Microstructural evolution of GCr15 steels with different C and Cr contents during austenitizing and quenching was studied. Thermodynamic analysis of cementite dissolution was implied to obtain the critical temperature...Microstructural evolution of GCr15 steels with different C and Cr contents during austenitizing and quenching was studied. Thermodynamic analysis of cementite dissolution was implied to obtain the critical temperature. The coordination number x in Fe_xCr_(3-x)C and the volume fraction of undissolved cementite were computed according to element conservation and equilibrium phase diagram. The M_S(martensite transformation temperature) was calculated by using empirical formula. The retained austenite content was calculated with further consideration of quenching temperature. The results showed that the coordination number and the undissolved cementite content were promoted by the austenitizing temperature and carbon content of the steel. Increasing Cr element reduced the coordination number.GCr15 steels with different components had nearly the same M_S when austenitization at 830 °C to 860 °C. The interaction of C and Cr complicated the evolution of M_S and retained austenite content. The results were in good agreement with the literature, which could guide to obtain specified retained austenite and/or carbides.展开更多
In this study,samples obtained from 1.3343 high-speed steel punches with TiN coatings were tested.The samples were subjected to heat treatment at different cryogenic temperatures(<196℃)and durations(12,24 and 36 h...In this study,samples obtained from 1.3343 high-speed steel punches with TiN coatings were tested.The samples were subjected to heat treatment at different cryogenic temperatures(<196℃)and durations(12,24 and 36 h),followed by tempering at two different temperatures(200,500℃).For performance testing,a ball-on-disk wear test setup was utilized and a total of 6 groups of samples were examined.The effects of cryo-treatment and tempering on microstructure were revealed through microstructural analysis with scanning electron microscopy(SEM),X-ray(XRD diffraction),and Rietveld analysis.Additionally,the hardness of the punches was measured with microhardness measurements.The optimal wear resistance was observed in the 36 h deep cryo-treated and 200℃tempered samples.The characterization study indicates that by cryogenic treatment a significant portion of the retained austenite transformed into martensite and secondary carbides formed,resulting in improved wear resistance and a slight increase in hardness.展开更多
This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-...This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.展开更多
The hot compression tests of 7Mo super austenitic stainless(SASS)were conducted to obtain flow curves at the temperature of 1000-1200℃and strain rate of 0.001 s^(-1)to 1 s^(-1).To predict the non-linear hot deformati...The hot compression tests of 7Mo super austenitic stainless(SASS)were conducted to obtain flow curves at the temperature of 1000-1200℃and strain rate of 0.001 s^(-1)to 1 s^(-1).To predict the non-linear hot deformation behaviors of the steel,back propagation-artificial neural network(BP-ANN)with 16×8×8 hidden layer neurons was proposed.The predictability of the ANN model is evaluated according to the distribution of mean absolute error(MAE)and relative error.The relative error of 85%data for the BP-ANN model is among±5%while only 42.5%data predicted by the Arrhenius constitutive equation is in this range.Especially,at high strain rate and low temperature,the MAE of the ANN model is 2.49%,which has decreases for 18.78%,compared with conventional Arrhenius constitutive equation.展开更多
Two different kinds of experimental techniques were used to in-situ study the austenite formation during intercritical annealing in C-Mn dual phase steel. The microstructure evolution was observed by confocal laser sc...Two different kinds of experimental techniques were used to in-situ study the austenite formation during intercritical annealing in C-Mn dual phase steel. The microstructure evolution was observed by confocal laser scanning microscope, and the austenite isothermal and non-isothermal transformation kinetics were studied by dilatometry. The results indicate that banded structure is produced for the reason of composition segregation and the competition between recrystallization and phase transformation. Austenite prefers to nucleate not only at ferrite/ferrite grain boundaries, but also inside the grains of ferrite.Furthermore, the austenitizing process is accomplished mainly via migration of the existing austenite/ferrite interface rather than nucleation of new grains. The incubation process can be divided into two stages which are controlled by carbon and manganese diffusion, respectively. During the incubation process, the nucleation rate of austenite decreases, and austenite growth changes from two-dimensional to one-dimensional. The partitioning coefficient, defined as the ratio of manganese content in the austenite to that in the adjacent ferrite, increases with increasing soaking time.展开更多
