North American Zinc-Based Sheet Steel Coatings Technology: Production and Product Performance Update and Challenges

摘要

Automotive industry requirements for steels capable of enabling increasingly fuel-efficient vehicles continue to drive process technology developments for North American hot-dip and electrogalvanizing lines (EGLs). Quality and productivity benchmarks also continue to be pushed to ever-higher levels. Two breakthrough products, zinc-coated hot press forming steels and third generation (3G) steel grades are subjects of intensive research and development. Also, dual phase (DP) and multi-phase grades with increasingly higher strengths continue to be developed. Such steel grades should satisfy automaker requirements and ensure the dominance of steel-based vehicle manufacturing for many years to come. The processing of these steels creates challenges for steel suppliers, and the approaches being taken to meet these challenges are described herein. In particular, the status of sheet steel pretreatments suitable for these grades is summarized, together with recent developments in coating line sections and coating control management. Several applications for ultra-high strength, cold-rolled steels (UHSS) that are heat-treated using continuous annealing line (CAL) processing benefit significantly from zinc-based electrogalvanized (EG) coatings; these have resulted in a resurgence of some North American UHSS-capable EGLs. An updated census of North American production coating lines is also provided. Challenges for the future continue to include further improved productivity, quality and process efficiency, and flexibility in line scheduling to minimize overall costs. The hot-dip coated UHSS products must meet the higher formability challenge of CAL-based uncoated and EG-coated UHSS. Overall, concerns by users of UHSS in regard to welding and hydrogen-induced delayed cracking need to be overcome.