Austenitic high-Mn steels with Mn contents between approximately 15 and 30 wt% gain much interest because of their excellent mechanical properties and the option for adjusting strain hardening behavior due to differen...Austenitic high-Mn steels with Mn contents between approximately 15 and 30 wt% gain much interest because of their excellent mechanical properties and the option for adjusting strain hardening behavior due to different deformation mechanisms. 2D and 3D composition-dependent stacking fault energy （SFE） maps indicate the effect of chemical composition and temperature on SFE and consequently on the deformation mechanisms. Three steels with different chemical compositions and the same or different SFE are characterized in quasi-static tensile tests. The control parameters of strain hardening behavior in the high-Mn austenitic steels are described, and consequences for future developments are discussed.展开更多
To understand the mechanism of the interfacial reaction between high-Mn and high-Al steel and MgO refractory,a series of laboratory experiments as well as thermodynamic calculations were performed.The effects of Mn an...To understand the mechanism of the interfacial reaction between high-Mn and high-Al steel and MgO refractory,a series of laboratory experiments as well as thermodynamic calculations were performed.The effects of Mn and Al contents in the steel and the reaction time on the interfacial reaction were investigated.It was observed that the erosion of the MgO refractory is caused by the reaction of Al and Mn in the steel with MgO in the refractory,which would lead to the formation of(Mn,Mg)O·Al_(2)O_(3) spinel and(Mn,Mg)O solid solution.The formation mechanism of the spinel and solid solution is as follows.The Al in the steel firstly reacts with MgO in the refractory to generate MgO·Al_(2)O_(3) spinel,and then,the spinel reacts with Mn in the steel to form(Mn,Mg)O·Al_(2)O_(3) spinel.Finally,the MnO in the spinel reacts with the MgO in the inner refractory to form(Mn,Mg)O solid solution.In addition,only(Mn,Mg)O·Al_(2)O_(3) spinel is present in the interfacial reaction layer of the refractory when the Al content in the steel is sufficient.展开更多
The effect of grain size on the mechanical properties of a high-manganese(Mn)austenitic steel was investigated via electron-backscattered diffraction,transmission electron microscope,X-ray diffraction,and tensile and ...The effect of grain size on the mechanical properties of a high-manganese(Mn)austenitic steel was investigated via electron-backscattered diffraction,transmission electron microscope,X-ray diffraction,and tensile and impact tests at 25°C and-196°C.The Hall–Petch strengthening coefficients for the yield strength of the high-Mn austenitic steels were 7.08 MPa mm 0.5 at 25°C,which increased to 14 MPa mm 0.5 at-196°C.The effect that the grain boundary strengthening had on improving the yield strength at-196°C was better than that at 25°C.The impact absorbed energies and the tensile elongations were enhanced with the increased grain size at 25°C,while they remained nearly unchanged at-196°C.The unchanged impact absorbed energies and the tensile elongations were primarily attributed to the emergence of the micro-twin at-196°C,which promoted the cleavage fracture in the steels with large-sized grains.Refining the grain size could improve the strength of the high-Mn austenitic steels without impairing their ductility and toughness at low temperature.展开更多
Deformation-induced microstructures of high-Mn austenite steel was investigated by metallography,X-ray diffraction and SEM.The ε-martensite and slip-bands are deformation-in- duced on the{111} planes,and appear as th...Deformation-induced microstructures of high-Mn austenite steel was investigated by metallography,X-ray diffraction and SEM.The ε-martensite and slip-bands are deformation-in- duced on the{111} planes,and appear as thin straight laths with 60～80° alignment difference be- tween them.It was found that ε-martensite and slip bands are kinked at fcc twin boundaries with the kinked angle 35～40°.The bands of equilateral triangle in the microstructure of tensile deformation are presented.展开更多
Assessing the stacking fault forming probability(P_(sf)) and stacking fault energy(SFE)in medium-or highMn base structural materials can anticipate and elucidate the microstructural evolution before and after deformat...Assessing the stacking fault forming probability(P_(sf)) and stacking fault energy(SFE)in medium-or highMn base structural materials can anticipate and elucidate the microstructural evolution before and after deformation.Typically,these two parameters have been determined from theoretical calculations and empirical results.However,the estimation of SFE values in Fe–Mn–C ternary systems is a longstanding debate due to the complicated nature of carbon:that is,whether the carbon doping indeed plays an important role in the formation of stacking faults;and how the amount of carbon atoms exist at grain boundaries or at internal grains with respect to the nominal carbon doping contents.Herein,the use of atom probe tomography and transmission electron microscopy(TEM)unveils the influence of carbondoping contents on the structural properties of dual-phase Fe–17 Mn–x C(x=0–1.56 at%)steels,such as carbon segregation free energy at grain boundaries,carbon concentration in