The hot deformation behavior of a new heat resistant steel Gl15 designed for 650 ℃ ultra-supercritical （USC） power plants was experimentally studied. Hot compression test was carried out in the temperature range of...The hot deformation behavior of a new heat resistant steel Gl15 designed for 650 ℃ ultra-supercritical （USC） power plants was experimentally studied. Hot compression test was carried out in the temperature range of 900-1 200 ℃ and the strain rate range of 0.1-20 s i by using Gleeble 3800 thermal-mechanical simulator, and the corresponding flow curves were obtained. Experimental results show that the flow stress increases with the decrease of deformation temperature and the increase of strain rate. The hot deformation activation energy of G115 steel was determined to be 494 kJ/mol and the constitutive equation was also obtained. For convenience of the practical applica-tion, a good approximate equation was obtained for calculating the peak stress values of Gl15 steel under different deformation conditions. At the strain value of 0.9, natural logarithm of the critical Zener Hollomon parameter Zc of Gl15 steel was determined to be in the scope of 49.67 and 50.65, above which there will be no dynamic recrystalliza-tion （DRX）. And natural logarithm of the critical Zener-Hollomon parameter Zc of Gl15 steel was determined to be in the scopes of 45.58 and 46.27, below which full DRX may occur. Then, the status diagram of dynamic micro structures of G115 steel was established. In addition, the strain rate sensitivity of Gl15 steel is not constant during the test temperature range and it increases linearly from 900 to 1 200 ℃. Therefore, hot deformation at higher tem- peratures would obtain better workability.展开更多
Fe-Cr-Ni heat resistant alloys with aluminum and silicon addition, alone and in combination, were melted using an intermediate frequency induction furnace with a non-oxidation method. By the oxidation weight gain meth...Fe-Cr-Ni heat resistant alloys with aluminum and silicon addition, alone and in combination, were melted using an intermediate frequency induction furnace with a non-oxidation method. By the oxidation weight gain method, the oxidation resistances of the test alloys were determined at 1,200 ℃ for 500 hours. According to the oxidation weight gains, the oxidation kinetic curves were plotted and the functions were regressed by the least squares method. The results show that the oxidation kinetic curves follow the power function of y = ax^b （a〉0, 0〈b〈1）. The effects of scale compositions on oxidation resistance were studied further by analyses using X-ray diffraction （XRD） and scanning electron microscope （SEM）. It is found that the composite scale compounds of Cr203, a-Al2O3, SiO2 and FeCr2O4, with compact structure and tiny grains, shows complete oxidation resistance at 1,200℃. When the composite scale lacks a-Al2O3 or SiO2, it becomes weak in oxidation resistance with a loose structure. By the criterion of standard Gibbs formation free energy, the model of the nucleation and growth of the composite scale is established. The forming of the composite scale is the result of the competition of being oxidized and reduced between aluminum, silicon and the matrix metal elements of iron, chromium and nickel. The protection of the composite scale is analyzed essentially by electrical conductivity and strength properties.展开更多
Based on dislocation reaction theory and Avrami equation, a constitutive equation model was developed to describe dynamic recovery and dynamic recrystallization during hot deformation of T122 heat resistant steel, whi...Based on dislocation reaction theory and Avrami equation, a constitutive equation model was developed to describe dynamic recovery and dynamic recrystallization during hot deformation of T122 heat resistant steel, which have taken the effect of dynamic strain aging into account. Uniaxial hot compression test had been carried out over a wide range of strain rate （0.01 to 10 s-1 ） and temperature （900 to 1 200 ~C） with the help of Gleeble 3500. Obtained experimental data was applied to determine the material parameters in proposed constitutive equations of T122 steel, by using the non-linear least square regress optimization method. The calculated constitutive equations are quantita- tively in good agreement with experimentally measured curves and microstructure observation. It shows that propose constitutive equation T122 steel is able to be used to predict flow stress of T122 steel during hot deformation in aus- tenite temperature scope.展开更多
The evolution of precipitates of S31042 steel during 700 ℃ aging was investigated by using a scanning elec- tron microscope, a transmission electron microscope, and electron energy spectrum technology. The various co...The evolution of precipitates of S31042 steel during 700 ℃ aging was investigated by using a scanning elec- tron microscope, a transmission electron microscope, and electron energy spectrum technology. The various combi nations of M23C6, MX, NbCrN, and σ and G phases in the steel were found at different aging states. In the begin ning of aging, M23C6 precipitates swiftly along the grain boundaries. When the aging time exceeds 6 000 h, precipita- ted M23C6 carbides along the grain boundaries turn to be granular. It was found that Si element segregates to grain boundaries during above process, which may enhance the granular shape of M23C6 carbides and its transformation to and G phases. When the aging time exceeds 10 000 h, various shaped a phase and granular G phase appear along the grain boundaries and there are no continuous M23C6 carbides along the grain boundaries. Meanwhile, a large quantity of granular M23C6 carbides and a minor amount of G phase precipitate near the grain boundaries. Based on the segre- gation of silicon to the grain boundaries, a precipitation evolution model during aging was concluded.展开更多
