Effects of Continuous Annealing Parameters on Microstructure and Mechanical Properties of Ultra-high Strength Dual Phase Steel

The continuous annealing of an ultra-high strength cold-rolled dual phase steel was simulated by using Gleeble-3500 thermal simulator.Scanning electron microscopy and tensile testing were used to investigate the effects of annealing temperature,annealing time and over-ageing temperature on the microstructure and mechanical properties of the steel.The results indicate that with the elevation of annealing temperature the yield strength and tensile strength reduced and the elongation increased.The amount of granular non-martensite increased in the microstructure including ferrite,martensite and a little granular non-martensite.The influence of annealing time on the mechanical properties of the dual phase steel was not obvious.The tensile strength reduced with increasing the over-ageing temperature.The yield strength,elongation and yield ratio increased with the over-ageing temperature increasing.There was yield plateau when the over-aging temperature was higher than 360 ℃.