A numerical study of stress distribution and fatigue behavior in terms of the effect of voids adjacent to inclusions was conducted with finite element modeling simulations under different assumptions.Fatigue mechanism...A numerical study of stress distribution and fatigue behavior in terms of the effect of voids adjacent to inclusions was conducted with finite element modeling simulations under different assumptions.Fatigue mechanisms were also analyzed accordingly.The results showed that the effects of inclusions on fatigue life will distinctly decrease if the mechanical properties are close to those of the steel matrix.For the inclusions,which are tightly bonded with the steel matrix,when the Young’s modulus is larger than that of the steel matrix,the stress will concentrate inside the inclusion;otherwise,the stress will concentrate in the steel matrix.If voids exist on the interface between inclusions and the steel matrix,their effects on the fatigue process differ with their positions relative to the inclusions.The void on one side of an inclusion perpendicular to the fatigue loading direction will aggravate the effect of inclusions on fatigue behavior and lead to a sharp stress concentration.The void on the top of inclusion along the fatigue loading direction will accelerate the debonding between the inclusion and steel matrix.展开更多
The mechanism of oxide inclusions in fatigue crack initiation in the very-high cycle fatigue(VHCF)regime was clarified by subjecting bearing steels deoxidized by Al(Al-deoxidized steel)and Si(Si-deoxidized steel)to ul...The mechanism of oxide inclusions in fatigue crack initiation in the very-high cycle fatigue(VHCF)regime was clarified by subjecting bearing steels deoxidized by Al(Al-deoxidized steel)and Si(Si-deoxidized steel)to ultrasonic tension-compression fatigue tests(stress ratio,R=−1)and analyzing the characteristics of the detected inclusions.Results show that the main types of inclusions in Si-and Al-deoxidized steels are silicate and calcium aluminate,respectively.The content of calcium aluminate inclusions larger than 15μm in Si-deoxidized steel is lower than that in Al-deoxidized steel,and the difference observed may be attributed to different inclusion generation processes during melting.Despite differences in their cleanliness and total oxygen contents,the Si-and Al-deoxidized steels show similar VHCF lives.The factors causing fatigue failure in these steels reveal distinct differences.Calcium aluminate inclusions are responsible for the cracks in Al-deoxidized steel.By comparison,most fatigue cracks in Si-deoxidized steel are triggered by the inhomogeneity of a steel matrix,which indicates that the damage mechanisms of the steel matrix can be a critical issue for this type of steel.A minor portion of the cracks in Si-deoxidized steel could be attributed to different types of inclusions.The mechanisms of fatigue fracture caused by calcium aluminate and silicate inclusions were further analyzed.Calcium aluminate inclusions first separate from the steel matrix and then trigger crack generation.Silicate inclusions and the steel matrix are closely combined in a fatigue process;thus,these inclusions have mild effects on the fatigue life of bearing steels.Si/Mn deoxidation is an effective method to produce high-quality bearing steel with a long fatigue life and good liquid steel fluidity.展开更多
A study was undertaken to investigate the performan ce of PCBN tool in the finish turning GCr15 bearing steel with different hardness between 30～64 HRC. The natural thermocouple was used to measure the cutting tem p ...A study was undertaken to investigate the performan ce of PCBN tool in the finish turning GCr15 bearing steel with different hardness between 30～64 HRC. The natural thermocouple was used to measure the cutting tem p erature, tool life and cutting temperature were investigated and compared. The m aterial can be heated by this instrument which using low voltage and high elec trical current, while PCBN can’t be heated by electrifying directly, so the ke ntanium layer coating over the PCBN is heated, so the PCBN is heated and its th ermoelectric property is got by this method. [TPP129,+60mm88mm,Y,PZ#] Fig.1 Effect of cutting depth and workpiec hardness on. the cutting temperatureThe objective was to determine the influence of the workpiece hardness on change s in cutting temperature and tool wear characterize. It can be found from Fig.1 that the cutting temperature show an increasing tendency with the improvement of workpiece hardness within the cutting speed scope when the workpiece hardness i s under HRC50. And on the other hand, it is found that the cutting temperature s how the downtrend with the improvement of workpiece hardness when the workpiece hardness is over HRC50. According to experimental results, the critical hard ness when turning hardened GCr15 bearing steel with PCBN tool is about HRC50. Th e wear causes of PCBN tool have been found out through taking photos on the micr o-shape of PCBN poly-laminate initial surface as well as face and flank of wea r tool and analysis on chemical elements. It is discovered that the PCBN tools a re not suitable for cutting the workpiece at nearly critical hardness, because n ear the critical hardness, PCBN wear at the highest speed. For researching the w ear rule of PCBN tool, the tool wear experiments have been carried on by using b earing steel GCr15 at hardness HRC40 and HRC60 with changing cutting speed. The indexes of tool life equations is gained under two kinds of conditions w hich are bigger than 0.6, so the effects of cutting speed on the PCBN tool are m uch less than that of carbide tool and ceramic tool.展开更多
The effect of Cr/Mn segregation on the abnormal banded structure of high carbon bearing steel was studied by reheating and hot rolling.With the use of an optical microscope, scanning electron microscope, transmission ...The effect of Cr/Mn segregation on the abnormal banded structure of high carbon bearing steel was studied by reheating and hot rolling.With the use of an optical microscope, scanning electron microscope, transmission electron microscope, and electron probe microanalyzer, the segregation characteristics of alloying elements in cast billet and their relationship with hot-rolled plate banded structure were revealed.The formation causes of an abnormal banded structure and the elimination methods were analyzed.Results indicate the serious positive segregation of C, Cr, and Mn alloy elements in the billet.Even distribution of Cr/Mn elements could not be achieved after 10 h of heat preservation at 1200℃, and the spacing of the element aggregation area increased, but the segregation index of alloy elements decreased.Obvious alloying element segregation characteristics are present in the banded structure of the hot-rolled plate.This distinct white band is composed of martensitic phases.The formation of this abnormal pearlite–martensite banded structure is due to the interaction between the undercooled austenite transformation behavior of hot-rolled metal and the segregation of its alloying elements.Under the air cooling after rolling, controlling the segregation index of alloy elements can reduce or eliminate the abnormal banded structure.展开更多