Research has been conducted about the hardness prediction for the carburizing and quenching process based on an optimized hardness simulation model,in accordance with the calculation rule of mixed phases.The coupling ...Research has been conducted about the hardness prediction for the carburizing and quenching process based on an optimized hardness simulation model,in accordance with the calculation rule of mixed phases.The coupling field model incorporates carburizing field analysis,temperature field analysis,phase transformation kinetics analysis and a modified hardness calculation model.In determination of the calculation model for hardness,calculation equations are given to be applied to low carbon content(x(C)<0.5%) for the child phases and the martensite hardness is calculated for high carbon content(x(C)>0.5%) in alloy.Then,the complete carburizing-quenching hardness calculation model is built,and the hardness simulation data are corrected considering the influence of residual austenite(RA) on hardness.Hardness simulations of the carburizing and quenching process of 17CrNiMo6 samples have been performed using DEFORM-HT_V10.2 and MATLAB R2013 a.Finally,a series of comparisons of simulation results and measured values show a good agreement between them,which validates the accuracy of the proposed mathematical model.展开更多
High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grad...High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.展开更多
Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels(PHS)was analyzed by optical metallography(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and...Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels(PHS)was analyzed by optical metallography(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).The results show that the microstructure of PHS is martensite,and two sizes of particles disperse in the martensite matrix during the forming and quenching process.The size of the bigger particles is between 100 and 200 nm,and the small particles are nanometer-sized.The quantity of the particles has a positive relation with the Ti content.More importantly,the microstructure and strengthening mechanism are affected by the precipitating behavior of the particles.Besides the prior austenite grain,martensite packet,block and lath are refined by Ti addition.The steels are strengthened by the fine grains,martensite substructure and precipitates.The uniformly distributed dislocation in the martensite lath,the density of which is between 3.0?10^(14) cm^(–2) and 5.0?10^(14) cm^(–2),strengthens the steels through associating with fine carbide particles.展开更多
To understand the solidification behavior of austenitic stainless steel in rotary electromagnetic-field, the influence of low-frequency rotary electromagnetic-field on solidification structure of austenitic stainless ...To understand the solidification behavior of austenitic stainless steel in rotary electromagnetic-field, the influence of low-frequency rotary electromagnetic-field on solidification structure of austenitic stainless steel in horizontal continuous casting was investigated based on industrial experiments. The results show that the solidification structure of austenitic stainless steel can be remarkably refined, the central porosity and shrinkage cavity can be remarkably decreased, and the equiaxed grains zone are enlarged by means of application of appropriate low-frequency electromagnetic-field parameters. The industrial trials verify that the stirring intensity of austenitic stainless steel should be higher compared with that of plain carbon steel. Electromagnetic stirring affects the macrostructure even if the average magnetic flux density of the electromagnetic stirring reaches 90 mT (amplitude reaches 141 mT) with the frequency of 3-4 Hz. Due to a higher viscosity, rotating speed of molten stainless steel is 20%-30% lower than that of molten carbon steel in the same magnetic flux density.展开更多
The effect of egg shell powder(ES) as an environmental friendly inhibitor was studied for its corrosion inhibitive tendency on N08904 austenitic stainless steel in simulated saline(3.5% NaCl) solution using potentiody...The effect of egg shell powder(ES) as an environmental friendly inhibitor was studied for its corrosion inhibitive tendency on N08904 austenitic stainless steel in simulated saline(3.5% NaCl) solution using potentiodynamic polarization, weight loss, and SEM/EDX at room temperature. The experimental data explained the effective performance of ES with values of 57%-100% inhibition efficiency, at 2 g-10 g inhibitor concentration from weight loss tests due to the inhibition of stainless steel. The electrochemical action was as a result of the ionized particles which inhibit the compound influencing the redox reaction mechanism causing surface corrosion. ES's best performance was achieved when 6 g of the inhibitor concentration was added to the saline medium. Corrosion rate value decreased progressively with the presence of inhibitor because of anions adsorption at the interface of the metal film. Corrosion potential(Ecorr) value was found to decrease from-0.3991 V to-0.3447 V in the presence of inhibitor at 2 g concentration, decreasing gradually to-0.2048 at 6 g inhibitor concentration. The compounds identified in the ES completely adsorbed onto the surface of stainless steel as observed from the EDX analysis. The ES adsorption on stainless steel surface obeyed Langmuir adsorption isotherm. A corroded morphology with pits was observed in the SEM results without ES which contrast the images obtained with the presence of ES.展开更多
