Bimetallic Roll Research Articles

Fatigue failure risk evaluation of bimetallic rolls in four‐high hot rolling mills

AbstractIn 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.

Fatigue Failure Analysis for Bimetallic Work Roll in Hot Strip Mills

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.

Effect of Conductive Circuits on Bonding Quality of Bimetallic Composite Roll Produced by Electroslag Remelting Cladding

Effect of Conductive Circuits on Bonding Quality of Bimetallic Composite Roll Produced by Electroslag Remelting Cladding

Tempering effect on residual stress in bimetallic roll

In this study, tempering effect on the residual stress is studied after uniform heating–quenching and nonuniform heating–quenching for bimetallic work roll. Results for uniform heating treatment showed that the maximum stress at the center decreases by 68% from 396 MPa to 126 MPa after the first and second tempering. Results for nonuniform heating treatment showed that the maximum stress at the center decreases by 47% from 309 MPa to 165 MPa after the first and second tempering. It may be concluded that nonuniform heating–quenching and tempering are useful for reducing the central tensile stress preventing cracks at the roll surface.

Solid-state phase transformation of ductile cast iron during electroslag remelting cladding

ABSTRACT A bimetallic composite roll with the cladding layer of high-speed steel (HSS) and the roll core of ductile cast iron (DCI) was manufactured by the electroslag remelting cladding (ESRC) technology, and the changes in the graphite morphology, matrix structure, and mechanical properties of the DCI core before and after the ESRC process were compared. The DCI core was first heated to a very high temperature and then cooled down to room temperature during ESRC which led to a deteriorative graphite morphology with a low spheroidisation rate, a large size, and a nonuniform distribution and also caused a solid-state phase transformation of the matrix structure from lamellar pearlite + few carbides to bainite + large amounts of carbides. Based on the changes of graphite sphericity, matrix structure, carbides content, the tensile strength and impact toughness of DCI before and after the ESRC process changed from 458 MPa, 3.02 J/cm2 to 417 MPa, 5.74 J/cm2, respectively.

Reduction of Residual Stress in Bimetallic Work Roll by Tempering

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 bycreep, whereas the transformation factors only slightly affect the result. Therefore, it is important to consider creep in the analysis.

Residual Stress Differences between Uniform and Non-Uniform Heating Treatment of Bimetallic Roll: Effect of Creep Behavior on Residual Stress

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.

Effect of tempering treatment upon the residual stress of bimetallic roll

Bimetallic rolls are widely used in steel rolling industries because of the excellent hardness, wear resistance, and high temperature properties. However, thermal stress is produced by heating-cooling thermal cycles, which is a great challenge for their practical application. Indeed, if severe thermal tensile stress is introduced into these rolls, it can assist the thermal cracks to propagate, even lead to the overall failure of rolls. In this paper, we investigated the effect of tempering treatment on the residual stress after the bimetallic rolls were subjected to quenching. Compared with the non-uniform heating-quenching process, the tempering process makes the maximum stress at the core decreased by 15% (from 275 MPa to 234 MPa) with considering martensite transformation but decreased by 26% (from 275 MPa to 201 MPa) without considering martensite transformation. For tempering process after uniform heating quenching, the maximum stress at the core decreases by 24% from 357 MPa to 273 MPa with considering martensite transformation but decreases by 30% from 357 MPa to 246 MPa without considering martensite transformation. And compared with the non-uniform heating-quenching process, the double tempering process makes the maximum stress at the core decreased by 8% (from 275 MPa to 253 MPa) with considering martensite transformation but decreased by 27% (from 275 MPa to 200 MPa) without considering martensite transformation.

