Evolution of the microstructure in the hot rolling process

Pietrzyk, M.; Kędzierski, Z.; Kusiak, H.; Madej, W.; Lenard, John

doi:10.1002/srin.199301570

Cited by 12 publications

(7 citation statements)

References 7 publications

(3 reference statements)

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“…This phenomenon is particularly noteworthy when thick material is rolled with smaller reduction ratio, which generally occurs in rough rolling sequence of plate mill. Researchers [2][3][4][5][6] studying hot flat rolling process have paid attention to this strong non-homogeneity of local strain variation over material thickness since austenite grain size varies over the material thickness to a great extent due to different volume fractions re-crystallized by non-homogeneous local strain variation over thickness. 7) Note the grain size is influenced by not only the amount of strain but also strain rate, temperature and interpass time between passes.…”

Section: Introductionmentioning

confidence: 99%

An Approximate Model for Local Strain Variation over Material Thickness and Its Applications to Thick Plate Rolling Process

Moon

Lee

2009

ISIJ Int.

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This paper presents a three-parameter approximate model which computes the local strain variation over thickness direction of thick material in the roll gap. The three parameters were determined through finite element analysis. With the proposed model, we then carried out a series of plate rolling simulation to examine the effect of the arithmetic average aspect ratio (ratio of contact length between work roll and material to mean material thickness in the roll gap) and reduction ratio on the local strain variation over material thickness as material goes through rolling at many passes.Results reveal that a certain amount of relative difference between local strain at center and that at surface always exists as arithmetic average aspect ratio increases for whole plate rolling process. It also shows that the magnitude of local strain at material center is only 69 % of that at surface during rolling no matter how we regulate incoming material thickness, radius of work roll, reduction ratio, roll speed and friction condition when arithmetic average aspect ratio is greater than 1.0. It has been found that the heavy reduction with arithmetic average aspect ratio, 0.9 might be an optimum condition for refining grain size over material thickness in an approximately uniform manner.KEY WORDS: local strain variation; material thickness; arithmetic average aspect ratio; peening effect; plate rolling.ables such as roll diameter, material dimension, frictional condition and roll speed are changed. Hence, practical use of the kinematic strain model was quite limited.Kim and Hwang 13) developed a data regression-based model to calculate the local strain variation over thickness of strip. Their model took into account the effect of the process variables mentioned above. Five parameters in their model were determined from FE simulation of strip rolling. Since their model has many parameters it gives high prediction accuracy as far as it is applied to the finishing stands in strip rolling mill. However, their model becomes problematic to be applied to the rough rolling sequence of plate mill where the thickness of material is about 7-8 times larger than that strip thickness.In this paper, we propose a three-parameter approximate model which computes the local strain behavior over thickness direction of thick material during rolling. Each parameter in the proposed model is expressed in terms of process variables such as roll speed, incoming thickness of material, its outgoing thickness, radius of work roll and contact length. The three parameters are determined through finite element simulation of plate rolling. The model proposed in this study is especially useful when the contact length-roll gap ratio, l d /H m is low, say, less than 1.0. The rough rolling sequence of an actual plate mill usually has low value of contact length-roll gap ratio.We then carried out a series of numerical analysis to investigate the effect of the process variables on the amount of local strain variation over material thickness. We also studied how th...

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Section: Introductionmentioning

confidence: 99%

An Approximate Model for Local Strain Variation over Material Thickness and Its Applications to Thick Plate Rolling Process

Moon

Lee

2009

ISIJ Int.

