The effect of mold electromagnetic stirring(M-EMS)on the solidification structure and solute segregation in the continuous casting bloom of U78CrV steel is investigated.The solute distribution in the macroscale is ana...The effect of mold electromagnetic stirring(M-EMS)on the solidification structure and solute segregation in the continuous casting bloom of U78CrV steel is investigated.The solute distribution in the macroscale is analyzed using a carbon–sulfur analyzer and that in the microscale is measured with an electron probe microanalyzer.The Image-J software is applied to analyze the number density and area ratio of segregation spots.The results show that the segregation spots are mainly located in the columnar to equiaxed transition zone and the equiaxed zone,which are enriched with C,Cr,and Mn elements.With the M-EMS applied,the columnar grain inclines to the upstream side.As the current intensity increases,the deflecting angle of columnar grain rises,especially with the current intensity larger than 300 A.Besides,the center segregation shows a declining trend and the area fraction of the equiaxed zone rises clearly.Moreover,it is found that the area ratio and number density of segregation spots increase with the higher current intensity of M-EMS.展开更多
While relationship between fracture mechanism and homogeneous microstructures has been fully understood,relationship between fracture mechanism and inhomogeneous microstructures such as the mesosegregation receives le...While relationship between fracture mechanism and homogeneous microstructures has been fully understood,relationship between fracture mechanism and inhomogeneous microstructures such as the mesosegregation receives less attention as it deserves.Fracture mechanism of the high-strength low-alloy(HSLA)steel considering the mesosegregation was investigated and its corre s ponding micro structure was characterized in this paper.Mesosegregation re fers to the inhomogeneous distribution of alloy elements during casting solidification,and leads to the formation of positive segregation zones(PSZ)and negative segregation zones(NSZ)in ingots.The fracture surface of impact sample exhibits the quasi-cleavage fracture at-21℃,and is divided into ductile and brittle fracture zone.Meanwhile,the PSZ and NSZ spread across ductile and brittle fracture zone randomly.In ductile fracture zone,micro-voids fracture mechanism covers the PSZ and NSZ,and higher deformation degree is shown in the PSZ.In brittle fracture zone,secondary cleavage cracks are observed in both PSZ and NSZ,but present bigger size and higher quantity in the NSZ.However,some regions of the PSZ still present micro-voids fracture mechanism in brittle fracture zone.It reveals that the microstructures in the PSZ exhibit a higher resistance ability to crack propagation than that in the NSZ.All observations above provide a better visualization of the microstructural factors that resist the crack propagation.It is important to map all information regarding the fracture mechanism and mesosegregation to allow for further acceptance and industrial use.展开更多
Thermo-electric currents in the presence of static magnetic fields generate significant electromagnetic forces(TEM forces).The thermo-electric currents are due to the Seebeck effect when temperature gradients exist in...Thermo-electric currents in the presence of static magnetic fields generate significant electromagnetic forces(TEM forces).The thermo-electric currents are due to the Seebeck effect when temperature gradients exist in the material. Those forces may produce various phenomena like pumping,stirring in liquid metals as well as solid motions,stresses in the solid metal.Those effects may be encountered especially during the solidification of metallic materials because of the existence of significant temperature gradients.In liquid metals the application of a static magnetic field enhances TEM convection at moderate intensity but also damps it when it is strong enough.This means that there exists a maximum of the convection which occurs when the Hartmann layers are comparable to the considered length scale.However,the smaller the length scales are(for example when primary or secondary dendrite arm spacings are considered),the higher the magnetic field strength which is needed to damp the TEM convection.So far,many solidification experiments on various types of alloys(e.g.,Sn-Pb,Al-Cu,Al-Si,Al-Ni etc.)have been carried out.The experiments have shown that TEM convection occurs both in the liquid bulk but also in the deep mushy zone.TEM convection may strongly influence the meso-macrosegregation patterns,the solidification structures and the grain boundaries leading to the striking grain boundary structure of the mushy zone.The flow pattern and accordingly the segregations may be controlled by changing the orientation of the applied magnetic field,i.e.,axial or transverse.We have shown that very high magnetic field strengths,up to 16 T,are needed to damp the TEM convection.Heuristic numerical and analytical investigations show that the TEM force density is very important in the liquid,but can be even more important in the solid.Indeed,for high Hartmann number,the electric currents are confined in a small skin layer near the solid boundaries leading to a decay of the flow.However,the situation is different in the solid,sinc展开更多
基金the support from the High Steel Center(HSC),S&T Program of Hebei(No.20311006D)National Natural Science Foundation of China(No.51904024)the Fundamental Research Funds for Central Universities(No.FRF-TP-18-098A1).
