A three-dimensional finite element model coupled with heat transfer,shrinkage accumulation and high temperature deformation was established forϕ690 mm round bloom in continuous casting,and it was verified by surface t...A three-dimensional finite element model coupled with heat transfer,shrinkage accumulation and high temperature deformation was established forϕ690 mm round bloom in continuous casting,and it was verified by surface temperature,shell thickness,contour shape and porosity size by measurement.The compensation area of the shrinkage zone increases as the reduction amount increases.The compensation effect by the reduction of the unit with liquid core is about two times higher than others with fully solid matrix at a given reduction amount.A mathematical method to determine the reduction parameters for large-sized round bloom during continuous casting was proposed by the multi-rollers strategy.For theϕ690 mm round bloom,the suitable reduction parameters for Nos.2–6 units are suggested as 15,15,10,10,10 mm with a casting speed of 0.26 m min^(-1)to close the shrinkage with a diameter of about 17.5 mm in average.The industrial test on the reduction of large-sized round bloom for LZ50 steel was carried out.A total amount of 65–70 mm reduction was realized in the bloom for different casting speeds.The maximum diameter of the central porosity is about 16.3 mm in the longitudinal section at the casting speed of 0.24 m min^(-1),and it decreases to 7.3 mm after 65 mm reduction.Meanwhile,the maximum diameter of the central porosity is about 18.7 mm at 0.26 m min^(-1),while it decreases to 4.1 mm by a reduction of 70 mm.Finally,the difference of the solidification end reduction on round bloom and rectangular or square bloom is theoretically compared.Low deformation resistance and high bulge effect were found in round bloom compared to rectangular bloom.According to the results about solidification contraction accumulation and reduction efficiency in round bloom,the suitable reduction zone to control the central porosity during continuous casting is suggested to be 0.5–1.0.展开更多
After the heavy reduction(HR)process was carried out at the solidification end of the continuous casting slab,the austenite grains were refined by recrystallization,which improved the thermoplasticity of the slab.Howe...After the heavy reduction(HR)process was carried out at the solidification end of the continuous casting slab,the austenite grains were refined by recrystallization,which improved the thermoplasticity of the slab.However,the reduction in deformation during the HR process initiated stress concentration at the slab surface,and the crack risk increased.To effectively evaluate the risk of slab surface cracks under these complex conditions,the effect of the HR on the austenite recrystallization and thermoplasticity of a microalloyed slab surface was investigated by 15-pass reduction thermal simulation according to the wide and thick slab continuous casting process.The softening fraction was introduced as a global internal variable to quantitatively analyze various recrystallized re-refined grains.After the critical strain reaches the critical strain of dynamic recrystallization,a variety of recrystallization modes alternately occur.Among them,the contribution rate of dynamic crystallization to the later refinement reaches more than 50%.The contribution rates of static recrystallization and metadynamic recrystallization to grain refinement are almost the same.The thermoplasticity of the slab surface first increases and then decreases with increasing reduction pass.It was verified by transmission electron microscopy that the main reason for the decrease in thermoplasticity is that the dislocation multiplication rate increases,resulting in a sharp increase in stress and a decrease in thermoplasticity.展开更多
基金This work is financially supported by the Fundamental Research Funds for the Central Universities(No.FRF-TP-19-017A3)National Natural Science Foundation of China(No.51874026).
文摘A three-dimensional finite element model coupled with heat transfer,shrinkage accumulation and high temperature deformation was established forϕ690 mm round bloom in continuous casting,and it was verified by surface temperature,shell thickness,contour shape and porosity size by measurement.The compensation area of the shrinkage zone increases as the reduction amount increases.The compensation effect by the reduction of the unit with liquid core is about two times higher than others with fully solid matrix at a given reduction amount.A mathematical method to determine the reduction parameters for large-sized round bloom during continuous casting was proposed by the multi-rollers strategy.For theϕ690 mm round bloom,the suitable reduction parameters for Nos.2–6 units are suggested as 15,15,10,10,10 mm with a casting speed of 0.26 m min^(-1)to close the shrinkage with a diameter of about 17.5 mm in average.The industrial test on the reduction of large-sized round bloom for LZ50 steel was carried out.A total amount of 65–70 mm reduction was realized in the bloom for different casting speeds.The maximum diameter of the central porosity is about 16.3 mm in the longitudinal section at the casting speed of 0.24 m min^(-1),and it decreases to 7.3 mm after 65 mm reduction.Meanwhile,the maximum diameter of the central porosity is about 18.7 mm at 0.26 m min^(-1),while it decreases to 4.1 mm by a reduction of 70 mm.Finally,the difference of the solidification end reduction on round bloom and rectangular or square bloom is theoretically compared.Low deformation resistance and high bulge effect were found in round bloom compared to rectangular bloom.According to the results about solidification contraction accumulation and reduction efficiency in round bloom,the suitable reduction zone to control the central porosity during continuous casting is suggested to be 0.5–1.0.
基金supported by the National Natural Science Foundation of China(51974078)the Applied Basic Research Program of Liaoning Province(2022JH2/101300002,2022JH25/10200003)the Applied Basic Research Program of Liaoning Province,and the State Key Laboratory of Metal Material for Marine Equipment and Application Project(SKLMEA-K202204).
文摘After the heavy reduction(HR)process was carried out at the solidification end of the continuous casting slab,the austenite grains were refined by recrystallization,which improved the thermoplasticity of the slab.However,the reduction in deformation during the HR process initiated stress concentration at the slab surface,and the crack risk increased.To effectively evaluate the risk of slab surface cracks under these complex conditions,the effect of the HR on the austenite recrystallization and thermoplasticity of a microalloyed slab surface was investigated by 15-pass reduction thermal simulation according to the wide and thick slab continuous casting process.The softening fraction was introduced as a global internal variable to quantitatively analyze various recrystallized re-refined grains.After the critical strain reaches the critical strain of dynamic recrystallization,a variety of recrystallization modes alternately occur.Among them,the contribution rate of dynamic crystallization to the later refinement reaches more than 50%.The contribution rates of static recrystallization and metadynamic recrystallization to grain refinement are almost the same.The thermoplasticity of the slab surface first increases and then decreases with increasing reduction pass.It was verified by transmission electron microscopy that the main reason for the decrease in thermoplasticity is that the dislocation multiplication rate increases,resulting in a sharp increase in stress and a decrease in thermoplasticity.