The conventional mould fluxes can not be applied to the continuous casting of RE alloyed heat resistant steel, because severe slag-metal interface reactions occur generally in the mold. To restrain the interface react...The conventional mould fluxes can not be applied to the continuous casting of RE alloyed heat resistant steel, because severe slag-metal interface reactions occur generally in the mold. To restrain the interface reaction and improve conditions for continuous casting, a new mould flux based on aluminate system was devised. The viscous properties were investigated. Scanning electron microscopy and X-ray diffraction were applied to detect and characterize the crystalline phases in the continuous cooling process. The results showed that appropriate addition of CeOcould avoid the precipitation of CaO and decrease the viscosity of the mould flux. Increasing the mass ratio of CaO /AlO, especially to a value exceeding 1, could worsen the stability of the mould flux. With a content of less than 14 wt.%, LiO could reduce the viscosity and breaking temperature, but its effect could be weakened for the promoted precipitation of LiAlO. To obtain a mould flux with stable viscous properties, such as viscosity and breaking temperature, appropriate contents of CeOand LiO should be controlled to around 10 wt.% and 14 wt.%, while the mass ratio of CaO /AlOshould not be more than 1.展开更多
The mechanism of brittleness of M152 martensitic heat resistant steel due to slow cooling during quenching was experimentally investigated. The mechanical property tests and microstructure observation were conducted b...The mechanism of brittleness of M152 martensitic heat resistant steel due to slow cooling during quenching was experimentally investigated. The mechanical property tests and microstructure observation were conducted by TEM and XRD. The results showed that the presence of irreversible brittleness during slow cooling of quenching for M152 steel is attributed to the continuous M23C6 precipitation along prior austenite grain boundaries and M2C along prior residual austenite film. The residual austenite in the steel was unstable and decomposed after the precipitation of second phase during the process of slow cooling of quenching. The low cooling rate within the temperature range from 820 ℃ to 660 ℃ plays a key role in impact toughness, and the precipitation of second phase in the same temperature range results in irreversible brittleness.展开更多
2.25Cr-1.6W-V-Nb developed in Japan, is a low alloy heat resistant steel with good comprehensive properties. Influence of long term creep at elevated temperature on the structure of 2.25Cr-1.6W-V-Nb steel was studied ...2.25Cr-1.6W-V-Nb developed in Japan, is a low alloy heat resistant steel with good comprehensive properties. Influence of long term creep at elevated temperature on the structure of 2.25Cr-1.6W-V-Nb steel was studied in this paper, and the micromechanism of creep strength degradation was elucidated, too. Both TEM observation and thermodynamic calculation reveal that during creep the transformation occurs from M7C3 and M23C6 to M6C, which can be cavity nucleation sites. Besides, creep at 600癈 also leads to the decrease of dislocation density, the coarsening and coalescence of M23C6, the nucleation of cavities and development of cracks. The strength decrease of 2.25Cr-1.6W-V-Nb steel after long term creep is related to the decrease of dislocation hardening, precipitation hardening, solution hardening, the nucleation of cavities and development of cracks.展开更多
The hot compression tests of Super304H austenitic heat resistant steel were carried out at 800-1200℃and 0.005-5 s^-1 using a Gleeble 3500 thermal-mechanical simulator,and its deformation behavior was analyzed.The res...The hot compression tests of Super304H austenitic heat resistant steel were carried out at 800-1200℃and 0.005-5 s^-1 using a Gleeble 3500 thermal-mechanical simulator,and its deformation behavior was analyzed.The results show that the flow stress of Super304H steel decreases with the decrease of strain rate and the increase of deformation temperature; the hot deformation activation energy of the steel is 485 kJ/mol.The hot deformation equation and the relationship between the peak stress and the deformation temperature and strain rate is obtained.The softening caused by deformation heating cannot be neglected when both the deformation temperature and strain rate are higher.展开更多
The application of rare earths(RE) in the Ni saving heat resistant steel was studied by metalloscopy,scanning electron microscopy(SEM),energy dispersive spectrometer(EDS),X-ray difference(XRD).Because the diffusion of...The application of rare earths(RE) in the Ni saving heat resistant steel was studied by metalloscopy,scanning electron microscopy(SEM),energy dispersive spectrometer(EDS),X-ray difference(XRD).Because the diffusion of chromium was promoted by RE,a dense and adhesive Cr2O3 layer could form rapidly at the early oxidation stage,which played a effective protection role;the pinning effect of silicon dioxide was enhanced by RE in the internal oxidation layer,which had a block effect on the diffusion of metal ions and oxygen ions at later stage of oxidation and resulted in that the high temperature oxidation rate of RE heat resistant steel was decreased.展开更多