複合ロールの残留応力に及ぼす熱処理条件およびロール直径の影響

複合ロールの残留応力に及ぼす熱処理条件およびロール直径の影響

Evaluation of Thermal Breakage in Bimetallic Work Roll Considering Heat Treated Residual Stress Combined with Thermal Stress during Hot Rolling

Bimetallic rolls are widely used in steel rolling industry because of their excellent hardness, wear resistance, and high temperature properties. Heat treated residual stresses consist of compressive stress in the shell and tensile stress in the core are produced in the bimetallic roll during heat treatment. In the subsequent hot rolling process, severe thermal stresses are caused by heating‐cooling thermal cycles at the roll surface. The combination of heat treated residual stresses and thermal stresses will cause a complex stress field in work roll during hot rolling process. The high combined tensile stress at the roll center may cause thermal breakage, once the tensile stress exceeds the material strength. Consequently, it is necessary to investigate the combined stresses to improve roll service life during hot rolling process. In this paper, the combined stresses in the work roll during hot rolling are investigated based on the FEM simulation, considering the heat treated residual stress after tempering process and thermal stress generated during hot rolling. In addition, the thermal breakage of work roll is evaluated in breakdown of water cooling systems and rolling incidents.

Usefulness of Non-Uniform Heating and Quenching Method for Residual Stress of Bimetallic Roll: FEM Simulation Considering Creep Behavior

Bimetallic rolls are widely used in steel rolling industries because of the excellent hardness, wear resistance, and high temperature properties. Controlling the residual stress distribution is important to improve the roll fatigue life due to the compressive residual stress at the roll surface. Recently, to reduce the tensile residual stress appearing at the roll center, quenching heat treatment is performed just after heating the roll non-uniformly instead of heating the roll uniformly with enough time. In this paper, therefore, the residual stresses are compared after between the uniform heating quenching and the non-uniform heating quenching on the basis of the FEM simulation. The results show that tensile stresses at the roll center for non-uniform heating are smaller than that for uniform heating by 400 MPa, although the same compressive stresses appear at the surface. The effect of creep on stress relaxation is also considered in this study. By considering creep, the maximum tensile residual stress decreases by 8% for uniform heating and by 15% for non-uniform heating.

Residual Stress Simulation for Hot Strip Bimetallic Roll during Quenching

Bimetallic rolls are widely used in hot rolling mills because of excellent hardness, wear resistance, and high temperature properties. Considerable residual stresses are produced for the bimetallic roll during quenching. Moreover, severe thermal stresses are caused by heating-cooling thermal cycles during subsequent hot rolling process. Fracture from the roll center may occur due to the residual stress adding to the thermal stress, and therefore, it is desirable to investigate the residual stress to improve roll service life. Therefore, FEM simulation of the bimetallic roll is performed for the quenching process. It should be noted that a large number of experimental data of the core and shell material are utilized for the wide range of temperature considering the quenching. The generation mechanism for the residual stress is discussed focusing on the effect of temperature gradient and phase transformation. Furthermore, the effects of shell–core ratio and diameter on residual stress are considered. Results show that the residual stress only slightly increases with increasing shell–core ratio, while significantly increases with increasing diameter.

FE modeling of the cooling and tempering steps of bimetallic rolling mill rolls

Numerical simulations enable the analysis of the stress and strain histories of bimetallic rolling mill rolls. The history of rolling mill rolls is simulated by thermo-mechanical metallurgical finite element code while considering two steps: post-casting cooling and subsequent tempering heat treatment. The model requires a notably large set of material parameters. For different phases and temperatures, Young modulus, yield limit and tangent plastic modulus are determined through compression tests. Rupture stresses and strains are obtained by tensile tests. Thermo-physical parameters are measured by such experimental methods as dilatometry, DSC (Differential Scanning Calorimetry) and Laser Flash methods. Such parameters as the transformation plasticity coefficients for the ferrite, pearlite and martensite phases are identified through an inverse method. From the simulation results, the profile of the stresses evolution at different critical times is presented. An analysis of the potential damage is proposed by comparing the predicted axial stress with rupture stresses. The perspective of the Ghosh and McClintock damage criteria is also investigated.

