Study On Mechanism And Control Of Porosity Defect Of Large Bar Rolling

With rapid development of computer technology and increasingly drastic market The internal defect of big bar is the main reason to cause quality problems of end-products. Porous defects like holes at core and cracks are the main defect forms of big bar. The porous defect at core of big bar is a problem very frequently occurred during production, which influences products quality seriously.In this paper, the reason to cause porous defects at core of bar is analysed systematically, and the theoretical and experimental research on control of hydrogen content in the molten steel and rolling process are carried out.The relative density is introduced firstly as indirect token of discrete distributed porous defects in the inner of bar, and volume compressible rigid-plastic finite element method is used to simulate the change of relative density at core of bar.The finite element simulation thermal-dynamic coupling model is established aiming at the actual situation of plant site, and the reliability of the model is verified through the analysis of data measured during rolling process.The rule of influence caused by process parameters, such as temperature, density, reduction, rolling speed, friction, etc., to pressing effect of porous defects at core of bar and thermaldynamics mechanism to improve pressing effect are revealed via the experimental simulation through changing parameter values, which provides theoretical basis for setting rolling process and optimization.The analysis on control of VD refining furnace is performed, and the influence of vacuum time, argon-blowing intensity and slag thickness to hydrogen content is discussed, and the control process of hydrogen content for vacuum treatment in Shigang is defined consequently, and finally high quality bloom is supplied for rolling of big bar.The utmost dimension of porous defects at bar core that can be pressed under certain rolling process is researched by simulation in order to analyse max.porous defects allowed for rolling stock but later can be pressed through rolling, and provide basis for judgement of stock quality. The optimization to existing rolling process is made according to actual situation of plant site in Shigang, and the simulation result shows that the quality of bar core is improved obviously. The existing rolling process is improved on the basis of the optimized process, and the production practice indicates that the porous defect of big bar is effectively controlled, and the practicality and reliability of improved process are verified as right solution.