Annealing processing parameters and microstructure evolution of 780MPa hot dip galvanizing TRIP steel

The effects of annealing processing on the mechanical properties and microstructure evolution of high strength hot dip galvanizing TRIP steel were investigated.The results show that the tensile strength over 780.00MPa and elongation over 24.00% can be obtained,and the mechanical properties are significantly influenced by intercritical annealing temperature and isothermal bainitic transformation time.When the intercritical annealing temperature is 850℃ and the isothermal bainitic transformation time is 30s,the steel has the best mechanical properties.Partial metastable austenite (with a lower carbon content) remained after bainitic transformation will be transformed into martensite in the later cooling stage.Therefore,the annealing microstructure is composed of ferrite,bainite,retained austenite and martensite.