The growth of proeutectoid ferrite in Fe-0.15%C-0.8 % Mn carbon steel during continuous cooling process was observed in situ and tracked dynamically by using a high temperature confocal scanning laser microscope （ HT...The growth of proeutectoid ferrite in Fe-0.15%C-0.8 % Mn carbon steel during continuous cooling process was observed in situ and tracked dynamically by using a high temperature confocal scanning laser microscope （ HTC SLM）, and the growing process was also investigated. The growth regularity of proeutectoid ferrite plates within austenite was obtained by analyzing the growth fashions and directions and quantitatively studying the growth rates. The results show that the proeutectoid ferrite plates grow in the fashion of creeping, twisting, branching off and de flection within austenite grain. The proeutectoid ferrite plates can grow up along preferential orientation but not strictly. Its growth direction fluctuates and changes in a small range. The growth rate also changes with the change in growth fashion and direction. When the proeutectoid ferrite grows in the fashion of deflection, the average growth rate of proeutectoid ferrite before its deflection is about 61.9, and 46.2 μm/s after the 15°deflection. At the begin ning of proeutectoid ferrite growing, there is a fast growing stage. As the tip of proeutectoid ferrite extends forward continuously, the growth rate will slow down. Therefore, it will induce the proeutectoid ferrite to deflect and grow along another favorable direction, then it will grow rapidly again.展开更多
By combining the α/γ interface migration and the carbon diffusion at the interface in Fe-C alloys, a mathematical model is constructed to describe the mixed-control mechanism for proeutectoid ferrite formation from ...By combining the α/γ interface migration and the carbon diffusion at the interface in Fe-C alloys, a mathematical model is constructed to describe the mixed-control mechanism for proeutectoid ferrite formation from austenite. In this model, the α/γ interface is treated as non-equilibrium interface, i.e., the carbon concentration of austenite at γ/α interface is obtained through theoretical calculation, instead of that assumed as the local equilibrium concentration. For isothermal precipitation of ferrite in Fe-C alloys, the calculated results show that the rate of interface migration decreases monotonically during the whole process, while the rate of carbon diffusion from γ/α interface into austenite increases to a peak value and then decreases. The process of ferrite growth may be considered as composed of three stages: the period of rapid growth, slow growth and finishing stage. The results also show that the carbon concentration of austenite at γ/α interface could not reach the thermodynamic equilibrium value even at the last stage of ferrite growth.展开更多
Growth kinetics of proeutectoid ferrite, including grain boundary face nucleated ferrite, grain boundary edge nucleated ferrite allotriomorph and intragranular ferrite idiomorph, were experimentally measured in an Fe-...Growth kinetics of proeutectoid ferrite, including grain boundary face nucleated ferrite, grain boundary edge nucleated ferrite allotriomorph and intragranular ferrite idiomorph, were experimentally measured in an Fe- 0.09C-1.5Mn-0.2Si steel and compared with theoretical calculation in local equilibrium and paraequilibrium modes. Grain boundary edge nucleated ferrite exhibited larger growth rate than grain boundary face nucleated ferrite and in- tragranular ferrite idiomorph. Experimental kinetics of proeutectoid ferrite was within the window defined by the lo- cal equilibrium and paraequilibrium limits. A transition of growth kinetics from paraequilibrium to local equilibrium was observed in the temperature range of 650--750 ℃, which can be explained in terms of solute drag.展开更多
The incubation period of proeutectoid ferrite transformation for Si-Mn transformation induced plasticity (TRIP) steel has been calculated by the Aaronson's incubation period model for transformation.The influences...The incubation period of proeutectoid ferrite transformation for Si-Mn transformation induced plasticity (TRIP) steel has been calculated by the Aaronson's incubation period model for transformation.The influences of chemical compositions and hot deformation of austenite on the incubation period have been taken into consideration in the calculation,and some parameters have been proposed and validated with the measured time temperature transformation (TTT) curves from dilation tests.The calculation results show that it is essential to take into account of the effect of solute atoms on the interfacial energy in the austenite grain boundaries.For hypoeutectoid steel,the incubation period of ferrite transformation increases with the increase of C and Mn contents,and C has a greater impact than that of Mn,while the incubation period of ferrite transformation decreases with the increase of Si content.Hot deformation shortens the incubation time and promotes austenite to ferrite transformation.展开更多
Proeutectoid ferrite with carbon content xo precipitating from austenite in a multicomponent steel at temperature T is supposed to be equivalent to proeutectoid ferrite with the same carbon content precipitating from...Proeutectoid ferrite with carbon content xo precipitating from austenite in a multicomponent steel at temperature T is supposed to be equivalent to proeutectoid ferrite with the same carbon content precipitating from austenite in Fe-C binary system at temperature T'.is described as the temperature difference of proeutectiod ferrite formation, and can be calculated from the Fe-X diagrams and the equilibrium temperature A3. By introducing Tf and basing on the thermodynamic model for Fe-C binary alloy, the driving force for phase transformation from austenite to proeutectoid ferrite in multicomponent steels has been successfully calculated. Through the Johnson-Mehl equation and using the data hem known TTT diagrams, the relationship between the chemical composition and the intedecial edenly packeter as well as activation energy for proeutectoid ferrite formation can be calculated. The starting curves of proeutectoid ferritic transformation calculated in this way in some hypo-proeutectoid structural steels agree well with the erperimental data.展开更多
基金Item Sponsored by Scientific Director Fund of National Natural Science Foundation of China(51141010)
文摘The growth of proeutectoid ferrite in Fe-0.15%C-0.8 % Mn carbon steel during continuous cooling process was observed in situ and tracked dynamically by using a high temperature confocal scanning laser microscope （ HTC SLM）, and the growing process was also investigated. The growth regularity of proeutectoid ferrite plates within austenite was obtained by analyzing the growth fashions and directions and quantitatively studying the growth rates. The results show that the proeutectoid ferrite plates grow in the fashion of creeping, twisting, branching off and de flection within austenite grain. The proeutectoid ferrite plates can grow up along preferential orientation but not strictly. Its growth direction fluctuates and changes in a small range. The growth rate also changes with the change in growth fashion and direction. When the proeutectoid ferrite grows in the fashion of deflection, the average growth rate of proeutectoid ferrite before its deflection is about 61.9, and 46.2 μm/s after the 15°deflection. At the begin ning of proeutectoid ferrite growing, there is a fast growing stage. As the tip of proeutectoid ferrite extends forward continuously, the growth rate will slow down. Therefore, it will induce the proeutectoid ferrite to deflect and grow along another favorable direction, then it will grow rapidly again.