A heat resistant gradient composite was synthesized in situ on steel with the self-propagating high temperature synthesis （SHS） reaction of 3Ni-Al-Ti-C system during casting. The phases, microstructure, and composit...A heat resistant gradient composite was synthesized in situ on steel with the self-propagating high temperature synthesis （SHS） reaction of 3Ni-Al-Ti-C system during casting. The phases, microstructure, and composition of the composite were analyzed by using an X-ray diffractometer （XRD）, and a scanning electron microscope （SEM） coupled with an energy-dispersive X-ray spectroscope （EDS）. The formation mechanism of the composite is also discussed. TiC/Ni3 Al/steel gradient composite is achieved by forming the gradient distributions of Fe, Ni, and Al, accompanied with the gradient variation of the microstructure from TiC/Nia A1, to TiC/Ni3 Al/steel, and to steel. The composite is in situ synthesized through whole reaction of 3Ni-Al-Ti-C system in liquid steel and densification procedure, and the liquid steel infiltrates into pores in the SHS product and forces liquid Ni3Al to form self-compaction further.展开更多
The ex-service steam tubes containing dissimilar metal weld(DMW)between high Cr ferritic steel T91 and austenitic stainless steel TP347H and the ex-service steam tubes containing DMW between low Cr ferritic steel G102...The ex-service steam tubes containing dissimilar metal weld(DMW)between high Cr ferritic steel T91 and austenitic stainless steel TP347H and the ex-service steam tubes containing DMW between low Cr ferritic steel G102 and austenitic stainless steel TP347H were obtained from coal-fired thermal power plants in China,and their microstructures at the nickel-based weld metal(WM)/ferritic steel interfaces and oxidation characteristics were investigated.After operating for 15,000 h at steam temperature of 541 C and steam pressure of 17.5 MPa,a G102/TP347H DMW failed along the WM/G102 steel interface,which was a dangerous premature failure mode without obvious plastic deformation.This interfacial failure was attributed to the interaction between oxidation and cracking along the interface,where fracture appeared to be related with the strain concentration at the interface.Oxide notch along the WM/G102 steel interface was the precursor of premature interfacial failure of DMW involving G102.For the DMW involving high Cr ferritic steel T91,ferritic steel side could form a Cr-rich passive film during service and thus would not be further oxidized after operating for 67,000 h at steam temperature of 541 C and steam pressure of 3.5 MPa.It was concluded that oxidation played a more important role in failure of these DMWs,and retarding the development of oxidation and avoiding the interfacial oxide notch would dramatically improve the service performance of steam tubes containing DMWs.展开更多
Fe-Cr-Ni heat resistant steels with different contents of Al and Si were cast in intermediate frequency induction furnace with non-oxidation method. With oxidation weight gain method, the oxidation resistance of test ...Fe-Cr-Ni heat resistant steels with different contents of Al and Si were cast in intermediate frequency induction furnace with non-oxidation method. With oxidation weight gain method, the oxidation resistance of test alloys was examined at 1 200 ℃ for 500 h. The effects of Al and Si on oxidation resistance were studied through analyses of X-ray diffraction （XRD） and scanning electron microscope （SEM）. It is shown that the composition of oxide scales is a decisive factor for the oxidation resistance of heat resistant steels. The compounded scale composed of Cr203, α-Al2O3, SiO2 and Fe （Ni）Cr2O4, with flat and compact structure, fine and even grains, exhibits complete oxidation resistance at 1 200 ℃. Its oxidation weight gain rate is only 0.081 g/（m^2.h）. By the criterion of standard Gibbs formation free energy, a model of nucleation and growth of the compounded scale was established. The formation of the compounded scale was the result of the competition of being oxidated and reduction among Al, Si, and the matrix metal elements of Fe, Cr and Ni. The protection of the compounded scale was analyzed from the perspectives of electrical conductivity and strength properties.展开更多
For steam tubes used in thermal power plant,the inner and outer walls were operated in high-temperature steam and flue gas environments respectively.In this study,structure,microstructure and chemical composition of o...For steam tubes used in thermal power plant,the inner and outer walls were operated in high-temperature steam and flue gas environments respectively.In this study,structure,microstructure and chemical composition of oxide films on inner and outer walls of exservice low Cr ferritic steel G102 tube and exservice high Cr ferritic steel T91 tube were analyzed.The oxide film was composed of outer oxide layer,inner oxide layer and internal oxidation zone.The outer oxide layer on the original surface of tube had a porous structure containing Fe oxides formed by diffusion and oxidation of Fe.More specially,the outer oxide layer formed in flue gas environment would mix with coal combustion products during the growth process.The inner oxide layer below the original surface of tube was made of Fe–Cr spinel.The internal oxidation zone was believed to be the precursor stage of inner oxide layer.The formation of internal oxidation zone was due to O diffusing along grain boundaries to form oxide.There were Fe–Cr–Si oxides discontinuously distributed along grain boundaries in the internal oxidation zone of G102,while there were Fe–Cr oxides continuously distributed along grain boundaries in that of T91.展开更多
The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electro...The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electron microscopy.Kinetic modeling was carried out using the software DICTRA.The results indicated Fe_2（W,Mo）Laves phase has formed during creep with 200 MPa applied stress at 883 Kfor 243 h.The experimental results showed a good agreement with thermodynamic calculations.The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa,whereas,creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa.Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature.Microstructures at the vicinity of fracture surface,the gage portion and the threaded ends of creep rupture specimens were also observed,indicating that creep tensile stress enhances the coarsening of Laves phase.展开更多
