Using Heat Treat Simulation to Characterize Sensitivity of Quench Hardening Response in Hot Mill Steel Work Rolls

Quench hardening of work rolls for steel rolling is used to impart both residual compression and hardness to the roll surface to promote durability, wear resistance and life. Minimizing required roll re-dressing and mill down time are important cost drivers for improved work roll surface life. Developing the necessary metallurgical and mechanical response of these rolls in heat treatment is complex, often involving a heating and quenching sequence in which thermal gradients are controlled at both the outer surface and by application of internal cooling through the roll’s hollow center. Depth of hardness, along with surface and internal residual stresses, are challenging to control. Typically, methods for developing such heat treating practices are based heavily on in-plant experimental trials, as well as “experience.”  

The advent of accurate heat treatment simulation allows for analytically based process engineering to be used to examine roll heat treatments to improve depth of hardening and overall metallurgical response. In this paper, virtual experiments are conducted to characterize practical heating, cooling and quenching regimes to study how varied practices may be used to control residual stress, hardness and metallurgical structure. Because of heat treatment’s highly non-linear nature, simulation is a valuable tool for examining part response sensitivities.  The relationship between residual stress and hardness is not straightforward, as will be shown. Therefore, the use of heat treatment modeling, which allows examination of the in-process thermal and transformation stresses in conjunction with microstructural changes, is an important design tool for understanding the heat treatment of these rolls.