The effect of C content (0.014-0.39 wt pct) on the paramagnetic-antiferromagnetic transition and γ→ε martensitic transformation of Fe-24Mn alloys has been investigated by the resistivity, dilation, tensile properti...The effect of C content (0.014-0.39 wt pct) on the paramagnetic-antiferromagnetic transition and γ→ε martensitic transformation of Fe-24Mn alloys has been investigated by the resistivity, dilation, tensile properties measurement and microstructure examination. The results have shown that C decreases T_N; increases the thermal expansion coefficients both above and below the T_N; increases the resistivity above the T_N and antiferromagnetic scattering resistivity below T_N. It strongly depresses the γ→ε martensitic transformation and reduces the M_s of Fe-24Mn alloys. Moreover, it increases the lattice parameter of austenite, enhances the tensile ductility, but almost does not affect the tensile strength. With increasing C content from 0.014 to 0.19 wt pct, the yield strength of Fe-24Mn alloy decreases obviously arising from the decreasing of preexisting ε martensite. but it increases from 0.19 to 0.39 wt pct C due to the solution hardening of C.展开更多
The effects of aging temperature on shape memory effect, mechanical properties and microstruc-ture of Fe-14Mn-5Si-8Cr-4Ni-0.2C shape memory alloy have been studied. The results showed that the second phase particles r...The effects of aging temperature on shape memory effect, mechanical properties and microstruc-ture of Fe-14Mn-5Si-8Cr-4Ni-0.2C shape memory alloy have been studied. The results showed that the second phase particles rich in chromium, manganese and silicon precipitate during aging, and thereby increase the hardness and strength of the alloy. The shape recovery ratio can be remarkably improved by aging and a maximum value can be obtained at 1223 K, which is 68% higher than that of the specimen in solid solution state. When the aging temperature is below 1223 K, the amount of second phase particles increases as the aging temperature increases. The size of austenite grain increases with increasing aging temperature. When the temperature is over 1223 K, the second phase particles can not precipitate. The lack of second phase particles and the increase of grain size make the hardness and shape recovery ratio drastically decrease, when the temperature is over 1223 K.展开更多
With electron microscopy the investigation on isothermal martensite transformation in an Fe20.5Ni-4.8Mn alloy has been carried out to clarify the effect of austenite state on the transformation, by applying pre-deform...With electron microscopy the investigation on isothermal martensite transformation in an Fe20.5Ni-4.8Mn alloy has been carried out to clarify the effect of austenite state on the transformation, by applying pre-deformation to austenite before isothermal holding. Under the condition without pre-deformation, the isothermal martensite products are lath martensite with {111}fhabit planes. Dislocations in austenite seem to contribute to nucleation of martensite, and in this nascent Stage austenite substructure has no obvious effect on martensite growth. The consequent thickening of martensite laths is apparently influenced by local austenite states, resulting in the changes in orientation, morphology as well as substructure of martensite lath. The kinetics of isothermal martensite transformation is controlled by intedece dislocation determined nucleation of martensite in primary stage, but to a larger extent, by the austenite accommodation for the shape strain of martensite in the thickening Stage展开更多
The intergranular carbides may significantly increase rupture life and ductility of the Fe-15Cr-25Ni alloy.This seems due to the grain boundary sliding and diffusion hindered by precipitation of intergranular carbides...The intergranular carbides may significantly increase rupture life and ductility of the Fe-15Cr-25Ni alloy.This seems due to the grain boundary sliding and diffusion hindered by precipitation of intergranular carbides,so the nucleation and growth rate of cracks or cavities are reduced.展开更多
The pulsed magnetic field induced martensitic transformation with isothermal and athermal kinetics in Fe-2Ni-4Mn(wt-%)alloy has been studied by means of magnetization measurements,optical microscopy and thermodymical ...The pulsed magnetic field induced martensitic transformation with isothermal and athermal kinetics in Fe-2Ni-4Mn(wt-%)alloy has been studied by means of magnetization measurements,optical microscopy and thermodymical analyses.It is shown that there exits a critical magnetic intensity for induing martensitic transformation at a given temperature above Ms.The critical magnetic field increases linearly with increasing ΔT= T-M_S.The magnetic field strongly promotes the athermal martensitic transforamtion and restrains the isothermal one.The entropy change ΔS for athermal transformation at Ms is 4.13 J/mol· K.The effect of magnetic field on martensitic transformation in Fe-21Ni-4Mn alloy is main- ly due to Zeeman effect.Lath,plate and butterfly martensities were observed under magnetic field.展开更多
