Critical cooling rate to avoid carbide precipitation during quenching of austenitic manganese steel was investigated by means of optical microscopy,image analyzer and numerical analysis.An efficient heat treatment ana...Critical cooling rate to avoid carbide precipitation during quenching of austenitic manganese steel was investigated by means of optical microscopy,image analyzer and numerical analysis.An efficient heat treatment analysis program including temperature-dependent material properties was developed for the prediction of cooling rate and probability of carbide precipitation during quenching by finite difference method.Time-dependent heat transfer coefficient was adopted to achieve more precise results.Area ratio of carbide precipitation was measured by image analyzer to determine the critical point of carbide precipitation.Temperature-dependent critical cooling rate at that point was calculated by the developed numerical program.Finally,the probability of carbide precipitation on the whole area of specimen can be predicted by the proposed numerical program and the numerical result of a specimen was compared with the experimental result.展开更多
Three types of steels were designed on the basis of GX40CrNiSi25-12 austenitic heat resistant steel by adding different Mn contents(2wt.%,6wt.%,and 12wt.%).Thermodynamic calculation,microstructure characterization and...Three types of steels were designed on the basis of GX40CrNiSi25-12 austenitic heat resistant steel by adding different Mn contents(2wt.%,6wt.%,and 12wt.%).Thermodynamic calculation,microstructure characterization and mechanical property tests were conducted to investigate the effect of Mn addition on the microstructure and mechanical properties of the austenitic heat resistant steel.Results show that the matrix structure in all the three types of steels at room temperature is completely austenite.Carbides NbC and M_(23)C_(6)precipitate at grain boundaries of austenite matrix.With the increase of Mn content,the number of carbides increases and their distribution becomes more uniform.With the Mn content increases from 1.99%to 12.06%,the ultimate tensile strength,yield strength and elongation increase by 14.6%,8.0%and 46.3%,respectively.The improvement of the mechanical properties of austenitic steels can be explained by utilizing classic theories of alloy strengthening,including solid solution strengthening,precipitation strengthening,and grain refinement.The increase in alloy strength can be attributed to solid solution strengthening and precipitation strengthening caused by the addition of Mn.The improvement of the plasticity of austenitic steels can be explained from two aspects:grain refinement and homogenization of precipitated phases.展开更多
This paper presents the in-situ TEM tensile observation of the nucleation and growth ofmartensite and the dislocation configuration change in metastable austenitic manganesesteels and the investigation of the composit...This paper presents the in-situ TEM tensile observation of the nucleation and growth ofmartensite and the dislocation configuration change in metastable austenitic manganesesteels and the investigation of the composition of phases and the content of elements inthe micro regions by XRD,EDAX respectively and concludes from the results that thestrengthening of martensite transformation and high density of dislocations lead to thehigh work-hardening capacity in the steel.展开更多
To further understand the hardening mechanism of austenitic manganese steel under actual working conditions, the work hardening ability was studied and the microstructures of austenitic manganese steel were observed u...To further understand the hardening mechanism of austenitic manganese steel under actual working conditions, the work hardening ability was studied and the microstructures of austenitic manganese steel were observed under different impact energies. The work hardening mechanism was also analyzed. The results show that the best strain hardening effect could be received only when the impact energy reaches or exceeds the critical impact energy. The microstructural observations reveal that dislocations, stacking faults and twins increase with raising impact energy of the tested specimens. The hardening mechanism changes at different hardening degrees. It is mainly dislocation and slip hardening below the critical impact energy, but it changes to the twinning hardening mechanism when the impact energy is above the critical impact energy.展开更多
By means of thermodynamic calculations, optical microscope, sweep electron microscope(SEM), transimssion electron microscope(TEM) and microcomposition detection, the modifying effect of RE and Ti on austenitic mangane...By means of thermodynamic calculations, optical microscope, sweep electron microscope(SEM), transimssion electron microscope(TEM) and microcomposition detection, the modifying effect of RE and Ti on austenitic manganese steel was investigated The results show that the constitutional supercooling of austenitic manganese steel during solidification can be improved and the dendritic crystals can be grown facilely, melted, isolated and multiplied by adding RE(Ce) In the melt the alloying elements Ti and C can form TiC directly which acts as nucleus of cementite and causes both primary and eutectic cementite to be granulated and refined so that the cementite network in this steel can be eliminated展开更多
