Microstructure and mechanical property in a high strength high-Al–low-Si hot-dip galvanized dual phase steel

Abstract

In this study, two important parameters of heat treatment, namely, cooling rate after intercritical annealing and 460 °C isothermal soaking time, were varied to simulate the hot-dip galvanizing processing in a high-Al–low-Si cold rolling dual phase (DP) steel. The results indicated that after the annealing processes, ferrite and martensite structure were obtained at room temperature for all the heat treatment schedules. The addition of Mn, Cr, Mo to the DP steel and the increase in cooling rate after intercritical annealing increased the hardenability and stability of austenite and decomposition of austenite to ferrite, pearlite and banite was avoided. When the cooling rate was 50 °C/s and at isothermal soaking time was 3 s, the studied steel obtained the best combination of mechanical properties with tensile strength of ∼962 MPa, total elongation of ∼20.5%, and the product of tensile strength and total elongation of ∼19,727 MPa%. The increase in strain hardenability, decrease in ferrite/martensite nanohardness ratio enhanced the ductility of the experimental steel. The refinement of ferrite grain size and increase in ferrite–ferrite grain boundary misorientation led to increase in ductile behavior.