Custom 465(C465)is a martensitic stainless steel known for its high strength,toughness,and corrosion resistance,widely used in aerospace,automotive,and medical industries.However,limited work has been conducted on its...Custom 465(C465)is a martensitic stainless steel known for its high strength,toughness,and corrosion resistance,widely used in aerospace,automotive,and medical industries.However,limited work has been conducted on its additive manufacturing(AM)and no dedicated heat treatments have been developed for additively manufactured C465 to optimize its strength-ductility trade-off.In this work,the C465 was fabricated via laser powder bed fusion.The effect of hot isostatic pressing,solid solution,cryogenic treatment(−78.5℃),and aging on the composition homogenization,austenite-to-martensite transition,and Ni_(3)Ti precipitation were systemically investigated.The atom probe tomography analysis reveals that Mo atoms accumulate on Ni_(3)Ti precipitate surfaces and inhibits the Ni_(3)Ti growth,con-tributing to the enhanced strength of C465.The modified heat treatment for additively manufactured C465 reaches comparable tensile strength with the wrought counterpart,yielding an ultimate tensile strength of 1773 MPa,yield strength of 1686 MPa,and elongation of 6.5%.A yield strength calculation model was proposed and validated with measured strength under various heat treatments,providing valuable insight for heat treatment design towards diverse industrial applications.展开更多
The microstructures and mechanical properties of Cr13 super martensitic stainless steel after different heat treatments were studied. The results show that the structures of the steel after quenching are of lath marte...The microstructures and mechanical properties of Cr13 super martensitic stainless steel after different heat treatments were studied. The results show that the structures of the steel after quenching are of lath martensite mixed with a small amount of retained austenite. With the raising quenching temperature, the original austenite grain size increases and the lath martensite gradually becomes thicker. The structures of the tempered steel are mixtures of tempered martensite and reversed austenite dispersed in the martensite matrix. The amount of reversed austenite is from 7.54% to 22. 49%. After different heat treatments, the tensile strength, the elongation and the HRC hardness of the steel are in the range of 813 1 070 MPa, 10.1%--21.2% and 21.33--32.37, respectively. The steel displays the best comprehensive mechanical properties after the sample is quenched at 1 050 ℃ followed by tempering at 650 ℃.展开更多
A series of heat treatments using the orthogonal experiment method were performed to study the microstruc- ture and mechanical properties of 1Cr12NiMo martensitic stainless steel containing various nitrogen content ad...A series of heat treatments using the orthogonal experiment method were performed to study the microstruc- ture and mechanical properties of 1Cr12NiMo martensitic stainless steel containing various nitrogen content addition. The results indicate that the optimal heat treatment is annealing at 830 ℃ for 1 h, austenitizing at 985 ℃ for 1 h followed by oil quenching, and tempering at 630 ℃ for 4 h followed by air cooling, Nitrogen addition to 1Cr12NiMo steel can effectively hinder the austenite grain growth, refine the martensite lath, and increase the strength and hardness. The impact toughness of this steel only shows a minor decrease as the nitrogen content increases.展开更多
In this study,the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel(BASE)and that modified with rare earth(REM)in 0.1 mol/L Na Cl solution were characterized.Techniques such as automatic secondary elec...In this study,the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel(BASE)and that modified with rare earth(REM)in 0.1 mol/L Na Cl solution were characterized.Techniques such as automatic secondary electron microscope(ASPEX PSEM detector),scanning electron microscope(SEM),transmission electron microscope(TEM),scanning Kelvin probe force microscope(SKP),potentiodynamic and potentiostatic polarizations were employed.The results obtained indicate that BASE steel contains Al_(2)O_(3)/Mn S,Al_(2)O_(3) and Mn S inclusions,while REM steels contain(La,Ce,Cr,Fe)-O and(La,Ce,Cr,Fe)-O-S inclusions.Compared with BASE steel,REM steel is more susceptible to induce the metastable pitting nucleation and repassivation,whereas it restrains the transition from metastable pitting to stable pitting.Adding 0.021%rare earth element to BASE steel can reduce the number and area of inclusions,while that of 0.058%can increase the number and enlarged the size of inclusions,which is also the reason that pitting corrosion resistance of 58 REM steel is slightly lower than that of 21 REM steel.In the process of pitting corrosion induced by Al_(2)O_(3)/Mn S inclusions,Mn S is preferentially anodic dissolved,and also the matrix contacted with Al_(2)O_(3) is subsequently anodic dissolved.For REM steels,anodic dissolution preferentially occurs at the boundary between inclusions and matrix,while(La,Ce,Cr,Fe)-O inclusions chemically dissolve in local acidic environment or are separated from steel matrix.The chemically dissolved substance(La^(3+) and Ce^(3+))of(La,Ce,Cr,Fe)-O inclusions are concentrated in pitting pits,which inhibits its continuous growth.展开更多
The effect of different heat treatments on the reversed austenite in Cr15 super martensitic stainless steel was investigated. The experimental results indicate that the microstructure of the steel is composed of tempe...The effect of different heat treatments on the reversed austenite in Cr15 super martensitic stainless steel was investigated. The experimental results indicate that the microstructure of the steel is composed of tempered martensite and diffused reversed austenite after quenching at 1 050 ℃ and tempering from 550 to 750 ℃. The volume fraction and size of reversed austenite increase with increasing tempering temperature and both of them reach the maximum value at 700 ℃. The volume fraction and size of reversed austenite decrease when the temperature is above 700 ℃. The transmission electron microscope （TEM） results indicate that the orientation relationship between tempered martensite and reversed austenite belongs to Kurdjmov-Sach （K-S） relationship.展开更多