文摘The effect of mold electromagnetic stirring(M-EMS)on the solidification structure and solute segregation in the continuous casting bloom of U78CrV steel is investigated.The solute distribution in the macroscale is analyzed using a carbon–sulfur analyzer and that in the microscale is measured with an electron probe microanalyzer.The Image-J software is applied to analyze the number density and area ratio of segregation spots.The results show that the segregation spots are mainly located in the columnar to equiaxed transition zone and the equiaxed zone,which are enriched with C,Cr,and Mn elements.With the M-EMS applied,the columnar grain inclines to the upstream side.As the current intensity increases,the deflecting angle of columnar grain rises,especially with the current intensity larger than 300 A.Besides,the center segregation shows a declining trend and the area fraction of the equiaxed zone rises clearly.Moreover,it is found that the area ratio and number density of segregation spots increase with the higher current intensity of M-EMS.
基金This work was financially supported by the National Natural Science Foundation of China(No.51801126).
文摘While relationship between fracture mechanism and homogeneous microstructures has been fully understood,relationship between fracture mechanism and inhomogeneous microstructures such as the mesosegregation receives less attention as it deserves.Fracture mechanism of the high-strength low-alloy(HSLA)steel considering the mesosegregation was investigated and its corre s ponding micro structure was characterized in this paper.Mesosegregation re fers to the inhomogeneous distribution of alloy elements during casting solidification,and leads to the formation of positive segregation zones(PSZ)and negative segregation zones(NSZ)in ingots.The fracture surface of impact sample exhibits the quasi-cleavage fracture at-21℃,and is divided into ductile and brittle fracture zone.Meanwhile,the PSZ and NSZ spread across ductile and brittle fracture zone randomly.In ductile fracture zone,micro-voids fracture mechanism covers the PSZ and NSZ,and higher deformation degree is shown in the PSZ.In brittle fracture zone,secondary cleavage cracks are observed in both PSZ and NSZ,but present bigger size and higher quantity in the NSZ.However,some regions of the PSZ still present micro-voids fracture mechanism in brittle fracture zone.It reveals that the microstructures in the PSZ exhibit a higher resistance ability to crack propagation than that in the NSZ.All observations above provide a better visualization of the microstructural factors that resist the crack propagation.It is important to map all information regarding the fracture mechanism and mesosegregation to allow for further acceptance and industrial use.
基金Item Sponsored by NSFC (China) and CNRS (France) through French-Chinese OPTIMAG project
文摘Thermo-electric currents in the presence of static magnetic fields generate significant electromagnetic forces(TEM forces).The thermo-electric currents are due to the Seebeck effect when temperature gradients exist in the material. Those forces may produce various phenomena like pumping,stirring in liquid metals as well as solid motions,stresses in the solid metal.Those effects may be encountered especially during the solidification of metallic materials because of the existence of significant temperature gradients.In liquid metals the application of a static magnetic field enhances TEM convection at moderate intensity but also damps it when it is strong enough.This means that there exists a maximum of the convection which occurs when the Hartmann layers are comparable to the considered length scale.However,the smaller the length scales are(for example when primary or secondary dendrite arm spacings are considered),the higher the magnetic field strength which is needed to damp the TEM convection.So far,many solidification experiments on various types of alloys(e.g.,Sn-Pb,Al-Cu,Al-Si,Al-Ni etc.)have been carried out.The experiments have shown that TEM convection occurs both in the liquid bulk but also in the deep mushy zone.TEM convection may strongly influence the meso-macrosegregation patterns,the solidification structures and the grain boundaries leading to the striking grain boundary structure of the mushy zone.The flow pattern and accordingly the segregations may be controlled by changing the orientation of the applied magnetic field,i.e.,axial or transverse.We have shown that very high magnetic field strengths,up to 16 T,are needed to damp the TEM convection.Heuristic numerical and analytical investigations show that the TEM force density is very important in the liquid,but can be even more important in the solid.Indeed,for high Hartmann number,the electric currents are confined in a small skin layer near the solid boundaries leading to a decay of the flow.However,the situation is different in the solid,sinc
