Phase Transformation And Its Effect On Strip Shape During Hot Finishing Rolling Of Non-oriented Electrical Steel

The non-oriented electrical steel with high added value has high requirements for the shape quality.In the actual production,the dual-phase rolling inevitably occurs during the hot finishing rolling process.There are uneven distribution of temperature,microstructure and properties across the whole width of strip,and also the latent heat released from phase transformation,the heterogeneous internal stress caused by thermal expansion and phase transformation expansion,and the buckling behavior affected by transverse uneven temperature and microstructure.All these factors have effects on hot strip shape,and result in a complex multi-field coupling rolling condition,which greatly increase the difficulty of shape control.The existing austenitic rolling model is difficult to achieve the precise prediction of hot strip shape of non-oriented electrical steel,which easily causes bad shape and unstable rolling.In this paper,the hot finishing rolling of non-oriented electrical steel is taken as the research object.From the thermodynamics experiment to the mathematical modeling and then to the secondary development of finite element simulation,the effects of transverse inhomogeneous temperature and microstructure,latent heat,thermal expansion and phase transformation expansion on the hot strip shape are revealed.The following innovation results have been achieved:(1)The high-temperature constitutive models of non-oriented electrical steel are established based on the dislocation density theory and the Arrhenius equation respectively.They not only reveal the differences between the hardening effect and softening effect in different phase regions from a microcosmic view,but also accurately calculate the deformation resistance and steady-state stress under different deformation conditions in each phase region,which set up the bridge to study the relationship between the microstructure evolution and the mechanical properties for non-oriented electrical steel.(2)The coupled temperature-phase transformation model and the rolls-strip integrated model are established,which are used to reveal the effects of phase transformation and latent heat on the hot finishing rolling strip profile.The transformation kinetics model and the latent heat model obtained from the experimental regression are embedded into the strip temperature model based on the two-dimensional alternating difference method,which realizes the coupling calculation of the temperature field and the phase field and improves the prediction accuracy of the field results of hot strip.Then the calculated field results are programmed as user subroutines into the rolls-strip integrated finite element model to comparatively analyze the effects of phase transformation and latent heat on the hot strip profile.(3)The interstand temperature-displacement coupling model and the rolls-strip integrated model are established,which are used to reveal the effects of thermal expansion and phase transformation expansion on the hot finishing rolling strip profile.The thermal expansion model and the phase transformation expansion model obtained from the experimental regression are programmed as user subroutines into the temperature-displacement coupling model of interstand strip,which calculates the thermal stress and phase transformation stress caused by above expansions.Then the stress results are taken into the rolls-strip integrated finite element model to comparatively analyze the effects of thermal expansion and phase transformation expansion on the hot strip profile.(4)Based on the elastic buckling theory of sheet,the inhomogeneous distribution of mechanical property due to the transverse uneven temperature and microstructure is considered and the effects of temperature and phase transformation on the buckling and post-buckling deformation behaviors are revealed.For the whole-width and local longitudinal wave shapes of strip located at the entrance and exit of stand in dual-phase region,the elastic modulus constant in the buckling theory is replaced by the transverse distribution function of tangent modulus.The effects of temperature and phase transformation on the critical buckling stress,wave length and wave height are analyzed,which improve the buckling theory.