The formation mechanism of "white band" and central carbon segregation of high-carbon Cr bearing steel concasting billets are discussed in this paper. The maximum oxygen content in the steel produced by conc...The formation mechanism of "white band" and central carbon segregation of high-carbon Cr bearing steel concasting billets are discussed in this paper. The maximum oxygen content in the steel produced by concasting process was 13 ?10-6 with an average oxygen content of 9.3?10-6. Comparison of metallurgical quality and fatigue property between the concasting steel （CC） and ingot casting steel （IC） showed that the carbon segregation （C/C0） in former steel was 0.921.10 and its fatigue life was equal to that of the latter steel.展开更多
The metallurgical properties and fatigue life of bearing steel processed by electric furnace (EAF), ladle refining (LF-VD), continuous casting (CC) and electroslag remelting (ESR) have been investigated. The main resu...The metallurgical properties and fatigue life of bearing steel processed by electric furnace (EAF), ladle refining (LF-VD), continuous casting (CC) and electroslag remelting (ESR) have been investigated. The main results obtained are as follows: (1) Due to low oxygen content and dispersion inclusions in steel, the fatigue life of LF-VD-IC or CC is three times as high as that of EAF steel; (2) The oxygen content in steel produced by CC process is about 9.0× 10-6, the carbon segregation (C/C0) is from 0.92 to 1. 10 and the fatigue life of CC steel is equal to that of ladle refining ingot casting steel; (3) Although the amount of inclusion and oxygen in ESR steel is higher than that of LF-VD-IC or CC steel, the fatigue life of ESR steel is higher than that of the latter because of its fine and well dispersed inclusions.展开更多
The effect of cerium(Ce)on the solidification microstructure of Cr_(4)Mo_(4)V bearing steel was investigated via a combined experimental and theoretical method.With a trace amount(0.056 wt%)of Ce addition,the coarse c...The effect of cerium(Ce)on the solidification microstructure of Cr_(4)Mo_(4)V bearing steel was investigated via a combined experimental and theoretical method.With a trace amount(0.056 wt%)of Ce addition,the coarse columnar grains in as-cast microstructure transform into equiaxed ones,and the average diameter is reduced from 56 to 27μm.The network-like and bulky primary MC and M2C carbides at the interdendritic regions become disconnected and refined,and their volume percentage decreases from4.15 vol%to 2.1 vol%.Ce-inclusions acting as heterogeneous nucleation agents of prior-austenite grains and Ce atoms segregating at grain boundaries,both contribute to the refinement of grains.Thermodynamic calculations reveal that primary carbides are precipitated afterγ-austenite forms near the end of the solidification process.The modification of primary carbides in size and amount is mainly attributed to the isolated remaining melt separated by refinedγ-austenite grains in which the nucleation of carbides is promoted,while the growth is restrained owing to the less segregation of alloying elements.展开更多
Non-metallic inclusion in steel is a very key factor affecting the fatigue life and quality stability of high-quality bearing steel.Inclusions mainly affect the fatigue life and toughness of the material by affecting ...Non-metallic inclusion in steel is a very key factor affecting the fatigue life and quality stability of high-quality bearing steel.Inclusions mainly affect the fatigue life and toughness of the material by affecting the continuity of the steel matrix,thereby endangering the safety and stability of the equipment.The research progress of inclusion formation,removal and modification was discussed.Based on the current research status of Al deoxidation or Si deoxidation process,the feasibility of non-alloy deoxidation process for high-quality bearing steel was proposed and discussed.C or H_(2) is used as non-alloy deoxidizer,and the deoxidation products are CO and H_(2)O gases,which are easy to be removed from the molten steel.There are few studies on the non-alloy deoxidation process,especially the research and application of C or H_(2) deoxidation for high-quality bearing steel.However,the non-alloy deoxidation process is of great significance for reducing oxygen content and improving cleanliness of high-quality bearing steel.Therefore,it is necessary to study the mechanism and kinetics of C and H_(2) deoxidation and analyze the factors affecting deoxidation effect systematically,so as to provide a solid theoretical basis for the practice of non-alloy deoxidation process for high-quality bearing steel.展开更多
High-nitrogen stainless bearing steel(HNSBS)with ultra-high tensile strength(∼2403 MPa)and good toughness(∼80.0 J)was obtained by V-microalloying,overcoming the strength-toughness trade-off of conventional V-free HN...High-nitrogen stainless bearing steel(HNSBS)with ultra-high tensile strength(∼2403 MPa)and good toughness(∼80.0 J)was obtained by V-microalloying,overcoming the strength-toughness trade-off of conventional V-free HNSBS.In this work,since V-microalloying facilitated the enrichment of interstitial atoms(C and N)in precipitates,the content of interstitial atoms in the matrix was reduced accordingly(i.e.,interstitial partitioning).On the one hand,V-microalloying reduced the substantial intergranular precipitates and transformed the precipitates from M_(23)C_(6)+M_(2)N into V-containing M_(23)C_(6)+M_(2)N+MN with multi-scale particle sizes,causing a coupling strengthening effect,which contributed to the toughness and additional strength increase.On the other hand,V-microalloying controlled interstitial partitioning,effectively refined coarse retained austenite(RA),increased the fraction of dislocation martensite,and reduced the fraction of twin martensite.The more film-like RA and dislocation martensite with high dislocation density coordinated plastic deformation and prevented crack propagation,thus obviously enhancing the strength and toughness of 0.2 V steel.This study provides a new route to develop high-performance HNSBS for aerospace applications.展开更多
The effects of magnesium(Mg)on the microstructure and properties of 440C stainless bearing steel melted under pressurized conditions were studied.Adding Mg improved the cleanliness of molten steel,modified the inclusi...The effects of magnesium(Mg)on the microstructure and properties of 440C stainless bearing steel melted under pressurized conditions were studied.Adding Mg improved the cleanliness of molten steel,modified the inclusions in steel,enhanced the distribution of carbides,and improved the mechanical properties and corrosion resistance of experimental steel.In detail,the contents of TO,S,and N in steel decreased from 0.0013 to 0.0003 wt.%,from 0.0032 to 0.0018 wt.%and from 0.0088 to 0.0049 wt.%,respectively.In addition,the transformation order of oxide inclusions in steel is Al_(2)O_(3)→MgO∙Al_(2)O_(3)→MgO,where the content of Mg in steel sharply increased from 0.00 to 29×10^(-4),81×10^(-4),and 160×10^(-4)wt.%,and the transformation order of S-containing inclusions in steel is MnS→Mg–S–Mn(–MgO)→Mg–O–S.Moreover,the number and size of inclusions and the proportion of large-size inclusions in steel decreased rapidly.Furthermore,the network structure of carbides in steel collapsed,the size of carbides was reduced,and the distribution was more uniform.Finally,the tensile strength,impact toughness,and pitting corrosion resistance of the experimental steel were significantly improved.展开更多