The effect of C,Mn and heat-treatment on work-hardening of austenitic Mn steel and the work-hardening mechanism have been investigated under non-severe impact loading condition.The results show that the ability of wor...The effect of C,Mn and heat-treatment on work-hardening of austenitic Mn steel and the work-hardening mechanism have been investigated under non-severe impact loading condition.The results show that the ability of work-hardening in- creases with the increase of C and aging tempera- ture but decreases with Mn.The work-hardening with high austenitic stability results mainly from dislocations,and that with low austenitic stability results mainly from combined effects of strain-in- duced martensite and high density of dislocations under non-severe impact loading conditions.The wear resistance of medium manganese steel (Mn7) is 1.64-2.46 times that of Hadfield steel (Mnl3).展开更多
The transfer behavior of nitrogen into the welding metal during gas tungsten arc welding process of 32Mn-7Cr-1Mo-0.3N steel was investigated. The effects of gas tungsten arc welding process variables, such as the volu...The transfer behavior of nitrogen into the welding metal during gas tungsten arc welding process of 32Mn-7Cr-1Mo-0.3N steel was investigated. The effects of gas tungsten arc welding process variables, such as the volume fraction of nitrogen in shielding gas, arc holding time and arc current on the nitrogen content in the welding metal were also evaluated. The results show that the volume fraction of nitrogen in gas mixture plays a major role in controlling the nitrogen content in the welding metal. It seems that there exhibits a maximum nitrogen content (depending) on the arc current and arc holding time. The optimum volume fraction of nitrogen in shielding gas is 4% or so. The role of gas tungsten arc welding processing parameters in controlling the transfer of nitrogen is further (confirmed) by the experimental results of gas tungsten arc welding process with feeding metal.展开更多
Plastic instability,including both the discontinuous yielding and stress serrations,has been frequently observed during the tensile deformation of medium-Mn steels(MMnS)and has been intensively studied in recent years...Plastic instability,including both the discontinuous yielding and stress serrations,has been frequently observed during the tensile deformation of medium-Mn steels(MMnS)and has been intensively studied in recent years.Unfortunately,research results are controversial,and no consensus has been achieved regarding the topic.Here,we first summarize all the possible factors that affect the yielding and flow stress serrations in MMnS,including the morphology and stability of austenite,the feature of the phase interface,and the deformation parameters.Then,we propose a universal mechanism to explain the conflicting experimental results.We conclude that the discontinuous yielding can be attributed to the lack of mobile dislocation before deformation and the rapid dislocation multiplication at the beginning of plastic deformation.Meanwhile,the results show that the stress serrations are formed due to the pinning and depinning between dislocations and interstitial atoms in austenite.Strain-induced martensitic transformation,influenced by the mechanical stability of austenite grain and deformation parameters,should not be the intrinsic cause of plastic instability.However,it can intensify or weaken the discontinuous yielding and the stress serrations by affecting the mobility and density of dislocations,as well as the interaction between the interstitial atoms and dislocations in austenite grains.展开更多
Microstructuring of steel resulting in directional solidification and texturing, previously observed in various metallic materials during pulsed laser processing, melt-spinning, high-gradient liquid metal melting, zon...Microstructuring of steel resulting in directional solidification and texturing, previously observed in various metallic materials during pulsed laser processing, melt-spinning, high-gradient liquid metal melting, zone melting etc., is reported for the first time in continuous wave diode laser processing of steels. Influence of laser interaction time on surface morphology/topology of austenitic manganese and pearlitic steels is investigated utilizing a wide rectangular multi-mode diode laser beam. X-ray diffraction analysis of the laser treated austenitic steel surface showed strong texturing influence, with preferred crystallographic orientation of γ-Fe crystals in the (200) plane, which increased with interaction time. In case of pearlitic steel, no such texturing influence could be observed. The free surface topologies were also observed to be different in each case, with well-aligned domes of γ-Fe observed in laser treated austenitic steel as compared to randomly oriented fine domes of metal oxides in pearlitic one. In situ surface temperature measurement during laser irradiation indicated higher temperature on pearlitic steel than in austenitic manganese steel owing to its lower effective thermal conductivity associated with higher oxide film formation.展开更多