Численное моделирование температурно-структурного состояния биметаллического прокатного валка в процессе его наплавки

Численное моделирование температурно-структурного состояния биметаллического прокатного валка в процессе его наплавки

Study of Residual Stresses in Bimetallic Work Rolls

An experimental campaign of compression tests, differential thermal analysis (DTA), differential scanning calorimetry (DSC), dilatometry and microstructure analysis has been performed, as well as the identification of the material data set for finite element (FE) analysis of bimetallic rolls. This article numerically investigates the stress and strain fields after the cooling stage and it checks their effect on the subsequent heat treatment step. As bimetallic rolls have a different material for core and shell, the effect of the roll size and the shell thickness on residual stresses is also studied.

Comparative Analysis of the Durability of Solid-Forged and Bimetallic Backup Rolls on Rolling Mills

A method has been developed for evaluating the durability of large solid-forged and bimetallic backup rolls on rolling mills with allowance for the residual stresses from heat treatment. Results are presented from a numerical study performed for a 600/1350 × 1420 four-high mill. The stresses created in the rolling operation are determined by solving a three-dimensional contact problem in the finite-element program ANSYS. The service life of the rolls is determined by calculating their durability in a deterministic formulation. The calculation is performed with the use of the Paris equation to describe the linear section of the kinetic diagram that characterizes fatigue fracture. It is shown that hard-faced bimetallic rolls subjected to carbide-intermetallide hardening last roughly twice as long as solid-forged rolls made of traditional low-alloy roll steels.

Research on the Interface Bonding Conditions of Bimetallic Rolls Manufactured by Liquid-Solid Bonding Method

Bimetallic rolls’ interfaces manufactured by liquid-solid bonding method have been studied in the manuscript. Effect of pretreatment method of roll core, pouring temperature and preheating temperature of core to the bonding of interfaces are analyzed. Line scanning to the element chromium is done with SEM, the effect of technology to the organize structure and element diffusion is researched; Shear stress experiment of interface is done to analyze the effect of technology to bond strength.

Theoretical and experimental analysis of the rolling process of bimetallic rods Cu-steel and Cu-Al

In this study, the authors present the results of their theoretical and experimental analysis of the rolling process of bimetallic rods in stretching passes. The bimetallic rods had different ratios of the yield stress between components. The original rods were round (21.7mm diameter) steel and aluminium rods, covered with 2.8mm copper layer. A numerical model for hot stretching passes rolling was proposed. In the model, the deformation of a bimetallic material was analysed by three-dimensional rigid–plastic finite-element method. The model simulated metal flow during rolling of bimetallic rods in round–oval series. The results of the experiments were compared with the finite-element calculations of the stress distribution and spread of Cu-steel and Cu-Al rods in the deformation zone. The analysis demonstrated that an appropriate selection of shape and size of oval pass allows production of even distribution of the copper layer in the bimetallic roll products. The results of comparison of calculated spread and experimental data confirmed good ability of proposed mathematical model, that is recommended for roll pass design at rolling of bimetallic rods.

Study of the high strenght steel- nodular iron interphase developed in bimetallic rolls produced by centrifugal casting

The interphase of bimetallic rolling rolls produced by centrifugal casting using a high speed steel to make the shell and a ductile gray iron for the core was studied. During the manufacturing method and especilly in the course of the slow cooling before demoulding and also during the characteristic long heat treatments always necessary, diffusion phenomena of both, carbon from the core to the shell, and of the shell alloying elements in the oposite direction, take place, giving different micostructures which can reduce the strength of the interphase. A metallographic analisys, using optical and electronic microscopies, was performed and, as a result of it, a highly decarburized region in the vicinity of the core and a very hard and brittle adyacent zone with an important accumulation of different carbides are the most relevant microstructural results.

New generation of wear-resistant bimetallic rolls for sheet mills

The Gontermann-Peipers Company has been a leading producer of different types of rolling-mill rolls for more than 100 years. The firm was studying the feasibility of using high-chromium steel to make rolls as early as the beginning of the 1960s. This material subsequently became the main material for making the work rolls and, later, the backup rolls of hot- and cold-rolled sheet and plate mills.