The morphology of manganese sulfide formed during thin slab continuous casting process in low-carbon steel produced by compact strip production （CSP） technique was investigated. Using transmission electron microscop...The morphology of manganese sulfide formed during thin slab continuous casting process in low-carbon steel produced by compact strip production （CSP） technique was investigated. Using transmission electron microscopy analysis, it was seen that a majority of manganese sulfides precipitated at austenite grain boundaries, the morphologies of which were spherical or close to the spherical shape and the size of MnS precipitates ranged from 30 nm to 100 nm. A mathematical model of the manganese sulfide precipitation in this process was developed based on classical nucleation theory. Under the given conditions, the starting and finishing precipitation temperatures of MnS in the continuous casting thin slab of the studied low-carbon steel are 1 189 ℃ and 1 171 ℃, respectively, and the average diameter of MnS precipitates is about 48 nm within this precipitation temperature range. The influences of chemical components and thermo-mechanical processing conditions on the precipitation behavior of MnS in the same process were also discussed.展开更多
Two experiments were carried out on the same compact strip production (CSP) line, which differs in that one of them experienced γ→α→γ thermal history. The differences in microstructure, precipitation, misorientat...Two experiments were carried out on the same compact strip production (CSP) line, which differs in that one of them experienced γ→α→γ thermal history. The differences in microstructure, precipitation, misorientation etc between two experiments were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD) and positron annihilation technique (PAT). The carbon concentration in matrix is more inhomogeneous in the experiment than that with γ→α→γ7 thermal history. The specific precipitation characteristic in the experiment without γ→α→γ thermal history is discussed on the basis of different carbon diffusion behavior and interaction between dislocation and excess carbon.展开更多
The microstructure characteristics and precipitation behavior of automobile beam steels produced by compact strip production （CSP） were investigated by use of scanning electron microscopy （SEM） transmission elect...The microstructure characteristics and precipitation behavior of automobile beam steels produced by compact strip production （CSP） were investigated by use of scanning electron microscopy （SEM） transmission electron microscopy （TEM） and X-ray energy dispersive spectroscopy. The result shows that the final microstructure is mainly composed of polygonal ferrite and small amount of pearlite, and the average ferrite grain size is about 3-6μm. Small amount addition Ti to aluminium-killed steel can help to refine the microstructure and improve the mechanical properties. A large number of fine precipitates have been observed in automobile beam steels. The mean particle size is about 10-30 nm. Remarkable strengthening and grain refinement can be obtained by these nano-particles.展开更多
Microalloying element Nb in low carbon steels produced by compact strip production （CSP） process plays an important role in inhibiting recrystallization, decreasing the transformation temperature and grain refinemen...Microalloying element Nb in low carbon steels produced by compact strip production （CSP） process plays an important role in inhibiting recrystallization, decreasing the transformation temperature and grain refinement.With decreasing the rolling temperature, dislocations can be pinned by carbonitrides and the strength is increased. Based on the two sublattice model, with metal atom sublattice and interstitial atom sublattice,a thermodynamic model for carbonitride was established to calculate the equilibrium between matrix and carbonitride. In the steel produced by CSP, the calculation results showed that the starting temperature of precipitation of Ti and Nb are 1340℃ and 1040℃, respectively. In the range of 890-950℃, Nb rapidly precipitated. And the maximum of the atomic fraction of Nb in carbonitride was about 0.68. The morphologies and energy spectrum of the precipitates showed that （NbTi） （CN） precipitated near the dislocations. The experiment results show that Nb rapidly precipitated when the temperature was lower than 970℃, and the atomic fraction of Nb in carbonitride was about 60%-80%. The calculation results are in agreement with the experiment data. Therefore the thermodynamic model can be a useful assistant tool in the research on the precipitates in the low carbon steels produced by CSP.展开更多
Hot strips of low carbon steels with Ti additive [-contain C 0.04 % -0. 07 % , Si≤0.6%, Mn≤0.6%, Ti 0. 060/00- 0.14% （mass percent）] prodvced by EAF-CSP （Electric Arc Furnaces-Compact Strip Production） process w...Hot strips of low carbon steels with Ti additive [-contain C 0.04 % -0. 07 % , Si≤0.6%, Mn≤0.6%, Ti 0. 060/00- 0.14% （mass percent）] prodvced by EAF-CSP （Electric Arc Furnaces-Compact Strip Production） process were examined by TEM, HREM and XRD. Carbonitrides with different N/C ratio were found in the sam- ples. The varying composition of the Ti-carbonitrides resulted from the supersaturation of Ti and temperature at which the compound was formed. In the tested steel, total mass fraction of the precipitates including cementite, carbonitride and a small quantity of Fe3O4, AO2O3 , Ti2 CS and A1N was about 0. 305 %. XRD results showed that about a quarter of the powder extracted by electrolysis was titanium nitrides, carbonitrides and carbides. Particle arrays formed by interphase precipitation could be observed either in slabs or in hot strips. The dominant reaction mecha- nisms were discussed. Compared with the conventional cold charge process, small amount of Ti addition would be more effective for orecipitation of fine orecioitates in the steels oroduced by CSP process.展开更多
