Optimization of mechanical properties of high strength bainitic steel using thermo-mechanical control and accelerated cooling process

High strength bainitic steel plates were produced by using thermo-mechanical control and accelerated cooling process to optimize the mechanical properties. The strength increased gradually with decreasing final accelerated cooling temperature. Compared with boron-free steel, the combined addition of titanium and boron into steel obviously increased the yield and tensile strengths, but decreased elongation and strain hardening exponent n value mainly due to the formation of lower transformation temperature microstructures, e.g. lath bainite/martensite. The impact load-deflection curves showed that the boron-free specimens normally have higher peak load and wider deflection than the titanium-boron specimens irrespective of strength. The lower impact toughness of the titanium-boron specimens exhibits the main mode of fracture micromechanism changed from ductile fracture to cleavage fracture.