carbides, microscopic identification, HSS; LiMaRC - Liège Materials Research Center
Abstract :
[en] High Speed Steel (HSS) cast rolls are used in front finishing stands of hot strip mills
(HSM). Good wear resistance and hardness at high temperatures, are defining
features of HSS.
Previous experience has shown that HSS rolls containing mainly hard MC carbides
have a high friction coefficient, which is detrimental for the rolling power consumption
and for the strip surface quality. On the other hand, HSS rolls containing eutectic rod
shaped carbides are brittle and more susceptible to spalling. To overcome these
problems, a suitable grade, called HSS7, that gives the best compromise between a
low friction coefficient and a high crack propagation and wear resistance was
developed. That alloy contains well-dispersed hard VC carbides improving wear, and
non-interconnected eutectic carbides of the M2C and M7C3 type, hindering crack
propagation.
All the metallurgical factors affecting the performance and damage of under rolling
condition in front finishing stands are reviewed: wear resistance, friction coefficient,
resistance to rolling incident, and oxide film formation.
The effect of nature, morphology and amount was for each of the carbides studied
and connected to the factor affecting the behaviour of the new grade developed.
Different techniques are used such as: differential thermal analysis, optical and
electron scanning microscopy and image analysis. A correlation with mechanical
properties was also performed.