The effects of rare-earth yttrium(Y)element on the microstructure,mechanical properties and corrosion properties of 20Cr13 martensitic stainless steel were investigated by optical microscopy,scanning electron microsco...The effects of rare-earth yttrium(Y)element on the microstructure,mechanical properties and corrosion properties of 20Cr13 martensitic stainless steel were investigated by optical microscopy,scanning electron microscopy and tensile test.Electrochemical experiments were carried out to study the effect of rare-earth element Y addition on corrosion resistance.The results showed that the addition of 0.02 wt.%rare-earth yttrium to martensitic stainless steel could affect the microstructure transformation,and Ac3 temperature was obviously increased.In the stainless steel after heat treatment,there were more pro-eutectoid ferrite in the steel with 0.02 wt.%yttrium.The mechanical test results showed that the addition of 0.02 wt.%yttrium could significantly improve the tensile strength and elongation of the steel,which was related to the influence of yttrium element on inclusions in the test steel.With the quenching temperature of 0.02 wt.%yttrium steel increasing,the content of the ferrite in steel was affected and the corrosion resistance was remarkably improved.展开更多
Single grit grinding is the simplified model to abstract the macro scale grinding.Finite element analysis is a strong tool to study the physical fields during a single grit grinding process,compared to experimental re...Single grit grinding is the simplified model to abstract the macro scale grinding.Finite element analysis is a strong tool to study the physical fields during a single grit grinding process,compared to experimental research.Based on the dynamic mechanical behavior of 2Cr12Ni4Mo3VNbN steel and the mathematical statistics of abrasive grit,modeling of the single grit grinding process was conducted by using commercial software AdvantEdge.The validation experiment was designed to validate the correctness of the FEA model by contrast with grinding force.The validation result shows that the FEA model can well describe the single grit grinding process.Then the grinding force and multi-physics fields were studied by experimental and simulation results.It was found that both the normal and tangential grinding forces were linearly related to the cutting speed and cutting depth.The maximum temperature is located in the subsurface of the workpiece in front of the grit,while the maximum stress and strain are located under the grit tip.The strain rate can reach as high as about 106 s–1 during the single grit grinding,which is larger than other traditional machining operations.展开更多
To improve the strength-toughness of 13Cr4NiMo martensitic stainless steel(13-4MSS),a thermal cyclic heat treatment(TCHT)combined with the advantage of tempering was proposed.The microstructures were characterized by ...To improve the strength-toughness of 13Cr4NiMo martensitic stainless steel(13-4MSS),a thermal cyclic heat treatment(TCHT)combined with the advantage of tempering was proposed.The microstructures were characterized by scanning electron microscopy,X-ray diffraction and electron backscattered diffraction,and the mechanical behaviors in terms of tensile properties and impact toughness were analyzed in correlation with microstructural evolution.It was found that grains and the martensitic matrix were refined by TCHT through the cyclic quenching transformation and austenite recrystallization,which was conducive to more nucleation quantity of reversed austenite during tempering.Two-sphericalcap nucleation model was used to explain the effect of refined grains of TCHT on the nucleation of reversed austenite.Grain refinement by TCHT improved the brittle fracture stress to reduce the ductile-brittle transition temperature and thus improved the cryogenic impact toughness of 13-4MSS.Reversed austenite distributed at the martensitic lath boundary enhances the crack arrest performance and increases the britle fracture stress.It is concluded that reasonable TCHT plus tempering process significantly improves the strength-toughness of 13-4MSS,reflecting the comprehensive effect of grain refinement and reversed austenite.展开更多
Multiple precipitating species in a 2.2 GPa grade precipitation-hardened martensitic stainless steel with balanced ductility were characterized at atomic scale by atom probe tomography.The results indicated that the c...Multiple precipitating species in a 2.2 GPa grade precipitation-hardened martensitic stainless steel with balanced ductility were characterized at atomic scale by atom probe tomography.The results indicated that the clustering of solute atoms was promoted with progressive aging treatments.(Cr,Mo)-rich carbide(M_(2)C)precipitated at the linear dislocations in the as-aged steels.Obvious segregation of Cr,Mo,and C at phase boundaries favored the precipitation of carbide and caused the formation of Cr-lean domains.Spinodal decomposition of martensitic matrix during aging led to the substantial precipitation of fine Cr-rich(α′Cr)phase.Compared with the first aging treated samples,a synergistic enhancement of both strength and ductility of the secondary aging treated(SAT)samples was primarily ascribed to the enhanced precipitation of Cr-rich phase.Additionally,Ni-rich filmy reversed austenite precipitated at the lath boundary,which was beneficial to the ductility of SAT samples.展开更多
A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out f...A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out for 15 h at 350℃ by means of DC- pulsed plasma in 25%N2＋ 75%H2 atmosphere. The microstructure, phase composition, and residual stresses profiles of the nitrided layers were determined by optical microscopy and X-ray diffraction. The microhardness profiles of the nitridied surfaces were also studied. The fatigue life, sliding wear, and erosion wear loss of the untreated specimens and plasma nitriding specimens were determined on the basis of a rotating bending fatigue tester, a ball-on-disc wear tester, and a solid particle erosion tester. The results show that the 350℃ nitrided surface is dominated by c-Fe3N and ON, which is supersaturated nitrogen solid solution. They have high hardness and chemical stabilities. So the low temperature plasma nitriding not only increases the surface hardness values but also improves the wear and erosion resistance. In addition, the fatigue limit of AISI 420 steel can also be improved by plasma nitriding at 350℃ because plasma nitriding produces residual compressive stress inside the modified layer.展开更多
