Formability analysis of extra-deep drawing steel

In the present work, formability of five sheets of aluminum-killed extra-deep drawing (EDD) low carbon steel sheets (with a wide variation in thickness) has been characterized. Forming limit diagrams (FLDs) have been determined experimentally by conducting punch-stretching experiments using suitably designed and fabricated tools. Formability, observed from FLDs, has been correlated with microstructure, mechanical properties and formability parameters like strain hardening coefficient (n) and normal anisotropy (r̄). The strain distribution in the material during punch-stretching under different states of strain has been studied. From the experimental results, it has been found that four of the five sheets have a favorable grain size and mechanical properties to meet the requirements of good formability. The suitability of these sheets for critical deep-drawing applications has been examined in terms of the level and range of critical strains in the FLD. These results correlated well with formability parameters. Earing tendency during drawing is expected to be high for one sheet due to its high planar anisotropy. The level of the FLD increased significantly with the sheet thickness. The effect of n and r̄ on the strain distribution characteristics has been analyzed.