Steelmaking Process and Continuous Casting for Billets, Medium-, Large- and Superlarge Blooms as Feedstock for the Cutting Edge General and Automotive Engineering Industry

by Giovanni Cairoli, Sepp Kohl

Publisher - SMS Concast AG, Thailand, Switzerland

Category - General Novel

Worldwide steelmakers are faced more than ever with new challenges in terms of final product quality, productivity and production cost issues. In addition environmental aspect are ever more demanding. We experience presently a trend form producing such grades not only in fully industrialized countries, but also in emerging markets, especially South East Asia, since automotive companies among other engineering steel consumers are shifting production facilities to these countries and subsequently are looking for cost-effective sourcing of state-of-the-art engineering steel. Special steels or “special bar quality”, as they are commonly named, comprise a wide range of final sizes from high quality wire like cold heading-, spring- and high carbon- steel wire to straight and coiled small bars, large bars (case hardening, gear steel, suspension steel, spring-steel, railway axles and wheels, bearing steel, and even some special large sections like rails. With few exceptions most of them are Aluminum killed as well as low alloyed. As separate category namely stainless steels - Austenitic, Ferritic, Martensitic and Duplex grades - have to be considered, even though produced in small tonnages. From the metallurgical point of view all these grades are custom-designed to cope with their specific intended mechanical and technological final product properties like utmost cleanness, flawless metallographic structure, machinability, subsequent heat treatment behavior, direct rolling, forging and cold forming ability. For such tasks and with respect to final dimensions the correct and optimized reduction ratio has to be chosen, always considering the type of hot-deformation process (direct rolling, re-rolling, open or closed die forging etc.). All these considerations require a carefully designed and dedicated process technology from raw material input, primary steelmaking, secondary refining processes, continuous casting and hot deformation in order to achieve the desired quality of the final product. Special steel is nowadays mostly produced in primary melting vessels with low impurity content of the molten steel. One special aspect is the state of oxidation of the steel before tapping from the furnace vessel as well are the additions during tapping for the purpose of slag conditioning, alloying and de oxidation. In the subsequent secondary metallurgical processes like ladle reheating furnace and vacuum treatment (VD or RH) the steel is refined to its final analysis with emphasis put on inclusion engineering, cleanness, gas content, fluidity and also the mechanical and physical properties of the final product. Continuous casting of these steels is the dominant process and has for most part substituted ingot casting. The section sizes for the continuous casters range from typically 130x130 mm to 1000 mm round, employing caster radii from 6 to 18m initial radii.. Special caster designs and features are necessary and are discussed thoroughly in very detail in this presentation. Finishing of long products is an important link in the process chain for engineering steel, thus guaranteeing a “zero defects” quality for the end-user of the material. SMS Concast together with its affiliates SMS Meer and other companies of the SMS Group has strong answers to the demanding tasks of the production of special engineering steels considering state-of-the-art and future technology aspects.

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