Laser powder bed fusion(LPBF)is a widely recognized additive manufacturing technology that can fabricate complex components rapidly through layer-by-layer formation.However,there is a paucity of research on the effect...Laser powder bed fusion(LPBF)is a widely recognized additive manufacturing technology that can fabricate complex components rapidly through layer-by-layer formation.However,there is a paucity of research on the effect of laser scanning speed on the cellular microstructure and mechanical properties of martensitic stainless steel.This study systematically investigated the influence of laser scanning speed on the cellular microstructure and mechanical properties of a developed Fe11Cr8Ni5Co3Mo martensitic stainless steel produced by LPBF.The results show that increasing the laser scanning speed from 400 to 1000 mm/s does not lead to a noticeable change in the phase fraction,but it reduces the average size of the cellular microstructure from 0.60 to 0.35μm.The scanning speeds of 400 and 1000 mm/s both had adverse effects on performances of sample,resulting in inadequate fusion and keyhole defects respectively.The optimal scanning speed for fabricating samples was determined to be 800 mm/s,which obtained the highest room temperature tensile strength and elongation,with the ultimate tensile strength measured at(1088.3±2.0)MPa and the elongation of(16.76±0.10)%.Furthermore,the mechanism of the evolution of surface morphology,defects,and energy input were clarified,and the relationship between cellular microstructure size and mechanical properties was also established.展开更多
The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms i...The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt%C and 0.5 wt%N after cryogenic treatment were investigated by the atom probe tomography.Carbon clusters begin to form after cryogenic treatment at-60℃and gradually increase with the decrease of cryogenic treatment temperature.While Mo–N and Cr–N pairs are homogeneously distributed in the matrix even after cryogenic treatment at-120℃,and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to-190℃.It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them.The stronger interaction between Cr,Mo atoms and N delays the segregation of N during the cryogenic treatment.Finally,the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.展开更多
Hot deformation behavior of 0.3 C-15 Cr-1 Mo-0.5 N high nitrogen martensitic stainless steel(HNMSS)was investigated in the temperature range of 1173-1473 K and at strain rates of 0.001-10 s-1 using a Gleeble 3500 ther...Hot deformation behavior of 0.3 C-15 Cr-1 Mo-0.5 N high nitrogen martensitic stainless steel(HNMSS)was investigated in the temperature range of 1173-1473 K and at strain rates of 0.001-10 s-1 using a Gleeble 3500 thermal-mechanical simulator.The true stress-strain curves of the studied HNMSS were measured and corrected to eliminate the effect of friction on the flow stress.The relationship between the flow stress and Zener-Hollomon parameter for the studied HNMSS wsa analyzed in the Arrhenius hyperbolic sine constitutive model by the law of Z=3.76×1015 sinh(0.004979σp)7.5022.The processing maps at different strains of the studied HNMSS were plotted,and its flow instability regions in hot working were also confirmed in combination with the microstructure examination.Moreover,the optimal hot deformation parameters of the studied HNMSS could be suggested at T=1303-1423 K andε=5-10 s-1 or T=1273-1473 K andε=0.005-0.04 s-1.展开更多
Two ingots of 4Cr13 martensitic stainless steel with different nitrogen contents,0.023 and 0.121 mass%,were produced by vacuum induction furnace and electroslag remelting.The microstructure and the microsegregation of...Two ingots of 4Cr13 martensitic stainless steel with different nitrogen contents,0.023 and 0.121 mass%,were produced by vacuum induction furnace and electroslag remelting.The microstructure and the microsegregation of the electroslag remelting ingot were analyzed by optical microscopy,scanning electron microscopy and electron microprobe analysis.Thermo-Calc software was used to calculate the nitrogen solubility changes during solidification of high nitrogen martensitic stainless steel and the equilibrium and non-equilibrium phase diagrams of 4Cr13 steel with different nitrogen contents.The solubility of nitrogen in 4Cr13 steel reached the lowest value of 0.118%before the start of the peritectic reaction.The microstructure of 4Cr13 steel was martensite,retained austenite and primary carbide M_(7)C_(3).Higher nitrogen content increased the content of retained austenite in martensitic stainless steel,inhibited the precipitation of primary carbides and refined the dendrites.Higher nitrogen content could effectively inhibit the microsegregation of C element in martensitic stainless steel;however,it had little effect on Cr,V,Nb and Ti.The peritectic reaction was first carried out in high nitrogen steel during solidification,which advanced the transformation of austenite and inhibited the microsegregation of C element.展开更多
A novel process based on centrifugal casting was developed to produce martensitic stainless steel for guideroll materials. Centrifugal casting provides a lower production cost and less of the thermal cracking defects ...A novel process based on centrifugal casting was developed to produce martensitic stainless steel for guideroll materials. Centrifugal casting provides a lower production cost and less of the thermal cracking defects which normally occur in the overlaid welding process. In this study, the effects of Ni on the microstructure and mechanical properties of martensitic stainless steel were investigated. The results show that the addition of Ni resulted in a decrease in the volume fraction of delta ferrite and an increase in the volume fraction of the retained austenite, respectively. Moreover, a tensile strength of 1600 MPa with an elongation of 4% were obtained after tempering at 500℃ for 2 h. These values were higher than those obtained by using the conventional overlaid process.展开更多