Considering the effect of intergranular carbides density,a modified model has been proposed to try to suit any common case of the fraction of intergranular carbides to total grain bounda- ry less than I,on the basis o...Considering the effect of intergranular carbides density,a modified model has been proposed to try to suit any common case of the fraction of intergranular carbides to total grain bounda- ry less than I,on the basis of the previous model for the grain boun dary precipitation strengthening.This modified model may by avilable to predict the changes in creep rate and its stress and temperature dependence of alloys due to intergrnular carbides.展开更多
文摘The effect of C content (0.014-0.39 wt pct) on the paramagnetic-antiferromagnetic transition and γ→ε martensitic transformation of Fe-24Mn alloys has been investigated by the resistivity, dilation, tensile properties measurement and microstructure examination. The results have shown that C decreases T_N; increases the thermal expansion coefficients both above and below the T_N; increases the resistivity above the T_N and antiferromagnetic scattering resistivity below T_N. It strongly depresses the γ→ε martensitic transformation and reduces the M_s of Fe-24Mn alloys. Moreover, it increases the lattice parameter of austenite, enhances the tensile ductility, but almost does not affect the tensile strength. With increasing C content from 0.014 to 0.19 wt pct, the yield strength of Fe-24Mn alloy decreases obviously arising from the decreasing of preexisting ε martensite. but it increases from 0.19 to 0.39 wt pct C due to the solution hardening of C.
文摘The effects of aging temperature on shape memory effect, mechanical properties and microstruc-ture of Fe-14Mn-5Si-8Cr-4Ni-0.2C shape memory alloy have been studied. The results showed that the second phase particles rich in chromium, manganese and silicon precipitate during aging, and thereby increase the hardness and strength of the alloy. The shape recovery ratio can be remarkably improved by aging and a maximum value can be obtained at 1223 K, which is 68% higher than that of the specimen in solid solution state. When the aging temperature is below 1223 K, the amount of second phase particles increases as the aging temperature increases. The size of austenite grain increases with increasing aging temperature. When the temperature is over 1223 K, the second phase particles can not precipitate. The lack of second phase particles and the increase of grain size make the hardness and shape recovery ratio drastically decrease, when the temperature is over 1223 K.
文摘With electron microscopy the investigation on isothermal martensite transformation in an Fe20.5Ni-4.8Mn alloy has been carried out to clarify the effect of austenite state on the transformation, by applying pre-deformation to austenite before isothermal holding. Under the condition without pre-deformation, the isothermal martensite products are lath martensite with {111}fhabit planes. Dislocations in austenite seem to contribute to nucleation of martensite, and in this nascent Stage austenite substructure has no obvious effect on martensite growth. The consequent thickening of martensite laths is apparently influenced by local austenite states, resulting in the changes in orientation, morphology as well as substructure of martensite lath. The kinetics of isothermal martensite transformation is controlled by intedece dislocation determined nucleation of martensite in primary stage, but to a larger extent, by the austenite accommodation for the shape strain of martensite in the thickening Stage
文摘The intergranular carbides may significantly increase rupture life and ductility of the Fe-15Cr-25Ni alloy.This seems due to the grain boundary sliding and diffusion hindered by precipitation of intergranular carbides,so the nucleation and growth rate of cracks or cavities are reduced.
文摘The pulsed magnetic field induced martensitic transformation with isothermal and athermal kinetics in Fe-2Ni-4Mn(wt-%)alloy has been studied by means of magnetization measurements,optical microscopy and thermodymical analyses.It is shown that there exits a critical magnetic intensity for induing martensitic transformation at a given temperature above Ms.The critical magnetic field increases linearly with increasing ΔT= T-M_S.The magnetic field strongly promotes the athermal martensitic transforamtion and restrains the isothermal one.The entropy change ΔS for athermal transformation at Ms is 4.13 J/mol· K.The effect of magnetic field on martensitic transformation in Fe-21Ni-4Mn alloy is main- ly due to Zeeman effect.Lath,plate and butterfly martensities were observed under magnetic field.
文摘Considering the effect of intergranular carbides density,a modified model has been proposed to try to suit any common case of the fraction of intergranular carbides to total grain bounda- ry less than I,on the basis of the previous model for the grain boun dary precipitation strengthening.This modified model may by avilable to predict the changes in creep rate and its stress and temperature dependence of alloys due to intergrnular carbides.