grain interior,interplanar D-spacings,and mean width of intrinsic stacking faults,which are essential for SFE estimation.We next determined the Psfvalues by two different methods,viz.,reciprocal-space electron diffraction measurements and stacking fault width measurements in real-space TEM images.Then,SFEs in the Fe–17 Mn–x C systems were calculated on the basis of the generally-known SFE equations.We found that the high amount of carbon doping gives rise to the increased SFE from 8.6 to 13.5 m J/m^(2)with non-linear variation.This SFE trend varies inversely with the mean width of localized stacking faults,which pass through both other stacking faults and pre-existingε-martensite plates without much difficulty at their intersecting zones.The high amount of carbon doping acts twofold,through increasing the segregation free energy(due to more carbon at grain boundaries)and large lattice expansion(due to increased soluble carbon at internal grains).The experimental data obtained here strengthens the composition-dependent SFE maps for predicting展开更多
Effects of Cr addition(0,3,and 6 wt%) on Charpy impact properties of Fe-C-Mn-Cr-based steels were studied by conducting dynamic compression tests at room and cryogenic temperatures.At room temperature,deformation mech...Effects of Cr addition(0,3,and 6 wt%) on Charpy impact properties of Fe-C-Mn-Cr-based steels were studied by conducting dynamic compression tests at room and cryogenic temperatures.At room temperature,deformation mechanisms of Charpy impacted specimens were observed as twinning induced plasticity(TWIP) without any transfo rmation induced plasticity(TRIP) in all the steels.At cryogenic temperature,many twins were populated in the Cr-added steels,but,interestingly,fine ε-martensite was found in the OCr steel,satisfying the Shoji-Nishiyama(S-N) orientation relationship,{111}γ//{0002}ε and <101>γ//<1120>ε.Even though the cryogenic-temperature staking fault energies(SFEs) of the three steel were situated in the TWIP regime,the martensitic transformation was induced by Mn-and Cr-segregated bands.In the OCr steel,SFEs of low-(Mn,Cr) bands lay between the TWIP and TRIP regimes which were sensitively affected by a small change of SFE.The dynamic compressive test results well showed the relation between segregation bands and the SFEs.Effects of Cr were known as not only increasing the SFE but also promoting the carbide precipitation.In order to identify the possibility of carbide formation,a precipitation kinetics simulation was conducted,and the predicted fractions of precipitated M23C6 were negligible,0.4-1.1×10-5,even at the low cooling rate of 10℃/s.展开更多
The formability of austenitic high-Mn steels is a critical issue in automotive applications under nonuniformly-deformed environments caused by dynamic strain aging.Among austenite stabilizing alloying elements in thos...The formability of austenitic high-Mn steels is a critical issue in automotive applications under nonuniformly-deformed environments caused by dynamic strain aging.Among austenite stabilizing alloying elements in those steels,Cu has been known as an effective element to enhance tensile properties via controlling the stacking fault energy and stability of austenite.The effects of Cu addition on formability,however,have not been sufficiently reported yet.In this study,the Cu addition effects on formability and surface characteristics in the austenitic high-Mn TRIP steels were analyzed in consideration of inhomogeneous microstructures containing the segregation of Mn and Cu.To reveal determining factors,various mechanical parameters such as total elongation,post elongation,strain hardening rate,normal anisotropy,and planar anisotropy were correlated to the hole-expansion and cup-drawing test results.With respect to microstructural parameters,roles of(Mn,Cu)-segregation bands and resultant Cu-rich FCC precipitates on the formability and surface delamination were also discussed.展开更多
采用埋弧焊工艺制备含镧(La)高锰奥氏体钢(Fe-24%Mn)焊缝金属,研究了La含量对焊缝金属微观组织、非金属夹杂物类型和尺寸分布及力学性能的影响。结果表明,当La含量依次为0、0.042%、0.098%时,焊缝金属中典型夹杂物分别为Mn-Al-Si氧化物+...采用埋弧焊工艺制备含镧(La)高锰奥氏体钢(Fe-24%Mn)焊缝金属,研究了La含量对焊缝金属微观组织、非金属夹杂物类型和尺寸分布及力学性能的影响。结果表明,当La含量依次为0、0.042%、0.098%时,焊缝金属中典型夹杂物分别为Mn-Al-Si氧化物+MnS复合夹杂物、La_(2)O_(3)夹杂物、La 2 O 2S夹杂物,夹杂物平均尺寸分别为0.56、0.43、0.48μm,数量密度分别为4845、5605、5950个/mm 2。与未添加La的焊缝金属相比,适量La的加入明显细化了焊缝金属凝固组织,并提高了其力学性能。其中La含量为0.042%的焊缝金属表现出最佳的力学性能,其断裂方式为韧性断裂,断口形貌表现为密集分布的小尺寸等轴韧窝。这可以归因于细小且数量众多的La_(2)O_(3)与初生奥氏体点阵的错配度低,有效促进了奥氏体异质形核,细化了凝固组织;另外,位于韧窝底部的La_(2)O_(3)与基体之间良好的结合能力有助于延缓裂纹扩展至夹杂物时的应力集中,从而增强了焊缝金属的力学性能。展开更多
基金support of the Deutsche Forschungsgemeinschaft(DFG) within the Collaborative Research Center(SFB) 761 "Steelab initio"
文摘Austenitic high-Mn steels with Mn contents between approximately 15 and 30 wt% gain much interest because of their excellent mechanical properties and the option for adjusting strain hardening behavior due to different deformation mechanisms. 2D and 3D composition-dependent stacking fault energy （SFE） maps indicate the effect of chemical composition and temperature on SFE and consequently on the deformation mechanisms. Three steels with different chemical compositions and the same or different SFE are characterized in quasi-static tensile tests. The control parameters of strain hardening behavior in the high-Mn austenitic steels are described, and consequences for future developments are discussed.