The micro structure of 10Cr15MoVCo electroslag remelting(ESR)ingot was observed using an optical microscope and a scanning electron microscope.There are differences in the number,size,and distribution of primary carbi...The micro structure of 10Cr15MoVCo electroslag remelting(ESR)ingot was observed using an optical microscope and a scanning electron microscope.There are differences in the number,size,and distribution of primary carbides in different positions of ESR ingot.The results show that the two-dimensional morphology of primary carbides is blocky,fibrous,and spherulitic.The three-dimensional morphology of primary carbides is blocky,spherulitic,fibrous,and short rods.X-ray diffraction results show that primary carbides are M_(7)C_(3) carbides.Electron backscattered diffraction results indicate that large-sized primary carbides consist of blocky,fibrous,and spherulitic carbides with different orientations.High-tem-perature diffusion annealing experiments show that as the temperature increases,the continuity between primary carbides decreases,and the precipitated secondary carbides disappear.The area fraction of primary carbides is reduced,but the morphology of primary carbide is unchanged.The effect of high-temperature diffusion annealing on the dissolution of M_(7)C_(3) primary carbon compounds in ESR ingot was limited.展开更多
The effect of electroslag remelting（ESR） on carbides in 8Cr13MoV martensitic stainless steel was experimentally studied. Phases precipitated from liquid steel during solidification were calculated using the Thermo-C...The effect of electroslag remelting（ESR） on carbides in 8Cr13MoV martensitic stainless steel was experimentally studied. Phases precipitated from liquid steel during solidification were calculated using the Thermo-Calc software. The carbon segregation was analyzed by original position analysis（OPA）, and the carbides were analyzed by optical microscopy（OM）, scanning electron microscopy（SEM）, energy-dispersive X-ray spectroscopy（EDS） and X-ray diffraction（XRD）. The results indicated that more uniform carbon distribution and less segregation were obtained in the case of samples subjected to the ESR process. After ESR, the amount of netty carbides decreased significantly, and the chromium and vanadium contents in the grain-boundary carbides was reduced. The total area and average size of carbides were obviously smaller after the ESR process. In the sample subjected to ESR, the morphology of carbides changed from lamellar and angular to globular or lump, whereas the types of carbides did not change; both M23C6 and M7C3 were present before and after the ESR process.展开更多
The effects of Cl ion concentration and pH values on the corrosion behavior of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel（UHSMSS） were investigated by a series of electrochemical tests combined ...The effects of Cl ion concentration and pH values on the corrosion behavior of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel（UHSMSS） were investigated by a series of electrochemical tests combined with observations by stereology microscopy and scanning electron microscopy. A critical Cl- ion concentration was found to exist（approximately 0.1wt%）, above which pitting occurred. The pitting potential decreased with increasing Cl- ion concentration. A UHSMSS specimen tempered at 600°C exhibited a better pitting corrosion resistance than the one tempered at 400°C. The corrosion current density and passive current density of the UHSMSS tempered at 600°C decreased with increasing pH values of the corrosion solution. The pits developed a shallower dish geometry with increasing polarization potential. A lacy cover on the pits of the UHSMSS tempered at 400°C accelerated pitting, whereas corrosion products deposited in the pits of the UHSMSS tempered at 600°C hindered pitting.展开更多
The mechanical and corrosive properties of 00Cr13Ni4Mo （S13 -4N） were tested and compared with those of 00Cr13Ni6Mo （S13 -6）. The effects of nitrogen on the properties of the steels were analyzed. The results of t...The mechanical and corrosive properties of 00Cr13Ni4Mo （S13 -4N） were tested and compared with those of 00Cr13Ni6Mo （S13 -6）. The effects of nitrogen on the properties of the steels were analyzed. The results of the tensile and corrosion tests show the strength,the ductility,and the pitting corrosion resistance of S13 -4N are higher, lower and poorer than those of S13 -6 respectively, when tempered at a temperature below 550 ℃and vice versa when the tempering temperature is higher than 550℃. The results of the X-ray diffraction （XRD） and the electron backscattered diffraction （EBSD） analyses reveal that inversed austenite appears at 550℃ and the amount of it peaks at 600 ℃ with the best ductility. And the total amount of the inversed austenite in S13 -6 is more than that in S13 -4N in different forms. Nitrogen performs better in terms of stabilizing inversed austenite while nickel is more favorable for forming inversed austenite, the amount and stability of which affect the ductility remarkably. The reason for the embrittlement of S13 -4N at 450℃ can be the result of carbide and nitride precipitating at grain boundaries.展开更多
Laser transformation hardening （LTH） was applied to the surface of the AISI 420 martensitic stainless steel by a pulsed Nd：YAG laser to obtain optimum hardness. The influences of process parameters （laser pulse en...Laser transformation hardening （LTH） was applied to the surface of the AISI 420 martensitic stainless steel by a pulsed Nd：YAG laser to obtain optimum hardness. The influences of process parameters （laser pulse energy, duration time, and travel speed） on the depth and hardness of laser treated area were investigated. Image analysis of SEM microstructure of AISI 420 showed that plate-like carbide have almost fully and （30-40）% of globular carbide particles dissolved into the matrix after laser transformation hardening by pulsed laser and the microstructure was refined to obtain controlled tempered martensite microstructure with 450 VHN hardness.展开更多
基金supported by the National Key Research and Development Program of China(No.2022YFB4600302)the Fundamental Research Funds for the Central Universities,China(No.FRF-IDRY-23-011).