The kinetic curves of the high-temperature oxidation of austenitic heat resistant stainless steel 1. 4828 at 1 050 ℃ were measured using a weighing method. It is shown that the oxidation curves at 1 050 ℃ followed t...The kinetic curves of the high-temperature oxidation of austenitic heat resistant stainless steel 1. 4828 at 1 050 ℃ were measured using a weighing method. It is shown that the oxidation curves at 1 050 ℃ followed the parabolic line law, and after 250 h of oxidation, the mass gain was about 80 g/m2. The surface morphology and structure of the oxide layers were studied by scanning electron microscopy and X-ray diffraction. A complicated oxide layer obtained at 1 050 ℃ was mainly composed, from inner to outer, of （FeSi） 3 04, Cr2 03, Fe2 03, and spinel oxides FeCr204 and NiMn204.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
Thermal analysis has been adopted to determine the liquidus and eutectic temperature of Fe-20%Cr-Mn alloy over range of Mn and C contents.Using regression analysis,the par- tial quasi-binary phase diagrams of Fe-Mn al...Thermal analysis has been adopted to determine the liquidus and eutectic temperature of Fe-20%Cr-Mn alloy over range of Mn and C contents.Using regression analysis,the par- tial quasi-binary phase diagrams of Fe-Mn alloy(solidification range)have been con- structed.And the effect of Mn content on liquidus and eutectic temperature was discussed.展开更多
Precipitation strengthening as well as solution strengthening is key mechanism for heat resistant steels.It is very important to characterize the precipitates in 9%Cr ferrite heat resistant steels,especially to show t...Precipitation strengthening as well as solution strengthening is key mechanism for heat resistant steels.It is very important to characterize the precipitates in 9%Cr ferrite heat resistant steels,especially to show the nanometer-sized particles.By transmission electronic microscope attached with an energy dispersive spectrometer as well as optical microscope,scanning electronic microscope,the microstructure and chemical composition of precipitates in a 9%Cr heat resistant steel after different heat treatments were investigated.It was found that the microstructure of normalized sample was martensite with fine NbC and Fe_3C.The microstructure of tempered sample is tempered martensite,and there mainly were two types of precipitates,M_(23)C_6 with the size range of 50-300 nm and MX with the size of 10-100 nm.Superfine M_(23)C_6 precipitated preferably on prior austenitic grain boundaries and martensitic lath boundaries,while nanometer-sized MX precipitates were distributed randomly.After short-term creep,Laves phase formed along grain boundaries of the 9%Cr steel,and M_(23)C_6 and MX precipitates were found to become coarser.More information about precipitates in the 9%Cr steel had been exhibited by atomic force microscopy.Thereby,distribution,size and shape of the precipitates as well as their compositions and structures were revealed.展开更多
Airless tires are essential for enhancing the safety,reliability,and convenience of maintenance of electric bicycles.Polyurethane(PU)is considered a promising candidate for such applications owing to its versatile pro...Airless tires are essential for enhancing the safety,reliability,and convenience of maintenance of electric bicycles.Polyurethane(PU)is considered a promising candidate for such applications owing to its versatile properties.However,their use is limited by insufficient heat resistance and excessive dynamic heat generation under cyclic loading.In this study,star-shaped trifunctional polypropylene glycerol(PPG3)was incorporated into conventional poly(tetramethylene glycol)(PTMG)and 4,4'-methylenediphenyl diisocyanate(MDI)-based systems to construct microporous star-shaped casting polyurethanes(SCPU),with water serving as a green foaming agent.Unlike conventional small-molecule trifunctional crosslinkers that create junctions within hard segment domains,PPG3 introduces long flexible arms between the hard segments,anchoring the crosslinking points at its molecular core.The large steric hindrance of PPG3 effectively suppresses soft segment crystallization and lowers the degree of microphase separation,whereas the crosslinked network restricts chain mobility,thereby reducing dynamic heat generation.These structural features also enhance the heat resistance,yielding a softening temperature of 183℃,which is 30.9%higher than that of polyurethane without PPG3.When applied to airless tires by casting SCPU into rubber treads,the fabricated hybrid airless tires achieved a rolling distance of over 3000 km under a load of 65 kg at 25km/h without structural failure,satisfying practical performance requirements.This strategy offers a simple,solvent-free,and environmentally friendly process,underscoring the potential of SCPU for scalable production of high-performance airless tires.展开更多
Polyimide(PI)is widely used in high-tech fields such as microelectronics,aerospace,and national defense because of its excellent optical properties,high-and low-temperature resistance,and good dimensional stability.To...Polyimide(PI)is widely used in high-tech fields such as microelectronics,aerospace,and national defense because of its excellent optical properties,high-and low-temperature resistance,and good dimensional stability.To achieve the desired properties of PI,the monomers 2,6-diaminopyrimidin-4-ol(DAPD)and 6-(2,3,5,6-tetrafluoro-4-vinylphenoxy)pyrimidin-2,4-diamine(DAFPD),which contains crosslinkable functional groups,were designed and synthesized successfully and copolymerized with 4,4'-oxydianiline(ODA)and 4,4-hexafluoroisopropylphthalic anhydride(6FDA).The prepared PI film(PI-3),with rigid backbones and loose packing had excellent heat resistance(Td5%=489℃)and optical properties(T450=82%).Furthermore,a crosslinked PI film(c-PI-3)with more heat-resistant(Td5%=524℃)and better mechanical properties(σ=125.46MPa),can be obtained through thermal crosslinking of tetrafluorostyrene.In addition,the changes in the properties caused by the proportion of DAFPD added during copolymerization are discussed comprehensively.This study provides a promising candidate for heat-resistant PI materials.展开更多
