12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

Galvanizing lines often apply pre-oxidation and reduction in their annealing cycle to ensure successful galvanizing of Advanced High Strength Steels with good coating appearance and excellent adhesion. Tata Steel uses flash pre-oxidation by means of an oxygen bar, by which an oxygen-rich gas mixture is blown onto the steel strip. The thickness of the Fe-oxide layer formed during the pre-oxidation step is crucial, as both too little and too much pre-oxidation can lead to poor adhesion and/or bare spots or coating defects. To ensure a continuous good coating quality in the Hot Dip Galvanizing line with various steel grades and process conditions, it is crucial to understand which parameters have the largest influence on the growth kinetics. Lab pre-oxidation studies are an important tool in this. In order to simulate the oxidation process by the oxygen bar in the lab, the hot dip process simulator was adjusted to allow an instant change of atmosphere at the sample. Furthermore, the oxidation of the sample was monitored with an in-situ optical measurement system. This study focusses on the effect of temperature, oxygen percentage, and chemistry of steel substrate and formed oxides during fast oxidation.