文摘Custom 465(C465)is a martensitic stainless steel known for its high strength,toughness,and corrosion resistance,widely used in aerospace,automotive,and medical industries.However,limited work has been conducted on its additive manufacturing(AM)and no dedicated heat treatments have been developed for additively manufactured C465 to optimize its strength-ductility trade-off.In this work,the C465 was fabricated via laser powder bed fusion.The effect of hot isostatic pressing,solid solution,cryogenic treatment(−78.5℃),and aging on the composition homogenization,austenite-to-martensite transition,and Ni_(3)Ti precipitation were systemically investigated.The atom probe tomography analysis reveals that Mo atoms accumulate on Ni_(3)Ti precipitate surfaces and inhibits the Ni_(3)Ti growth,con-tributing to the enhanced strength of C465.The modified heat treatment for additively manufactured C465 reaches comparable tensile strength with the wrought counterpart,yielding an ultimate tensile strength of 1773 MPa,yield strength of 1686 MPa,and elongation of 6.5%.A yield strength calculation model was proposed and validated with measured strength under various heat treatments,providing valuable insight for heat treatment design towards diverse industrial applications.
文摘The microstructures and mechanical properties of Cr13 super martensitic stainless steel after different heat treatments were studied. The results show that the structures of the steel after quenching are of lath martensite mixed with a small amount of retained austenite. With the raising quenching temperature, the original austenite grain size increases and the lath martensite gradually becomes thicker. The structures of the tempered steel are mixtures of tempered martensite and reversed austenite dispersed in the martensite matrix. The amount of reversed austenite is from 7.54% to 22. 49%. After different heat treatments, the tensile strength, the elongation and the HRC hardness of the steel are in the range of 813 1 070 MPa, 10.1%--21.2% and 21.33--32.37, respectively. The steel displays the best comprehensive mechanical properties after the sample is quenched at 1 050 ℃ followed by tempering at 650 ℃.
基金supported by the National Key Technology R&D Program,China(No.2011BAA06B02)
文摘A series of heat treatments using the orthogonal experiment method were performed to study the microstruc- ture and mechanical properties of 1Cr12NiMo martensitic stainless steel containing various nitrogen content addition. The results indicate that the optimal heat treatment is annealing at 830 ℃ for 1 h, austenitizing at 985 ℃ for 1 h followed by oil quenching, and tempering at 630 ℃ for 4 h followed by air cooling, Nitrogen addition to 1Cr12NiMo steel can effectively hinder the austenite grain growth, refine the martensite lath, and increase the strength and hardness. The impact toughness of this steel only shows a minor decrease as the nitrogen content increases.
基金supported by the National Natural Science Foundation of China(No.51801219)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2019193)+1 种基金the Scientific Research Project of China Three Gorges Corporation(No.JD-YJ-05006)the National Key Research and Development Program of China(No.2017YFB0702302)。
文摘In this study,the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel(BASE)and that modified with rare earth(REM)in 0.1 mol/L Na Cl solution were characterized.Techniques such as automatic secondary electron microscope(ASPEX PSEM detector),scanning electron microscope(SEM),transmission electron microscope(TEM),scanning Kelvin probe force microscope(SKP),potentiodynamic and potentiostatic polarizations were employed.The results obtained indicate that BASE steel contains Al_(2)O_(3)/Mn S,Al_(2)O_(3) and Mn S inclusions,while REM steels contain(La,Ce,Cr,Fe)-O and(La,Ce,Cr,Fe)-O-S inclusions.Compared with BASE steel,REM steel is more susceptible to induce the metastable pitting nucleation and repassivation,whereas it restrains the transition from metastable pitting to stable pitting.Adding 0.021%rare earth element to BASE steel can reduce the number and area of inclusions,while that of 0.058%can increase the number and enlarged the size of inclusions,which is also the reason that pitting corrosion resistance of 58 REM steel is slightly lower than that of 21 REM steel.In the process of pitting corrosion induced by Al_(2)O_(3)/Mn S inclusions,Mn S is preferentially anodic dissolved,and also the matrix contacted with Al_(2)O_(3) is subsequently anodic dissolved.For REM steels,anodic dissolution preferentially occurs at the boundary between inclusions and matrix,while(La,Ce,Cr,Fe)-O inclusions chemically dissolve in local acidic environment or are separated from steel matrix.The chemically dissolved substance(La^(3+) and Ce^(3+))of(La,Ce,Cr,Fe)-O inclusions are concentrated in pitting pits,which inhibits its continuous growth.
文摘The effect of different heat treatments on the reversed austenite in Cr15 super martensitic stainless steel was investigated. The experimental results indicate that the microstructure of the steel is composed of tempered martensite and diffused reversed austenite after quenching at 1 050 ℃ and tempering from 550 to 750 ℃. The volume fraction and size of reversed austenite increase with increasing tempering temperature and both of them reach the maximum value at 700 ℃. The volume fraction and size of reversed austenite decrease when the temperature is above 700 ℃. The transmission electron microscope （TEM） results indicate that the orientation relationship between tempered martensite and reversed austenite belongs to Kurdjmov-Sach （K-S） relationship.