基金Sponsored by National Basic Research Program of China(2010CB630804)National High Technology Research and Development Program of China(2012AA03A501)
文摘The hot deformation behavior of a new heat resistant steel Gl15 designed for 650 ℃ ultra-supercritical （USC） power plants was experimentally studied. Hot compression test was carried out in the temperature range of 900-1 200 ℃ and the strain rate range of 0.1-20 s i by using Gleeble 3800 thermal-mechanical simulator, and the corresponding flow curves were obtained. Experimental results show that the flow stress increases with the decrease of deformation temperature and the increase of strain rate. The hot deformation activation energy of G115 steel was determined to be 494 kJ/mol and the constitutive equation was also obtained. For convenience of the practical applica-tion, a good approximate equation was obtained for calculating the peak stress values of Gl15 steel under different deformation conditions. At the strain value of 0.9, natural logarithm of the critical Zener Hollomon parameter Zc of Gl15 steel was determined to be in the scope of 49.67 and 50.65, above which there will be no dynamic recrystalliza-tion （DRX）. And natural logarithm of the critical Zener-Hollomon parameter Zc of Gl15 steel was determined to be in the scopes of 45.58 and 46.27, below which full DRX may occur. Then, the status diagram of dynamic micro structures of G115 steel was established. In addition, the strain rate sensitivity of Gl15 steel is not constant during the test temperature range and it increases linearly from 900 to 1 200 ℃. Therefore, hot deformation at higher tem- peratures would obtain better workability.
基金supported financially by Komatsu of Japan,grant number31370011370804,in Shandong University,China.
文摘Fe-Cr-Ni heat resistant alloys with aluminum and silicon addition, alone and in combination, were melted using an intermediate frequency induction furnace with a non-oxidation method. By the oxidation weight gain method, the oxidation resistances of the test alloys were determined at 1,200 ℃ for 500 hours. According to the oxidation weight gains, the oxidation kinetic curves were plotted and the functions were regressed by the least squares method. The results show that the oxidation kinetic curves follow the power function of y = ax^b （a〉0, 0〈b〈1）. The effects of scale compositions on oxidation resistance were studied further by analyses using X-ray diffraction （XRD） and scanning electron microscope （SEM）. It is found that the composite scale compounds of Cr203, a-Al2O3, SiO2 and FeCr2O4, with compact structure and tiny grains, shows complete oxidation resistance at 1,200℃. When the composite scale lacks a-Al2O3 or SiO2, it becomes weak in oxidation resistance with a loose structure. By the criterion of standard Gibbs formation free energy, the model of the nucleation and growth of the composite scale is established. The forming of the composite scale is the result of the competition of being oxidized and reduced between aluminum, silicon and the matrix metal elements of iron, chromium and nickel. The protection of the composite scale is analyzed essentially by electrical conductivity and strength properties.
基金Sponsored by National High-Tech Research and Development Program (863Program) of China (2003AA331060)
文摘Based on dislocation reaction theory and Avrami equation, a constitutive equation model was developed to describe dynamic recovery and dynamic recrystallization during hot deformation of T122 heat resistant steel, which have taken the effect of dynamic strain aging into account. Uniaxial hot compression test had been carried out over a wide range of strain rate （0.01 to 10 s-1 ） and temperature （900 to 1 200 ~C） with the help of Gleeble 3500. Obtained experimental data was applied to determine the material parameters in proposed constitutive equations of T122 steel, by using the non-linear least square regress optimization method. The calculated constitutive equations are quantita- tively in good agreement with experimentally measured curves and microstructure observation. It shows that propose constitutive equation T122 steel is able to be used to predict flow stress of T122 steel during hot deformation in aus- tenite temperature scope.
文摘The evolution of precipitates of S31042 steel during 700 ℃ aging was investigated by using a scanning elec- tron microscope, a transmission electron microscope, and electron energy spectrum technology. The various combi nations of M23C6, MX, NbCrN, and σ and G phases in the steel were found at different aging states. In the begin ning of aging, M23C6 precipitates swiftly along the grain boundaries. When the aging time exceeds 6 000 h, precipita- ted M23C6 carbides along the grain boundaries turn to be granular. It was found that Si element segregates to grain boundaries during above process, which may enhance the granular shape of M23C6 carbides and its transformation to and G phases. When the aging time exceeds 10 000 h, various shaped a phase and granular G phase appear along the grain boundaries and there are no continuous M23C6 carbides along the grain boundaries. Meanwhile, a large quantity of granular M23C6 carbides and a minor amount of G phase precipitate near the grain boundaries. Based on the segre- gation of silicon to the grain boundaries, a precipitation evolution model during aging was concluded.
