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
The refractory niobium bearing minerals,Samarskite,Fergusonite,Betafite and Pyrochlore of the ore sample obtained from Kadabora,Egypt,was subjected to sulfuric acid leaching using acid concentrations varied from 17.6 ...The refractory niobium bearing minerals,Samarskite,Fergusonite,Betafite and Pyrochlore of the ore sample obtained from Kadabora,Egypt,was subjected to sulfuric acid leaching using acid concentrations varied from 17.6 to 4.5 mol/ L. The extraction of niobium from the sulfate leach liquors was done using the synthesized 8,9-dihydro[1,2,4]triazolo[1,5-a]quinazolin6(7H)-one dissolved in methylene chloride. It has been found that extraction efficiency of 84% was achieved by contacting equal volumes of 0.32% extractant with 4.5 mol/L sulfate solution for 15 min. The stripping was performed by 0.5 mol/L HF with efficiency of 86.7%.展开更多
The CASTRIP* process produces a range of high strength Ultra-thin Cast Strip (UCS) products (380-550 MPa) in thicknesses between 0.9 mm and 1.5 mm, which is very challenging to produce via conventional hot and cold ro...The CASTRIP* process produces a range of high strength Ultra-thin Cast Strip (UCS) products (380-550 MPa) in thicknesses between 0.9 mm and 1.5 mm, which is very challenging to produce via conventional hot and cold rolled processing routes. The twin roll CASTRIP process fully exploits the hardenability and strengthening potential of Nb in a low C-Mn-Nb-V microalloyed steel type. Significant microstructural strengthening from solute Nb was obtained, even at low microalloying levels, as well as modest Mn additions, through enhancing the hardenability and further strengthening was obtained in coated products by exploiting age hardening during processing on a continuous hot dip galvanising line. Atom probe tomography and TEM determined that Nb was retained in solid solution and subsequent age hardening resulted from the formation of Nb and V rich nanosized particles. Age hardening was achieved without loss of ductility producing galvanised strip with an excellent strength-ductility combination (Y.S. 】600 MPa, T.E. 】10%).展开更多
HTP practice,alloyed with low-carbon (less than 0.06%) and high-niobium (up to 0.11%),has been developed to produce large-wall X80 hot rolled strip for 2nd West-East Gas Pipeline project successfully.In this paper,exi...HTP practice,alloyed with low-carbon (less than 0.06%) and high-niobium (up to 0.11%),has been developed to produce large-wall X80 hot rolled strip for 2nd West-East Gas Pipeline project successfully.In this paper,existing status of niobium at different rolling stage,such as reheating,rough rolling and final product and strengthening effects have been presented and analyzed systematically.Some technological questions concerrned,such as the mixed grain occurred on the delay table,dynamic recrystallization during the finish rolling course,γ→αtransformation and final microstructure obtained at low coiling temperature,have been explored further.Analytical results presented increased recrystallization stop temperature due to high niobium contents can provide the requisite to remove waiting-temperature operation of transfer bar before finish rolling to ensure controlled effect of traditional low-temperature,which is benificial not only to production efficiency,but also to uniformity of austenite microstructure.Secondly,dynamic-recrystallization occurred during finish rolling may reduce the density of dislocation,but will better the grain gradient along the thickness because the dynamic recrystallization proceeds instantly,which is beneficial to reduce the appearance of separation of impact fracture.Finally,the lower coiling temperature than traditional TMCP practice,up to 300℃,is a key factor to obtain low-carbon bainite microstructure composed of acicular ferrite and small amount M/A component,which results in high strength and excellent low-temperature toughness.展开更多
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.
文摘The refractory niobium bearing minerals,Samarskite,Fergusonite,Betafite and Pyrochlore of the ore sample obtained from Kadabora,Egypt,was subjected to sulfuric acid leaching using acid concentrations varied from 17.6 to 4.5 mol/ L. The extraction of niobium from the sulfate leach liquors was done using the synthesized 8,9-dihydro[1,2,4]triazolo[1,5-a]quinazolin6(7H)-one dissolved in methylene chloride. It has been found that extraction efficiency of 84% was achieved by contacting equal volumes of 0.32% extractant with 4.5 mol/L sulfate solution for 15 min. The stripping was performed by 0.5 mol/L HF with efficiency of 86.7%.
文摘The CASTRIP* process produces a range of high strength Ultra-thin Cast Strip (UCS) products (380-550 MPa) in thicknesses between 0.9 mm and 1.5 mm, which is very challenging to produce via conventional hot and cold rolled processing routes. The twin roll CASTRIP process fully exploits the hardenability and strengthening potential of Nb in a low C-Mn-Nb-V microalloyed steel type. Significant microstructural strengthening from solute Nb was obtained, even at low microalloying levels, as well as modest Mn additions, through enhancing the hardenability and further strengthening was obtained in coated products by exploiting age hardening during processing on a continuous hot dip galvanising line. Atom probe tomography and TEM determined that Nb was retained in solid solution and subsequent age hardening resulted from the formation of Nb and V rich nanosized particles. Age hardening was achieved without loss of ductility producing galvanised strip with an excellent strength-ductility combination (Y.S. 】600 MPa, T.E. 】10%).
文摘HTP practice,alloyed with low-carbon (less than 0.06%) and high-niobium (up to 0.11%),has been developed to produce large-wall X80 hot rolled strip for 2nd West-East Gas Pipeline project successfully.In this paper,existing status of niobium at different rolling stage,such as reheating,rough rolling and final product and strengthening effects have been presented and analyzed systematically.Some technological questions concerrned,such as the mixed grain occurred on the delay table,dynamic recrystallization during the finish rolling course,γ→αtransformation and final microstructure obtained at low coiling temperature,have been explored further.Analytical results presented increased recrystallization stop temperature due to high niobium contents can provide the requisite to remove waiting-temperature operation of transfer bar before finish rolling to ensure controlled effect of traditional low-temperature,which is benificial not only to production efficiency,but also to uniformity of austenite microstructure.Secondly,dynamic-recrystallization occurred during finish rolling may reduce the density of dislocation,but will better the grain gradient along the thickness because the dynamic recrystallization proceeds instantly,which is beneficial to reduce the appearance of separation of impact fracture.Finally,the lower coiling temperature than traditional TMCP practice,up to 300℃,is a key factor to obtain low-carbon bainite microstructure composed of acicular ferrite and small amount M/A component,which results in high strength and excellent low-temperature toughness.