文摘The effects of rare-earth yttrium(Y)element on the microstructure,mechanical properties and corrosion properties of 20Cr13 martensitic stainless steel were investigated by optical microscopy,scanning electron microscopy and tensile test.Electrochemical experiments were carried out to study the effect of rare-earth element Y addition on corrosion resistance.The results showed that the addition of 0.02 wt.%rare-earth yttrium to martensitic stainless steel could affect the microstructure transformation,and Ac3 temperature was obviously increased.In the stainless steel after heat treatment,there were more pro-eutectoid ferrite in the steel with 0.02 wt.%yttrium.The mechanical test results showed that the addition of 0.02 wt.%yttrium could significantly improve the tensile strength and elongation of the steel,which was related to the influence of yttrium element on inclusions in the test steel.With the quenching temperature of 0.02 wt.%yttrium steel increasing,the content of the ferrite in steel was affected and the corrosion resistance was remarkably improved.
基金Projects(U1537202,51575305)supported by the National Natural Science Foundation of ChinaProject(61328302)supported by National Security Major Basic Research Program of China
文摘Single grit grinding is the simplified model to abstract the macro scale grinding.Finite element analysis is a strong tool to study the physical fields during a single grit grinding process,compared to experimental research.Based on the dynamic mechanical behavior of 2Cr12Ni4Mo3VNbN steel and the mathematical statistics of abrasive grit,modeling of the single grit grinding process was conducted by using commercial software AdvantEdge.The validation experiment was designed to validate the correctness of the FEA model by contrast with grinding force.The validation result shows that the FEA model can well describe the single grit grinding process.Then the grinding force and multi-physics fields were studied by experimental and simulation results.It was found that both the normal and tangential grinding forces were linearly related to the cutting speed and cutting depth.The maximum temperature is located in the subsurface of the workpiece in front of the grit,while the maximum stress and strain are located under the grit tip.The strain rate can reach as high as about 106 s–1 during the single grit grinding,which is larger than other traditional machining operations.
基金supported by Specific Research Project of Guangxi for Research Bases and Talents(Grant No.GuiKe AD19245145)Natural Science Foundation of Guangxi Province(Grant No.2018GXNSFBA281106).
文摘To improve the strength-toughness of 13Cr4NiMo martensitic stainless steel(13-4MSS),a thermal cyclic heat treatment(TCHT)combined with the advantage of tempering was proposed.The microstructures were characterized by scanning electron microscopy,X-ray diffraction and electron backscattered diffraction,and the mechanical behaviors in terms of tensile properties and impact toughness were analyzed in correlation with microstructural evolution.It was found that grains and the martensitic matrix were refined by TCHT through the cyclic quenching transformation and austenite recrystallization,which was conducive to more nucleation quantity of reversed austenite during tempering.Two-sphericalcap nucleation model was used to explain the effect of refined grains of TCHT on the nucleation of reversed austenite.Grain refinement by TCHT improved the brittle fracture stress to reduce the ductile-brittle transition temperature and thus improved the cryogenic impact toughness of 13-4MSS.Reversed austenite distributed at the martensitic lath boundary enhances the crack arrest performance and increases the britle fracture stress.It is concluded that reasonable TCHT plus tempering process significantly improves the strength-toughness of 13-4MSS,reflecting the comprehensive effect of grain refinement and reversed austenite.
基金This work was financially supported by the National“13th Five-year Plan”high-tech Research and Development Program of China(YE-17T60270B).
文摘Multiple precipitating species in a 2.2 GPa grade precipitation-hardened martensitic stainless steel with balanced ductility were characterized at atomic scale by atom probe tomography.The results indicated that the clustering of solute atoms was promoted with progressive aging treatments.(Cr,Mo)-rich carbide(M_(2)C)precipitated at the linear dislocations in the as-aged steels.Obvious segregation of Cr,Mo,and C at phase boundaries favored the precipitation of carbide and caused the formation of Cr-lean domains.Spinodal decomposition of martensitic matrix during aging led to the substantial precipitation of fine Cr-rich(α′Cr)phase.Compared with the first aging treated samples,a synergistic enhancement of both strength and ductility of the secondary aging treated(SAT)samples was primarily ascribed to the enhanced precipitation of Cr-rich phase.Additionally,Ni-rich filmy reversed austenite precipitated at the lath boundary,which was beneficial to the ductility of SAT samples.
基金supported by National Natural Science Foundation of China(Nos.50171054 and 50671085)National High Technical Research and Development Programme of China(No.2007AA03Z521).
文摘A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out for 15 h at 350℃ by means of DC- pulsed plasma in 25%N2＋ 75%H2 atmosphere. The microstructure, phase composition, and residual stresses profiles of the nitrided layers were determined by optical microscopy and X-ray diffraction. The microhardness profiles of the nitridied surfaces were also studied. The fatigue life, sliding wear, and erosion wear loss of the untreated specimens and plasma nitriding specimens were determined on the basis of a rotating bending fatigue tester, a ball-on-disc wear tester, and a solid particle erosion tester. The results show that the 350℃ nitrided surface is dominated by c-Fe3N and ON, which is supersaturated nitrogen solid solution. They have high hardness and chemical stabilities. So the low temperature plasma nitriding not only increases the surface hardness values but also improves the wear and erosion resistance. In addition, the fatigue limit of AISI 420 steel can also be improved by plasma nitriding at 350℃ because plasma nitriding produces residual compressive stress inside the modified layer.
