The thermal and metallurgical state of steel strip during hot rolling: Part II. Factors influencing rolling loads
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INTRODUCTION
IN the finishing train of a hot-strip mill for rolling steel, the transfer bar from the roughing mill is reduced in thickness to the final gage in successive stands. Of paramount importance in this operation are the shape and gage control during roiling and the concomitant changes in microstructure which determine the final mechanical properties. Deformation of the steel in the roll bite provides the driving force for microstructural change and also has a profound influence on the shape and gage of the product. The driving force for structure-modifying metallurgical phenomena, such as dynamic or static recovery and recrystallization, is the strain imparted by the deformation, the distribution of which is characterized by the reduction per pass, the rolling speed, the temperature distribution, and the steel composition. These variables also strongly influence the roll forces which, together with the design of the roll stand and the associated control systems, have an effect on gage variations and the shape of the product. II.
LITERATURE REVIEW
Of the parameters that influence deformation resistance, temperature is particularly important, because the flow stress of steel is exponentially dependent on temperature. Despite its importance, very few attempts have been made to quantify the temperature distribution in the C. DEVADAS, formerly Graduate Student, The Centre for Metallurgical Process Engineering, The University of British Columbia, is Research Engineer, Comalco Research Centre, Melbourne, Victoria 3074, Australia. D. BARAGAR and G. RUDDLE, Research Scientists, are with CANMET, Metals Technology Laboratory, Ottawa, ON KIA 0GI. I.V. SAMARASEKERA, Professor, The Centre for Metallurgical Process Engineering, and E.B. HAWBOLT, Professor, Department of Metals and Materials Engineering, are with The University of British Columbia, Vancouver, BC V6T lW5 Canada. Manuscript submitted September 5, 1989. METALLURGICAL TRANSACTIONS A
rolled steel during contact in the roll bite. This is because of the difficulty of making measurements during industrial rolling. As a result, the roll/strip interface heattransfer coefficient has not been adequately characterized, as was reported in an earlier paper, m The theories proposed for predicting roll forces have, in general, assumed an average temperature within the roll bite or an average temperature through the thickness at any location within the roll bite for the purpose of calculating flow stress. I2,3,4] The Sims 14] model is one of the most widely used; it is based on the assumption of sticking friction at the interface and homogeneous deformation. The Sims equation utilizes an average value for the flow stress in the roll bite. Application of Sims' equation to industrial rolling was facilitated.by Cook and McCrum, tS] who developed charts for computing the geometric factors that appeared in Sims' original formulation. Alexander, t6j on the other hand, facilitated the application of Orowan's t3] formulation by developing a numerical solution for the basic equ
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