Influence of Delta Phase Morphology in Galvannealed Coated Steels on Formability

It is well known that coating microstructure can affect the frictional behavior and the formability of galvannealed steels. Several studies are available in literature describing the influence of different coating phases, such as, gamma, delta and zeta phases, on press formability. In the present study, the authors have investigated the effect of the surface morphology, specifically of the delta phase of galvannealed coating on press formability. Formability tests including conditions of (a) complete metal lockdown and (b) significant metal movement in the dies were conducted. It was found that cubic delta coatings seem to perform better (reduced splitting) in forming operations which are accompanied by significant sliding in the blankholder area than rod delta coatings. This paper presents the results of the formability evaluation for samples with different delta phase morphology and correlation with traditionally used measures for evaluation of surface behavior such as the frictional behavior and surface roughness.