To investigate the effect of alternating magnetic field on austenite transformation process in the case of rapid heating,the austenite kinetics model of AISI 1045 steel was built for spot continual induction hardening...To investigate the effect of alternating magnetic field on austenite transformation process in the case of rapid heating,the austenite kinetics model of AISI 1045 steel was built for spot continual induction hardening(SCIH)process.The results shows that the effect of alternating magnetic field on austenite transformation fraction reaches the maximum(about 3%)when heating rate is the lowest.Relatively low magnetic flux density still has a certain effect on the austenite transformation process during the SCIH process.Concave surface structure can reduce the influence scope of alternating magnetic field on surface in all cases and the minimum influence scope appears when the feed path of inductor is longitudinal.Convex surface structure can minimize the influence scope of alternating magnetic field in depth when the feed path of inductor is longitudinal.The austenite distribution of transitional region on surface for horizontal movement is more uniform than that for longitudinal movement.The austenite distribution of transitional region in depth for longitudinal movement is more uniform than that for horizontal movement.The simulated results are consistent with the experimental results and the austenite transformation kinetics model developed for SCIH process is valid.展开更多
The influence of chemical composition and cold deformation on aging precipitation behavior of 18Cr-16Mn-2Mo-I.IN （HNS-A）, 18Cr-16Mn-I.3N （HNS-B）, 18Cr-18Mn-2Mo-0.96N （HNS-C） and 18Cr-18Mn-2Mo-0.77N （I-INS-D） h...The influence of chemical composition and cold deformation on aging precipitation behavior of 18Cr-16Mn-2Mo-I.IN （HNS-A）, 18Cr-16Mn-I.3N （HNS-B）, 18Cr-18Mn-2Mo-0.96N （HNS-C） and 18Cr-18Mn-2Mo-0.77N （I-INS-D） high nitrogen austenitic stainless steels was investigated. The results show that the ＂nose＂ temperatures and incubation periods of the initial time-temperature-precipitation （TTP） curves of aged HNSs are found to be 850 ℃, 60 s; 850 ℃, 45 s; 850 ℃, 60 s and 900 ℃, 90 s, respectively. Based on the analysis of SAD patterns, the coarse cellular Cr2N precipitate which presents a lamellar structure has a hexagonal structure of a=0.478 nm and c=0.444 nm. The Z phase corresponding to a composition of Fe36Cr^2Mo10, is determined to be a body-centered cubic structure ofa=0.892 nm. The precipitating sensitivity presents no more difference with the nitrogen content increasing from 0.77% to 0.96%, but exhibits so obviously that the cellular precipitates nearly overspread the whole field. The addition of Mo element can restrain the TTP curves moving left and down, which means decreasing the sensitivity of aging precipitation. With increasing the cold deformation, the sensitivity of precipitation increases obviously.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
Austenitic stainless steel(ASS) and High nickel steel(HNS) welding consumables are being used for welding Q&T steels, as they have higher solubility for hydrogen in austenitic phase, to avoid hydrogen induced crac...Austenitic stainless steel(ASS) and High nickel steel(HNS) welding consumables are being used for welding Q&T steels, as they have higher solubility for hydrogen in austenitic phase, to avoid hydrogen induced cracking(HIC) but they are very expensive. In recent years, the developments of low hydrogen ferritic steel(LHF) consumables that contain no hygroscopic compounds are utilized for welding Q&T steels. Heat affected zone(HAZ) softening is another critical issue during welding of armour grade Q&T steels and it depends on the welding process employed and the weld thermal cycle. In this investigation an attempt has been made to study the influence of welding consumables and welding processes on metallurgical characteristics of armour grade Q&T steel joints by various metallurgical characterization procedures. Shielded metal arc welding(SMAW) and flux cored arc welding(FCAW) processes were used for making welds using ASS, LHF and HNS welding consumables. The joints fabricated by using LHF consumables offered lower degree of HAZ softening and there is no evidence of HIC in the joints fabricated using LHF consumables.展开更多
The shielding and corrosion properties of the Alloy 709 advanced austenitic stainless steel have been investigated as a candidate canister material in spent fuel dry casks.The results revealed that the experimental an...The shielding and corrosion properties of the Alloy 709 advanced austenitic stainless steel have been investigated as a candidate canister material in spent fuel dry casks.The results revealed that the experimental and computational data of the linear and mass attenuation coefficients of the alloy are in good agreement,in which the attenuation coefficient values decreased with increasing photon energy.Alloy 709 was shown to exhibit the highest linear attenuation coefficient against gamma rays when compared to 304 and 316 stainless steels.On the other hand,Alloy 709 exhibited no considerable weight change over a 69-day period in circulating salt brines corrosion testing,while it showed an exponential increase of corrosion current density with temperature in acidic and basic corrosive solutions during electrochemical polarization corrosion testing.Furthermore,Alloy 709 was the least corroded steel compared to other austenitic stainless steels in both acidic and basic solutions.The optimistic results of the shielding and corrosion properties of Alloy 709 due to its chemical composition,suggest utilizing it as a canister material in spent nuclear fuel dry casks.展开更多
