Simulation of the behaviour of voids in steel plates during hot rolling

Abstract

The prime objective of the work is to predict the behaviour of voids in the steel slab during hot rolling and to assess the tendency of the void to closure, depending on the process parameters. The rigid-plastic thermal-mechanical finite-element program is used for the purpose. The model which simulates the general case of deformation of a single void in a matrix undergoing plastic deformation is developed. This model allows the investigation of the influence of the stress state on the void's behaviour. Finite element calculations carried out for the industrial hot plate rolling process supply information regarding the stress state during rolling depending on the process technological parameters. These data are used as boundary conditions in the void's closure model and, in consequence, allow the analysis of the influence of rolling technology on the void's behaviour. Simulation des Porenverhaltens in Stahlgrobblechen wahrend des Warmwalzens. Hauptanliegen dieser Arbeit ist die Vorhersage des Verhaltens von Poren in Stahlbrammen beim Warmwalzen. Hierzu gehbrt auch die Absehatzunq des PorenverschweiBens in Abhangigkeit von den ProzeBparametern. Hierzu wird das starr-plastische Finite-Elemente-Programm herangezogen. Das Modell wird fOr den allgemeinen Fall -plastische Umformung einer Matrix mit einer einzelnen Pore -entwickelt. Das Modell ermbglicht die Untersuchung des Einflusses des Spannungszustandes auf das Porenverhalten. Finite-Elemente-Berechnungen fOr das Warmwa)zen von Grobblechen im industriellen MaBstab liefern Informationen Ober den Spannungszustand wahrsnd des Walzens in Abhangigkeit von den technologischen ProzeBparametern. Diese Daten gehen als Randbedingungen in das Modell der PorenverschweiBung ein. Auf diese Weise ermbglichen sie die Analyse des Einflusses der Walztechnologie auf das Porenverhalten.

A geometry-dependent model for void closure in hot metal forming

“…It is explained by the fact that the temperature gradient induces more compressive stress states in the bulk of workpieces. Pietrzyk et al [12] confirmed the favourable effect of pre-cooling workpieces in hot rolling. Överstam and Jarl [10] also pointed out a coupled effect between friction and temperature regarding their effect on void closure.…”

“…As a consequence, the values of closure coefficients B (respectively coefficients C) are given by a linear combination of bðγ 1 Þ, bðγ 2 Þ and bðγ 3 Þ (respectively cðγ 1 Þ, cðγ 2 Þ and cðγ 3 Þ), according to Eq. (12).…”

“…However, this agreement decreases when deformation increases. Using the Zhang model, the prediction leads to a L 2 -norm error on the range [7][8][9][10][11][12][13][14][15][16][17]%, while it is on the range [3-9]% for the new proposed model. The error is mainly due to the analytical function that is expressed to model the void volume evolution during deformation.…”

Split Ends and Cracking Problem During Hot Rolling of Continuously Cast Steel Billets

“…The slab and/or the sheet in the roll gap were divided into three zones, and different kinematical admissible velocity fields were assumed for each zone. Pietrzick et al [15] used a rigid-plastic thermalmechanical finite-element program to examine the behavior of voids inside a steel slab during hot rolling and to assess the tendency of void closure. The effect of void shapes round and rectangular was studied by Dyi-Cheng Chen and Yeong-Maw Hwang [16].…”

Theoretical study of void closure in nonlinear plastic materials

“…Various methods, such as upper bound analysis [2][3][4][5] , finite element method [1,[6][7][8][9][10][11][12] and experimental investigation [12][13][14] are used to develop predictive measures for void closure during forging and rolling processes. In these studies, a few macroscopic voids are often introduced to analyze the deformation of voids.…”