite grain boundary area and the reheating austenite nucleation rate. So the finer reheating quenching microstructure is obtained， and the strength and toughness after tempering are also enhanced. Lath martensite is obtained under continuous watercooling condition. Granular bainite is obtained under aircooling condition with uneven distribution of carbon element， which is beneficial to the strength after quenching and tempering. The mechanical properties are optimized by controlled rolling and interrupted cooling process after heat treatment.

Key words: low alloy quenched and tempered steel, mechanical properties, controlled rolling and controlled cooling, austenitization, quenching