The systematic chemical compositions including common C, Si, Mn, Al, and micro-alloying elements of Ti and Nb were designed for high volume fraction of retained austenite as much as possible. The thermo-cycle experime...The systematic chemical compositions including common C, Si, Mn, Al, and micro-alloying elements of Ti and Nb were designed for high volume fraction of retained austenite as much as possible. The thermo-cycle experiments were conducted by using Gleeble 2000 thermo-dynamic test machine for finding the appropriate composition. The experimental results showed that chemical composition had a significant effect on retained austenite, and the appropriate compositions were determined for commercial production of TRIP steels.展开更多
The effects of annealing time and temperature on the retained austenite content and mechanical properties of 0.2C-7Mn steel were studied.The retained austenite content of 0.2C-7Mn steel was compared with that of 0.2C-...The effects of annealing time and temperature on the retained austenite content and mechanical properties of 0.2C-7Mn steel were studied.The retained austenite content of 0.2C-7Mn steel was compared with that of 0.2C-5Mn steel.It is found that 0.2C-7Mn steel exhibits a similar variation trend of retained austenite content as 0.2C-5Mn steel.However,in detail,these trends are different.0.2C-7Mn steel contains approximately 7.5vol%retained austenite after austenitization and quenching.The stability of the reversed austenite in 0.2C-7Mn steel is lower than that in 0.2C-5Mn steel;in contrast,the equilibrium reversed austenite fraction of 0.2C-7Mn steel is substantially greater than that of 0.2C-5Mn steel.Therefore,the retained austenite content in 0.2C-7Mn steel reaches 53.1vol%.The tensile results show that long annealing time and high annealing temperature may not favor the enhancement of mechanical properties of 0.2C-7Mn steel.The effect of retained austenite on the tensile strength of the steel depends on the content of retained austenite;in contrast,the 0.2%yield strength linearly decreases with increasing retained austenite content.展开更多
Two austenitic Mn steels(Fe-17 Mn and Fe-17 Mn-3 Al(wt%, so as the follows)) were subjected to thermomechanical processing(TMP) consisting of forging followed by solutionization and hot rolling. The rolled samples wer...Two austenitic Mn steels(Fe-17 Mn and Fe-17 Mn-3 Al(wt%, so as the follows)) were subjected to thermomechanical processing(TMP) consisting of forging followed by solutionization and hot rolling. The rolled samples were annealed at 650 and 800°C to relieve the internal stress and to induce recrystallization. The application of TMP and heat treatment to the Fe-17 Mn/Fe-17 Mn-3 Al steels refined the austenite grain size from 169 μm in the as-solutionized state to 9–13 μm, resulting in a substantial increase in hardness from HV 213 to HV 410 for the Fe-17 Mn steel and from HV 210 to HV 387 for the Fe-17 Mn-3 Al steel. The elastic modulus values, as evaluated by the nanoindentation technique, increased from(175 ± 11) to(220 ± 12) GPa and from(163 ± 15) to(205 ± 13) GPa for the Fe-17 Mn and Fe-17 Mn-3 Al steels, respectively. The impact energy of the thermomechanically processed austenitic Mn steels was lower than that of the steels in their as-solutionized state. The addition of Al to the Fe-17 Mn steel decreased the hardness and elastic modulus but increased the impact energy.展开更多
文摘Critical cooling rate to avoid carbide precipitation during quenching of austenitic manganese steel was investigated by means of optical microscopy,image analyzer and numerical analysis.An efficient heat treatment analysis program including temperature-dependent material properties was developed for the prediction of cooling rate and probability of carbide precipitation during quenching by finite difference method.Time-dependent heat transfer coefficient was adopted to achieve more precise results.Area ratio of carbide precipitation was measured by image analyzer to determine the critical point of carbide precipitation.Temperature-dependent critical cooling rate at that point was calculated by the developed numerical program.Finally,the probability of carbide precipitation on the whole area of specimen can be predicted by the proposed numerical program and the numerical result of a specimen was compared with the experimental result.
基金supported by the National Natural Science Foundation of China(Grant No.52275370)the Key R&D Program of Hubei Province,China(Grant Nos.2022BAD100,2021BAA048)the Open Fund of Hubei Longzhong Laboratory(Grant No.2022ZZ-04).