基金supported by the National Natural Science Foundation of China(51374059,51304042)the Fundamental Research Funds for the Central Universities of China(N130402020)the Key Science and Technology Program of Liaoning Province(2012221013)
文摘The conventional mould fluxes can not be applied to the continuous casting of RE alloyed heat resistant steel, because severe slag-metal interface reactions occur generally in the mold. To restrain the interface reaction and improve conditions for continuous casting, a new mould flux based on aluminate system was devised. The viscous properties were investigated. Scanning electron microscopy and X-ray diffraction were applied to detect and characterize the crystalline phases in the continuous cooling process. The results showed that appropriate addition of CeOcould avoid the precipitation of CaO and decrease the viscosity of the mould flux. Increasing the mass ratio of CaO /AlO, especially to a value exceeding 1, could worsen the stability of the mould flux. With a content of less than 14 wt.%, LiO could reduce the viscosity and breaking temperature, but its effect could be weakened for the promoted precipitation of LiAlO. To obtain a mould flux with stable viscous properties, such as viscosity and breaking temperature, appropriate contents of CeOand LiO should be controlled to around 10 wt.% and 14 wt.%, while the mass ratio of CaO /AlOshould not be more than 1.
基金Item Sponsored by National Key Technologies Research and Development Program of China (2009AA03Z509)
文摘The mechanism of brittleness of M152 martensitic heat resistant steel due to slow cooling during quenching was experimentally investigated. The mechanical property tests and microstructure observation were conducted by TEM and XRD. The results showed that the presence of irreversible brittleness during slow cooling of quenching for M152 steel is attributed to the continuous M23C6 precipitation along prior austenite grain boundaries and M2C along prior residual austenite film. The residual austenite in the steel was unstable and decomposed after the precipitation of second phase during the process of slow cooling of quenching. The low cooling rate within the temperature range from 820 ℃ to 660 ℃ plays a key role in impact toughness, and the precipitation of second phase in the same temperature range results in irreversible brittleness.
基金The work is supported by the National Natural Science Foundation of China under the grant No.50071029 and No.50101004. The authors would like to thank Harbin Boilers Works for supplying creep rupture data and specimens of 2.25Cr-1.6W-V-Nb steel.
文摘2.25Cr-1.6W-V-Nb developed in Japan, is a low alloy heat resistant steel with good comprehensive properties. Influence of long term creep at elevated temperature on the structure of 2.25Cr-1.6W-V-Nb steel was studied in this paper, and the micromechanism of creep strength degradation was elucidated, too. Both TEM observation and thermodynamic calculation reveal that during creep the transformation occurs from M7C3 and M23C6 to M6C, which can be cavity nucleation sites. Besides, creep at 600癈 also leads to the decrease of dislocation density, the coarsening and coalescence of M23C6, the nucleation of cavities and development of cracks. The strength decrease of 2.25Cr-1.6W-V-Nb steel after long term creep is related to the decrease of dislocation hardening, precipitation hardening, solution hardening, the nucleation of cavities and development of cracks.
基金supported by the Project of National Science Technology Support Plan of China(No.2007BAE51B02)
文摘The hot compression tests of Super304H austenitic heat resistant steel were carried out at 800-1200℃and 0.005-5 s^-1 using a Gleeble 3500 thermal-mechanical simulator,and its deformation behavior was analyzed.The results show that the flow stress of Super304H steel decreases with the decrease of strain rate and the increase of deformation temperature; the hot deformation activation energy of the steel is 485 kJ/mol.The hot deformation equation and the relationship between the peak stress and the deformation temperature and strain rate is obtained.The softening caused by deformation heating cannot be neglected when both the deformation temperature and strain rate are higher.
文摘The application of rare earths(RE) in the Ni saving heat resistant steel was studied by metalloscopy,scanning electron microscopy(SEM),energy dispersive spectrometer(EDS),X-ray difference(XRD).Because the diffusion of chromium was promoted by RE,a dense and adhesive Cr2O3 layer could form rapidly at the early oxidation stage,which played a effective protection role;the pinning effect of silicon dioxide was enhanced by RE in the internal oxidation layer,which had a block effect on the diffusion of metal ions and oxygen ions at later stage of oxidation and resulted in that the high temperature oxidation rate of RE heat resistant steel was decreased.