Quantitative prediction of phase content is of great importance to control and optimize the heat treat-ment process of steels.In this work,a model for predicting the phase content of tempered high carbon steels was pr...Quantitative prediction of phase content is of great importance to control and optimize the heat treat-ment process of steels.In this work,a model for predicting the phase content of tempered high carbon steels was proposed by taking a martensitic 100Cr6 bearing steel as a model case.The microstructural transformations during tempering were studied using thermal analysis,transmission electron microscopy(TEM),and X-ray diffraction(XRD).Kinetics analysis of thermal evolution by employing the isoconver-sional method,and assisted by TEM and XRD characterization,were performed to quantitatively estimate the volume fractions of different phases after tempering.A series of isothermal tempering experiments were designed to verify the model.The predicted results were in good agreement with the experimental results of XRD and electrolytic extraction measurements.展开更多
Effects of varied levels of cerium(28×10-6,65×10^(-6) and 150×10^(-6))on inclusions in a high-carbon chromium bearing steel at different stages(before adding cerium,after adding cerium for 1,5,10 min an...Effects of varied levels of cerium(28×10-6,65×10^(-6) and 150×10^(-6))on inclusions in a high-carbon chromium bearing steel at different stages(before adding cerium,after adding cerium for 1,5,10 min and ingot)were studied using laboratory experiments.An automatic scanning electron microscope system with energy-dispersive spectroscopy was used to analyze the amount,composition,size and morphology of inclusions in the steel at different stages.When the cerium content in the molten steel increased from 0 to 150×10^(-6),the evolution sequence of inclusions was as follows:Al_(2)O_(3)→CeAl11O18→CeAlO_(3)→Ce_(2)O_(2)S.After 28×10^(-6) cerium was added,Al_(2)O_(3) inclusions were modified into CeAl_(11)O_(18) inclusions in the molten steel and then were further transformed into Al2O3 and CeAlO3 inclusions in the solid steel during cooling.With the addition of 65×10^(-6) cerium,inclusions in the molten steel were modified into CeAlO_(3) and a small number of Ce2O2S inclusions.When the addition amount of cerium increased to 150×10^(-6),inclusions were transformed to Ce_(2)O_(2)S.The size of inclusions in the molten steel decreased obviously with cerium addition.On the other hand,the size of inclusions increased during the cooling process in solid steels of No.1 steel(with 28×10^(-6) cerium)and No.2 steel(with 65×10^(-6) cerium).During the cooling process,unmodified MnS inclusions were precipitated in the solid steel of No.1 steel and wrapped outside the Al2O3 and CeAlO_(3) inclusions to form large complex inclusions.During the cooling process of No.2 steel,the inclusion size of CeAlO_(3) increased due to the collision and polymerization.In the No.3 steel(with 150×10^(-6) cerium),the average size of inclusions decreased rapidly and remained at a lower size during the cooling process,which was beneficial to improving the fatigue life of the steel.展开更多
The influences of primary carbide size and type on the sliding wear behavior and rolling contact fatigue (RCF) properties of M50 bearing steel were systematically investigated under oil lubrication condition. A major ...The influences of primary carbide size and type on the sliding wear behavior and rolling contact fatigue (RCF) properties of M50 bearing steel were systematically investigated under oil lubrication condition. A major breakthrough was achieved in the influence of primary carbide on tribological behavior. The opposite effect brought by primary carbide size on the sliding wear resistance and RCF life of M50 bearing steel was determined. Wear resistance increased with an increase in the studied primary carbide size, whereas RCF life decreased significantly. Compared with the 0 R and R positions with a relatively small carbide size, the wear volume of the 1/2 R position with a large carbide size was the smallest. Compared with the 0 R and R positions, the L10 life of the 1/2 R position decreased by 82.7% and 84.8%, respectively. On the basis of the statistical correlation between primary carbide size and the two tribological properties, a critical maximum carbide size of 5-10 μm was proposed to achieve optimal tribological performance. This research suggests that the equivalent diameter of the primary carbide should be controlled to be smaller than 10 μm, but further decreasing primary carbide size to less than 5 μm is unnecessary. The influence of primary carbide type in M50 bearing steel on sliding wear resistance was also discussed. Results indicate that the MC-type carbides with higher elastic modulus and microhardness exhibit better wear resistance than the M2C-type carbides.展开更多
In the long traditional process of steelmaking,excess oxygen is blown into the converter,and alloying elements are used for deoxidation.This inevitably results in excessive deoxidation of products remaining within the...In the long traditional process of steelmaking,excess oxygen is blown into the converter,and alloying elements are used for deoxidation.This inevitably results in excessive deoxidation of products remaining within the steel liquid,affecting the cleanliness of the steel.With the increasing requirements for steel performance,reducing the oxygen content in the steel liquid and ensuring its high cleanliness is necessary.After more than a hundred years of development,the total oxygen content in steel has been reduced from approximately 100×10^(-6)to approximately 10×10^(-6),and it can be controlled below 5×10^(-6)in some steel grades.A relatively stable and mature deoxidation technology has been formed,but further reducing the oxygen content in steel is no longer significant for improving steel quality.Our research team developed a deoxidation technology for bearing steel by optimizing the entire conventional process.The technology combines silicon–manganese predeoxidation,ladle furnace diffusion deoxidation,and vacuum final deoxidation.We successfully conducted industrial experiments and produced interstitial-free steel with natural decarbonization predeoxidation.Non-aluminum deoxidation was found to control the oxygen content in bearing steel to between 4×10^(-6) and 8×10^(-6),altering the type of inclusions,eliminating large particle Ds-type inclusions,improving the flowability of the steel liquid,and deriving a higher fatigue life.The natural decarbonization predeoxidation of interstitial-free steel reduced aluminum consumption and production costs and significantly improved the quality of cast billets.展开更多
The grain refinement and macrosegregation control of GCr15 bearing steel were investigated under a type of rarelyused electromagnetic stirring,vertical electromagnetic stirring( V-EMS),in continuous casting. V-EMS can...The grain refinement and macrosegregation control of GCr15 bearing steel were investigated under a type of rarelyused electromagnetic stirring,vertical electromagnetic stirring( V-EMS),in continuous casting. V-EMS can create an upward electromagnetic force and generate longitudinal loop convection,which enables the better mixing of the upper part with the lower part of the liquid steel. The results showed that applying V-EMS can enlarge the region of the equiaxed grain,decrease the secondary dendrite arm spacing( SDAS) and reduce the segregation of both carbon and sulfur. After applying V-EMS,liquid steel with a high solute concentration is brought to the dendrite tips,making the dendrite arms partially melt. The length of the dendrite fragment is approximately 1. 8 mm,10 to 12 times the SDAS. Upon increasing the amount of cooling water from 2. 0 to 3. 5 m^3/h,the dendrite fragments exhibit an obvious aggregation following V-EMS. Finally,a criterion for dendrite fragmentation under VEMS was derived based on the dendrite fragmentation theory of Campanella et al.展开更多
