A Model for Predicting Residual Hydrogen Content in Blooms and Billets Stacked in Large Industrial Piles

Hydrogen is highly detrimental for mechanical properties and internal quality of steel products. Hydrogen is captured in liquid steel from different sources, also depending on the different stages of the manufacturing process. During the liquid stages, the most effective countermeasure to reduce the hydrogen content is vacuum degassing. Nonetheless, not all the products undergo this process and then the cooling stage becomes fundamental to avoid hydrogen embrittlement phenomena. To be effective for hydrogen release, the cooling path needs to be suitably slow without abrupt temperature gradients. In industry, products are piled according to strategies following logistic rather than metallurgical logics, with very poor control of the cooling strategy. The paper presents a simplified and practical model, which predicts the final hydrogen content in blooms and billets with square or rectangular section after the slow cooling in a large pile by computing the cooling path of each product. The model allows identifying those products, where the residual hydrogen content after cooling is excessive, which are therefore more likely to show hydrogen embrittlement-related problems. It allows simulation of different piling strategies for each specific product and is therefore useful in order to preliminarily identify the best piling procedure to avoid hydrogen embrittlement