ZL205 A alloys with large thin-walled shape were continuously processed by coupling travelling magnetic fields(TMF)with sequential solidification,to eliminate the shrinkage defects and optimize the mechanical performa...ZL205 A alloys with large thin-walled shape were continuously processed by coupling travelling magnetic fields(TMF)with sequential solidification,to eliminate the shrinkage defects and optimize the mechanical performance.Through experiments and simulations,the parameter optimization of TMF and the influence on feeding behavior,microstructure and properties were systematically studied.The results indicate that the magnetic force maximizes at the excitation current of 20 A and frequency of 200 Hz under the experimental conditions of this study,and increases from center to side-walls,which is more convenient to process thin-walled castings.TMF can break secondary dendritic arm and dendrites overlaps,widen feeding channels,prolong the feeding time,optimize the feeding paths,eliminate shrinkage defects and improve properties.Specifically,for as-cast state,TMF with excitation current of 20 A increases ultimate tensile strength,elongation and micro-hardness from 186 MPa,7.3%and 82.1 kg/mm^(2) to 221 MPa,11.7%and 100.5 kg/mm^(2),decreases porosity from 1.71%to 0.22%,and alters brittle fracture to ductile fracture.展开更多
The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software. The actual and simulated solidification structures...The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software. The actual and simulated solidification structures were compared under mold electromagnetic stirring （MEMS） conditions （current of 300 A and frequency of 3 Hz）. Thereafter, the solidification structures of the large round billet were investigated under different superheats, casting speeds, and secondary cooling intensities. Finally, the effect of the MEMS current on the solidification structures was obtained under fixed superheat, casting speed, secondary cooling intensity, and MEMS frequency. The model accurately simulated the actual solidification structures of any steel, regardless of its size and the parameters used in the continuous casting process. The ratio of the central equiaxed grain zone was found to increase with decreasing superheat, increasing casting speed, decreasing secondary cooling intensity, and increasing MEMS current. The grain size obviously decreased with decreasing superheat and increasing MEMS current but was less sensitive to the casting speed and secondary cooling intensity.展开更多
The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper....The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper. The achievements fully satisfeid the technical requirements of the large 700 MW stainless steel hydraulic turbine runner for the Three Gorges Hydropower Station, and become the major technical support for the design and manufacture of the largest 700 MW hydraulic turbine generator unit in the world developed through our own efforts. The characteristics of a new high yield to tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel with ultra low carbon and high cleanliness are also described. Over the next ten years, the large martensitic stainless steel castings and advanced manufacturing technologies will see a huge demand in clean energy industry such as nuclear power, hydraulic power at home and abroad. Therefore, the new high yield o tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel materials, the fast and flexible manufacturing technologies of large size castings, and new environment friendly sustainable process will face new challenges and opportunities.展开更多
Understanding the solidification characteristics and microsegregation under varying cooling rates is essential to comprehend the formation of center cracks in large section round billets.P91 high-alloy steel was taken...Understanding the solidification characteristics and microsegregation under varying cooling rates is essential to comprehend the formation of center cracks in large section round billets.P91 high-alloy steel was taken as the research object.The peritectic solidification process,steel solidification shrinkage and microsegregation of solute elements at different cooling rates were studied and revealed by high-temperature confocal scanning laser microscopy,Thermo-Calc thermodynamic software,hybrid laser microscopy and electron probe microanalysis.The results showed that as the cooling rate increased from 10 to 100℃/min,the percentage ofδ-Fe involved in peritectic reaction decreased from 98.6%to 36.4%,the surface roughness of the sample decreased from 8.59 to 5.14μm,and the volume shrinkage decreased from 5.92%to 2.18%.Moreover,the solidification path enters the crack sensitivity area at lower cooling rates(10 and 50℃/min),while the solidification path is far from the crack susceptibility area at higher cooling rate(100℃/min).With the increase in cooling rate,the segregation deviation parameters of the elements V,C,Mo and Cr were decreased by 9.52%,22.2%,29.4%and 70.5%,respectively.Solidification path changed and microsegregation weakened by adjusting cooling mode might be a way to improve central crack.展开更多
基金financial supports from the National Key Research and Development Program of China(2017YFA0403804)the National Natural Science Foundation of China(51425402,51671073)。
文摘ZL205 A alloys with large thin-walled shape were continuously processed by coupling travelling magnetic fields(TMF)with sequential solidification,to eliminate the shrinkage defects and optimize the mechanical performance.Through experiments and simulations,the parameter optimization of TMF and the influence on feeding behavior,microstructure and properties were systematically studied.The results indicate that the magnetic force maximizes at the excitation current of 20 A and frequency of 200 Hz under the experimental conditions of this study,and increases from center to side-walls,which is more convenient to process thin-walled castings.TMF can break secondary dendritic arm and dendrites overlaps,widen feeding channels,prolong the feeding time,optimize the feeding paths,eliminate shrinkage defects and improve properties.Specifically,for as-cast state,TMF with excitation current of 20 A increases ultimate tensile strength,elongation and micro-hardness from 186 MPa,7.3%and 82.1 kg/mm^(2) to 221 MPa,11.7%and 100.5 kg/mm^(2),decreases porosity from 1.71%to 0.22%,and alters brittle fracture to ductile fracture.