文摘Three types of steels were designed on the basis of GX40CrNiSi25-12 austenitic heat resistant steel by adding different Mn contents(2wt.%,6wt.%,and 12wt.%).Thermodynamic calculation,microstructure characterization and mechanical property tests were conducted to investigate the effect of Mn addition on the microstructure and mechanical properties of the austenitic heat resistant steel.Results show that the matrix structure in all the three types of steels at room temperature is completely austenite.Carbides NbC and M_(23)C_(6)precipitate at grain boundaries of austenite matrix.With the increase of Mn content,the number of carbides increases and their distribution becomes more uniform.With the Mn content increases from 1.99%to 12.06%,the ultimate tensile strength,yield strength and elongation increase by 14.6%,8.0%and 46.3%,respectively.The improvement of the mechanical properties of austenitic steels can be explained by utilizing classic theories of alloy strengthening,including solid solution strengthening,precipitation strengthening,and grain refinement.The increase in alloy strength can be attributed to solid solution strengthening and precipitation strengthening caused by the addition of Mn.The improvement of the plasticity of austenitic steels can be explained from two aspects:grain refinement and homogenization of precipitated phases.
文摘This paper presents the in-situ TEM tensile observation of the nucleation and growth ofmartensite and the dislocation configuration change in metastable austenitic manganesesteels and the investigation of the composition of phases and the content of elements inthe micro regions by XRD,EDAX respectively and concludes from the results that thestrengthening of martensite transformation and high density of dislocations lead to thehigh work-hardening capacity in the steel.
基金supported by the Special Foundation for Introducing and Selecting Talent in Hefei University of Technology, China (No. 2004000197)
文摘To further understand the hardening mechanism of austenitic manganese steel under actual working conditions, the work hardening ability was studied and the microstructures of austenitic manganese steel were observed under different impact energies. The work hardening mechanism was also analyzed. The results show that the best strain hardening effect could be received only when the impact energy reaches or exceeds the critical impact energy. The microstructural observations reveal that dislocations, stacking faults and twins increase with raising impact energy of the tested specimens. The hardening mechanism changes at different hardening degrees. It is mainly dislocation and slip hardening below the critical impact energy, but it changes to the twinning hardening mechanism when the impact energy is above the critical impact energy.
文摘By means of thermodynamic calculations, optical microscope, sweep electron microscope(SEM), transimssion electron microscope(TEM) and microcomposition detection, the modifying effect of RE and Ti on austenitic manganese steel was investigated The results show that the constitutional supercooling of austenitic manganese steel during solidification can be improved and the dendritic crystals can be grown facilely, melted, isolated and multiplied by adding RE(Ce) In the melt the alloying elements Ti and C can form TiC directly which acts as nucleus of cementite and causes both primary and eutectic cementite to be granulated and refined so that the cementite network in this steel can be eliminated
文摘The effect of C,Mn and heat-treatment on work-hardening of austenitic Mn steel and the work-hardening mechanism have been investigated under non-severe impact loading condition.The results show that the ability of work-hardening in- creases with the increase of C and aging tempera- ture but decreases with Mn.The work-hardening with high austenitic stability results mainly from dislocations,and that with low austenitic stability results mainly from combined effects of strain-in- duced martensite and high density of dislocations under non-severe impact loading conditions.The wear resistance of medium manganese steel (Mn7) is 1.64-2.46 times that of Hadfield steel (Mnl3).
基金Project(59771001) supported by the National Natural Science Foundation of China
文摘The transfer behavior of nitrogen into the welding metal during gas tungsten arc welding process of 32Mn-7Cr-1Mo-0.3N steel was investigated. The effects of gas tungsten arc welding process variables, such as the volume fraction of nitrogen in shielding gas, arc holding time and arc current on the nitrogen content in the welding metal were also evaluated. The results show that the volume fraction of nitrogen in gas mixture plays a major role in controlling the nitrogen content in the welding metal. It seems that there exhibits a maximum nitrogen content (depending) on the arc current and arc holding time. The optimum volume fraction of nitrogen in shielding gas is 4% or so. The role of gas tungsten arc welding processing parameters in controlling the transfer of nitrogen is further (confirmed) by the experimental results of gas tungsten arc welding process with feeding metal.
基金support from the National Natural Science Foundation of China(Nos.51831002,51904028,and 52233018)the Beijing Municipal Natural Science Foundation(No.2242048)the Fundamental Research Funds for the Central Universities,China(No.FRF-EYIT-23-08).
