EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

3rd generation advanced high-strength steel (AHSS) grades are complex materials with special chemical compositions and multiphase microstructures. The annealing and galvanizing process of these grades is different and places new demands on the plant technology. One of them is the prevention of surface faults. Bare spots can occur due to a higher content of alloying elements like silicon or manganese. Prevention is possible with the PrOBOX®-Technology for pre-oxidation. Another important topic is a precisely controlled and very flexible heating and cooling processes. The PrOBOX®-Technology is a proven solution for hot-dip galvanizing of high-alloyed steel grades without wettability problems, which normally occur during the conventional galvanizing process. The strip surface is therefore purposefully oxidized and reduced during the process. The technology is characterized by a very accurate formation of the iron oxide layer thickness, which is also measured. Another highlight is a specific technology which makes sure that the major part of the injected oxygen migrates into the strip surface. In addition, contamination of the furnace atmosphere by excessively discharged oxygen is prevented. Crucial for the production of modern grades is an appropriate furnace technology. The highly-efficient radiant-tube furnaces are equipped with powerful heating and cooling systems and facilities for quench and tempering. The newly developed I-Furnace optimizes the heat treatment and production process. It smartly combines a mathematical/physical model to control the furnace and to optimize production with an online strength measurement system and a newly developed annealing microstructure model to predict material properties after the heat treatment. This paper presents concepts for modern galvanizing lines for the production of 3rd generation advanced high-strength steel grades. It focusses on the pre-oxidation technology as well as on cooling technology and furnace control.