Characteristics of bainitic transformation and its effects on the mechanical properties in quenching and partitioning steels

Steel treated by quenching and partitioning exhibits an excellent combination of strength and ductility by taking advantage of the transformation-induced plasticity effect of retained austenite. Therefore, the precise tailoring of retained austenite is crucial for quenching and partitioning steels. However, austenite decomposition including bainitic transformation during partitioning is usually neglected, and consequently, its effects on the mechanical properties are not clear. Here, we elucidate the significant role of bainitic transformation during the partitioning process in the microstructure and mechanical properties of 0.2C-2.82Mn-1.58Si steel subjected to one-step quenching and partitioning process and two-step quenching and partitioning process. The results show that the occurrence of bainitic transformation during the Q&P process is responsible for the increased amount of retained austenite due to the optimization of carbon redistribution in addition to carbon partitioning, leading to a significant improvement in uniform elongation and total elongation without clearly compromising the tensile strength. An increase in the quenching temperature stimulates bainitic transformation; as a result, the amount of retained austenite is increased, and more blocky austenite is retained due to the optimization of carbon redistribution during bainitic transformation. Moreover, an increase in the bainite volume fraction and the various morphologies of retained austenite lead to excellent work hardening performance, thereby significantly improving the elongation.

Automated summary

Steel treated by quenching and partitioning process shows an excellent combination of strength and ductility by utilizing the transformation-induced plasticity effect of retained austenite. The occurrence of bainitic transformation during the partitioning process significantly influences the microstructure and mechanical properties of the steel, especially on the elongation performance.