On the basis of transformation kinetics and thermodynamics, the austenite-ferrite transformation start temperature during deformation was predicted for several grades of low-carbon steels under different processing co...On the basis of transformation kinetics and thermodynamics, the austenite-ferrite transformation start temperature during deformation was predicted for several grades of low-carbon steels under different processing conditions. Results indicate that Ar3d temperature mostly depended on alloying composition and processing parameters. Ar3d increased as strain rate or strain increased for the same steel grade. In view of enhancement of deformation on transformation, the basic kinetics model was established to simulate deformation induced transformation behavior, using which the influence of the deformation stored energy and effective deformation ledge on the nucleation and growth can be considered. The simulated results are in good agreement with experiment results.展开更多
Ultrafine Ni0.5Zn0.5 Fe2O4 powder was prepared by PVA aided chemical method. The powder and sintered pellets were characterised by X-ray diffraction (XRD), vibrating sample magnetometry (VSM), thermogravimetric analys...Ultrafine Ni0.5Zn0.5 Fe2O4 powder was prepared by PVA aided chemical method. The powder and sintered pellets were characterised by X-ray diffraction (XRD), vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA) and complex impedance (Cl) analysis. The particles are found to be in the size range of 15 to 26 nm for various annealing temperatures. The coercivity, saturation magnetisation, Neel temperature and electrical conductivity are found to vary with sintering time at 800℃ for the pellet samples. The variations in the above intrinsic properties are explained qualitatively展开更多
The microstructures of a SS400 steel after thermomechanical control process（TMCP） in an industrial production were observed by optical microscope,scanning electron microscope（SEM） and transmission electron microsc...The microstructures of a SS400 steel after thermomechanical control process（TMCP） in an industrial production were observed by optical microscope,scanning electron microscope（SEM） and transmission electron microscope（TEM）.The results indicated that the size of ferrite grains was 4-5μm,and transmission of ferrite was around 70%.The types of the ultrafine ferrite grains were analyzed and the strengthening mechanisms were discussed.The results show that the ultrafine ferrite grains came from three processes,i.e.deformation induced ferrite transformation（DIFT）.dynamic recrystallization of ferrite and accelerated cooling process.The increase in the strength of the material was mainly due to the grain refining.展开更多
In the current study,a 0.3C-2Si-2Mn-0.28Mo (in wt%) steel with high hardenability was deformed at a relatively low temperature followed by isothermal static phase transformation.This novel thermomechanical processing ...In the current study,a 0.3C-2Si-2Mn-0.28Mo (in wt%) steel with high hardenability was deformed at a relatively low temperature followed by isothermal static phase transformation.This novel thermomechanical processing made it possible to successfully produce an ultrafine ferrite grained structure (～2 μm) in the absence of both dynamic phase transformation and controlled cooling.The use of a model Ni-30Fe austenitic alloy showed that the low temperature deformation induced very fine intragranular defects throughout the microstructure,which would then act as fine spaced ferrite nucleation sites at an early stage of phase transformation.As a result,the coarsening of ferrite was extremely limited during isothermal phase transformation,resulting a very fine ferrite grained structure;even nanoscale in the region of the prior austenite grain boundary.展开更多
基金This work was financially supported by the High Technology Development Program(No.2001AA339030)the National Nat ural Science Foundation of China(No.50100404).
文摘On the basis of transformation kinetics and thermodynamics, the austenite-ferrite transformation start temperature during deformation was predicted for several grades of low-carbon steels under different processing conditions. Results indicate that Ar3d temperature mostly depended on alloying composition and processing parameters. Ar3d increased as strain rate or strain increased for the same steel grade. In view of enhancement of deformation on transformation, the basic kinetics model was established to simulate deformation induced transformation behavior, using which the influence of the deformation stored energy and effective deformation ledge on the nucleation and growth can be considered. The simulated results are in good agreement with experiment results.
文摘Ultrafine Ni0.5Zn0.5 Fe2O4 powder was prepared by PVA aided chemical method. The powder and sintered pellets were characterised by X-ray diffraction (XRD), vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA) and complex impedance (Cl) analysis. The particles are found to be in the size range of 15 to 26 nm for various annealing temperatures. The coercivity, saturation magnetisation, Neel temperature and electrical conductivity are found to vary with sintering time at 800℃ for the pellet samples. The variations in the above intrinsic properties are explained qualitatively
基金This work was financially supported by the National Natural Science Foundation of China and Shanghai Bao Steel （No. 50271015）.
文摘The microstructures of a SS400 steel after thermomechanical control process（TMCP） in an industrial production were observed by optical microscope,scanning electron microscope（SEM） and transmission electron microscope（TEM）.The results indicated that the size of ferrite grains was 4-5μm,and transmission of ferrite was around 70%.The types of the ultrafine ferrite grains were analyzed and the strengthening mechanisms were discussed.The results show that the ultrafine ferrite grains came from three processes,i.e.deformation induced ferrite transformation（DIFT）.dynamic recrystallization of ferrite and accelerated cooling process.The increase in the strength of the material was mainly due to the grain refining.
基金supported by grants through the Australian Research Councilan ARC Laureate Fellowship (PDH)
文摘In the current study,a 0.3C-2Si-2Mn-0.28Mo (in wt%) steel with high hardenability was deformed at a relatively low temperature followed by isothermal static phase transformation.This novel thermomechanical processing made it possible to successfully produce an ultrafine ferrite grained structure (～2 μm) in the absence of both dynamic phase transformation and controlled cooling.The use of a model Ni-30Fe austenitic alloy showed that the low temperature deformation induced very fine intragranular defects throughout the microstructure,which would then act as fine spaced ferrite nucleation sites at an early stage of phase transformation.As a result,the coarsening of ferrite was extremely limited during isothermal phase transformation,resulting a very fine ferrite grained structure;even nanoscale in the region of the prior austenite grain boundary.