文摘The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software. The actual and simulated solidification structures were compared under mold electromagnetic stirring （MEMS） conditions （current of 300 A and frequency of 3 Hz）. Thereafter, the solidification structures of the large round billet were investigated under different superheats, casting speeds, and secondary cooling intensities. Finally, the effect of the MEMS current on the solidification structures was obtained under fixed superheat, casting speed, secondary cooling intensity, and MEMS frequency. The model accurately simulated the actual solidification structures of any steel, regardless of its size and the parameters used in the continuous casting process. The ratio of the central equiaxed grain zone was found to increase with decreasing superheat, increasing casting speed, decreasing secondary cooling intensity, and increasing MEMS current. The grain size obviously decreased with decreasing superheat and increasing MEMS current but was less sensitive to the casting speed and secondary cooling intensity.
文摘The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper. The achievements fully satisfeid the technical requirements of the large 700 MW stainless steel hydraulic turbine runner for the Three Gorges Hydropower Station, and become the major technical support for the design and manufacture of the largest 700 MW hydraulic turbine generator unit in the world developed through our own efforts. The characteristics of a new high yield to tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel with ultra low carbon and high cleanliness are also described. Over the next ten years, the large martensitic stainless steel castings and advanced manufacturing technologies will see a huge demand in clean energy industry such as nuclear power, hydraulic power at home and abroad. Therefore, the new high yield o tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel materials, the fast and flexible manufacturing technologies of large size castings, and new environment friendly sustainable process will face new challenges and opportunities.
基金supported by the National Natural Science Foundation of China(No.52074207 and No.52304358)the Natural Science Basic Research Program of Shaanxi(No.2023-JC-QN-0376)Shaanxi Province Innovation Ability Support Plan(No.2023-CX-TD-53).
文摘Understanding the solidification characteristics and microsegregation under varying cooling rates is essential to comprehend the formation of center cracks in large section round billets.P91 high-alloy steel was taken as the research object.The peritectic solidification process,steel solidification shrinkage and microsegregation of solute elements at different cooling rates were studied and revealed by high-temperature confocal scanning laser microscopy,Thermo-Calc thermodynamic software,hybrid laser microscopy and electron probe microanalysis.The results showed that as the cooling rate increased from 10 to 100℃/min,the percentage ofδ-Fe involved in peritectic reaction decreased from 98.6%to 36.4%,the surface roughness of the sample decreased from 8.59 to 5.14μm,and the volume shrinkage decreased from 5.92%to 2.18%.Moreover,the solidification path enters the crack sensitivity area at lower cooling rates(10 and 50℃/min),while the solidification path is far from the crack susceptibility area at higher cooling rate(100℃/min).With the increase in cooling rate,the segregation deviation parameters of the elements V,C,Mo and Cr were decreased by 9.52%,22.2%,29.4%and 70.5%,respectively.Solidification path changed and microsegregation weakened by adjusting cooling mode might be a way to improve central crack.
