Robust processes for reheating and rolling by controlling oxidation

Purpose and goal

The purpose of the project is to increase the understanding of the oxidation behavior of high-alloy stainless steels at hot processes in manufacturing, and to study subsequent pickling. The project has increased the understanding of catastrophic oxidation that can occur at reheating, and thereby giving less scrapped material. In addition, working environment benefits are seen with volatile MoO3 bounded to applied coating systems. For annealing and pickling, it is primarily the heating curve that affects the oxide morphology and following pickling, with less effect on atmosphere.

Expected results and effects

Applied coatings have little effect in preventing oxidation that occurs at reheating and homogenization before hot-rolling, confirmed by lab, pilot and full-scale trials. Reducing the amount of scrap, and surface defects, should primarily be done through controlled heating time. Coatings have mainly work environment benefits. Different combustion gases have little effect on oxide generation and pickling behavior, which motivates, alternative combustion gases. The main effect is the heating curve at annealing, which affects the oxide structure, and subsequent pickling.

Planned approach and implementation

The project has included lab experiments using synthetic gases when oxidising small samples, and pilot trials with a combustion gases and larger samples. Finally the work was demonstrated in full scale industrial trials. Thermodynamic calculations were used to identify coating systems that can be used to react with molybdenum oxide, and also stable at reheating. Several different characterization methods have been used. Scratch-testing in combination with high-resolution SEM characterization was valuable to capture oxide morphology and adhesive properties.