基金Item Sponsored by National High-Tech Research and Development Programof China (2002AA331180)High Education Council of Jiangsu Province for Key-Lab Project (Kjsmcx 04004)
文摘A heat resistant gradient composite was synthesized in situ on steel with the self-propagating high temperature synthesis （SHS） reaction of 3Ni-Al-Ti-C system during casting. The phases, microstructure, and composition of the composite were analyzed by using an X-ray diffractometer （XRD）, and a scanning electron microscope （SEM） coupled with an energy-dispersive X-ray spectroscope （EDS）. The formation mechanism of the composite is also discussed. TiC/Ni3 Al/steel gradient composite is achieved by forming the gradient distributions of Fe, Ni, and Al, accompanied with the gradient variation of the microstructure from TiC/Nia A1, to TiC/Ni3 Al/steel, and to steel. The composite is in situ synthesized through whole reaction of 3Ni-Al-Ti-C system in liquid steel and densification procedure, and the liquid steel infiltrates into pores in the SHS product and forces liquid Ni3Al to form self-compaction further.
基金National Natural Science Foundation of China(Project 51901113 and 51775300)the State Key Laboratory of Tribology in Tsinghua University,and the State Key Lab of Advanced Welding and Joining in Harbin Institute of Technology(No.AWJ-21M03).
文摘The ex-service steam tubes containing dissimilar metal weld(DMW)between high Cr ferritic steel T91 and austenitic stainless steel TP347H and the ex-service steam tubes containing DMW between low Cr ferritic steel G102 and austenitic stainless steel TP347H were obtained from coal-fired thermal power plants in China,and their microstructures at the nickel-based weld metal(WM)/ferritic steel interfaces and oxidation characteristics were investigated.After operating for 15,000 h at steam temperature of 541 C and steam pressure of 17.5 MPa,a G102/TP347H DMW failed along the WM/G102 steel interface,which was a dangerous premature failure mode without obvious plastic deformation.This interfacial failure was attributed to the interaction between oxidation and cracking along the interface,where fracture appeared to be related with the strain concentration at the interface.Oxide notch along the WM/G102 steel interface was the precursor of premature interfacial failure of DMW involving G102.For the DMW involving high Cr ferritic steel T91,ferritic steel side could form a Cr-rich passive film during service and thus would not be further oxidized after operating for 67,000 h at steam temperature of 541 C and steam pressure of 3.5 MPa.It was concluded that oxidation played a more important role in failure of these DMWs,and retarding the development of oxidation and avoiding the interfacial oxide notch would dramatically improve the service performance of steam tubes containing DMWs.
基金Supported by Shandong Science and Technology Key Projects (No2007GG30003004)
文摘Fe-Cr-Ni heat resistant steels with different contents of Al and Si were cast in intermediate frequency induction furnace with non-oxidation method. With oxidation weight gain method, the oxidation resistance of test alloys was examined at 1 200 ℃ for 500 h. The effects of Al and Si on oxidation resistance were studied through analyses of X-ray diffraction （XRD） and scanning electron microscope （SEM）. It is shown that the composition of oxide scales is a decisive factor for the oxidation resistance of heat resistant steels. The compounded scale composed of Cr203, α-Al2O3, SiO2 and Fe （Ni）Cr2O4, with flat and compact structure, fine and even grains, exhibits complete oxidation resistance at 1 200 ℃. Its oxidation weight gain rate is only 0.081 g/（m^2.h）. By the criterion of standard Gibbs formation free energy, a model of nucleation and growth of the compounded scale was established. The formation of the compounded scale was the result of the competition of being oxidated and reduction among Al, Si, and the matrix metal elements of Fe, Cr and Ni. The protection of the compounded scale was analyzed from the perspectives of electrical conductivity and strength properties.
基金supported by the National Natural Science Foundation of China (Nos.51901113 and 51775300)the State Key Laboratory of Tribology in Tsinghua University, and the State Key Lab of Advanced Welding and Joining in Harbin Institute of Technology (No.AWJ-21M03)。
文摘For steam tubes used in thermal power plant,the inner and outer walls were operated in high-temperature steam and flue gas environments respectively.In this study,structure,microstructure and chemical composition of oxide films on inner and outer walls of exservice low Cr ferritic steel G102 tube and exservice high Cr ferritic steel T91 tube were analyzed.The oxide film was composed of outer oxide layer,inner oxide layer and internal oxidation zone.The outer oxide layer on the original surface of tube had a porous structure containing Fe oxides formed by diffusion and oxidation of Fe.More specially,the outer oxide layer formed in flue gas environment would mix with coal combustion products during the growth process.The inner oxide layer below the original surface of tube was made of Fe–Cr spinel.The internal oxidation zone was believed to be the precursor stage of inner oxide layer.The formation of internal oxidation zone was due to O diffusing along grain boundaries to form oxide.There were Fe–Cr–Si oxides discontinuously distributed along grain boundaries in the internal oxidation zone of G102,while there were Fe–Cr oxides continuously distributed along grain boundaries in that of T91.
基金Item Sponsored by National Natural Science Foundation of China(51201061,51475315)China Postdoctoral Science Foundation(2015M571804)Natural Science Foundation of Jiangsu Province of China(BK20150329)
文摘The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electron microscopy.Kinetic modeling was carried out using the software DICTRA.The results indicated Fe_2（W,Mo）Laves phase has formed during creep with 200 MPa applied stress at 883 Kfor 243 h.The experimental results showed a good agreement with thermodynamic calculations.The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa,whereas,creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa.Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature.Microstructures at the vicinity of fracture surface,the gage portion and the threaded ends of creep rupture specimens were also observed,indicating that creep tensile stress enhances the coarsening of Laves phase.
