Development of 40 to 50 kg/mm2 Tensile Strength, Highly Formable Cold-Rolled Low Carbon Steel by α + γ Phase Annealing

The effects of key alloy and process parameters on the mechanical properties of high strength, highly formable low carbon sheet steels have been determined by a combination of laboratory processing, Taguchi Design of Experiments method, and multiple linear regression analysis. Factors studied include C, Mn, P, hot mill coiling temperature, in-line annealing temperature, and annealing line speed. Tensile strength levels were varied from 40 to 50 kg/mm² with elongation of 30 to 40%. Annealing conditions were varied from partial to full recrystallization in both the single and α + γ two phase region. Effects of the chemistry and process parameters on the mechanical properties will be discussed, with particular emphasis on conditions required to produce a hot dipped galvannealed product meeting 45 kg/mm² tensile strength and 35% elongation minimum requirements.