Effects of Oil Type, Weight and Storage Time on Formability of Galvannealed Sheet Steels

Oil type, weight and storage time effects on formability of galvannealed sheet steels were examined in punch stretching (LDH) and friction (DBS) tests. The effects of oil weights between 1 and 8 g/m² and storage times up to three months were examined. The results suggest that application of prelube or mill oil of about 3 g/m² is desirable to maximize formability. Lower amounts of oil could lower punch stretchability somewhat from the maximum values. On the other hand, oil weights beyond 3 g/m² did not appear to offer additional improvements in formability. DBS friction coefficients did not change with oil weight or storage time. Storage caused some variability in punch stretching test results for samples with the mill oil. The results indicate that prelube is beneficial for the formability of galvannealed sheet steels in the specific forming modes tested here, and the benefits continue after storage for up to three months. While an oil weight of 3 g/m² may be excessive from a coil handling and storage perspective, the potential of achieving similar levels of formability with a lighter coating of prelube compared to a heavier coating of mill oil may be worth considering.