The electronic structure of ferrite (tempered martensite phase) in high Co-Ni secondary hardened martensitic steel has been investigated. The local density of states (LOOS) of alloying elements in the steel displays t...The electronic structure of ferrite (tempered martensite phase) in high Co-Ni secondary hardened martensitic steel has been investigated. The local density of states (LOOS) of alloying elements in the steel displays the relationship between solid solubility and the shape of the LDOS. The bond order integral (BOI) between atoms in the steel shows that the directional bonding of the p orbital of Si or C leads to the brittleness of the steel. At last, ΣBOI between atoms demonstrate that C, Co, Mn, Cr, Mo, Si strengthen the alloyed steel through solid-solution effects.展开更多
The phase volume fraction has an important role in the match of the strength and plasticity of dual phase steel.The different bainite contents(18–53 vol.%)in polygonal ferrite and bainite(PF+B)dual phase steel were o...The phase volume fraction has an important role in the match of the strength and plasticity of dual phase steel.The different bainite contents(18–53 vol.%)in polygonal ferrite and bainite(PF+B)dual phase steel were obtained by controlling the relaxation finish temperature during the rolling process.The effect of bainite volume fraction on the tensile deformability was systematically investigated via experiments and crystal plasticity finite element model(CPFEM)simulation.The experimental results showed that the steel showed optimal strain hardenability and strength–plasticity matching when the bainite reached 35%.The 3D-CPFEM models with the same grain size and texture characters were established to clarify the influence of stress/strain distribution on PF+B dual phase steel with different bainite contents.The simulation results indicated that an appropriate increase in the bainite content(18%–35%)did not affect the interphase strain difference,but increased the stress distribution in both phases,as a result of enhancing the coordinated deformability of two phases and improving the strength–plasticity matching.When the bainite content increased to 53%,the stress/strain difference between the two phases was greatly increased,and plastic damage between the two phases was caused by the reduction of the coordinated deformability.展开更多
The variation of the O_(2) content in the suction gas,in the range from 7 to 30 vol.%,during the iron ore sintering process,is investigated.Miniaturized laboratory-scale sintering experiments are carried out using an ...The variation of the O_(2) content in the suction gas,in the range from 7 to 30 vol.%,during the iron ore sintering process,is investigated.Miniaturized laboratory-scale sintering experiments are carried out using an industry-like raw mixture to study the effects of O_(2) variation on the sintering process with particular emphasis on the off-gas composition,specific sintering parameters and the sinter strength as well as the chemical composition of the sinter.After the ignition at the bed surface,the gas hood is placed on the sintering column,allowing a synthetic gas mixture to be drawn through the sinter bed until the burn-through point is reached.For additional interpretation of the experimental results,the theoretical coke combustion rate as a function of the oxygen partial pressure was calculated and plotted against the experimentally measured peak temperature in the sinter bed of the respective sinter series.An increasing O_(2) content in the suction gas results in a faster flame front speed combined with a more gradual temperature rise of the heat wave and longer dwell time in the melt phase formation temperature range.Due to the more pronounced flame front,both sinter yield and strength increase,resulting in lower return rates.Below 12 vol.%O_(2),a sharp decrease in sinter yield and strength can be observed,probably due to the low extent of melt phase formation and the associated minor formation of silico ferrite of calcium and aluminum(SFCA).The carbon burnout as well as the calcination increases with increasing the O_(2) content in the suction gas,resulting in higher levels of CO_(2) in the off-gas,with more or less constant amounts of CO above 15 vol.%O_(2).The amounts of NO and SO_(2) show a similar trend with a continuous increase with increasing O_(2) supply,with the SO_(2) breakthrough starting earlier and being released over a shorter period.The chemical analysis of the sinter indicates the highest Fe(II)values in the range of 12–21 vol.%O_(2) in the suction gas.展开更多
Precipitates in an 11% Cr ferritic/martensitic steel containing Nd with tempering and creep conditions were investigated using transmission electron microscope with energy-dispersive X-ray spectroscopy. The precipitat...Precipitates in an 11% Cr ferritic/martensitic steel containing Nd with tempering and creep conditions were investigated using transmission electron microscope with energy-dispersive X-ray spectroscopy. The precipitates in the steel with a tempering condition were identified to be Cr-rich M23C6 carbide, Nb-rich/V-rich/Ta–Nb-rich MX carbides, Nbrich MX carbonitride, and Fe-rich M5C2 carbide. Nd-rich carbonitride, which is not known to have been reported previously in steels, was also detected in the steel after tempering. Most of the Nb-rich MX precipitates were dissolved, whereas the amount of Ta-rich MX precipitates was increased significantly in the steel after a creep test at 600 °C at an applied stress of180 MPa for 1,100 h. No Fe2 W Laves phase has been detected in the steel after tempering.（Fe, Cr）2W Laves phase with a relatively large size was observed in the steel after the creep test.展开更多
The deformation and micro-voids formation mechanisms in ferrite / bainite（ F / B） multi-phase steel with the volume fraction of bainite less than 50% were studied by numerical simulation and experimental observation...The deformation and micro-voids formation mechanisms in ferrite / bainite（ F / B） multi-phase steel with the volume fraction of bainite less than 50% were studied by numerical simulation and experimental observation. The results show that the micro-strain concentrates at the soft / hard phase（ F / B） interface in the multi-phase steel,which should be correlated with the mechanism of incoordinate deformation. During the necking of the steel,the micro-voids initially form around the F / B interface,which also form in ferrite and bainite with the severe strain. The micro-voids in bainite are more dense and finer than those in ferrite. The failure mechanism of bainite is the coalescence of micro-voids,and the failure mechanism of ferrite is the growth and tearing of micro-voids. Due to the different failure mechanisms of ferrite and bainite,a suitable part of soft phase would be beneficial to the capability of anti-failure of F / B multi-phase steel during the ductile fracture.展开更多
文摘The electronic structure of ferrite (tempered martensite phase) in high Co-Ni secondary hardened martensitic steel has been investigated. The local density of states (LOOS) of alloying elements in the steel displays the relationship between solid solubility and the shape of the LDOS. The bond order integral (BOI) between atoms in the steel shows that the directional bonding of the p orbital of Si or C leads to the brittleness of the steel. At last, ΣBOI between atoms demonstrate that C, Co, Mn, Cr, Mo, Si strengthen the alloyed steel through solid-solution effects.