The effect of boron on hot strips of low carbon steel produced by compact strip production （CSP） to reduce the strength to a certain degree was investigated, which is quite different from that of high-strength low a...The effect of boron on hot strips of low carbon steel produced by compact strip production （CSP） to reduce the strength to a certain degree was investigated, which is quite different from that of high-strength low alloy steel. The mechanical properties and microstructural evolution of the hot strip were studied using optical microscopy and tensile tests. By means of an electrolytic dissolution technique and Thermo-Cal calculation, the precipitates containing boron were analyzed and detected. From the electron backscattered diffraction analysis, it can be deciphered whether the microstructure has recrystallized or not. Furthermore, the effect of boron segregation on the recrystallization or non-recrystallization conditions can be distinguished. The segregation behavior of boron was investigated in boron-containing steel. The nonequilibrium segregation of boron during processing was discussed on the basis of the forming complexes with vacancies that migrate to the boundaries prior to annihilation, which was confirmed by the subsequent cold rolling with annealing experiments.展开更多
Multiphase microstructure significantly increases the strength,usually at the expense of flangeability because of lacking microstructure homogeneity.To further improve the strength-flangeability of multiphase steel,th...Multiphase microstructure significantly increases the strength,usually at the expense of flangeability because of lacking microstructure homogeneity.To further improve the strength-flangeability of multiphase steel,the microstructural homogeneity was advanced by adjusting the hard martensite/austenite(M/A)islands.The strength-flangeability was measured via uniaxial tensile tests and hole expansion tests.Their microstructures were characterized using a scanning electron microscope equipped with an electron backscatter diffraction detector and a transmission electron microscope.Nanoindentation tests were supplementally used to quantitatively reveal the microstructural homogeneity of the steels.Results show that the adjusted multiphase steel achieves an excellent ultimate tensile strength(~800 MPa)and flangeability(~135%hole expansion ratio).A promising homogeneous multiphase microstructure was obtained by controlling undercooled austenite transformed at about 600℃.This microstructure consists of soft polygonal ferrite,blocky bainitic ferrite,and hard M/A islands.The volume fraction of M/A islands is around 5%,and the average size is less than l pm.Detailed nanoindentation analysis indicated that the participation of M/A islands impressively influenced the microstructural homogeneity.Weakened strain partition and better mechanical compatibility were present in the adjusted multiphase steel since the plasticity initiation started late,which resulted in a positive flangeability.Moreover,avoiding M/A islands distributed in the chain along the rolling direction on the matrix hindered the possibility of voids coalescing into cracks and stabilized the flanging performance.展开更多
基金Item Sponsored by National Natural Science Foundation of China (50334010) and Fokying Tung Education Foundation (104017)
文摘The morphology of manganese sulfide formed during thin slab continuous casting process in low-carbon steel produced by compact strip production （CSP） technique was investigated. Using transmission electron microscopy analysis, it was seen that a majority of manganese sulfides precipitated at austenite grain boundaries, the morphologies of which were spherical or close to the spherical shape and the size of MnS precipitates ranged from 30 nm to 100 nm. A mathematical model of the manganese sulfide precipitation in this process was developed based on classical nucleation theory. Under the given conditions, the starting and finishing precipitation temperatures of MnS in the continuous casting thin slab of the studied low-carbon steel are 1 189 ℃ and 1 171 ℃, respectively, and the average diameter of MnS precipitates is about 48 nm within this precipitation temperature range. The influences of chemical components and thermo-mechanical processing conditions on the precipitation behavior of MnS in the same process were also discussed.
基金Authors acknowledge the financial support from the National Natural Science Foundation of China(No.50334010).
文摘Two experiments were carried out on the same compact strip production (CSP) line, which differs in that one of them experienced γ→α→γ thermal history. The differences in microstructure, precipitation, misorientation etc between two experiments were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD) and positron annihilation technique (PAT). The carbon concentration in matrix is more inhomogeneous in the experiment than that with γ→α→γ7 thermal history. The specific precipitation characteristic in the experiment without γ→α→γ thermal history is discussed on the basis of different carbon diffusion behavior and interaction between dislocation and excess carbon.
基金Item Sponsored by National Science and Technology Support Program for 11th Five-Year Plan of China (2006BAE03A06)
文摘The microstructure characteristics and precipitation behavior of automobile beam steels produced by compact strip production （CSP） were investigated by use of scanning electron microscopy （SEM） transmission electron microscopy （TEM） and X-ray energy dispersive spectroscopy. The result shows that the final microstructure is mainly composed of polygonal ferrite and small amount of pearlite, and the average ferrite grain size is about 3-6μm. Small amount addition Ti to aluminium-killed steel can help to refine the microstructure and improve the mechanical properties. A large number of fine precipitates have been observed in automobile beam steels. The mean particle size is about 10-30 nm. Remarkable strengthening and grain refinement can be obtained by these nano-particles.
