Research On Damage Model In High Temperature And Prediction Of The Fracture In Extra-heavy Backup Roll Forging

Heavy backup roll is a key part of steckel mill, therefore it needs high reliability during theperiod of enlistment. The heating and the stressing state of the workpiece is quite complicated in theforging process, easily resulting defects such as cracks，which will cause scrape of the wholeworkpiece. This paper focuses on studying the formation mechanism and evolution of crack, andpredicting it, then directing process design and optimization. The work is one of the important topicsin the field of plastic forming. Ductile fracture criterion is of great significance to predicting internaldamage which occurs in the process of metal forging.The paper focus on the damage model in high temperature and prediction of the fracture inextra-heavy backup roll forging. Tensile specimens of45Cr4NiMoV steel were prepared throughmachining. The specimens were stretched through Gleeble-1500D with different temperature anddifferent strain rate to obtain true stress-strain curve of45Cr4NiMoVsteel, from which the finaltensile strengthσ UTS, ultimate tensile true stressσ limitand true strainε limitwere obtained.By adding Zener-Hollomon parameter, a new damage model in high temperature is createdwhich base on the Normalized Cockcroft&Latham damage model. A strain rate parameter fortemperature compensation, impact of temperature and strain rate on the damage threshold wasoverall considered. Then,45Cr4NiMoV steel hot deformation essence was studied, that it was aprocess controlled by hot activation energy.Based on the Deform-3D finite element platform, finite element model was created to simulatebackup roll forging process included upsetting, stretching and quartet hammering to octagon with45Cr4NiMoV steel. The changes of temperature, equivalent stress and strain, and principle stressduring the process were analyzed, also, damage value changes of the backup roll during the process were predicted. The model calculation and predication show good agreement with the experimentalresults. As a result, it can provide parameter reference for preparing backup roll forging procedure.According to Normalized Cockcroft&Latham damage model and Gleeble Fracture Limitmethod, this paper presents exploratory research on damage through heavy backup roll forging with45Cr4NiMoV steel. The research provides important basis for improving quality and performance ofbackup roll.