The solidification structure, microstructure evolution during rolling andprecipitates with nanometers in dimension of the low carbon steels produced by CSP process with thinslabs have been studied in recent years. Imp...The solidification structure, microstructure evolution during rolling andprecipitates with nanometers in dimension of the low carbon steels produced by CSP process with thinslabs have been studied in recent years. Important differences in microstructure and mechanicalproperties between the CSP products and the conventional one were observed. These differences mayarise from the much rapider solidification rate and cooling rate after casting of the thin slabs.Some aspects of the microstructure for the low carbon steels of the CSP thin slabs are summarizedand compared with the conventional one.展开更多
In comparison with conventional production for hot strips, compact strip production (CSP) brings about some new micro-structural phenomena. Investigations were carried out to clarify the grain refinement mechanism of ...In comparison with conventional production for hot strips, compact strip production (CSP) brings about some new micro-structural phenomena. Investigations were carried out to clarify the grain refinement mechanism of low carbon steel strips produced by the EAF-CSP process. Samples, obtained from the same rolling stock during continuous rolling, were examined through SEM, TEM and XEDS. Thin slabs have a dominant columnar structure and the spacing of the secondary dendrite arms ranges from 90 to -125 μm. The average grain sizes for the central area of the samples from the 1st to 6th pass are 41.6, 25.2, 21.4, 20.2, 13.1, 6.7 μm, respectively. Large number of nanometer oxide and sulfide have been found in the low carbon steel produced by the CSP process. The grain refinement mechanism can be summarized as follows: finer solidification structure of the thin slab; austenite recrystalliza-tion at higher temperature and stain accumulation at lower temperature caused by the great reduction of single rolling pass during continuous rolling; nano-scaled precipitates of sulfide and oxide which drag grain boundaries of austenite or ferrite to prevent the grain coarsening.展开更多
Low-carbon steel sheets DC04 used in the automotive industry were subjected to cold rolling for thickness reduction from 20% to 89%. The desired thickness was achieved by successive reductions using a rolling mill. Th...Low-carbon steel sheets DC04 used in the automotive industry were subjected to cold rolling for thickness reduction from 20% to 89%. The desired thickness was achieved by successive reductions using a rolling mill. The influence of thickness reduction on the microstructure was studied by scanning electron microscopy. Microstructure evolution was characterized by the distortion of grains and the occurrence of the oriented grain structure for high cold work. A mechanism of grain restructuring for high cold work was described. The occurrence of voids was discussed in relation with cold work. The evolution of voids at the grain boundaries and inside the grains was also considered. To characterize the grain size, the Feret diameter was measured and the grain size distribution versus cold work was discussed. The chemical homogeneity of the sample was also analyzed.展开更多
In a typical process, low carbon steel was annealed at two different temperatures （660℃ and 750℃）, and then was temper rolled to improve the mechanical properties. Pre-straining and baking treatments were subseque...In a typical process, low carbon steel was annealed at two different temperatures （660℃ and 750℃）, and then was temper rolled to improve the mechanical properties. Pre-straining and baking treatments were subsequently carried out to measure the bake-hardening （BH） values. The influences of annealing temperature and temper rolling on the BH behavior of the steel were investigated. The results indicated that the microstructure evolution during temper rolling was related to carbon atoms and dislocations. After an apparent increase, the BH value of the steel significantly decreased when the temper rolling reduction was increased from 0%to 5%. This was attributed to the increase in solute carbon concentration and dislocation density. The maximum BH values of the steel annealed at 660℃ and 750℃ were 80 MPa and 89 MPa at the reductions of 3%and 4%, respectively. Moreover, increasing the annealing temperature from 660 to 750℃ resulted in an ob-vious increase in the BH value due to carbide dissolution.展开更多
The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation wa...The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation was investigated by optical mi- croscope to analyze and summarize the microstructure evolution law of T12 deformed in semi-solid state. The experiment results show that the grain shape before deformation of the semi-solid T12 steel displays globule or ellipse by the electromagnetic stirring, the distribution of solid and liquid phases is homogeneous. But the microstructure of semi-solid product after rheo-rolling exhibits macrosegregation that the distribution of liquid and solid phases changes, the liquid phases divorce from the solid phases. In the transverse section, most of the solid phases get together in the center of the specimen, the liquid phases flow to the surface or the edge of the specimen, and the grains occur plastic deformation while reduction increased. In longitudinal section, the middle micro- structure of the specimen is more homogeneous than that at the head or tail, the head microstructure is similar to the tail and the size of the grains is not homogeneous.展开更多
The influences of the heating rate, annealing temperature and soaking time during continuous annealing on the microstructure evolution and bake hardening behavior of the low carbon steel were investigated. After 2% pr...The influences of the heating rate, annealing temperature and soaking time during continuous annealing on the microstructure evolution and bake hardening behavior of the low carbon steel were investigated. After 2% pres- training, bake treatment （180 ℃ × 20 min） was carried out to measure BH （bake hardening） values. The results showed that, with the increase of the annealing temperature, the grain size increased except for annealing in the in- tercritical region. Furthermore, the BH value increased and the mean grain size reduced with increasing the heating rate from 5 to 80 ℃/s. The BH value was very low before complete recrystallization. After a significant decrease from 630 to 720 ℃ , the BH value enhanced when the steel was annealed at 750 ℃. With the increase of the soaking time from 20 to 100 s, the BH value reduced linearly due to the segregation of solute C atoms.展开更多
基金Supported by the State foundation for key project: New Generation of Steels (No: G1998061500)]
文摘The solidification structure, microstructure evolution during rolling andprecipitates with nanometers in dimension of the low carbon steels produced by CSP process with thinslabs have been studied in recent years. Important differences in microstructure and mechanicalproperties between the CSP products and the conventional one were observed. These differences mayarise from the much rapider solidification rate and cooling rate after casting of the thin slabs.Some aspects of the microstructure for the low carbon steels of the CSP thin slabs are summarizedand compared with the conventional one.
