The oxidation behaviors of three austenitic cast steels with different morphologies of primary carbides at 950℃ in air were investigated using scanning electron microscopy,energy dispersive spectroscopy,and focused i...The oxidation behaviors of three austenitic cast steels with different morphologies of primary carbides at 950℃ in air were investigated using scanning electron microscopy,energy dispersive spectroscopy,and focused ion beam/transmission electron microscopy.Their oxidation kinetics followed a logarithmic law,and the oxidation rate can be significantly decreased as long as a continuous silica layer formed at the scale/substrate interface.When the local Si concentration was inadequate,internal oxidation occurred beneath the oxide scale.The spallation of oxides during cooling can be inhibited with the formation of internal oxidation,owing to the reduced mismatch stress between the oxide scale and the substrate.The“Chinese-script”primary Nb(C,N)was superior to the dispersed primary Nb(C,N)in suppressing the oxidation penetration in the interdendritic region by supplying a high density of quick-diffusion Cr channels.In addition,the innermost and outermost oxidation layers were enriched with Cr,whereas the Cr evaporation in the outermost layer was significant when the water vapor concentration in the environment was high enough.These findings further the understanding regarding the oxidation behavior of austenitic cast steels and will promote the alloy development for exhaust components.展开更多
The objective of this investigation is to study the influence of vanadium(5.0wt%–10.0wt%) and chromium(0–9.0wt%) on the microstructure and hardness of Cr-V-Mn-Ni white cast irons with spheroidal vanadium carbide...The objective of this investigation is to study the influence of vanadium(5.0wt%–10.0wt%) and chromium(0–9.0wt%) on the microstructure and hardness of Cr-V-Mn-Ni white cast irons with spheroidal vanadium carbides. The alloys' microstructural features are presented and discussed with regard to the distribution of phase elements. The structural constituents of the alloys are spheroidal VC, proeutectoid cementite, ledeburite eutectic, rosette-shaped carbide eutectic(based on M7C3), pearlite, martensite, and austenite. Their combinations and area fraction(AF) ratios are reported to be influenced by the alloys' chemical composition. Spheroidized VC particles are found to be sites for the nucleation of carbide eutectics. Cr and V are shown to substitute each other in the VC and M7C3 carbides, respectively. Chromium alloying leads to the formation of a eutectic(γ-Fe + М7С3), preventing the appearance of proeutectoid cementite in the structure. Vanadium and chromium are revealed to increase the total carbide fraction and the amount of austenite in the matrix. Cr is observed to play a key role in controlling the metallic matrix microstructure.展开更多
基金finacially supported by the University Research Program between Ford Motor Company and the University of Science and Technology Beijing,and the Fundamental Research Funds for the Central Universities(Nos.FRF-IC-16-005 and FRF-IC-19-009)。
文摘The oxidation behaviors of three austenitic cast steels with different morphologies of primary carbides at 950℃ in air were investigated using scanning electron microscopy,energy dispersive spectroscopy,and focused ion beam/transmission electron microscopy.Their oxidation kinetics followed a logarithmic law,and the oxidation rate can be significantly decreased as long as a continuous silica layer formed at the scale/substrate interface.When the local Si concentration was inadequate,internal oxidation occurred beneath the oxide scale.The spallation of oxides during cooling can be inhibited with the formation of internal oxidation,owing to the reduced mismatch stress between the oxide scale and the substrate.The“Chinese-script”primary Nb(C,N)was superior to the dispersed primary Nb(C,N)in suppressing the oxidation penetration in the interdendritic region by supplying a high density of quick-diffusion Cr channels.In addition,the innermost and outermost oxidation layers were enriched with Cr,whereas the Cr evaporation in the outermost layer was significant when the water vapor concentration in the environment was high enough.These findings further the understanding regarding the oxidation behavior of austenitic cast steels and will promote the alloy development for exhaust components.
基金the Muroran Institute of Technology for funding this project
文摘The objective of this investigation is to study the influence of vanadium(5.0wt%–10.0wt%) and chromium(0–9.0wt%) on the microstructure and hardness of Cr-V-Mn-Ni white cast irons with spheroidal vanadium carbides. The alloys' microstructural features are presented and discussed with regard to the distribution of phase elements. The structural constituents of the alloys are spheroidal VC, proeutectoid cementite, ledeburite eutectic, rosette-shaped carbide eutectic(based on M7C3), pearlite, martensite, and austenite. Their combinations and area fraction(AF) ratios are reported to be influenced by the alloys' chemical composition. Spheroidized VC particles are found to be sites for the nucleation of carbide eutectics. Cr and V are shown to substitute each other in the VC and M7C3 carbides, respectively. Chromium alloying leads to the formation of a eutectic(γ-Fe + М7С3), preventing the appearance of proeutectoid cementite in the structure. Vanadium and chromium are revealed to increase the total carbide fraction and the amount of austenite in the matrix. Cr is observed to play a key role in controlling the metallic matrix microstructure.