The effects of traditional heat treatment(quenching and then tempering)and deep cryogenic treatment on the microstructure and mechanical properties of a low-carbon high-alloy martensitic bearing steel were studied by ...The effects of traditional heat treatment(quenching and then tempering)and deep cryogenic treatment on the microstructure and mechanical properties of a low-carbon high-alloy martensitic bearing steel were studied by Rockwell hardness test,X-ray diffractometry,scanning electron microscopy and transmission electron microscopy.The results show that the deep cryogenic treatment promotes the transformation of the retained austenite to martensite during cooling,which leads to the hardness of the sample after deep cryogenic treatment higher than that at the quenched state.Also,the carbon content in the martensite matrix after different treatments was calculated and the results indicated that deep cryogenic treatment can promote the segregation of carbon atoms in martensite to dislocations.The segregated carbon atoms act as and grow into nuclei for the formation of fine carbide particles during subsequent tempering.And this resulted in the fact that the hardness of the tempered experimental steel after deep cryogenic treatment is higher than that without deep cryogenic treatment.展开更多
Pulse magneto-oscillation(PMO)added during solidification could affect the solidification structure and macrosegregation.A modified thermal simulation equipment was applied to prepare GCr15 bearing steel continuous ca...Pulse magneto-oscillation(PMO)added during solidification could affect the solidification structure and macrosegregation.A modified thermal simulation equipment was applied to prepare GCr15 bearing steel continuous casting billets with different PMO peak currents.Then,metallographic analysis,component analysis and numerical simulation were adopted to study the influence of PMO peak current and its mechanism.The sample with 150 K_(I)A PMO peak current treatment has little difference with the samples without PMO treatment on solidification structure and macrosegregation.As the peak currents are 250 and 350 K_(I)A,the columnar zone increases and macrosegregation aggravated.When 450 K_(I)A peak current is selected,the equiaxed grain ratio is enlarged,and the dendritic grains are refined,and the macrosegregation of C,Cr,Si and Mn is decreased significantly.By analyzing,different convections induced by PMO with various peak currents are the key factor to change the solidification structure and macrosegregation.展开更多
Microstructure and mechanical properties in core of a carburizing 20CrNi2MoV bearing steel subjected to cryogenic treatment were investigated.Conventional treatment sample was quenched and tempered at 180℃ for 2 h.Cr...Microstructure and mechanical properties in core of a carburizing 20CrNi2MoV bearing steel subjected to cryogenic treatment were investigated.Conventional treatment sample was quenched and tempered at 180℃ for 2 h.Cryogenic treatment samples were quenched,cryogenically treated at−80 and−196℃ for 4 h,slowly returned to room temperature and thereafter tempered at 180℃ for 2 h,and finally tempered at 180℃ for 2 h.The scanning electron microscope,electron backscattering diffraction,X-ray diffraction and transmission electron microscope were adopted for microstructure characterization.The results show that cryogenic treatment increases the fraction of high-angle grain boundaries and the precipitation of finely dispersed carbides in the matrix,decreases the volume fraction of inter-lath retained austenite,and hence improves the strength and hardness.Compared with the conventional treatment,the hardness,yield strength and ultimate tensile strength of the steel after cryogenic treatment are increased by 11.7%,12.6%and 18.3%,respectively,while the impact energy is decreased by 9.8%.展开更多
The sliding wear property of high-carbon nanostructured bainitic bearing steel with the equal initial hardness and different microstructures was investigated,and the reasons for the difference of wear resistance betwe...The sliding wear property of high-carbon nanostructured bainitic bearing steel with the equal initial hardness and different microstructures was investigated,and the reasons for the difference of wear resistance between the cementite-bearing(CB)and cementite-free(CF)specimens were analyzed.The results show that CF specimens have lower mass loss and surface roughness and shallower wear depth than CB specimens during wear process.Compared with CB specimen,CF specimen presents superior wear resistance.This is due to two reasons:(1)a lot of retained austenite in CF specimen is easy to produce TRIP effect and be transformed into martensite during wear process,which notably increased the surface hardness of worn specimen;(2)there is a nondestructive oxide layer in the surface of cementite-free worn specimen,which can protect the surface of worn specimen from destruction.Under the combined effect of retained austenite and oxide layer,the loss of matrix is reduced.Thus,CF specimen exhibits high wear resistance.It reveals that the wear mechanism of high-carbon nanostructured bainitic bearing steel with different microstructures can provide a reference for improving the wear resistance in high-carbon nanostructured bainitic bearing steel in future.展开更多
The effect of the axial static magnetic field(ASMF)on cleanliness and microstructure in magnetically controlled electroslag remelted GCr15 bearing steel ingots was investigated experimentally.The results show that a m...The effect of the axial static magnetic field(ASMF)on cleanliness and microstructure in magnetically controlled electroslag remelted GCr15 bearing steel ingots was investigated experimentally.The results show that a magnetically controlled spin-vibration induced by the interaction of the ASMFs and the remelting current exists at the consumable electrode tip,resulting in thinner liquid melt film and smaller droplets.With the increase in magnetic flux density,the optimization effect of ASMFs on electroslag remelting process increases and reaches the peak with a 40 mT ASMF,then decreases.The cleanliness of the ingots was improved,and the count of inclusions larger than 5μm was reduced.The microstructure of the ingots processed with a 40 mT ASMF was significantly refined.The depth of the metallic molten pool was reduced from 45.2 to 17.5 mm with the application of 40 mT ASMF.The tensile strength,impact toughness,and Rockwell hardness of the ingots obtained under the 40 mT ASMF were significantly improved.The mechanisms of the spin-vibration occurring at the electrode tip end were interpreted in detail to elucidate the effect of ASMFs.展开更多
基金This work was financially supported by the Fundamental Research Funds for the Central Universities(No.FRF-TP-20-026A1)the China Postdoctoral Science Foundation(No.2020M680348)the State Key Laboratory of Advanced Metallurgy Foundation of China(No.41620001).