To study the mechanics of work-hardening and annealing-softening, a series of experiments were conducted on samples of 304 austenitic stainless steel sheets. In addition, transmission electron microscopy （TEM）, scan...To study the mechanics of work-hardening and annealing-softening, a series of experiments were conducted on samples of 304 austenitic stainless steel sheets. In addition, transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, and tensile testing were carried out to study changes and mechanisms of the stainless steel structures and properties during work-hardening and annealing-softening. The results indicate that annealing at low temperatures （100-500 ~C） can only remove partial residual stresses in the sample and the softening via annealing is not obvious. Bright annealing and rapid cooling in a protective atmosphere can completely soften the cold-worked material. In addition, the low-temperature sample without a protective atmosphere only has a little oxidation on the surface, but at higher temperature the oxidized layer is very thick. Thus, high-temperature annealing should include bright annealing.展开更多
In order to reduce the cost of the austenitic stainless steels(ASSs),the expensive austenite former(nickel) is often substituted by manganese.However,manganese is generally seen to have a detrimental effect on the cor...In order to reduce the cost of the austenitic stainless steels(ASSs),the expensive austenite former(nickel) is often substituted by manganese.However,manganese is generally seen to have a detrimental effect on the corrosion resistance.In the present study,the feasibility of laser surface modification of a lean-alloyed ASS(FeCrMn) for enhancing pitting corrosion resistance was investigated.Laser surface modification of FeCrMn was successfully achieved by a 2.3 kW high power diode laser(HPDL).Cyclic polarization tests for FeCrMn after laser surface modification in 3.5% NaCl solution at 25 ℃ were performed by using a potentiostat.The pitting resistance of the laser-modified specimens was found to be significantly improved as reflected by the noble shift in pitting potential.This could be attributed to redistribution of manganese sulphide leading to a more homogenous and refined microstructure.Pitting corrosion resistance of the laser-treated FeCrMn followed by subsequent citric acid passivation was found to be further improved as reflected by the noble shift in pitting potential to 0.18 V.展开更多
基金Project(51575414)supported by National Natural Science Foundation of ChinaProject(IRT13087)supported by the Innovative Research Team Development Program of Ministry of Education of ChinaProject(2015AAA005)supported by the project of Important Science and Technology Innovation Program of Hubei Province,China
文摘Microstructural evolution of GCr15 steels with different C and Cr contents during austenitizing and quenching was studied. Thermodynamic analysis of cementite dissolution was implied to obtain the critical temperature. The coordination number x in Fe_xCr_(3-x)C and the volume fraction of undissolved cementite were computed according to element conservation and equilibrium phase diagram. The M_S(martensite transformation temperature) was calculated by using empirical formula. The retained austenite content was calculated with further consideration of quenching temperature. The results showed that the coordination number and the undissolved cementite content were promoted by the austenitizing temperature and carbon content of the steel. Increasing Cr element reduced the coordination number.GCr15 steels with different components had nearly the same M_S when austenitization at 830 °C to 860 °C. The interaction of C and Cr complicated the evolution of M_S and retained austenite content. The results were in good agreement with the literature, which could guide to obtain specified retained austenite and/or carbides.
基金Project supported by the Haier GroupProject supported by the Eskisehir Osmangazi University,Türkiye。
文摘In this study,samples obtained from 1.3343 high-speed steel punches with TiN coatings were tested.The samples were subjected to heat treatment at different cryogenic temperatures(<196℃)and durations(12,24 and 36 h),followed by tempering at two different temperatures(200,500℃).For performance testing,a ball-on-disk wear test setup was utilized and a total of 6 groups of samples were examined.The effects of cryo-treatment and tempering on microstructure were revealed through microstructural analysis with scanning electron microscopy(SEM),X-ray(XRD diffraction),and Rietveld analysis.Additionally,the hardness of the punches was measured with microhardness measurements.The optimal wear resistance was observed in the 36 h deep cryo-treated and 200℃tempered samples.The characterization study indicates that by cryogenic treatment a significant portion of the retained austenite transformed into martensite and secondary carbides formed,resulting in improved wear resistance and a slight increase in hardness.