基金This work was supported by the National Natural Science Foundation of China under grant Nos. 50334010 and 50271009.
文摘Microalloying element Nb in low carbon steels produced by compact strip production （CSP） process plays an important role in inhibiting recrystallization, decreasing the transformation temperature and grain refinement.With decreasing the rolling temperature, dislocations can be pinned by carbonitrides and the strength is increased. Based on the two sublattice model, with metal atom sublattice and interstitial atom sublattice,a thermodynamic model for carbonitride was established to calculate the equilibrium between matrix and carbonitride. In the steel produced by CSP, the calculation results showed that the starting temperature of precipitation of Ti and Nb are 1340℃ and 1040℃, respectively. In the range of 890-950℃, Nb rapidly precipitated. And the maximum of the atomic fraction of Nb in carbonitride was about 0.68. The morphologies and energy spectrum of the precipitates showed that （NbTi） （CN） precipitated near the dislocations. The experiment results show that Nb rapidly precipitated when the temperature was lower than 970℃, and the atomic fraction of Nb in carbonitride was about 60%-80%. The calculation results are in agreement with the experiment data. Therefore the thermodynamic model can be a useful assistant tool in the research on the precipitates in the low carbon steels produced by CSP.
基金Item Sponsored by National Natural Science Foundation of China (50371009)
文摘Hot strips of low carbon steels with Ti additive [-contain C 0.04 % -0. 07 % , Si≤0.6%, Mn≤0.6%, Ti 0. 060/00- 0.14% （mass percent）] prodvced by EAF-CSP （Electric Arc Furnaces-Compact Strip Production） process were examined by TEM, HREM and XRD. Carbonitrides with different N/C ratio were found in the sam- ples. The varying composition of the Ti-carbonitrides resulted from the supersaturation of Ti and temperature at which the compound was formed. In the tested steel, total mass fraction of the precipitates including cementite, carbonitride and a small quantity of Fe3O4, AO2O3 , Ti2 CS and A1N was about 0. 305 %. XRD results showed that about a quarter of the powder extracted by electrolysis was titanium nitrides, carbonitrides and carbides. Particle arrays formed by interphase precipitation could be observed either in slabs or in hot strips. The dominant reaction mecha- nisms were discussed. Compared with the conventional cold charge process, small amount of Ti addition would be more effective for orecipitation of fine orecioitates in the steels oroduced by CSP process.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50774110)Fok Ying Tong Edu-cation Foundation (No.104017).
文摘The effect of boron on hot strips of low carbon steel produced by compact strip production （CSP） to reduce the strength to a certain degree was investigated, which is quite different from that of high-strength low alloy steel. The mechanical properties and microstructural evolution of the hot strip were studied using optical microscopy and tensile tests. By means of an electrolytic dissolution technique and Thermo-Cal calculation, the precipitates containing boron were analyzed and detected. From the electron backscattered diffraction analysis, it can be deciphered whether the microstructure has recrystallized or not. Furthermore, the effect of boron segregation on the recrystallization or non-recrystallization conditions can be distinguished. The segregation behavior of boron was investigated in boron-containing steel. The nonequilibrium segregation of boron during processing was discussed on the basis of the forming complexes with vacancies that migrate to the boundaries prior to annihilation, which was confirmed by the subsequent cold rolling with annealing experiments.
基金financial support from the National Natural Science Foundation of China (Grant Nos.52274372 and 52201101)the National Key R&D Program of China (2021YFB3702404)the Fundamental Research Funds for the Central Universities (FRF-TP-22-013A1).
文摘Multiphase microstructure significantly increases the strength,usually at the expense of flangeability because of lacking microstructure homogeneity.To further improve the strength-flangeability of multiphase steel,the microstructural homogeneity was advanced by adjusting the hard martensite/austenite(M/A)islands.The strength-flangeability was measured via uniaxial tensile tests and hole expansion tests.Their microstructures were characterized using a scanning electron microscope equipped with an electron backscatter diffraction detector and a transmission electron microscope.Nanoindentation tests were supplementally used to quantitatively reveal the microstructural homogeneity of the steels.Results show that the adjusted multiphase steel achieves an excellent ultimate tensile strength(~800 MPa)and flangeability(~135%hole expansion ratio).A promising homogeneous multiphase microstructure was obtained by controlling undercooled austenite transformed at about 600℃.This microstructure consists of soft polygonal ferrite,blocky bainitic ferrite,and hard M/A islands.The volume fraction of M/A islands is around 5%,and the average size is less than l pm.Detailed nanoindentation analysis indicated that the participation of M/A islands impressively influenced the microstructural homogeneity.Weakened strain partition and better mechanical compatibility were present in the adjusted multiphase steel since the plasticity initiation started late,which resulted in a positive flangeability.Moreover,avoiding M/A islands distributed in the chain along the rolling direction on the matrix hindered the possibility of voids coalescing into cracks and stabilized the flanging performance.
