Effect Of Breakdown Rolling Process Of Bearing Steel On Core Void Closure

Bearing steel with high and uniform hardness,wear resistance and high elastic limit is widely used in electric power,metallurgical engineering,shipbuilding,aerospace,national defense and military industry,construction engineering and other fields.Bearing steel usually works under the extreme conditions of high temperature,high load and high cycles,so it has extremely strict requirements for the quality of bearing steel.The core void defect is the main reason for the unqualified flaw detection of large bearing steel bar.In this paper,the finite element analysis software Marc /Super Form is used to analyze the three-dimensional modeling of bearing steel large bar breakdown rolling process.Through the simulation analysis of different rolling schedule,different billet initial temperature,different descaling treatment before rolling and different roll diameter,in order to improve the deep permeability of deformation and the effect of void closure,the cross-section deformation,equivalent strain,void closure condition and temperature field of rolled bar in each pass were studied.It is of great practical significance to improve the quality of the core of bearing steel bar and the optimization of rolling process.The main research contents and conclusions are as follows:(1)Based on the diagnosis of the original 9-pass rolling schedule of bearing steel and the analysis of the deformation and void closure conditions of each pass,it is found that in the existing 9-pass rolling schedule,the value of the closure conditions of the core void of the rolled piece in the first few passes of rough rolling is low,the void closure ability of the core is poor,the strain does not penetrate into the core,and the void type defects of the core can not be improved.(2)The results show that the porosity defects in the center of the rolled piece can be improved by the two modified schedules,but the maximum rolling force of the 7-pass schedule is higher than that of the roughing mill.(3)The influence of these factors on the strain depth and void closure condition of the rolling parts is analyzed by the finite element simulation by changing the initial rolling temperature,descaling condition before rolling and roll diameter.It is concluded that the porosity defects in the core of the rolling parts can be improved by increasing the initial temperature of the rolling piece,setting the high pressure water descaling,increasing the descaling time and increasing the roll diameter.(4)It is found that the qualified rate of flaw detection can reach more than 95%when the intermediate billet produced by the optimized process plan is used to produce the subsequent bearing steel bar,which proves the rationality of the process plan optimization.