基金the support of the National Natural Science Foundation of China(Grant Nos.52274337 and 52174317)。
文摘To understand the mechanism of the interfacial reaction between high-Mn and high-Al steel and MgO refractory,a series of laboratory experiments as well as thermodynamic calculations were performed.The effects of Mn and Al contents in the steel and the reaction time on the interfacial reaction were investigated.It was observed that the erosion of the MgO refractory is caused by the reaction of Al and Mn in the steel with MgO in the refractory,which would lead to the formation of(Mn,Mg)O·Al_(2)O_(3) spinel and(Mn,Mg)O solid solution.The formation mechanism of the spinel and solid solution is as follows.The Al in the steel firstly reacts with MgO in the refractory to generate MgO·Al_(2)O_(3) spinel,and then,the spinel reacts with Mn in the steel to form(Mn,Mg)O·Al_(2)O_(3) spinel.Finally,the MnO in the spinel reacts with the MgO in the inner refractory to form(Mn,Mg)O solid solution.In addition,only(Mn,Mg)O·Al_(2)O_(3) spinel is present in the interfacial reaction layer of the refractory when the Al content in the steel is sufficient.
基金supported financially by the National Key Research and Development Program of China (No.2017YFB0305100)
文摘The effect of grain size on the mechanical properties of a high-manganese(Mn)austenitic steel was investigated via electron-backscattered diffraction,transmission electron microscope,X-ray diffraction,and tensile and impact tests at 25°C and-196°C.The Hall–Petch strengthening coefficients for the yield strength of the high-Mn austenitic steels were 7.08 MPa mm 0.5 at 25°C,which increased to 14 MPa mm 0.5 at-196°C.The effect that the grain boundary strengthening had on improving the yield strength at-196°C was better than that at 25°C.The impact absorbed energies and the tensile elongations were enhanced with the increased grain size at 25°C,while they remained nearly unchanged at-196°C.The unchanged impact absorbed energies and the tensile elongations were primarily attributed to the emergence of the micro-twin at-196°C,which promoted the cleavage fracture in the steels with large-sized grains.Refining the grain size could improve the strength of the high-Mn austenitic steels without impairing their ductility and toughness at low temperature.
文摘Deformation-induced microstructures of high-Mn austenite steel was investigated by metallography,X-ray diffraction and SEM.The ε-martensite and slip-bands are deformation-in- duced on the{111} planes,and appear as thin straight laths with 60～80° alignment difference be- tween them.It was found that ε-martensite and slip bands are kinked at fcc twin boundaries with the kinked angle 35～40°.The bands of equilateral triangle in the microstructure of tensile deformation are presented.