文摘A numerical study of stress distribution and fatigue behavior in terms of the effect of voids adjacent to inclusions was conducted with finite element modeling simulations under different assumptions.Fatigue mechanisms were also analyzed accordingly.The results showed that the effects of inclusions on fatigue life will distinctly decrease if the mechanical properties are close to those of the steel matrix.For the inclusions,which are tightly bonded with the steel matrix,when the Young’s modulus is larger than that of the steel matrix,the stress will concentrate inside the inclusion;otherwise,the stress will concentrate in the steel matrix.If voids exist on the interface between inclusions and the steel matrix,their effects on the fatigue process differ with their positions relative to the inclusions.The void on one side of an inclusion perpendicular to the fatigue loading direction will aggravate the effect of inclusions on fatigue behavior and lead to a sharp stress concentration.The void on the top of inclusion along the fatigue loading direction will accelerate the debonding between the inclusion and steel matrix.
基金This work was financially supported by the National Natural Science Foundation of China(No.51774031)the Fundamental Research Funds for the Central Universities(No.FRF-TP-20-026A1)the State Key Laboratory of Advanced Metallurgy Foundation(No.41620001).
文摘The mechanism of oxide inclusions in fatigue crack initiation in the very-high cycle fatigue(VHCF)regime was clarified by subjecting bearing steels deoxidized by Al(Al-deoxidized steel)and Si(Si-deoxidized steel)to ultrasonic tension-compression fatigue tests(stress ratio,R=−1)and analyzing the characteristics of the detected inclusions.Results show that the main types of inclusions in Si-and Al-deoxidized steels are silicate and calcium aluminate,respectively.The content of calcium aluminate inclusions larger than 15μm in Si-deoxidized steel is lower than that in Al-deoxidized steel,and the difference observed may be attributed to different inclusion generation processes during melting.Despite differences in their cleanliness and total oxygen contents,the Si-and Al-deoxidized steels show similar VHCF lives.The factors causing fatigue failure in these steels reveal distinct differences.Calcium aluminate inclusions are responsible for the cracks in Al-deoxidized steel.By comparison,most fatigue cracks in Si-deoxidized steel are triggered by the inhomogeneity of a steel matrix,which indicates that the damage mechanisms of the steel matrix can be a critical issue for this type of steel.A minor portion of the cracks in Si-deoxidized steel could be attributed to different types of inclusions.The mechanisms of fatigue fracture caused by calcium aluminate and silicate inclusions were further analyzed.Calcium aluminate inclusions first separate from the steel matrix and then trigger crack generation.Silicate inclusions and the steel matrix are closely combined in a fatigue process;thus,these inclusions have mild effects on the fatigue life of bearing steels.Si/Mn deoxidation is an effective method to produce high-quality bearing steel with a long fatigue life and good liquid steel fluidity.
文摘A study was undertaken to investigate the performan ce of PCBN tool in the finish turning GCr15 bearing steel with different hardness between 30～64 HRC. The natural thermocouple was used to measure the cutting tem p erature, tool life and cutting temperature were investigated and compared. The m aterial can be heated by this instrument which using low voltage and high elec trical current, while PCBN can’t be heated by electrifying directly, so the ke ntanium layer coating over the PCBN is heated, so the PCBN is heated and its th ermoelectric property is got by this method. [TPP129,+60mm88mm,Y,PZ#] Fig.1 Effect of cutting depth and workpiec hardness on. the cutting temperatureThe objective was to determine the influence of the workpiece hardness on change s in cutting temperature and tool wear characterize. It can be found from Fig.1 that the cutting temperature show an increasing tendency with the improvement of workpiece hardness within the cutting speed scope when the workpiece hardness i s under HRC50. And on the other hand, it is found that the cutting temperature s how the downtrend with the improvement of workpiece hardness when the workpiece hardness is over HRC50. According to experimental results, the critical hard ness when turning hardened GCr15 bearing steel with PCBN tool is about HRC50. Th e wear causes of PCBN tool have been found out through taking photos on the micr o-shape of PCBN poly-laminate initial surface as well as face and flank of wea r tool and analysis on chemical elements. It is discovered that the PCBN tools a re not suitable for cutting the workpiece at nearly critical hardness, because n ear the critical hardness, PCBN wear at the highest speed. For researching the w ear rule of PCBN tool, the tool wear experiments have been carried on by using b earing steel GCr15 at hardness HRC40 and HRC60 with changing cutting speed. The indexes of tool life equations is gained under two kinds of conditions w hich are bigger than 0.6, so the effects of cutting speed on the PCBN tool are m uch less than that of carbide tool and ceramic tool.
文摘The effect of Cr/Mn segregation on the abnormal banded structure of high carbon bearing steel was studied by reheating and hot rolling.With the use of an optical microscope, scanning electron microscope, transmission electron microscope, and electron probe microanalyzer, the segregation characteristics of alloying elements in cast billet and their relationship with hot-rolled plate banded structure were revealed.The formation causes of an abnormal banded structure and the elimination methods were analyzed.Results indicate the serious positive segregation of C, Cr, and Mn alloy elements in the billet.Even distribution of Cr/Mn elements could not be achieved after 10 h of heat preservation at 1200℃, and the spacing of the element aggregation area increased, but the segregation index of alloy elements decreased.Obvious alloying element segregation characteristics are present in the banded structure of the hot-rolled plate.This distinct white band is composed of martensitic phases.The formation of this abnormal pearlite–martensite banded structure is due to the interaction between the undercooled austenite transformation behavior of hot-rolled metal and the segregation of its alloying elements.Under the air cooling after rolling, controlling the segregation index of alloy elements can reduce or eliminate the abnormal banded structure.
