Surface condition Effects on Advanced High Strength Steels Processing for the automotive industry

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Hot dip galvanization is a technology typically used to produce Zinc-coated sheet products for atmospheric corrosion protection of different industrial products (e.g. automotive industry). This process can be run continuously from Rolling to the final coated product leading to high production rate, which is necessary to meet production demand. One difficulty encountered during continuous galvanization is related to temperature control. Steel sheets moving at high speed in a controlled atmosphere furnace make the use of thermocouples difficult. Temperature is rather controlled indirectly by emittance readings using pyrometers that give more flexibility. However, they are sensitive to the material emissivity which is largely influenced by surface properties. Since strip delivered to the galvanizing line can have variations in roughness and thickness profiles, emissivity variation is inevitable. It has been shown that 2-3% variation in thickness can results in a 16-22°C temperature variation. This deviation is of significant consequence during intercritical annealing of advanced high strength steels. The objective of the proposed project is to understand and validate the effects of various surface characteristics on the quality of galvanized products. The project will first quantify the influence of surface characteristics on temperature readings and consequently on the process control. Second, the effect of temperature variation on mechanical properties of Advanced high-strength steels and zinc adherence will be studied using advanced characterization techniques. The results of this work will provide the necessary information to Canadian steel companies that need to decide if it is worth investing in costly temperature monitoring technologies such as multiple wave length pyrometers. It will also contribute to improve product quality through a better understanding of the relationships between process parameters and quality. Moreover, this collaborative project will create the perfect environment to train three graduate students over three years. The project objective will be achieved putting together the knowledge of two Canadian universities and the know-how of the International Zinc Association (IZA).