Correlation of morphological anisotropy and Lankford value of deep drawing sheets hot-rolled by compact strip production

Cold-rolled steel sheets in automotive applications require an excellent deep draw ability, which is characterized by the Lankford value (r-value). In this study, a correlation was identified between r-value and pancake-shaped grain flatness which is indicated as the ratio of grain diameter in the rolling direction (RD) and normal direction (ND) of sheets (d r/d n). A mathematical model $$\left( {r = e^{0.345\left( {d_n^{ - 1/2} - d_r^{ - 1/2} } \right)} } \right)$$ was developed to calculate r-value by the microstructure of steel sheets hot-rolled by compact strip production (CSP). It is shown that the r-value is higher, if the microstructure of steel sheet is of pancake-shaped grains elongated in the rolling direction. The calculated r-value is confirmed to fit exactly to the measured one from the large-scale production.