文摘This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.
文摘The hot compression tests of 7Mo super austenitic stainless(SASS)were conducted to obtain flow curves at the temperature of 1000-1200℃and strain rate of 0.001 s^(-1)to 1 s^(-1).To predict the non-linear hot deformation behaviors of the steel,back propagation-artificial neural network(BP-ANN)with 16×8×8 hidden layer neurons was proposed.The predictability of the ANN model is evaluated according to the distribution of mean absolute error(MAE)and relative error.The relative error of 85%data for the BP-ANN model is among±5%while only 42.5%data predicted by the Arrhenius constitutive equation is in this range.Especially,at high strain rate and low temperature,the MAE of the ANN model is 2.49%,which has decreases for 18.78%,compared with conventional Arrhenius constitutive equation.
基金Project(2013AA031601)supported by the National High Technology Research and Development Program of ChinaProject(2012BAF04B01)supported by the National Science and Technology Pillar Program During the 12th Five-year Plan Period of China
文摘Two different kinds of experimental techniques were used to in-situ study the austenite formation during intercritical annealing in C-Mn dual phase steel. The microstructure evolution was observed by confocal laser scanning microscope, and the austenite isothermal and non-isothermal transformation kinetics were studied by dilatometry. The results indicate that banded structure is produced for the reason of composition segregation and the competition between recrystallization and phase transformation. Austenite prefers to nucleate not only at ferrite/ferrite grain boundaries, but also inside the grains of ferrite.Furthermore, the austenitizing process is accomplished mainly via migration of the existing austenite/ferrite interface rather than nucleation of new grains. The incubation process can be divided into two stages which are controlled by carbon and manganese diffusion, respectively. During the incubation process, the nucleation rate of austenite decreases, and austenite growth changes from two-dimensional to one-dimensional. The partitioning coefficient, defined as the ratio of manganese content in the austenite to that in the adjacent ferrite, increases with increasing soaking time.
基金Projects(51535012,U1604255)supported by the National Natural Science Foundation of ChinaProject(2016JC2001)supported by the Key Research and Development Program of Hunan Province,China
文摘Research has been conducted about the hardness prediction for the carburizing and quenching process based on an optimized hardness simulation model,in accordance with the calculation rule of mixed phases.The coupling field model incorporates carburizing field analysis,temperature field analysis,phase transformation kinetics analysis and a modified hardness calculation model.In determination of the calculation model for hardness,calculation equations are given to be applied to low carbon content(x(C)<0.5%) for the child phases and the martensite hardness is calculated for high carbon content(x(C)>0.5%) in alloy.Then,the complete carburizing-quenching hardness calculation model is built,and the hardness simulation data are corrected considering the influence of residual austenite(RA) on hardness.Hardness simulations of the carburizing and quenching process of 17CrNiMo6 samples have been performed using DEFORM-HT_V10.2 and MATLAB R2013 a.Finally,a series of comparisons of simulation results and measured values show a good agreement between them,which validates the accuracy of the proposed mathematical model.
文摘High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.
基金Project(U1460101)supported by the National Natural Science Foundation of ChinaProject(20120006120002)supported by Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels(PHS)was analyzed by optical metallography(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).The results show that the microstructure of PHS is martensite,and two sizes of particles disperse in the martensite matrix during the forming and quenching process.The size of the bigger particles is between 100 and 200 nm,and the small particles are nanometer-sized.The quantity of the particles has a positive relation with the Ti content.More importantly,the microstructure and strengthening mechanism are affected by the precipitating behavior of the particles.Besides the prior austenite grain,martensite packet,block and lath are refined by Ti addition.The steels are strengthened by the fine grains,martensite substructure and precipitates.The uniformly distributed dislocation in the martensite lath,the density of which is between 3.0?10^(14) cm^(–2) and 5.0?10^(14) cm^(–2),strengthens the steels through associating with fine carbide particles.