文摘The formation mechanism of "white band" and central carbon segregation of high-carbon Cr bearing steel concasting billets are discussed in this paper. The maximum oxygen content in the steel produced by concasting process was 13 ?10-6 with an average oxygen content of 9.3?10-6. Comparison of metallurgical quality and fatigue property between the concasting steel （CC） and ingot casting steel （IC） showed that the carbon segregation （C/C0） in former steel was 0.921.10 and its fatigue life was equal to that of the latter steel.
文摘The metallurgical properties and fatigue life of bearing steel processed by electric furnace (EAF), ladle refining (LF-VD), continuous casting (CC) and electroslag remelting (ESR) have been investigated. The main results obtained are as follows: (1) Due to low oxygen content and dispersion inclusions in steel, the fatigue life of LF-VD-IC or CC is three times as high as that of EAF steel; (2) The oxygen content in steel produced by CC process is about 9.0× 10-6, the carbon segregation (C/C0) is from 0.92 to 1. 10 and the fatigue life of CC steel is equal to that of ladle refining ingot casting steel; (3) Although the amount of inclusion and oxygen in ESR steel is higher than that of LF-VD-IC or CC steel, the fatigue life of ESR steel is higher than that of the latter because of its fine and well dispersed inclusions.
基金Project supported by the National Natural Science Foundation of China(52031013,52173305,52233017)the National Key Research and Development Program(2018YFA0702900)。
文摘The effect of cerium(Ce)on the solidification microstructure of Cr_(4)Mo_(4)V bearing steel was investigated via a combined experimental and theoretical method.With a trace amount(0.056 wt%)of Ce addition,the coarse columnar grains in as-cast microstructure transform into equiaxed ones,and the average diameter is reduced from 56 to 27μm.The network-like and bulky primary MC and M2C carbides at the interdendritic regions become disconnected and refined,and their volume percentage decreases from4.15 vol%to 2.1 vol%.Ce-inclusions acting as heterogeneous nucleation agents of prior-austenite grains and Ce atoms segregating at grain boundaries,both contribute to the refinement of grains.Thermodynamic calculations reveal that primary carbides are precipitated afterγ-austenite forms near the end of the solidification process.The modification of primary carbides in size and amount is mainly attributed to the isolated remaining melt separated by refinedγ-austenite grains in which the nucleation of carbides is promoted,while the growth is restrained owing to the less segregation of alloying elements.
基金Key Research and Development Projects in Hebei Province of China (21311002D)Hebei Natural Resources Fund Project of China (E2021417001)for supporting this work.
文摘Non-metallic inclusion in steel is a very key factor affecting the fatigue life and quality stability of high-quality bearing steel.Inclusions mainly affect the fatigue life and toughness of the material by affecting the continuity of the steel matrix,thereby endangering the safety and stability of the equipment.The research progress of inclusion formation,removal and modification was discussed.Based on the current research status of Al deoxidation or Si deoxidation process,the feasibility of non-alloy deoxidation process for high-quality bearing steel was proposed and discussed.C or H_(2) is used as non-alloy deoxidizer,and the deoxidation products are CO and H_(2)O gases,which are easy to be removed from the molten steel.There are few studies on the non-alloy deoxidation process,especially the research and application of C or H_(2) deoxidation for high-quality bearing steel.However,the non-alloy deoxidation process is of great significance for reducing oxygen content and improving cleanliness of high-quality bearing steel.Therefore,it is necessary to study the mechanism and kinetics of C and H_(2) deoxidation and analyze the factors affecting deoxidation effect systematically,so as to provide a solid theoretical basis for the practice of non-alloy deoxidation process for high-quality bearing steel.
基金sponsored by the National Natural Science Foundation of China(Grant Nos.U1960203,52004060,and 52174308)Fundamental Research Funds for the Central Universities(Grant Nos.N2125017 and N2225031)+1 种基金Program of Introducing Talents of Discipline to Universities(Grant No.B21001)Liaoning Pilot Base Project(No.2022JH24/10200026)。
文摘High-nitrogen stainless bearing steel(HNSBS)with ultra-high tensile strength(∼2403 MPa)and good toughness(∼80.0 J)was obtained by V-microalloying,overcoming the strength-toughness trade-off of conventional V-free HNSBS.In this work,since V-microalloying facilitated the enrichment of interstitial atoms(C and N)in precipitates,the content of interstitial atoms in the matrix was reduced accordingly(i.e.,interstitial partitioning).On the one hand,V-microalloying reduced the substantial intergranular precipitates and transformed the precipitates from M_(23)C_(6)+M_(2)N into V-containing M_(23)C_(6)+M_(2)N+MN with multi-scale particle sizes,causing a coupling strengthening effect,which contributed to the toughness and additional strength increase.On the other hand,V-microalloying controlled interstitial partitioning,effectively refined coarse retained austenite(RA),increased the fraction of dislocation martensite,and reduced the fraction of twin martensite.The more film-like RA and dislocation martensite with high dislocation density coordinated plastic deformation and prevented crack propagation,thus obviously enhancing the strength and toughness of 0.2 V steel.This study provides a new route to develop high-performance HNSBS for aerospace applications.
基金the National Natural Science Foundation of China(Nos.U1760206 and 52074075).
文摘The effects of magnesium(Mg)on the microstructure and properties of 440C stainless bearing steel melted under pressurized conditions were studied.Adding Mg improved the cleanliness of molten steel,modified the inclusions in steel,enhanced the distribution of carbides,and improved the mechanical properties and corrosion resistance of experimental steel.In detail,the contents of TO,S,and N in steel decreased from 0.0013 to 0.0003 wt.%,from 0.0032 to 0.0018 wt.%and from 0.0088 to 0.0049 wt.%,respectively.In addition,the transformation order of oxide inclusions in steel is Al_(2)O_(3)→MgO∙Al_(2)O_(3)→MgO,where the content of Mg in steel sharply increased from 0.00 to 29×10^(-4),81×10^(-4),and 160×10^(-4)wt.%,and the transformation order of S-containing inclusions in steel is MnS→Mg–S–Mn(–MgO)→Mg–O–S.Moreover,the number and size of inclusions and the proportion of large-size inclusions in steel decreased rapidly.Furthermore,the network structure of carbides in steel collapsed,the size of carbides was reduced,and the distribution was more uniform.Finally,the tensile strength,impact toughness,and pitting corrosion resistance of the experimental steel were significantly improved.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51605355 and 52104381)the National Key R&D Program of China(No.2020YFA0714900)+2 种基金“111 Project”(No.B17034)the Innovative Research TeamDevelopment Program of Ministry of Education of China(No.IRT_17R83)the China Postdoctoral Science Foundation(No.2021M702539)and the State Key Laboratory for Advanced Metals and Materials.
