Investigation of Phase Transformation of Forged Steel Cold Rolls Due toHeat Affecting and Prevent its Failure

摘要

In rolling Industries, cold rolls are chosen of low alloy steel heat treated to about 60 RCin 50 millimeter depth on surface. Troostite phase which happens in some cases in temperedmartensite has lower fracture toughness, although its ductility is a little more. In rolling process,some technological problems seldom take place, and the roll might be locally heated accidentally.In cold rolling technology, this effect may cause a phase change in metallurgical structure on thesurface of the cold work forged steel rolls, named Troostite. However, the rolls which subjected tothis problem have no mechanical defect to be detected by NDT, but these kinds of affected rollsmay be failed in working (rolling) by fracture, spalling or cracks. So Troostite is a harmful phasefor rolls and causes lots of losses for rolling companies. The following paper is a practical industrialapproach to show and follow thermal instability of roll surface and metallurgical change of thesurface from sorbite to troostite by diffusion mechanism, due to any improper mill usage.