文摘Plastic instability,including both the discontinuous yielding and stress serrations,has been frequently observed during the tensile deformation of medium-Mn steels(MMnS)and has been intensively studied in recent years.Unfortunately,research results are controversial,and no consensus has been achieved regarding the topic.Here,we first summarize all the possible factors that affect the yielding and flow stress serrations in MMnS,including the morphology and stability of austenite,the feature of the phase interface,and the deformation parameters.Then,we propose a universal mechanism to explain the conflicting experimental results.We conclude that the discontinuous yielding can be attributed to the lack of mobile dislocation before deformation and the rapid dislocation multiplication at the beginning of plastic deformation.Meanwhile,the results show that the stress serrations are formed due to the pinning and depinning between dislocations and interstitial atoms in austenite.Strain-induced martensitic transformation,influenced by the mechanical stability of austenite grain and deformation parameters,should not be the intrinsic cause of plastic instability.However,it can intensify or weaken the discontinuous yielding and the stress serrations by affecting the mobility and density of dislocations,as well as the interaction between the interstitial atoms and dislocations in austenite grains.
文摘Microstructuring of steel resulting in directional solidification and texturing, previously observed in various metallic materials during pulsed laser processing, melt-spinning, high-gradient liquid metal melting, zone melting etc., is reported for the first time in continuous wave diode laser processing of steels. Influence of laser interaction time on surface morphology/topology of austenitic manganese and pearlitic steels is investigated utilizing a wide rectangular multi-mode diode laser beam. X-ray diffraction analysis of the laser treated austenitic steel surface showed strong texturing influence, with preferred crystallographic orientation of γ-Fe crystals in the (200) plane, which increased with interaction time. In case of pearlitic steel, no such texturing influence could be observed. The free surface topologies were also observed to be different in each case, with well-aligned domes of γ-Fe observed in laser treated austenitic steel as compared to randomly oriented fine domes of metal oxides in pearlitic one. In situ surface temperature measurement during laser irradiation indicated higher temperature on pearlitic steel than in austenitic manganese steel owing to its lower effective thermal conductivity associated with higher oxide film formation.
文摘The systematic chemical compositions including common C, Si, Mn, Al, and micro-alloying elements of Ti and Nb were designed for high volume fraction of retained austenite as much as possible. The thermo-cycle experiments were conducted by using Gleeble 2000 thermo-dynamic test machine for finding the appropriate composition. The experimental results showed that chemical composition had a significant effect on retained austenite, and the appropriate compositions were determined for commercial production of TRIP steels.
基金supported by the National Natural Science Foundation of China (Nos. 51371057 and 51471094)the Major State Basic Research Development Program of China (No.2010CB630803)
文摘The effects of annealing time and temperature on the retained austenite content and mechanical properties of 0.2C-7Mn steel were studied.The retained austenite content of 0.2C-7Mn steel was compared with that of 0.2C-5Mn steel.It is found that 0.2C-7Mn steel exhibits a similar variation trend of retained austenite content as 0.2C-5Mn steel.However,in detail,these trends are different.0.2C-7Mn steel contains approximately 7.5vol%retained austenite after austenitization and quenching.The stability of the reversed austenite in 0.2C-7Mn steel is lower than that in 0.2C-5Mn steel;in contrast,the equilibrium reversed austenite fraction of 0.2C-7Mn steel is substantially greater than that of 0.2C-5Mn steel.Therefore,the retained austenite content in 0.2C-7Mn steel reaches 53.1vol%.The tensile results show that long annealing time and high annealing temperature may not favor the enhancement of mechanical properties of 0.2C-7Mn steel.The effect of retained austenite on the tensile strength of the steel depends on the content of retained austenite;in contrast,the 0.2%yield strength linearly decreases with increasing retained austenite content.
文摘Two austenitic Mn steels(Fe-17 Mn and Fe-17 Mn-3 Al(wt%, so as the follows)) were subjected to thermomechanical processing(TMP) consisting of forging followed by solutionization and hot rolling. The rolled samples were annealed at 650 and 800°C to relieve the internal stress and to induce recrystallization. The application of TMP and heat treatment to the Fe-17 Mn/Fe-17 Mn-3 Al steels refined the austenite grain size from 169 μm in the as-solutionized state to 9–13 μm, resulting in a substantial increase in hardness from HV 213 to HV 410 for the Fe-17 Mn steel and from HV 210 to HV 387 for the Fe-17 Mn-3 Al steel. The elastic modulus values, as evaluated by the nanoindentation technique, increased from(175 ± 11) to(220 ± 12) GPa and from(163 ± 15) to(205 ± 13) GPa for the Fe-17 Mn and Fe-17 Mn-3 Al steels, respectively. The impact energy of the thermomechanically processed austenitic Mn steels was lower than that of the steels in their as-solutionized state. The addition of Al to the Fe-17 Mn steel decreased the hardness and elastic modulus but increased the impact energy.
