To investigate the microsegregation phenomena and complex （Ti, Nb）（C, N） precipitation behavior during continuous casting, a unidirectional solidification unit was employed to simulate the solidification process. ...To investigate the microsegregation phenomena and complex （Ti, Nb）（C, N） precipitation behavior during continuous casting, a unidirectional solidification unit was employed to simulate the solidification process. The samples of Ti, Nb-addition steels after unidirectional solidification were examined using field emission scanning electron microscope （FE-SEM） and electron probe X-ray microanalyzer （EPMA）. In such specimens, dendrite structure and mushy zone can be detected along the solidification direction. It shows that the addition of titanium, niobium to high-strength low-alloyed （HSLA） steel results in undesirable （Ti, Nb）（C, N） precipitation because of microsegregation. The effect of cooling rate on （Ti, Nb）（C, N） precipitation was investigated. The composition of large precipitates was determined using FE-SEM with EDS. Large （Ti, Nb）（C, N） precipitates could be divided into three kinds according to the composition and morphology. With the cooling rate increasing, Ti-rich （Ti, Nb）（C, N） precipitates are transformed to Nb-rich （Ti, Nb）（C, N） precipitates.展开更多
The entrapment behavior of Ar bubbles onto the solidifying front of molten steel in the continuous casting mold was investigated. The dynamic model of bubble and particle entrapment was developed in order to consider ...The entrapment behavior of Ar bubbles onto the solidifying front of molten steel in the continuous casting mold was investigated. The dynamic model of bubble and particle entrapment was developed in order to consider the effect of surface tension gradient induced forces(Marangoni force) due to the gradient of sulfur concentration and temperature. The numerical analysis and water model experiment were performed to apply the present model for various conditions. The calculation result is compared with experimental results and plant data in continuous casting mold as well. It shows that the thermal Marangoni force could play an important role and this model predicts the bubble behavior in the vicinity of solid/liquid interface more precisely.展开更多
In order to suppress the surface cracking induced by Cu during reheating and hot rolling process,Cu enrichment and its migration at the steel-scale interface was investigated during heating of steel cast at temperatur...In order to suppress the surface cracking induced by Cu during reheating and hot rolling process,Cu enrichment and its migration at the steel-scale interface was investigated during heating of steel cast at temperatures between 1000℃and 1200℃in N_2-O_2 and N_7-H_2O atmospheres.For oxidation of Cu containing steel,Cu enriched phase was formed by the preferential oxidation of Fe and the enrichment and migration behavior of Cu depends on the oxidation temperature,steel chemistry and atmosphere condition.Ni in steel induced the formation of solid Cu and Ni enriched phase at steel/scale interface and in scale layer and the formation of uneven steel/scale interface, which suppresses the Cu enrichment because of extrusion of Cu enriched region before the formation of liquid phase.On the other hand,Sn addition promotes the liquid Cu formation at steel/scale interface and penetration into grain boundary of Cu enriched phase by decreasing solidus temperature and solubility limit.In addition,for oxidation at 1 200℃,the behavior of Cu at and around the steel-scale interface was found dependent to a large extent on morphology of the oxide scale formed during oxidation.At the early stage of oxidation,Cu-rich phase formed and accumulated at the steel scale interface under both O_2-N_2 and H_2O-N_2 atmospheres.As the oxidation proceeded,however,Cu enrichment at and its migration from the steel-scale interface were vastly different for different oxidizing atmospheres.In the case of O_2-N_2 oxidation,an oxide layer formed initially at the steel surface, but soon after a gap was developed at the steel-scale interface and grew in its size,which practically separated the scale from the steel substrate.The scale layer formed under this condition was porous.The Cu-rich phase initially formed at the interface was found migrating to the scale layer,leaving no Cu-rich phase at the interface.In the case of H_2O-N_2 oxidation,however,the scale layer formed was dense and tightly attached to the steel surface,and the Cu rich-phase continued to accumulate at the interface.Regarding the behavior of Cu-rich phase formed at the interface,it is proposed with experimental evidences that,when a gap forms at the steel-scale interface,it is the vaporization of Cu in the Cu-rich phase through the gap that brings Cu to the scale.展开更多
MnO-SiO_2-Al_2O_3-MnS oxysulfide system has been investigated by experimental phase diagram and activity measurement coupled with thermodynamic modeling.Phase equilibria of the MnO-MnS,MnO-SiO_2-MnS, MnO-Al_2O_3-MnS a...MnO-SiO_2-Al_2O_3-MnS oxysulfide system has been investigated by experimental phase diagram and activity measurement coupled with thermodynamic modeling.Phase equilibria of the MnO-MnS,MnO-SiO_2-MnS, MnO-Al_2O_3-MnS and MnO-SiO_2-Al_2O_3-MnS systems under low oxygen partial pressure have been experimentally investigated for the temperature range of 1 185 to 1 500℃using equilibration and quenching techniques. Equilibrium phases were analyzed by scanning electron microscope,electron probe X-ray microanalysis(EPMA), and differential thermal analysis(DTA ).Phase diagrams were successfully constructed for the systems investigated.Two ternary compounds in the MnO-SiO_2-MnS system were found.Activities of MnO and MnS in MnO-SiO_2-Al_2O_3-MnS liquid oxysulfide solution from very low sulfur concentration to high sulfur concentration at solid MnS saturation were investigated employing gas/liquid/Pt - Mn alloy under controlled atmosphere at 1 500℃.As X(SiO_2)/(X(MnO) + X(SiO_2)) increases in liquid oxysulfide solution,activity coefficient of MnO decreases while that of MnS increases.As X(AlO_(1.5)) increases,the activity coefficient of MnS increases while no remarkable change was observed for the activity coefficient of MnO.Quantitative analysis of the thermodynamic properties of the oxysulfide solution as well as phase diagram of the system was also earned out by employing the Modified Quasichemical Model in the quadruplet approximation.In view of inclusion utilization for free - cutting steel,it might have an advantage to decrease the Al_2O_3 content and increase the MnO/SiO_2 ratio.展开更多
文摘To investigate the microsegregation phenomena and complex （Ti, Nb）（C, N） precipitation behavior during continuous casting, a unidirectional solidification unit was employed to simulate the solidification process. The samples of Ti, Nb-addition steels after unidirectional solidification were examined using field emission scanning electron microscope （FE-SEM） and electron probe X-ray microanalyzer （EPMA）. In such specimens, dendrite structure and mushy zone can be detected along the solidification direction. It shows that the addition of titanium, niobium to high-strength low-alloyed （HSLA） steel results in undesirable （Ti, Nb）（C, N） precipitation because of microsegregation. The effect of cooling rate on （Ti, Nb）（C, N） precipitation was investigated. The composition of large precipitates was determined using FE-SEM with EDS. Large （Ti, Nb）（C, N） precipitates could be divided into three kinds according to the composition and morphology. With the cooling rate increasing, Ti-rich （Ti, Nb）（C, N） precipitates are transformed to Nb-rich （Ti, Nb）（C, N） precipitates.