基金financially supported by the National Natural Science Foundation of China(Nos.U2141205,52371002,and 52374366)the Fundamental Research Funds for the Central Universities(Nos.06109125 and 06930007)Fundamental Research Funds for the Central Universities(No.FRF-BD-23-02).
文摘Laser powder bed fusion(LPBF)is a widely recognized additive manufacturing technology that can fabricate complex components rapidly through layer-by-layer formation.However,there is a paucity of research on the effect of laser scanning speed on the cellular microstructure and mechanical properties of martensitic stainless steel.This study systematically investigated the influence of laser scanning speed on the cellular microstructure and mechanical properties of a developed Fe11Cr8Ni5Co3Mo martensitic stainless steel produced by LPBF.The results show that increasing the laser scanning speed from 400 to 1000 mm/s does not lead to a noticeable change in the phase fraction,but it reduces the average size of the cellular microstructure from 0.60 to 0.35μm.The scanning speeds of 400 and 1000 mm/s both had adverse effects on performances of sample,resulting in inadequate fusion and keyhole defects respectively.The optimal scanning speed for fabricating samples was determined to be 800 mm/s,which obtained the highest room temperature tensile strength and elongation,with the ultimate tensile strength measured at(1088.3±2.0)MPa and the elongation of(16.76±0.10)%.Furthermore,the mechanism of the evolution of surface morphology,defects,and energy input were clarified,and the relationship between cellular microstructure size and mechanical properties was also established.
基金supported by the National Natural Science Foundation of China(No.51871212)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC04000000)+1 种基金the Major Scientific and Technological Projects of Jiangxi Province(No.20194ABC28011)the Project to Strengthen Industrial Development at the Grass-roots Level(TC190A4DA/35)。
文摘The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt%C and 0.5 wt%N after cryogenic treatment were investigated by the atom probe tomography.Carbon clusters begin to form after cryogenic treatment at-60℃and gradually increase with the decrease of cryogenic treatment temperature.While Mo–N and Cr–N pairs are homogeneously distributed in the matrix even after cryogenic treatment at-120℃,and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to-190℃.It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them.The stronger interaction between Cr,Mo atoms and N delays the segregation of N during the cryogenic treatment.Finally,the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.
基金supported by the National Natural Science Foundation of China(No.51871212)the 2018 Regional Key Project on the Science and Technology Service from Shanghai Branch of Chinese Academy of Sciences(STS,SHBCAS)the Supporting Project for STS,SHBCAS in Fujian Province
文摘Hot deformation behavior of 0.3 C-15 Cr-1 Mo-0.5 N high nitrogen martensitic stainless steel(HNMSS)was investigated in the temperature range of 1173-1473 K and at strain rates of 0.001-10 s-1 using a Gleeble 3500 thermal-mechanical simulator.The true stress-strain curves of the studied HNMSS were measured and corrected to eliminate the effect of friction on the flow stress.The relationship between the flow stress and Zener-Hollomon parameter for the studied HNMSS wsa analyzed in the Arrhenius hyperbolic sine constitutive model by the law of Z=3.76×1015 sinh(0.004979σp)7.5022.The processing maps at different strains of the studied HNMSS were plotted,and its flow instability regions in hot working were also confirmed in combination with the microstructure examination.Moreover,the optimal hot deformation parameters of the studied HNMSS could be suggested at T=1303-1423 K andε=5-10 s-1 or T=1273-1473 K andε=0.005-0.04 s-1.
基金This work was supported by the National Natural Science Foundation of China(Grant No.51874030)the Guangdong YangFan Innovative and Entepreneurial Research Team Program(Grant No.2016YT03C071)the Guangdong Science and Technology Special Fund Project(Grant No.SDZX202005).
文摘Two ingots of 4Cr13 martensitic stainless steel with different nitrogen contents,0.023 and 0.121 mass%,were produced by vacuum induction furnace and electroslag remelting.The microstructure and the microsegregation of the electroslag remelting ingot were analyzed by optical microscopy,scanning electron microscopy and electron microprobe analysis.Thermo-Calc software was used to calculate the nitrogen solubility changes during solidification of high nitrogen martensitic stainless steel and the equilibrium and non-equilibrium phase diagrams of 4Cr13 steel with different nitrogen contents.The solubility of nitrogen in 4Cr13 steel reached the lowest value of 0.118%before the start of the peritectic reaction.The microstructure of 4Cr13 steel was martensite,retained austenite and primary carbide M_(7)C_(3).Higher nitrogen content increased the content of retained austenite in martensitic stainless steel,inhibited the precipitation of primary carbides and refined the dendrites.Higher nitrogen content could effectively inhibit the microsegregation of C element in martensitic stainless steel;however,it had little effect on Cr,V,Nb and Ti.The peritectic reaction was first carried out in high nitrogen steel during solidification,which advanced the transformation of austenite and inhibited the microsegregation of C element.
