The σ-phase precipitation in 20% cold-worked 15Cr-15Ni titanium-modified austenitic stainless steel was studied during long-term aging treatment.During the isothermal aging stage,the amount of a-phase was significant...The σ-phase precipitation in 20% cold-worked 15Cr-15Ni titanium-modified austenitic stainless steel was studied during long-term aging treatment.During the isothermal aging stage,the amount of a-phase was significantly increased at beginning and gradually became constant.The aging time only slightly affected the size and morphology of the σ-phase.Conversely,during the isochronal aging stage,the amount ofσ-phase grew rapidly with the increase in the aging temperature.The σ-phase with a large amount of stacking faults was prone to nucleate around the（Ti,Mo）C particles or at the grain boundaries.The（Ti,Mo）C particles can act as effective nucleation sites,where the σ-phase directly precipitates from the austenitic matrix.From this work,the growth of σ-phase is found to be influenced by the aging temperature,and a new mechanism of σ-phase precipitation from austenite has been proposed.展开更多
The precipitation kinetics of secondary phases in two austeno-ferritic lean duplex stainless steels（lean DSS）were examined after aging the materials at 800 ℃.Owing to the instability of ferrite,all DSS are known to...The precipitation kinetics of secondary phases in two austeno-ferritic lean duplex stainless steels（lean DSS）were examined after aging the materials at 800 ℃.Owing to the instability of ferrite,all DSS are known to be sensitive to solid-state phase transformations in the critical temperature range 600-1,000 ℃ and different secondary phases may form,depending on composition and microstructure.The performed thermodynamic simulations revealed the proneness to the precipitation of such phases also have been done in lean DSS,but only information on the equilibrium microstructures were achieved.Therefore,the materials were aged at various times,in order to verify the simulations and determine the precipitation kinetics.The occurred structural modifications were observed and quantified by scanning electron microscope and X-ray diffraction measurements,determining phase type,composition and volumetric fraction.At 800 ℃,grade 2101 was found to be only affected by Cr_2N nitrides precipitation,whereas a significant amount of σ-phase was found to form in LDX 2404 for treatment longer than 1 h,almost totally replacing ferrite after 50 h.Up to now,the intermetallic σ-phase has been observed only in the high alloyed DSS,and the unexpected precipitation in grade 2404 highlighted that the increased content of molybdenum in this steel might be considered as determinant for the formation.展开更多
文摘The σ-phase precipitation in 20% cold-worked 15Cr-15Ni titanium-modified austenitic stainless steel was studied during long-term aging treatment.During the isothermal aging stage,the amount of a-phase was significantly increased at beginning and gradually became constant.The aging time only slightly affected the size and morphology of the σ-phase.Conversely,during the isochronal aging stage,the amount ofσ-phase grew rapidly with the increase in the aging temperature.The σ-phase with a large amount of stacking faults was prone to nucleate around the（Ti,Mo）C particles or at the grain boundaries.The（Ti,Mo）C particles can act as effective nucleation sites,where the σ-phase directly precipitates from the austenitic matrix.From this work,the growth of σ-phase is found to be influenced by the aging temperature,and a new mechanism of σ-phase precipitation from austenite has been proposed.
文摘The precipitation kinetics of secondary phases in two austeno-ferritic lean duplex stainless steels（lean DSS）were examined after aging the materials at 800 ℃.Owing to the instability of ferrite,all DSS are known to be sensitive to solid-state phase transformations in the critical temperature range 600-1,000 ℃ and different secondary phases may form,depending on composition and microstructure.The performed thermodynamic simulations revealed the proneness to the precipitation of such phases also have been done in lean DSS,but only information on the equilibrium microstructures were achieved.Therefore,the materials were aged at various times,in order to verify the simulations and determine the precipitation kinetics.The occurred structural modifications were observed and quantified by scanning electron microscope and X-ray diffraction measurements,determining phase type,composition and volumetric fraction.At 800 ℃,grade 2101 was found to be only affected by Cr_2N nitrides precipitation,whereas a significant amount of σ-phase was found to form in LDX 2404 for treatment longer than 1 h,almost totally replacing ferrite after 50 h.Up to now,the intermetallic σ-phase has been observed only in the high alloyed DSS,and the unexpected precipitation in grade 2404 highlighted that the increased content of molybdenum in this steel might be considered as determinant for the formation.
