The work roll is one of the most important tools in the steel rolling industry. Work rolls are used under extremely severe conditions such as high temperature, high loading, and an aggressive atmosphere. To meet those demands, bimetallic rolls have recently been used to replace conventional single material rolls. Usually, a compressive residual stress is introduced to prevent surface cracking. However, a tensile residual stress at the center appears to balance the compressive residual stress. This center residual stress sometimes causes roll failure. In this paper, therefore, a simulation is performed using the finite element method (FEM) for the quenching process of the bimetallic roll by considering the creep behavior. Then the effect of pre-heating conditions is discussed. The results show that the maximum stress point for the tensile stress at the roll center for non-uniform heating is 24% less than that achieved with uniform heating, although the same compressive stresses appear at the surface. Then, using different work roll diameters, the center tensile residual stress for non-uniform heating is found to be smaller than the uniform heating. Also, it is found that the area ratios of the shell-core only have a small influence on the residual stress of the bimetallic roll for both heating treatments.

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.

In hot rolling of steels, bimetallic rolls consisting of high‐speed steel and ductile casting iron are extensively used because of their excellent hardness and wear resistance although the fatigue failure study is not available. To extend the roll life service, herein, a 3D finite element method is applied to investigate the residual stress and the rolling stress of the bimetallic work roll in the four‐high rolling mill. The residual stress is analyzed by considering preheating, quenching, and tempering. Using the results as an initial condition, the rolling stress analysis is carried out consecutively. Then, the fatigue failure risk is discussed focusing on several critical points subjected to the largest stress amplitude inside of the work roll. The accuracy of the simple superposition method is also discussed to evaluate the risk conveniently.

In this paper, the complex variable function method is used to obtain the hypersingular integral equations for the interaction between straight and curved cracks problem in plane elasticity. The curved length coordinate method and suitable quadrature rule are used to solve the integrals for the unknown function, which are later used to evaluate the stress intensity factor, SIF. Three types of stress modes are presented for the numerical results.

In hot rolling mills, bimetallic rolls are used because of the excellent hardness and wear resistance by applying high‐speed steel (HSS) and ductile casting iron (DCI). Because most of the previous studies focused on surface spalling, almost no study is available for internal fatigue failure based on the stress during the rolling. In this study, therefore, a three‐dimensional finite element method is applied to investigate the rolling stress of the work roll in the four‐high rolling mill. A suitable chamfer geometry in the backup roll is discussed as well as the standard wear profile by considering those effects on the fatigue. Then, to evaluate the fatigue risk under compressive mean stress, the fatigue limit lines in the stress amplitude versus mean stress diagram are newly discussed. With the aid of previous experience in industries, the fatigue fracture risk is discussed by focusing on three critical points inside the work roll.