Die Materials and Treatments with Electrogalvaniied Steels

Frictional characteristics and galling tendencies were examined for three sheet metal forming die materials - cast steel, gray cast iron, and nodular cast iron - with four die treatments - unhardened, flame hardened, ion nitrided, and chrome plated. Repetitive testing was performed using a draw bead simulator and an electrogalvanized, free zinc coated steel with a nominal coating weight of 70 g/m² per side. No die material/treatment condition significantly decreased friction. Higher friction was exhibited with chrome plated cast iron draw beads. Pickup of zinc on the draw beads varied with both die material and treatment. Surface irregularities arising from substrate characteristics interacting with surface treatments caused extreme die pickup. Depending on the natureand hardness of the draw bead surface treatment, the adherence of this zinc to the draw beads could be quite weak, minimizing continued local buildup. For electrogalvanized steel, ion nitrided cast iron dies and chrome plated or ion nitrided steel dies appear to offer the best combinations of consistent friction and minimal zinc transfer.