Hot Rolling Process Optimization for Hot Shortness Problem

Abstract

Tramp element is defined as elements cannot be refined in conventional steel refinement methods due to thermodynamic nature of element. These elements cannot be oxidized in steel and refined with oxidization – slag formation method due to lower oxygen affinity than iron. Tramp elements accumulate in steel within every recycling. These elements are; Cu, Ni, Sn, Sb and As. The problem with tramp elements is they have detrimental effects on steel properties. Hot shortness is a problem occurs in tramp element containing steel especially with copper. During the annealing enrichment of copper under the surface occurs because of selective oxidation of iron on surface. Enriched copper beneath the mill scale transforms to liquid form. Liquid copper migrates to austenite grain boundaries then with mechanical force of rolling process causes cracks on steel surface.
This study is aimed to explain and understand hot shortness behaviour under different circumstances. In this study copper is artificially alloyed to steel to simulate hot rolling performance of steel with tramp element containing steel. Hot rolling process is carried out for two different annealing temperature and effects of S, P and Mn alloying is investigated. Crack formation and crack numbers are calculated and optical and SEM imaging is done for crack behaviour observation. Results promoted that annealing treatment and alloying can be effective against hot shortness.