Carmakers now tend to reduce the weights of their vehicles, or at the very least, to curb weight increases deriving from the introduction of additional safety and comfort pieces of equipment. The trend is clearly driven by environmental laws on fuel consumption and exhaust emission control. In this framework, the competition between materials will be intensified and, in the future, some long-held steel positions may start looking somewhat insecure. This is particularly true for frames and car body components, for which various manufacturers have already experienced with aluminium-based solutions. It is now generally recognised that the steel industry can only protect its market share by proposing new stronger grades, making it possible to go thinner and lighter. These materials must not only exhibit the desired level of mechanical strength, but also maintain an adequate deep drawing capability, as commonly measured by average Lankford coefficient r, isotropy Ar, and strain hardening coefficient n. At present, practically all car models feature electrogalvanised (EZ), pure zinc hot-dip galvanised (GI) or galvannealed (GA) body protective coatings, allowing long-term anticorrosion guarantees. Combining high strength, deep drawing performances and adequate galvanisability however often proves challenging, and implies mastering all metallurgical mechanisms put in operation at every step of the production sequence. The steelmaking community has actively addressed this problem, as is testified by an impressive body of publications and international scientific conferences. In this context, the response of several high-strength deep-drawing steels to hot-dip galvanising was investigated in the course of an earlier Rhesca simulation-based ILZRO project. The target was to achieve yield strengths between 200 and 400 MPa, tensile strengths of about 500 MPa, elongations higher than 20%, Lank-ford coefficients over 2 and strain hardening coefficients of more than 0.2. It was concluded that, although these steels are somewhat more difficult to galvanise than reference IFs, conditions could always be worked out to obtain good quality coatings. This paper reports on a subsequent piece of work involving Rhesca simulation and pilot line continuous annealing and hot-dip galvanising. It was carried out on an experimental steel that had been shown to qualify as a satisfactory non-ageing, high-strength, deep-drawing material in the uncoated, cold-rolled and annealed condition.
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