文摘The kinetic curves of the high-temperature oxidation of austenitic heat resistant stainless steel 1. 4828 at 1 050 ℃ were measured using a weighing method. It is shown that the oxidation curves at 1 050 ℃ followed the parabolic line law, and after 250 h of oxidation, the mass gain was about 80 g/m2. The surface morphology and structure of the oxide layers were studied by scanning electron microscopy and X-ray diffraction. A complicated oxide layer obtained at 1 050 ℃ was mainly composed, from inner to outer, of （FeSi） 3 04, Cr2 03, Fe2 03, and spinel oxides FeCr204 and NiMn204.
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Thermal analysis has been adopted to determine the liquidus and eutectic temperature of Fe-20%Cr-Mn alloy over range of Mn and C contents.Using regression analysis,the par- tial quasi-binary phase diagrams of Fe-Mn alloy(solidification range)have been con- structed.And the effect of Mn content on liquidus and eutectic temperature was discussed.
文摘Precipitation strengthening as well as solution strengthening is key mechanism for heat resistant steels.It is very important to characterize the precipitates in 9%Cr ferrite heat resistant steels,especially to show the nanometer-sized particles.By transmission electronic microscope attached with an energy dispersive spectrometer as well as optical microscope,scanning electronic microscope,the microstructure and chemical composition of precipitates in a 9%Cr heat resistant steel after different heat treatments were investigated.It was found that the microstructure of normalized sample was martensite with fine NbC and Fe_3C.The microstructure of tempered sample is tempered martensite,and there mainly were two types of precipitates,M_(23)C_6 with the size range of 50-300 nm and MX with the size of 10-100 nm.Superfine M_(23)C_6 precipitated preferably on prior austenitic grain boundaries and martensitic lath boundaries,while nanometer-sized MX precipitates were distributed randomly.After short-term creep,Laves phase formed along grain boundaries of the 9%Cr steel,and M_(23)C_6 and MX precipitates were found to become coarser.More information about precipitates in the 9%Cr steel had been exhibited by atomic force microscopy.Thereby,distribution,size and shape of the precipitates as well as their compositions and structures were revealed.
基金financially supported by the National Natural Science Foundation of China(No.52303063)Hubei Provincial Department of Education Guided Scientific Research Project(No.B2024056)。
文摘Airless tires are essential for enhancing the safety,reliability,and convenience of maintenance of electric bicycles.Polyurethane(PU)is considered a promising candidate for such applications owing to its versatile properties.However,their use is limited by insufficient heat resistance and excessive dynamic heat generation under cyclic loading.In this study,star-shaped trifunctional polypropylene glycerol(PPG3)was incorporated into conventional poly(tetramethylene glycol)(PTMG)and 4,4'-methylenediphenyl diisocyanate(MDI)-based systems to construct microporous star-shaped casting polyurethanes(SCPU),with water serving as a green foaming agent.Unlike conventional small-molecule trifunctional crosslinkers that create junctions within hard segment domains,PPG3 introduces long flexible arms between the hard segments,anchoring the crosslinking points at its molecular core.The large steric hindrance of PPG3 effectively suppresses soft segment crystallization and lowers the degree of microphase separation,whereas the crosslinked network restricts chain mobility,thereby reducing dynamic heat generation.These structural features also enhance the heat resistance,yielding a softening temperature of 183℃,which is 30.9%higher than that of polyurethane without PPG3.When applied to airless tires by casting SCPU into rubber treads,the fabricated hybrid airless tires achieved a rolling distance of over 3000 km under a load of 65 kg at 25km/h without structural failure,satisfying practical performance requirements.This strategy offers a simple,solvent-free,and environmentally friendly process,underscoring the potential of SCPU for scalable production of high-performance airless tires.
基金supported by the National Key Research and Development Program of China(No.2022YFB3603101)。
文摘Polyimide(PI)is widely used in high-tech fields such as microelectronics,aerospace,and national defense because of its excellent optical properties,high-and low-temperature resistance,and good dimensional stability.To achieve the desired properties of PI,the monomers 2,6-diaminopyrimidin-4-ol(DAPD)and 6-(2,3,5,6-tetrafluoro-4-vinylphenoxy)pyrimidin-2,4-diamine(DAFPD),which contains crosslinkable functional groups,were designed and synthesized successfully and copolymerized with 4,4'-oxydianiline(ODA)and 4,4-hexafluoroisopropylphthalic anhydride(6FDA).The prepared PI film(PI-3),with rigid backbones and loose packing had excellent heat resistance(Td5%=489℃)and optical properties(T450=82%).Furthermore,a crosslinked PI film(c-PI-3)with more heat-resistant(Td5%=524℃)and better mechanical properties(σ=125.46MPa),can be obtained through thermal crosslinking of tetrafluorostyrene.In addition,the changes in the properties caused by the proportion of DAFPD added during copolymerization are discussed comprehensively.This study provides a promising candidate for heat-resistant PI materials.