基金the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(2020R1A4A3079417)(No.2021R1A2C4002622)by the Future Material Discovery Program of the NRFfunded by the MSIP of Korea(No.2021M3D1A1021236)。
文摘Assessing the stacking fault forming probability(P_(sf)) and stacking fault energy(SFE)in medium-or highMn base structural materials can anticipate and elucidate the microstructural evolution before and after deformation.Typically,these two parameters have been determined from theoretical calculations and empirical results.However,the estimation of SFE values in Fe–Mn–C ternary systems is a longstanding debate due to the complicated nature of carbon:that is,whether the carbon doping indeed plays an important role in the formation of stacking faults;and how the amount of carbon atoms exist at grain boundaries or at internal grains with respect to the nominal carbon doping contents.Herein,the use of atom probe tomography and transmission electron microscopy(TEM)unveils the influence of carbondoping contents on the structural properties of dual-phase Fe–17 Mn–x C(x=0–1.56 at%)steels,such as carbon segregation free energy at grain boundaries,carbon concentration in grain interior,interplanar D-spacings,and mean width of intrinsic stacking faults,which are essential for SFE estimation.We next determined the Psfvalues by two different methods,viz.,reciprocal-space electron diffraction measurements and stacking fault width measurements in real-space TEM images.Then,SFEs in the Fe–17 Mn–x C systems were calculated on the basis of the generally-known SFE equations.We found that the high amount of carbon doping gives rise to the increased SFE from 8.6 to 13.5 m J/m^(2)with non-linear variation.This SFE trend varies inversely with the mean width of localized stacking faults,which pass through both other stacking faults and pre-existingε-martensite plates without much difficulty at their intersecting zones.The high amount of carbon doping acts twofold,through increasing the segregation free energy(due to more carbon at grain boundaries)and large lattice expansion(due to increased soluble carbon at internal grains).The experimental data obtained here strengthens the composition-dependent SFE maps for predicting
基金supported financially by the Korea University Grant for the eighth author, the Ministry of Knowledge Economy (No. 10044574-2013-45)Brain Korea 21 Plus Project for Center for Creative Industrial materialsKorea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (No. P0002020, The Competency Development Program for Industry Specialist)。
文摘Effects of Cr addition(0,3,and 6 wt%) on Charpy impact properties of Fe-C-Mn-Cr-based steels were studied by conducting dynamic compression tests at room and cryogenic temperatures.At room temperature,deformation mechanisms of Charpy impacted specimens were observed as twinning induced plasticity(TWIP) without any transfo rmation induced plasticity(TRIP) in all the steels.At cryogenic temperature,many twins were populated in the Cr-added steels,but,interestingly,fine ε-martensite was found in the OCr steel,satisfying the Shoji-Nishiyama(S-N) orientation relationship,{111}γ//{0002}ε and <101>γ//<1120>ε.Even though the cryogenic-temperature staking fault energies(SFEs) of the three steel were situated in the TWIP regime,the martensitic transformation was induced by Mn-and Cr-segregated bands.In the OCr steel,SFEs of low-(Mn,Cr) bands lay between the TWIP and TRIP regimes which were sensitively affected by a small change of SFE.The dynamic compressive test results well showed the relation between segregation bands and the SFEs.Effects of Cr were known as not only increasing the SFE but also promoting the carbide precipitation.In order to identify the possibility of carbide formation,a precipitation kinetics simulation was conducted,and the predicted fractions of precipitated M23C6 were negligible,0.4-1.1×10-5,even at the low cooling rate of 10℃/s.
基金supported by the Korea Institute for Advancement of Technology(KIAT)grant funded by the Korea Government(MOTIE)(Grant No.P0002019)the Korea University Grant for the fifth authorthe Brain Korea 21 PLUS Project for Center for Creative Industrial Materials。
文摘The formability of austenitic high-Mn steels is a critical issue in automotive applications under nonuniformly-deformed environments caused by dynamic strain aging.Among austenite stabilizing alloying elements in those steels,Cu has been known as an effective element to enhance tensile properties via controlling the stacking fault energy and stability of austenite.The effects of Cu addition on formability,however,have not been sufficiently reported yet.In this study,the Cu addition effects on formability and surface characteristics in the austenitic high-Mn TRIP steels were analyzed in consideration of inhomogeneous microstructures containing the segregation of Mn and Cu.To reveal determining factors,various mechanical parameters such as total elongation,post elongation,strain hardening rate,normal anisotropy,and planar anisotropy were correlated to the hole-expansion and cup-drawing test results.With respect to microstructural parameters,roles of(Mn,Cu)-segregation bands and resultant Cu-rich FCC precipitates on the formability and surface delamination were also discussed.
文摘采用埋弧焊工艺制备含镧(La)高锰奥氏体钢(Fe-24%Mn)焊缝金属,研究了La含量对焊缝金属微观组织、非金属夹杂物类型和尺寸分布及力学性能的影响。结果表明,当La含量依次为0、0.042%、0.098%时,焊缝金属中典型夹杂物分别为Mn-Al-Si氧化物+MnS复合夹杂物、La_(2)O_(3)夹杂物、La 2 O 2S夹杂物,夹杂物平均尺寸分别为0.56、0.43、0.48μm,数量密度分别为4845、5605、5950个/mm 2。与未添加La的焊缝金属相比,适量La的加入明显细化了焊缝金属凝固组织,并提高了其力学性能。其中La含量为0.042%的焊缝金属表现出最佳的力学性能,其断裂方式为韧性断裂,断口形貌表现为密集分布的小尺寸等轴韧窝。这可以归因于细小且数量众多的La_(2)O_(3)与初生奥氏体点阵的错配度低,有效促进了奥氏体异质形核,细化了凝固组织;另外,位于韧窝底部的La_(2)O_(3)与基体之间良好的结合能力有助于延缓裂纹扩展至夹杂物时的应力集中,从而增强了焊缝金属的力学性能。
