@phdthesis{oai:kyutech.repo.nii.ac.jp:00007733,
 author = {Bin Aridi,  Mohd Radzi},
 month = {2022-07-01},
 note = {1 Introduction||2 Residual stress after the heating quenching treatment of the bimetallic work roll||3 Residual stress after the heating, quenching, and tempering treatment of the bimetallic work roll||4 Rolling stress and fatigue failure during rolling analysis||5 Actual stress and fatigue failure during consecutive rolling analysis||6 Main Conclusion, In hot rolling of steel, high-speed bimetallic work rolls consisting of high-carbon highspeed steel （HSS） for the outer layer and ductile casting iron （DCI） for the inner layer are widely used. To extend the life of the roll, as the roll usage conditions become stricter, such as high-load rolling due to the increased strength of the rolled material, measures against fatigue fracture starting from the inside of the roll such as the HSS/DCI boundary and inner layer are becoming important. Therefore, in this study, the rolling stress during the use of the bimetallic work roll in a 4-high rolling mill is clarified. In particular, based on the fatigue fracture cases that occurred inside the work roll, the risk of fatigue fracture is considered by focusing on some dangerous areas. The risk of fatigue failure in consideration of the residual stress introduced into the rolls is also considered. This paper consists of 6 chapters and is organized as follows. Chapter 1 introduced the bimetallic work roll used in the 4-high rolling mill. Previous research on the development of HSS bimetallic work rolls by improving wear and surface resistance is explained. The manufacturing method, residual stress, and past roll breakage accidents are also summarized. Then, the necessity to clarify the rolling stress when this roll is used in a 4-high rolling mill is explained and the evaluation of the fatigue risk in consideration of the residual stress is also studied. In Chapter 2, an appropriate quenching process is discussed to improve the bimetallic roll quality and increase their strength reliability since the heat treatment can control the residual stress. The data of material properties required for the analysis are clarified, and it is shown that the compressive stress is generated on the roll surface and tensile stress is generated on the roll center after quenching. On the other hand, the residual stress of non-uniform heating quenching is also discussed, in which the rolls are heated uniformly and then rapidly cooled. As a result, the maximum tensile stress of non-uniform heat quenching can be reduced by 20% to 30% from the maximum tensile stress of uniform heat quenching. In addition, the effects of roll diameter and area ratio on residual stress have been clarified. In Chapter 3, the effect of additional heat treatment called tempering after quenching is explained to reduce internal stress. Similar thermo-elasto-plastic finite element simulation is performed in consideration of creep, and the residual stress distribution after the two tempering processes is compared for both uniform heating quenching and non-uniform heating quenching. Reduction of tensile residual stress at the center of the inner layer can be clarified by tempering after uniform heating quenching and non-uniform heating quenching. In this tempering process, the residual stress inside the roll is reduced by stress relaxation due to the creep effect. Chapter 4 focuses on clarifying the rolling stress distribution that fluctuates in response to roll rotation inside the bimetallic work rolls, which has not been studied so far. Normally, bimetallic work rolls are used for rolling by introducing appropriate residual stress by pre-heating, quenching, and tempering heat treatment, but it is considered that the heat treatment conditions differ depending on each roll manufacturer. Therefore, in this chapter, rolling analysis with no residual stress is considered to clarify the mechanical stress. The relationship between the stress amplitude and the fatigue limit under the compressive mean stress, which has not been studied in fatigue so far, is studied and a new fatigue limit line for the compressive stress field as a durability diagram is proposed. Then, concerning past roll fatigue damage cases, fatigue fracture is discussed focusing on three dangerous points in the work roll. Since the maximum stress amplitude is caused by the rolled steel, it can be concluded that the most dangerous point is at the center of the roll axis inside the HSS / DCI boundary. In Chapter 5, in order to evaluate the fatigue fracture risk according to the actual roll, the rolling analysis is generated under the initial condition of having roll residual stress. The risk of internal fatigue fracture is discussed using a similar approach in Chapter 4. In addition, since the consecutive FEM analysis for each roll rotation requires a great deal of time and effort, it is clarified that the accuracy when the residual stress and rolling stress are simply superposed as a simple evaluation method. As a result, it is shown that the superposition method can evaluate the risk of fatigue fracture more safely than the consecutive FEM analysis. It is also shown that when the defect size at the center point of the roll is 5 mm or more, there is a risk of fatigue fracture at the center. Chapter 6 summarizes the main conclusions of this study., 九州工業大学博士学位論文 学位記番号：工博甲第529号 学位授与年月日：令和3年9月24日, 令和3年度},
 school = {九州工業大学},
 title = {Fatigue Failure Analysis of the Bimetallic Work Roll in Four-High Rolling Mill},
 year = {}
}