Abstract: Low-carbon bainitic steel is a new type steel with high strength, high toughness and multiple uses, its emergency is an inevitable result of social demand and the development of modern metallurgical technology. At present, the low-carbon bainitic steel is extensively used in construction machinery. However, the low-carbon bainitic steel is usually composed of several kinds of microstructures, so the corresponding relation between the mechanical performances of the steel and bainite structure cannot be directly reflected. In view of this situation, controlled rolling and cooling experiments of low-carbon Mn-B-Cr-Mo-Nb steel are carried out in a domestic iron and steel corporation. By the control of final cooling temperature, three low-carbon bainitic steels with different microstructure are obtained. They are respectively composed of granular bainite, lath bainite, and granular bainite + lath bainite. After tensile and impact tests，the results indicate that under the condition of identical chemical composition, the granular bainitic steel is the lowest in strength and is the best in toughness and plasticity, the lath bainitic steel is the highest in strength and is the weakest in toughness and plasticity, and the steel composed of granular bainite and lath bainite is medium in strength, toughness and plasticity. So it can be known that the final cooling temperature plays an important role in microstructure and mechanical performances of hot rolled plate. Accordingly, the comprehensive mechanical performances of low-carbon bainitic steel can be further improved by the control of medium-temperature transformation microstructure.

Key words: Granular bainite, Lath bainite, Low-carbon bainitic steel, M/A island