JFE Steel Corporation has begun producing its recently developed “GI JAZ” high-lubricity hot-dip galvanised (GI) steel sheet, which it claims offers dramatically improved press ‘formability’ for use in automobile bodies.
GI steel sheet, which is hot-dip galvanised to coat its surface of steel substrate with pure zinc for strong corrosion resistance, is used mainly by European and American automobile manufacturers.
GI JAZ incorporates the high-lubricity technology used in “JAZ” (JFE Advanced Zinc) on GA steel sheet, which is heated after galvanising to alloy the galvanised layer with iron of steel substrate to improve both its ability to be spot-welded and its corrosion resistance after painting.
JAZ is mass produced mainly for Japanese automobile manufacturers. Most overseas automobile manufacturers use GI steel sheet or electrocardiogram (EG) steel sheet for rust-proof parts.
Pre-phosphated EG steel sheet (EG Prephos), which is coated with an outer layer of zinc phosphate for high lubricity, is widely used because of its good press formability, but it incurs high processing costs for electroplating and zinc phosphate coating.
GI JAZ, which achieves formability equal to that of EG Prephos, also boasts a reduced friction coefficient because its surface modified layer , like that for JAZ, reduces adhesion between the stamping tools and galvanised layer.
GI JAZ, similar to JAZ, allows automobile manufacturers greater freedom in vehicle structure and design, and helps them to stabilize press processes and reduce defects.
Press forming tests of GI JAZ were performed with an automobile fender. The range of blank holding force that enables good press forming without any cracking or wrinkling was twice as wide as that for common GI steel sheets.