基金This work was supported by the National Natural Science Foundation of China under grant No.50075053the Emphasized Item of Development Funds of Science and Technology of Shanghai City,China(No.03H201).
文摘By combining the α/γ interface migration and the carbon diffusion at the interface in Fe-C alloys, a mathematical model is constructed to describe the mixed-control mechanism for proeutectoid ferrite formation from austenite. In this model, the α/γ interface is treated as non-equilibrium interface, i.e., the carbon concentration of austenite at γ/α interface is obtained through theoretical calculation, instead of that assumed as the local equilibrium concentration. For isothermal precipitation of ferrite in Fe-C alloys, the calculated results show that the rate of interface migration decreases monotonically during the whole process, while the rate of carbon diffusion from γ/α interface into austenite increases to a peak value and then decreases. The process of ferrite growth may be considered as composed of three stages: the period of rapid growth, slow growth and finishing stage. The results also show that the carbon concentration of austenite at γ/α interface could not reach the thermodynamic equilibrium value even at the last stage of ferrite growth.
基金Item Sponsored by National Natural Science Foundation of China(50734004)
文摘Growth kinetics of proeutectoid ferrite, including grain boundary face nucleated ferrite, grain boundary edge nucleated ferrite allotriomorph and intragranular ferrite idiomorph, were experimentally measured in an Fe- 0.09C-1.5Mn-0.2Si steel and compared with theoretical calculation in local equilibrium and paraequilibrium modes. Grain boundary edge nucleated ferrite exhibited larger growth rate than grain boundary face nucleated ferrite and in- tragranular ferrite idiomorph. Experimental kinetics of proeutectoid ferrite was within the window defined by the lo- cal equilibrium and paraequilibrium limits. A transition of growth kinetics from paraequilibrium to local equilibrium was observed in the temperature range of 650--750 ℃, which can be explained in terms of solute drag.
基金the Scientific and Technical Supporting Program of China during the 11th Five-Year Plan(No.2006BAE03A08)
文摘The incubation period of proeutectoid ferrite transformation for Si-Mn transformation induced plasticity (TRIP) steel has been calculated by the Aaronson's incubation period model for transformation.The influences of chemical compositions and hot deformation of austenite on the incubation period have been taken into consideration in the calculation,and some parameters have been proposed and validated with the measured time temperature transformation (TTT) curves from dilation tests.The calculation results show that it is essential to take into account of the effect of solute atoms on the interfacial energy in the austenite grain boundaries.For hypoeutectoid steel,the incubation period of ferrite transformation increases with the increase of C and Mn contents,and C has a greater impact than that of Mn,while the incubation period of ferrite transformation decreases with the increase of Si content.Hot deformation shortens the incubation time and promotes austenite to ferrite transformation.
文摘Proeutectoid ferrite with carbon content xo precipitating from austenite in a multicomponent steel at temperature T is supposed to be equivalent to proeutectoid ferrite with the same carbon content precipitating from austenite in Fe-C binary system at temperature T'.is described as the temperature difference of proeutectiod ferrite formation, and can be calculated from the Fe-X diagrams and the equilibrium temperature A3. By introducing Tf and basing on the thermodynamic model for Fe-C binary alloy, the driving force for phase transformation from austenite to proeutectoid ferrite in multicomponent steels has been successfully calculated. Through the Johnson-Mehl equation and using the data hem known TTT diagrams, the relationship between the chemical composition and the intedecial edenly packeter as well as activation energy for proeutectoid ferrite formation can be calculated. The starting curves of proeutectoid ferritic transformation calculated in this way in some hypo-proeutectoid structural steels agree well with the erperimental data.