文摘Quantitative prediction of phase content is of great importance to control and optimize the heat treat-ment process of steels.In this work,a model for predicting the phase content of tempered high carbon steels was proposed by taking a martensitic 100Cr6 bearing steel as a model case.The microstructural transformations during tempering were studied using thermal analysis,transmission electron microscopy(TEM),and X-ray diffraction(XRD).Kinetics analysis of thermal evolution by employing the isoconver-sional method,and assisted by TEM and XRD characterization,were performed to quantitatively estimate the volume fractions of different phases after tempering.A series of isothermal tempering experiments were designed to verify the model.The predicted results were in good agreement with the experimental results of XRD and electrolytic extraction measurements.
基金support from the Natural Science Foundation of Hebei Province(Grant No.E2021203062)S&T Program of Hebei(Grant No.20311006D)the High Steel Center(HSC)at North China University of Technology,Yanshan University and University of Science and Technology Beijing.
文摘Effects of varied levels of cerium(28×10-6,65×10^(-6) and 150×10^(-6))on inclusions in a high-carbon chromium bearing steel at different stages(before adding cerium,after adding cerium for 1,5,10 min and ingot)were studied using laboratory experiments.An automatic scanning electron microscope system with energy-dispersive spectroscopy was used to analyze the amount,composition,size and morphology of inclusions in the steel at different stages.When the cerium content in the molten steel increased from 0 to 150×10^(-6),the evolution sequence of inclusions was as follows:Al_(2)O_(3)→CeAl11O18→CeAlO_(3)→Ce_(2)O_(2)S.After 28×10^(-6) cerium was added,Al_(2)O_(3) inclusions were modified into CeAl_(11)O_(18) inclusions in the molten steel and then were further transformed into Al2O3 and CeAlO3 inclusions in the solid steel during cooling.With the addition of 65×10^(-6) cerium,inclusions in the molten steel were modified into CeAlO_(3) and a small number of Ce2O2S inclusions.When the addition amount of cerium increased to 150×10^(-6),inclusions were transformed to Ce_(2)O_(2)S.The size of inclusions in the molten steel decreased obviously with cerium addition.On the other hand,the size of inclusions increased during the cooling process in solid steels of No.1 steel(with 28×10^(-6) cerium)and No.2 steel(with 65×10^(-6) cerium).During the cooling process,unmodified MnS inclusions were precipitated in the solid steel of No.1 steel and wrapped outside the Al2O3 and CeAlO_(3) inclusions to form large complex inclusions.During the cooling process of No.2 steel,the inclusion size of CeAlO_(3) increased due to the collision and polymerization.In the No.3 steel(with 150×10^(-6) cerium),the average size of inclusions decreased rapidly and remained at a lower size during the cooling process,which was beneficial to improving the fatigue life of the steel.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDC04040402)the financial and facility support for Liaoning Key Laboratory of Aero-engine Material Tribology.
文摘The influences of primary carbide size and type on the sliding wear behavior and rolling contact fatigue (RCF) properties of M50 bearing steel were systematically investigated under oil lubrication condition. A major breakthrough was achieved in the influence of primary carbide on tribological behavior. The opposite effect brought by primary carbide size on the sliding wear resistance and RCF life of M50 bearing steel was determined. Wear resistance increased with an increase in the studied primary carbide size, whereas RCF life decreased significantly. Compared with the 0 R and R positions with a relatively small carbide size, the wear volume of the 1/2 R position with a large carbide size was the smallest. Compared with the 0 R and R positions, the L10 life of the 1/2 R position decreased by 82.7% and 84.8%, respectively. On the basis of the statistical correlation between primary carbide size and the two tribological properties, a critical maximum carbide size of 5-10 μm was proposed to achieve optimal tribological performance. This research suggests that the equivalent diameter of the primary carbide should be controlled to be smaller than 10 μm, but further decreasing primary carbide size to less than 5 μm is unnecessary. The influence of primary carbide type in M50 bearing steel on sliding wear resistance was also discussed. Results indicate that the MC-type carbides with higher elastic modulus and microhardness exhibit better wear resistance than the M2C-type carbides.
基金financially supported by the National Natural Science Foundation of China (No.52174297)。
文摘In the long traditional process of steelmaking,excess oxygen is blown into the converter,and alloying elements are used for deoxidation.This inevitably results in excessive deoxidation of products remaining within the steel liquid,affecting the cleanliness of the steel.With the increasing requirements for steel performance,reducing the oxygen content in the steel liquid and ensuring its high cleanliness is necessary.After more than a hundred years of development,the total oxygen content in steel has been reduced from approximately 100×10^(-6)to approximately 10×10^(-6),and it can be controlled below 5×10^(-6)in some steel grades.A relatively stable and mature deoxidation technology has been formed,but further reducing the oxygen content in steel is no longer significant for improving steel quality.Our research team developed a deoxidation technology for bearing steel by optimizing the entire conventional process.The technology combines silicon–manganese predeoxidation,ladle furnace diffusion deoxidation,and vacuum final deoxidation.We successfully conducted industrial experiments and produced interstitial-free steel with natural decarbonization predeoxidation.Non-aluminum deoxidation was found to control the oxygen content in bearing steel to between 4×10^(-6) and 8×10^(-6),altering the type of inclusions,eliminating large particle Ds-type inclusions,improving the flowability of the steel liquid,and deriving a higher fatigue life.The natural decarbonization predeoxidation of interstitial-free steel reduced aluminum consumption and production costs and significantly improved the quality of cast billets.
基金supported by the National Natural Science Foundation of China(No.50834009)the Key Project of the Ministry of Education of China(No.311014)the 111 Project of China(No.B07015)
文摘The grain refinement and macrosegregation control of GCr15 bearing steel were investigated under a type of rarelyused electromagnetic stirring,vertical electromagnetic stirring( V-EMS),in continuous casting. V-EMS can create an upward electromagnetic force and generate longitudinal loop convection,which enables the better mixing of the upper part with the lower part of the liquid steel. The results showed that applying V-EMS can enlarge the region of the equiaxed grain,decrease the secondary dendrite arm spacing( SDAS) and reduce the segregation of both carbon and sulfur. After applying V-EMS,liquid steel with a high solute concentration is brought to the dendrite tips,making the dendrite arms partially melt. The length of the dendrite fragment is approximately 1. 8 mm,10 to 12 times the SDAS. Upon increasing the amount of cooling water from 2. 0 to 3. 5 m^3/h,the dendrite fragments exhibit an obvious aggregation following V-EMS. Finally,a criterion for dendrite fragmentation under VEMS was derived based on the dendrite fragmentation theory of Campanella et al.