基金Project(CSTC2007BB4216) supported by the Natural Science Foundation of Chongqing,China
文摘To understand the solidification behavior of austenitic stainless steel in rotary electromagnetic-field, the influence of low-frequency rotary electromagnetic-field on solidification structure of austenitic stainless steel in horizontal continuous casting was investigated based on industrial experiments. The results show that the solidification structure of austenitic stainless steel can be remarkably refined, the central porosity and shrinkage cavity can be remarkably decreased, and the equiaxed grains zone are enlarged by means of application of appropriate low-frequency electromagnetic-field parameters. The industrial trials verify that the stirring intensity of austenitic stainless steel should be higher compared with that of plain carbon steel. Electromagnetic stirring affects the macrostructure even if the average magnetic flux density of the electromagnetic stirring reaches 90 mT (amplitude reaches 141 mT) with the frequency of 3-4 Hz. Due to a higher viscosity, rotating speed of molten stainless steel is 20%-30% lower than that of molten carbon steel in the same magnetic flux density.
文摘The effect of egg shell powder(ES) as an environmental friendly inhibitor was studied for its corrosion inhibitive tendency on N08904 austenitic stainless steel in simulated saline(3.5% NaCl) solution using potentiodynamic polarization, weight loss, and SEM/EDX at room temperature. The experimental data explained the effective performance of ES with values of 57%-100% inhibition efficiency, at 2 g-10 g inhibitor concentration from weight loss tests due to the inhibition of stainless steel. The electrochemical action was as a result of the ionized particles which inhibit the compound influencing the redox reaction mechanism causing surface corrosion. ES's best performance was achieved when 6 g of the inhibitor concentration was added to the saline medium. Corrosion rate value decreased progressively with the presence of inhibitor because of anions adsorption at the interface of the metal film. Corrosion potential(Ecorr) value was found to decrease from-0.3991 V to-0.3447 V in the presence of inhibitor at 2 g concentration, decreasing gradually to-0.2048 at 6 g inhibitor concentration. The compounds identified in the ES completely adsorbed onto the surface of stainless steel as observed from the EDX analysis. The ES adsorption on stainless steel surface obeyed Langmuir adsorption isotherm. A corroded morphology with pits was observed in the SEM results without ES which contrast the images obtained with the presence of ES.
基金Projects(51905390,51575415)supported by the National Natural Science Foundation of China。
文摘To investigate the effect of alternating magnetic field on austenite transformation process in the case of rapid heating,the austenite kinetics model of AISI 1045 steel was built for spot continual induction hardening(SCIH)process.The results shows that the effect of alternating magnetic field on austenite transformation fraction reaches the maximum(about 3%)when heating rate is the lowest.Relatively low magnetic flux density still has a certain effect on the austenite transformation process during the SCIH process.Concave surface structure can reduce the influence scope of alternating magnetic field on surface in all cases and the minimum influence scope appears when the feed path of inductor is longitudinal.Convex surface structure can minimize the influence scope of alternating magnetic field in depth when the feed path of inductor is longitudinal.The austenite distribution of transitional region on surface for horizontal movement is more uniform than that for longitudinal movement.The austenite distribution of transitional region in depth for longitudinal movement is more uniform than that for horizontal movement.The simulated results are consistent with the experimental results and the austenite transformation kinetics model developed for SCIH process is valid.
基金Project(51304041) supported by the National Natural Science Foundation of ChinaProject(N100402015) supported by Fundamental Research Funds for the Central Universities of China+1 种基金Project(2012AA03A502) supported by the National High Technology Research and Development Program of ChinaProject supported by Program for Liaoning Innovative Research Team in University,China
文摘The influence of chemical composition and cold deformation on aging precipitation behavior of 18Cr-16Mn-2Mo-I.IN （HNS-A）, 18Cr-16Mn-I.3N （HNS-B）, 18Cr-18Mn-2Mo-0.96N （HNS-C） and 18Cr-18Mn-2Mo-0.77N （I-INS-D） high nitrogen austenitic stainless steels was investigated. The results show that the ＂nose＂ temperatures and incubation periods of the initial time-temperature-precipitation （TTP） curves of aged HNSs are found to be 850 ℃, 60 s; 850 ℃, 45 s; 850 ℃, 60 s and 900 ℃, 90 s, respectively. Based on the analysis of SAD patterns, the coarse cellular Cr2N precipitate which presents a lamellar structure has a hexagonal structure of a=0.478 nm and c=0.444 nm. The Z phase corresponding to a composition of Fe36Cr^2Mo10, is determined to be a body-centered cubic structure ofa=0.892 nm. The precipitating sensitivity presents no more difference with the nitrogen content increasing from 0.77% to 0.96%, but exhibits so obviously that the cellular precipitates nearly overspread the whole field. The addition of Mo element can restrain the TTP curves moving left and down, which means decreasing the sensitivity of aging precipitation. With increasing the cold deformation, the sensitivity of precipitation increases obviously.