文摘A novel process based on centrifugal casting was developed to produce martensitic stainless steel for guideroll materials. Centrifugal casting provides a lower production cost and less of the thermal cracking defects which normally occur in the overlaid welding process. In this study, the effects of Ni on the microstructure and mechanical properties of martensitic stainless steel were investigated. The results show that the addition of Ni resulted in a decrease in the volume fraction of delta ferrite and an increase in the volume fraction of the retained austenite, respectively. Moreover, a tensile strength of 1600 MPa with an elongation of 4% were obtained after tempering at 500℃ for 2 h. These values were higher than those obtained by using the conventional overlaid process.
基金This work was supported by the Guangdong YangFan Innovative&Entrepreneurial Research Team Program(No.2016YT03C071)the Guangdong Science and Technology Special Fund Project(No.SDZX202005)the National Natural Science Foundation of China(Nos.51874030 and 51904022).
文摘The micro structure of 10Cr15MoVCo electroslag remelting(ESR)ingot was observed using an optical microscope and a scanning electron microscope.There are differences in the number,size,and distribution of primary carbides in different positions of ESR ingot.The results show that the two-dimensional morphology of primary carbides is blocky,fibrous,and spherulitic.The three-dimensional morphology of primary carbides is blocky,spherulitic,fibrous,and short rods.X-ray diffraction results show that primary carbides are M_(7)C_(3) carbides.Electron backscattered diffraction results indicate that large-sized primary carbides consist of blocky,fibrous,and spherulitic carbides with different orientations.High-tem-perature diffusion annealing experiments show that as the temperature increases,the continuity between primary carbides decreases,and the precipitated secondary carbides disappear.The area fraction of primary carbides is reduced,but the morphology of primary carbide is unchanged.The effect of high-temperature diffusion annealing on the dissolution of M_(7)C_(3) primary carbon compounds in ESR ingot was limited.
基金financially supported by the National Natural Science Foundation of China (No. 51444004)China Postdoctoral Science Foundation (No. 2014M560047)
文摘The effect of electroslag remelting（ESR） on carbides in 8Cr13MoV martensitic stainless steel was experimentally studied. Phases precipitated from liquid steel during solidification were calculated using the Thermo-Calc software. The carbon segregation was analyzed by original position analysis（OPA）, and the carbides were analyzed by optical microscopy（OM）, scanning electron microscopy（SEM）, energy-dispersive X-ray spectroscopy（EDS） and X-ray diffraction（XRD）. The results indicated that more uniform carbon distribution and less segregation were obtained in the case of samples subjected to the ESR process. After ESR, the amount of netty carbides decreased significantly, and the chromium and vanadium contents in the grain-boundary carbides was reduced. The total area and average size of carbides were obviously smaller after the ESR process. In the sample subjected to ESR, the morphology of carbides changed from lamellar and angular to globular or lump, whereas the types of carbides did not change; both M23C6 and M7C3 were present before and after the ESR process.
基金financially supported by the National Natural Science Foundation of China (No.51171023)the Fundamental Research Funds for the Central Universities (No.FRF-TP-14-011C1)the Major State Basic Research Development Program of China (No.2014CB643300)
文摘The effects of Cl ion concentration and pH values on the corrosion behavior of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel（UHSMSS） were investigated by a series of electrochemical tests combined with observations by stereology microscopy and scanning electron microscopy. A critical Cl- ion concentration was found to exist（approximately 0.1wt%）, above which pitting occurred. The pitting potential decreased with increasing Cl- ion concentration. A UHSMSS specimen tempered at 600°C exhibited a better pitting corrosion resistance than the one tempered at 400°C. The corrosion current density and passive current density of the UHSMSS tempered at 600°C decreased with increasing pH values of the corrosion solution. The pits developed a shallower dish geometry with increasing polarization potential. A lacy cover on the pits of the UHSMSS tempered at 400°C accelerated pitting, whereas corrosion products deposited in the pits of the UHSMSS tempered at 600°C hindered pitting.
文摘The mechanical and corrosive properties of 00Cr13Ni4Mo （S13 -4N） were tested and compared with those of 00Cr13Ni6Mo （S13 -6）. The effects of nitrogen on the properties of the steels were analyzed. The results of the tensile and corrosion tests show the strength,the ductility,and the pitting corrosion resistance of S13 -4N are higher, lower and poorer than those of S13 -6 respectively, when tempered at a temperature below 550 ℃and vice versa when the tempering temperature is higher than 550℃. The results of the X-ray diffraction （XRD） and the electron backscattered diffraction （EBSD） analyses reveal that inversed austenite appears at 550℃ and the amount of it peaks at 600 ℃ with the best ductility. And the total amount of the inversed austenite in S13 -6 is more than that in S13 -4N in different forms. Nitrogen performs better in terms of stabilizing inversed austenite while nickel is more favorable for forming inversed austenite, the amount and stability of which affect the ductility remarkably. The reason for the embrittlement of S13 -4N at 450℃ can be the result of carbide and nitride precipitating at grain boundaries.
基金supported by the Tarbiat Modares University and Iranian National Center for Laser Science and Technology
文摘Laser transformation hardening （LTH） was applied to the surface of the AISI 420 martensitic stainless steel by a pulsed Nd：YAG laser to obtain optimum hardness. The influences of process parameters （laser pulse energy, duration time, and travel speed） on the depth and hardness of laser treated area were investigated. Image analysis of SEM microstructure of AISI 420 showed that plate-like carbide have almost fully and （30-40）% of globular carbide particles dissolved into the matrix after laser transformation hardening by pulsed laser and the microstructure was refined to obtain controlled tempered martensite microstructure with 450 VHN hardness.
