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Cold steel rolls and too many other cold work dies are chosen
of low alloy steel heat treated to about 60 RC in 50 millimeter depth on surface.
Troostite phase which happens in some cases in tempered martensite has lower
fracture toughness, although its ductility is a little more. In Industrial practical
process condition, some technological problems seldom take place, and the part
might be locally heated because of the accident. This effect may cause a phase
change in metallurgical structure on the surface of the cold steel rolls or dies,
named Troostite. However, the parts which subjected to this problem have no
mechanical defect to be detected by NDT, but these kinds of affected part may be
failed in working (rolling) by fracture, spalling or cracks. So Troostite is a
harmful phase for rolls and other cold work tools which cause lots of losses to the
companies. The following paper is a practical industrial approach to show and
follow thermal instability of roll surface and metallurgical change of the surface
from sorbite to troostite and its failure or fracture due to any improper usage.