Reduction of Residual Stress in Bimetallic Work Roll by Tempering

Abstract

Bimetallic rolls are used in steel rolling industries because of their excellent hardness and wear resistance. To reduce the center residual stress, quenching heating treatment is performed immediately after heating the roll nonuniformly instead of uniformly. In this study, we found that by using a nonuniform heating quenching method the maximum tensile stress that appears near the shell-core boundary was decreased by about 26%. It may be concluded that nonuniform heating quenching is useful in reducing the risk of roll failure by decreasing the center tensile stress without decreasing the surface compressive stress. Analysis including a tempering process was also conducted. It was found that for uniform heating quenching, the maximum stress at the center of the roll decreases by 33% from 396 MPa to 264 MPa after the first tempering and the maximum stress decreases by about 54% after a second tempering.On the other hand, with nonuniform heating quenching, the maximum stress decreases by 25% from 286 MPa to 214 MPa after the first tempering and by about 46% after the second tempering. This tempering effect is mainly caused by creep, whereas the transformation factors only slightly affect the result. Therefore, it is important to consider creep in the analysis.

Fatigue Failure Analysis for Bimetallic Work Roll in Hot Strip Mills

“…Then, the rolling stress analysis is carried out. As the detail of the residual stress analysis is indicated in the previous paper, [ 30–33 ] this section mainly focuses on the method of rolling stress analysis. In this study, the fatigue of the work roll is focused as the fatigue failure of the backup roll hardly happens.…”

“…The direct constrain method is used for contact analysis between work roll and backup roll. In this study, the previous residual stress analysis [ 30–33 ] described in Appendix A is extended to rolling stress analysis. First, the same simulation is carried out using 3D modeling in Figure 4 instead of the axisymmetric FEM modelling used in the previous study.…”

“…In this study, the roll residual stress is considered as an initial condition of the rolling stress analysis. As the detail of the residual stress simulation is described in the previous papers, [ 30–33 ] the outline of residual stress simulation is briefly introduced in the Appendix A. In roll companies, the surface residual stress of the roll is always confirmed after tempering the roll using the nondestructive inspections such as X‐ray diffraction method and ultrasonic method.…”

“…The tensile stress which may cause debonding is almost constant along the z ‐direction. These residual stresses can be analyzed considering two tempering processes as described details in previous studies [ 30–33 ] using the axisymmetric FEM model.…”

“…In our recent studies, the residual stress was discussed by analyzing quenching and tempering as the appropriate compressive residual stress prevents thermal cracking at the roll surface. [ 30–33 ] In this article, therefore, after analyzing the residual stress, the rolling stress will be clarified by applying the rolling analysis where the work roll and the backup roll are subjected to the total rolling force as shown in Figure 1. [ 34,35 ] Then, the risk of internal fatigue fracture will be discussed by considering the fatigue of the roll material by focusing on some critical points empirically known.…”