Fundamental Research On Chamfered Mold Applied In The Production Of Special Steel Bloom

In view of 320mm×280mm special steel bloom,according to actual production conditions,the solidification heat transfer models of right-angle bloom and chamfered bloom were established respectively,and the similarities and differences of temperature field distribution were calculated and analyzed.The corner temperature changes of bloom under different shapes were studied.The therm-mechanics coupling models of right-angle bloom and chamfered bloom under soft reduction were established respectively,and the effects of different types of soft reduction on the stress change process of bloom were studied.The surface temperature of right-angle bloom and chamfered bloom in straightening section and the macrostructure of transverse and longitudinal section were studied.The main conclusions are as follows.(1)During solidification of chamfered bloom,the corner temperature is higher than that of right-angle bloom.After cooling inside the mold,i.e.0.8m from the liquid level of the mold,the minimum value of the corner temperature of the right-angle bloom is 975?,and the minimum value of the corner temperature of the chamfered bloom is 1037?.After the secondary cooling,i.e.at 10.31 m from the liquid level of the mold,the corner temperature of the right-angle bloom is 888?,and the corner temperature of the chamfered bloom is 923?.At the end of air cooling,i.e.29.31 m away from the liquid level of the mold,the minimum value of the corner temperature of the right-angle bloom is 723?,and the corner temperature of the chamfered bloom is 766?.(2)The corner temperature of the bloom increases with the length of chamfer surface increasing while the chamfer angle remains unchanged at 35°.With the increases of chamfer angle,the bloom angle temperature increases at first point and then decreases,while the chamfer surface length remains unchanged at 50 mm.(3)When the total pressure reduction of 13.5mm(2mm,3mm,3.5mm,3mm,2mm)in Scheme A is applied,the maximum equivalent stress at the corner appears at the position of No.3 roller,which the right-angle bloom and chamfered bloom are 42 MPa and 36 MPa,respectively.When the total pressure reduction of 11.5mm(3mm,3.5mm,3mm,2mm)in Scheme B is applied,the maximum equivalent stress at the corner appears at the position of No.3 roller,which the right-angle bloom and chamfered bloom are 37 MPa and 34 MPa,respectively.(4)During the soft reduction,the normal stress at the solidification front of the central region of the chamfered bloom is greater than that of the right-angle bloom.The pressing process has a stronger supplementary effect on the solidification shrinkage of the liquid core of the chamfered bloom,and the improvement on the central segregation of the chamfered bloom is better than that of the right-angle bloom.The distance of 50~70mm from the upper and lower surfaces of the bloom is the concentrated area of shear stress,which is easy to produce cracks.(5)When facing the same reduction(3mm,3.5mm,2.9mm,2mm),the pressure of chamfered bloom at No.1~4 roller is 0.48 MPa,1.23 MPa,0.57 MPa,1.66 MPa lower than that of right-angle bloom respectively.The temperature measurement results show that the difference between the right-angle bloom and the chamfered bloom at the corner of the straightening section is 60?.During the test,the corners of the finished chamfered blooms have no cracks.The distribution range of center segregation of 40 K chamfered blooms are smaller than that of right-angle blooms.V-shaped segregation on the longitudinal section of 82 B chamfer bloom is improved,and the number of central shrinkage cavities in segregation zone of V-shaped segregation of 82 B steel chamfered bloom is less than that of right-angle bloom.