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“…In consequence, the thermalmechanical-microstructural model is developed; this model has been validated experimentally in the laboratory conditions and, finally, has been applied to the simulation of hot rolling [6,10] and forging [I 11 processes and proved to be very helpful in designing the technological parameters. Microstructural component of the model has been validated experimentally in a number of rolling and forging tests [10,12]. Fig.…”

Section: Conventional Approachmentioning

confidence: 99%

“…1 that the calculated austenite grain size is within the standard deviation of the measurements. A larger number of results and the microstructures for all the experiments are given in [12].…”

Section: Conventional Approachmentioning

confidence: 99%

“…Presented results show the ability of the model to design the optimum rolling technology taking the microstructure and the properties of the product in the consideration. Experimental validation of the model [10, 12,14] showed its very good predictive ability for normal hot forming conditions. It was, however, observed during the investigation that the model fails for the critical conditions such as forming in the temperature close to the transformation temperature or applying the deformations close to the critical for the static recrystallization.…”

Section: Conventional Approachmentioning

confidence: 99%

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Numerical simulation of strain hardening and recrystallization in the hot forming processes

Pietrzyk

1993

J. Phys. IV France

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Recent developments for the finite-element modelling of the plastic forming of the metallic materials are described in the paper. The model consists of three parts; mechanical, thermal and microstructural components. First two are described in earlier publication and the focus here is put on the modelling of the microstructural phenomena. Two approaches are described. First uses conventional closed-form equations describing processes of recrystallization and grain growth. Second employs three differential equations giving time derivatives of the dislocation density, recrystallized volume fraction and the grain size.

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“…Authors' solutions for bulk forming processes have been validated experimentally in the thermal and mechanical parts for the compression [4;5], rolling [6] and drawing [7] processes and their good predictive ability has been confirmed. Some experiments including measurements of grain size have also been performed for flat rolling [8] and rolling in grooves [9]. It seems, however, that validation of the microstructural part of the model in the non-stationary process with significantly nonuniform fields of strains and temperatures would be of a special importance.…”

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confidence: 99%

Validation of the thermomechanical microstructural model for closed‐die forging

et al. 1994

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The objective of the paper is the assessment of the predictive ability of the thermomechanical-microstructural model for the closed-die forging process. The model combines the rigid-plastic flow formulation with the finite element solution of the Fourier equation with the closed-form equations describing processes of recrystallization and grain growth. Experimental validation of the mechanical and thermal components of the model is presented in earlier publications; present work focuses on the microstructural part. Experiment includes closed-die forging of the carbon-manganese steel samples and the measurements of the grain size on the cross-sections of the forgings after the deformation. Spherical samples, which involve significant inhomogeneity of the strain and the temperature fields, have been chosen for a presentation of the results. GOltlgkelt eines thermomechanlschenModells fOr das Formschmleden. Gegenstand der vorliegenden Arbeit ist die Bewertung der Genauigkeit von Vorausberechnungen, die ein thermomechanisches Medell !Or das Formschmieden liefert. Dieses Medell verbindet die Formulierung fur starr-plastisches FlieBen, die FE-Losung der Fourier-Gleichung und die Gleichungen, die Rekristallisationsprozesse und Kornwachstum beschreiben. Die Oberpri.ifung der Rechenergebnisse anhand experimenteller Werte sowohl !Or die mechanischen wie die thermischen Komponenten des Modells erfolgte bereits in fri.iheren Veroffentlichungen. Der vorliegende Teil konzentriert sich auf die Mikrostruktur. Versuche umfaBten das Formschmieden von C-Mn-Stahl. Nach erfolgter Formanderung wurde die KorngroBe i.iber dem Querschnitt der geschmiedeten Proben gemessen. Die Ergebnisse werden an kugeligen Proben, die starke lnhomogenitaten in Formanderung und Temperaturfeldern aufwiesen, erlautert.

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Evolution of the microstructure in the hot rolling process

Cited by 12 publications

References 7 publications

An Approximate Model for Local Strain Variation over Material Thickness and Its Applications to Thick Plate Rolling Process

An Approximate Model for Local Strain Variation over Material Thickness and Its Applications to Thick Plate Rolling Process

Numerical simulation of strain hardening and recrystallization in the hot forming processes

Validation of the thermomechanical microstructural model for closed‐die forging

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