基金supported by the Project of Liaoning Marine Economic Development(Development of high strength pipeline steel for submarine oil and gas transmission)State Key Laboratory of Metal Material for Marine Equipment and Application Funding(No.SKLMEA-K202205).
文摘The phase volume fraction has an important role in the match of the strength and plasticity of dual phase steel.The different bainite contents(18–53 vol.%)in polygonal ferrite and bainite(PF+B)dual phase steel were obtained by controlling the relaxation finish temperature during the rolling process.The effect of bainite volume fraction on the tensile deformability was systematically investigated via experiments and crystal plasticity finite element model(CPFEM)simulation.The experimental results showed that the steel showed optimal strain hardenability and strength–plasticity matching when the bainite reached 35%.The 3D-CPFEM models with the same grain size and texture characters were established to clarify the influence of stress/strain distribution on PF+B dual phase steel with different bainite contents.The simulation results indicated that an appropriate increase in the bainite content(18%–35%)did not affect the interphase strain difference,but increased the stress distribution in both phases,as a result of enhancing the coordinated deformability of two phases and improving the strength–plasticity matching.When the bainite content increased to 53%,the stress/strain difference between the two phases was greatly increased,and plastic damage between the two phases was caused by the reduction of the coordinated deformability.
基金Open access funding provided by Montanuniversität Leoben.
文摘The variation of the O_(2) content in the suction gas,in the range from 7 to 30 vol.%,during the iron ore sintering process,is investigated.Miniaturized laboratory-scale sintering experiments are carried out using an industry-like raw mixture to study the effects of O_(2) variation on the sintering process with particular emphasis on the off-gas composition,specific sintering parameters and the sinter strength as well as the chemical composition of the sinter.After the ignition at the bed surface,the gas hood is placed on the sintering column,allowing a synthetic gas mixture to be drawn through the sinter bed until the burn-through point is reached.For additional interpretation of the experimental results,the theoretical coke combustion rate as a function of the oxygen partial pressure was calculated and plotted against the experimentally measured peak temperature in the sinter bed of the respective sinter series.An increasing O_(2) content in the suction gas results in a faster flame front speed combined with a more gradual temperature rise of the heat wave and longer dwell time in the melt phase formation temperature range.Due to the more pronounced flame front,both sinter yield and strength increase,resulting in lower return rates.Below 12 vol.%O_(2),a sharp decrease in sinter yield and strength can be observed,probably due to the low extent of melt phase formation and the associated minor formation of silico ferrite of calcium and aluminum(SFCA).The carbon burnout as well as the calcination increases with increasing the O_(2) content in the suction gas,resulting in higher levels of CO_(2) in the off-gas,with more or less constant amounts of CO above 15 vol.%O_(2).The amounts of NO and SO_(2) show a similar trend with a continuous increase with increasing O_(2) supply,with the SO_(2) breakthrough starting earlier and being released over a shorter period.The chemical analysis of the sinter indicates the highest Fe(II)values in the range of 12–21 vol.%O_(2) in the suction gas.
基金financially supported by Key Program of National Natural Science Foundation of China (No. 51034011)ITER-National Magnetic Confinement Fusion Program (No.2011GB113001)National Science and Technology Major Project (No.2011ZX06004-009)
文摘Precipitates in an 11% Cr ferritic/martensitic steel containing Nd with tempering and creep conditions were investigated using transmission electron microscope with energy-dispersive X-ray spectroscopy. The precipitates in the steel with a tempering condition were identified to be Cr-rich M23C6 carbide, Nb-rich/V-rich/Ta–Nb-rich MX carbides, Nbrich MX carbonitride, and Fe-rich M5C2 carbide. Nd-rich carbonitride, which is not known to have been reported previously in steels, was also detected in the steel after tempering. Most of the Nb-rich MX precipitates were dissolved, whereas the amount of Ta-rich MX precipitates was increased significantly in the steel after a creep test at 600 °C at an applied stress of180 MPa for 1,100 h. No Fe2 W Laves phase has been detected in the steel after tempering.（Fe, Cr）2W Laves phase with a relatively large size was observed in the steel after the creep test.
基金Item Sponsored by National Basic Research Program of China(2010CB630801)
文摘The deformation and micro-voids formation mechanisms in ferrite / bainite（ F / B） multi-phase steel with the volume fraction of bainite less than 50% were studied by numerical simulation and experimental observation. The results show that the micro-strain concentrates at the soft / hard phase（ F / B） interface in the multi-phase steel,which should be correlated with the mechanism of incoordinate deformation. During the necking of the steel,the micro-voids initially form around the F / B interface,which also form in ferrite and bainite with the severe strain. The micro-voids in bainite are more dense and finer than those in ferrite. The failure mechanism of bainite is the coalescence of micro-voids,and the failure mechanism of ferrite is the growth and tearing of micro-voids. Due to the different failure mechanisms of ferrite and bainite,a suitable part of soft phase would be beneficial to the capability of anti-failure of F / B multi-phase steel during the ductile fracture.
