Effect of Final Cooling Temperature on Mechanical Properties of a Water Cooled Mn-Series Low Carbon Bainitic Steel as 8Mn2SiNb

Abstract

The effect of final cooling temperature on the mechanical properties of a water cooled Mn-series low carbon bainitic steel as 8Mn2SiNb has been investigated in this paper. The results indicate that the optimum final cooling temperature is 450 °C, followed by air cooling to room temperature. Compared with air cooling, the condition of water cooling to 450 °C increases the tensile strength and yield strength about 13.3% (From 805MPa to 929MPa) and 59.0%(From 464MPa to 741MPa) respectively, remaining 21.5% elongation and 151J toughness. SEM observation reveals that the microstructure of the steel after water cooling to 450 °C is mainly granular bainite +lath martensite +refined grain boundary allotriomorphic ferrite (FGBA). Compared with air cooling, the condition of water cooling to 450 °C increases the volume fraction of strengthening phase (M-A island) from 28.2% to 38.1%.