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Armament Research Board (ARMREB), New Delhi for funding this project work (Project no. MAA/03/ 41)
文摘Austenitic stainless steel(ASS) and High nickel steel(HNS) welding consumables are being used for welding Q&T steels, as they have higher solubility for hydrogen in austenitic phase, to avoid hydrogen induced cracking(HIC) but they are very expensive. In recent years, the developments of low hydrogen ferritic steel(LHF) consumables that contain no hygroscopic compounds are utilized for welding Q&T steels. Heat affected zone(HAZ) softening is another critical issue during welding of armour grade Q&T steels and it depends on the welding process employed and the weld thermal cycle. In this investigation an attempt has been made to study the influence of welding consumables and welding processes on metallurgical characteristics of armour grade Q&T steel joints by various metallurgical characterization procedures. Shielded metal arc welding(SMAW) and flux cored arc welding(FCAW) processes were used for making welds using ASS, LHF and HNS welding consumables. The joints fabricated by using LHF consumables offered lower degree of HAZ softening and there is no evidence of HIC in the joints fabricated using LHF consumables.
基金supported by the Russell Family Foundation Grant for research on High Level Waste Packages and Dry Casksthe Department of Nuclear Engineering at North Carolina State University。
文摘The shielding and corrosion properties of the Alloy 709 advanced austenitic stainless steel have been investigated as a candidate canister material in spent fuel dry casks.The results revealed that the experimental and computational data of the linear and mass attenuation coefficients of the alloy are in good agreement,in which the attenuation coefficient values decreased with increasing photon energy.Alloy 709 was shown to exhibit the highest linear attenuation coefficient against gamma rays when compared to 304 and 316 stainless steels.On the other hand,Alloy 709 exhibited no considerable weight change over a 69-day period in circulating salt brines corrosion testing,while it showed an exponential increase of corrosion current density with temperature in acidic and basic corrosive solutions during electrochemical polarization corrosion testing.Furthermore,Alloy 709 was the least corroded steel compared to other austenitic stainless steels in both acidic and basic solutions.The optimistic results of the shielding and corrosion properties of Alloy 709 due to its chemical composition,suggest utilizing it as a canister material in spent nuclear fuel dry casks.
基金Project(2009D005002000003) supported by the Foundation for Fostering Outstanding Talents of Beijing,China
文摘To study the mechanics of work-hardening and annealing-softening, a series of experiments were conducted on samples of 304 austenitic stainless steel sheets. In addition, transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, and tensile testing were carried out to study changes and mechanisms of the stainless steel structures and properties during work-hardening and annealing-softening. The results indicate that annealing at low temperatures （100-500 ~C） can only remove partial residual stresses in the sample and the softening via annealing is not obvious. Bright annealing and rapid cooling in a protective atmosphere can completely soften the cold-worked material. In addition, the low-temperature sample without a protective atmosphere only has a little oxidation on the surface, but at higher temperature the oxidized layer is very thick. Thus, high-temperature annealing should include bright annealing.
基金supported by research grant from the Science and Technology Development Fund(FDCT)of MacauSAR(Grant No.070/2011/A3)
文摘In order to reduce the cost of the austenitic stainless steels(ASSs),the expensive austenite former(nickel) is often substituted by manganese.However,manganese is generally seen to have a detrimental effect on the corrosion resistance.In the present study,the feasibility of laser surface modification of a lean-alloyed ASS(FeCrMn) for enhancing pitting corrosion resistance was investigated.Laser surface modification of FeCrMn was successfully achieved by a 2.3 kW high power diode laser(HPDL).Cyclic polarization tests for FeCrMn after laser surface modification in 3.5% NaCl solution at 25 ℃ were performed by using a potentiostat.The pitting resistance of the laser-modified specimens was found to be significantly improved as reflected by the noble shift in pitting potential.This could be attributed to redistribution of manganese sulphide leading to a more homogenous and refined microstructure.Pitting corrosion resistance of the laser-treated FeCrMn followed by subsequent citric acid passivation was found to be further improved as reflected by the noble shift in pitting potential to 0.18 V.