文摘The entrapment behavior of Ar bubbles onto the solidifying front of molten steel in the continuous casting mold was investigated. The dynamic model of bubble and particle entrapment was developed in order to consider the effect of surface tension gradient induced forces(Marangoni force) due to the gradient of sulfur concentration and temperature. The numerical analysis and water model experiment were performed to apply the present model for various conditions. The calculation result is compared with experimental results and plant data in continuous casting mold as well. It shows that the thermal Marangoni force could play an important role and this model predicts the bubble behavior in the vicinity of solid/liquid interface more precisely.
文摘In order to suppress the surface cracking induced by Cu during reheating and hot rolling process,Cu enrichment and its migration at the steel-scale interface was investigated during heating of steel cast at temperatures between 1000℃and 1200℃in N_2-O_2 and N_7-H_2O atmospheres.For oxidation of Cu containing steel,Cu enriched phase was formed by the preferential oxidation of Fe and the enrichment and migration behavior of Cu depends on the oxidation temperature,steel chemistry and atmosphere condition.Ni in steel induced the formation of solid Cu and Ni enriched phase at steel/scale interface and in scale layer and the formation of uneven steel/scale interface, which suppresses the Cu enrichment because of extrusion of Cu enriched region before the formation of liquid phase.On the other hand,Sn addition promotes the liquid Cu formation at steel/scale interface and penetration into grain boundary of Cu enriched phase by decreasing solidus temperature and solubility limit.In addition,for oxidation at 1 200℃,the behavior of Cu at and around the steel-scale interface was found dependent to a large extent on morphology of the oxide scale formed during oxidation.At the early stage of oxidation,Cu-rich phase formed and accumulated at the steel scale interface under both O_2-N_2 and H_2O-N_2 atmospheres.As the oxidation proceeded,however,Cu enrichment at and its migration from the steel-scale interface were vastly different for different oxidizing atmospheres.In the case of O_2-N_2 oxidation,an oxide layer formed initially at the steel surface, but soon after a gap was developed at the steel-scale interface and grew in its size,which practically separated the scale from the steel substrate.The scale layer formed under this condition was porous.The Cu-rich phase initially formed at the interface was found migrating to the scale layer,leaving no Cu-rich phase at the interface.In the case of H_2O-N_2 oxidation,however,the scale layer formed was dense and tightly attached to the steel surface,and the Cu rich-phase continued to accumulate at the interface.Regarding the behavior of Cu-rich phase formed at the interface,it is proposed with experimental evidences that,when a gap forms at the steel-scale interface,it is the vaporization of Cu in the Cu-rich phase through the gap that brings Cu to the scale.
文摘MnO-SiO_2-Al_2O_3-MnS oxysulfide system has been investigated by experimental phase diagram and activity measurement coupled with thermodynamic modeling.Phase equilibria of the MnO-MnS,MnO-SiO_2-MnS, MnO-Al_2O_3-MnS and MnO-SiO_2-Al_2O_3-MnS systems under low oxygen partial pressure have been experimentally investigated for the temperature range of 1 185 to 1 500℃using equilibration and quenching techniques. Equilibrium phases were analyzed by scanning electron microscope,electron probe X-ray microanalysis(EPMA), and differential thermal analysis(DTA ).Phase diagrams were successfully constructed for the systems investigated.Two ternary compounds in the MnO-SiO_2-MnS system were found.Activities of MnO and MnS in MnO-SiO_2-Al_2O_3-MnS liquid oxysulfide solution from very low sulfur concentration to high sulfur concentration at solid MnS saturation were investigated employing gas/liquid/Pt - Mn alloy under controlled atmosphere at 1 500℃.As X(SiO_2)/(X(MnO) + X(SiO_2)) increases in liquid oxysulfide solution,activity coefficient of MnO decreases while that of MnS increases.As X(AlO_(1.5)) increases,the activity coefficient of MnS increases while no remarkable change was observed for the activity coefficient of MnO.Quantitative analysis of the thermodynamic properties of the oxysulfide solution as well as phase diagram of the system was also earned out by employing the Modified Quasichemical Model in the quadruplet approximation.In view of inclusion utilization for free - cutting steel,it might have an advantage to decrease the Al_2O_3 content and increase the MnO/SiO_2 ratio.