文摘In comparison with conventional production for hot strips, compact strip production (CSP) brings about some new micro-structural phenomena. Investigations were carried out to clarify the grain refinement mechanism of low carbon steel strips produced by the EAF-CSP process. Samples, obtained from the same rolling stock during continuous rolling, were examined through SEM, TEM and XEDS. Thin slabs have a dominant columnar structure and the spacing of the secondary dendrite arms ranges from 90 to -125 μm. The average grain sizes for the central area of the samples from the 1st to 6th pass are 41.6, 25.2, 21.4, 20.2, 13.1, 6.7 μm, respectively. Large number of nanometer oxide and sulfide have been found in the low carbon steel produced by the CSP process. The grain refinement mechanism can be summarized as follows: finer solidification structure of the thin slab; austenite recrystalliza-tion at higher temperature and stain accumulation at lower temperature caused by the great reduction of single rolling pass during continuous rolling; nano-scaled precipitates of sulfide and oxide which drag grain boundaries of austenite or ferrite to prevent the grain coarsening.
基金the Romanian Ministry of Education and Research for CNCS Grant, project number PCCE ID100/2010
文摘Low-carbon steel sheets DC04 used in the automotive industry were subjected to cold rolling for thickness reduction from 20% to 89%. The desired thickness was achieved by successive reductions using a rolling mill. The influence of thickness reduction on the microstructure was studied by scanning electron microscopy. Microstructure evolution was characterized by the distortion of grains and the occurrence of the oriented grain structure for high cold work. A mechanism of grain restructuring for high cold work was described. The occurrence of voids was discussed in relation with cold work. The evolution of voids at the grain boundaries and inside the grains was also considered. To characterize the grain size, the Feret diameter was measured and the grain size distribution versus cold work was discussed. The chemical homogeneity of the sample was also analyzed.
基金supported by the National Natural Science Foundation of China(51174247)
文摘In a typical process, low carbon steel was annealed at two different temperatures （660℃ and 750℃）, and then was temper rolled to improve the mechanical properties. Pre-straining and baking treatments were subsequently carried out to measure the bake-hardening （BH） values. The influences of annealing temperature and temper rolling on the BH behavior of the steel were investigated. The results indicated that the microstructure evolution during temper rolling was related to carbon atoms and dislocations. After an apparent increase, the BH value of the steel significantly decreased when the temper rolling reduction was increased from 0%to 5%. This was attributed to the increase in solute carbon concentration and dislocation density. The maximum BH values of the steel annealed at 660℃ and 750℃ were 80 MPa and 89 MPa at the reductions of 3%and 4%, respectively. Moreover, increasing the annealing temperature from 660 to 750℃ resulted in an ob-vious increase in the BH value due to carbide dissolution.
基金This work was financially supported by the National Natural Science Foundation of China and Baosteel (No.50174003).
文摘The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation was investigated by optical mi- croscope to analyze and summarize the microstructure evolution law of T12 deformed in semi-solid state. The experiment results show that the grain shape before deformation of the semi-solid T12 steel displays globule or ellipse by the electromagnetic stirring, the distribution of solid and liquid phases is homogeneous. But the microstructure of semi-solid product after rheo-rolling exhibits macrosegregation that the distribution of liquid and solid phases changes, the liquid phases divorce from the solid phases. In the transverse section, most of the solid phases get together in the center of the specimen, the liquid phases flow to the surface or the edge of the specimen, and the grains occur plastic deformation while reduction increased. In longitudinal section, the middle micro- structure of the specimen is more homogeneous than that at the head or tail, the head microstructure is similar to the tail and the size of the grains is not homogeneous.
基金Sponsored by National Natural Science Foundation of China(51174247)
文摘The influences of the heating rate, annealing temperature and soaking time during continuous annealing on the microstructure evolution and bake hardening behavior of the low carbon steel were investigated. After 2% pres- training, bake treatment （180 ℃ × 20 min） was carried out to measure BH （bake hardening） values. The results showed that, with the increase of the annealing temperature, the grain size increased except for annealing in the in- tercritical region. Furthermore, the BH value increased and the mean grain size reduced with increasing the heating rate from 5 to 80 ℃/s. The BH value was very low before complete recrystallization. After a significant decrease from 630 to 720 ℃ , the BH value enhanced when the steel was annealed at 750 ℃. With the increase of the soaking time from 20 to 100 s, the BH value reduced linearly due to the segregation of solute C atoms.