基金The work was financially supported by the National Natural Science Foundation of China(Grant No.51761022).
文摘The effects of traditional heat treatment(quenching and then tempering)and deep cryogenic treatment on the microstructure and mechanical properties of a low-carbon high-alloy martensitic bearing steel were studied by Rockwell hardness test,X-ray diffractometry,scanning electron microscopy and transmission electron microscopy.The results show that the deep cryogenic treatment promotes the transformation of the retained austenite to martensite during cooling,which leads to the hardness of the sample after deep cryogenic treatment higher than that at the quenched state.Also,the carbon content in the martensite matrix after different treatments was calculated and the results indicated that deep cryogenic treatment can promote the segregation of carbon atoms in martensite to dislocations.The segregated carbon atoms act as and grow into nuclei for the formation of fine carbide particles during subsequent tempering.And this resulted in the fact that the hardness of the tempered experimental steel after deep cryogenic treatment is higher than that without deep cryogenic treatment.
基金financially supported by the National Key Research and Development Program of China(2020YFB2008400)National Natural Science Foundation of China(U1760204)Key Research&Development Program of Hebei province(20311006D).
文摘Pulse magneto-oscillation(PMO)added during solidification could affect the solidification structure and macrosegregation.A modified thermal simulation equipment was applied to prepare GCr15 bearing steel continuous casting billets with different PMO peak currents.Then,metallographic analysis,component analysis and numerical simulation were adopted to study the influence of PMO peak current and its mechanism.The sample with 150 K_(I)A PMO peak current treatment has little difference with the samples without PMO treatment on solidification structure and macrosegregation.As the peak currents are 250 and 350 K_(I)A,the columnar zone increases and macrosegregation aggravated.When 450 K_(I)A peak current is selected,the equiaxed grain ratio is enlarged,and the dendritic grains are refined,and the macrosegregation of C,Cr,Si and Mn is decreased significantly.By analyzing,different convections induced by PMO with various peak currents are the key factor to change the solidification structure and macrosegregation.
基金The authors are grateful to the funding by National High Technology Research and Development Program of China(863 Program,Grant No.2012AA03A503).
文摘Microstructure and mechanical properties in core of a carburizing 20CrNi2MoV bearing steel subjected to cryogenic treatment were investigated.Conventional treatment sample was quenched and tempered at 180℃ for 2 h.Cryogenic treatment samples were quenched,cryogenically treated at−80 and−196℃ for 4 h,slowly returned to room temperature and thereafter tempered at 180℃ for 2 h,and finally tempered at 180℃ for 2 h.The scanning electron microscope,electron backscattering diffraction,X-ray diffraction and transmission electron microscope were adopted for microstructure characterization.The results show that cryogenic treatment increases the fraction of high-angle grain boundaries and the precipitation of finely dispersed carbides in the matrix,decreases the volume fraction of inter-lath retained austenite,and hence improves the strength and hardness.Compared with the conventional treatment,the hardness,yield strength and ultimate tensile strength of the steel after cryogenic treatment are increased by 11.7%,12.6%and 18.3%,respectively,while the impact energy is decreased by 9.8%.
基金The authors acknowledge financial support from the National Key R&D Program of China(2017YFB0304501)the National Natural Science Foundation of China(Nos.51831008,51871192 and 52001275)+1 种基金the Natural Science Foundation of Hebei Province(E2020203058,E2018203271)the Innovation Funding Project for Postgraduate of Hebei Province(CXZZBS2020058).
文摘The sliding wear property of high-carbon nanostructured bainitic bearing steel with the equal initial hardness and different microstructures was investigated,and the reasons for the difference of wear resistance between the cementite-bearing(CB)and cementite-free(CF)specimens were analyzed.The results show that CF specimens have lower mass loss and surface roughness and shallower wear depth than CB specimens during wear process.Compared with CB specimen,CF specimen presents superior wear resistance.This is due to two reasons:(1)a lot of retained austenite in CF specimen is easy to produce TRIP effect and be transformed into martensite during wear process,which notably increased the surface hardness of worn specimen;(2)there is a nondestructive oxide layer in the surface of cementite-free worn specimen,which can protect the surface of worn specimen from destruction.Under the combined effect of retained austenite and oxide layer,the loss of matrix is reduced.Thus,CF specimen exhibits high wear resistance.It reveals that the wear mechanism of high-carbon nanostructured bainitic bearing steel with different microstructures can provide a reference for improving the wear resistance in high-carbon nanostructured bainitic bearing steel in future.
基金This work is supported by the National Key Research and Development Program of China under Grant numbers of 2016YFB0300401,2018YFF0109404,and 2016YFB0301401the National Natural Science Foundation of China under Grant numbers of U1860202,U1732276,50134010,51704193,51904184,and 52004156the Users with Excellence Program of Hefei Science Center CAS under Grant number of 2019HSC-UE010,and the Changjiang Scholar Program of Chinese Ministry of Education.
文摘The effect of the axial static magnetic field(ASMF)on cleanliness and microstructure in magnetically controlled electroslag remelted GCr15 bearing steel ingots was investigated experimentally.The results show that a magnetically controlled spin-vibration induced by the interaction of the ASMFs and the remelting current exists at the consumable electrode tip,resulting in thinner liquid melt film and smaller droplets.With the increase in magnetic flux density,the optimization effect of ASMFs on electroslag remelting process increases and reaches the peak with a 40 mT ASMF,then decreases.The cleanliness of the ingots was improved,and the count of inclusions larger than 5μm was reduced.The microstructure of the ingots processed with a 40 mT ASMF was significantly refined.The depth of the metallic molten pool was reduced from 45.2 to 17.5 mm with the application of 40 mT ASMF.The tensile strength,impact toughness,and Rockwell hardness of the ingots obtained under the 40 mT ASMF were significantly improved.The mechanisms of the spin-vibration occurring at the electrode tip end were interpreted in detail to elucidate the effect of ASMFs.
