希特勒演讲中文字幕Effects of processing and manufacturing of high nitrogen-containing stainless steels on their mechanical,corrosion and wear properties
H.Ha
Ènninen a,*,J.Romu b ,R.Ilola a ,J.Tervo c ,A.Laitinen d a
Institute for Advanced Materials,Joint Rearch Centre Petten,P .O.Box 2,1755Petten,The Netherlands
b
Laboratory of Engineering Materials,Department of Mechanical Engineering,Helsinki University of Technology,
Puumiehenkuja 3,P .O.Box 4200,FIN-02015HUT,Finland
c
VTT Manufacturing Technology,P .O.Box 1702,Metallimiehenkuja 6,FIN-02044VTT,Finland
d
Santasalo Powdermet Oy,P .O.Box 306,FIN-33101Tampere,Finland
Abstract
The effects of N alloying through different processing and manufacturing routes on metallurgical,mechanical,corrosion and wear properties of high N-containing stainless steels have been studied.Nitrogen alloying has a well de®ned and marked improving effect on mechanical and corrosion properties of the steels until the solubility limit of N is reached and nitride precipitation exhibits its deleterious effects on the properties.It is also demonstrated that N alloying contributes signi®cantly to sliding wear and cavitation erosion resistance of stainless steels.The processing and manufacturing technologies of high N-containing stainless steels are evaluated with main emphasis in P/M fabrication including solid-state nitriding of the metal powder.#2001Elvier Science B.V .All rights rerved.
Keywords:High nitrogen steel;Duplex stainless steel;Nitrogen;Mechanical properties;Corrosion;Wear
1.Introduction
Development of new stainless steels occurs mainly in the area of N alloying of austenitic stainless st
eels or develop-ment of new duplex stainless steels (DSSs),where N alloy-ing is also a key topic.The developments are summarized in a number of recent conferences devoted to high nitrogen steels (HNSs)[1±5]and DSSs [6±11].It has been propod that a N-alloyed steel can be considered as an HNS,when the N concentration is higher than 0.4wt.%in austenitic steels and higher than 0.08wt.%in martensitic steels [1,2].In DSS,where N is esntially partitioned in the austenite pha such a de®nition is more complex.Nowadays,it is convenient to conclude that ``high''in this ca means intentionally raid N content by appropriate alloying or by pressure or powder metallurgy [12].In alloy development of N-containing steels,the emphasis up to now has largely been on austenitic and DSSs,where replacement of Ni and improvement of mechanical and corrosion properties have been the targets in austenitic grades,whereas in DSS grades weldability is an additional target.In martensitic steels,the microstructural re®nement and homogeneity obtained by N alloying result in better high temperature mechanical and corrosion/oxidation properties.
2.Austenitic steels礼仪知识
High nitrogen austenitic stainless steels with remarkable mechanical and corrosion properties in solution-annealed condition can be produced even with conventional steel making process up to 0.4wt.%N.In order to produce steels with higher N content,methods such as:(i)pressur-ized induction
furnace melting;(ii)pressurized plasma furnace melting;(iii)pressurized electroslag remelting (PESR);or (iv)powder metallurgy with hot isostatic press-ing (P/M-HIP)have to be employed [1±5].In P/M produc-tion,following techniques:(i)pressurized gas atomization;(ii)nitriding in ¯uidized bed reactor or rotating furnace;(iii)HIP nitriding;and/or (iv)reactive mechanical alloying,have been employed [3±5].Nitrogen in solid solution is the most bene®cial alloying element in promoting high strength in austenitic stainless steels without affecting their good ductility and toughness properties as long as the solubility limit of N in austenite is not exceeded (<0.9wt.%N depend-ing on composition).As the solubility limit is exceeded,Cr 2N precipitates or gas porosity formation takes place in welding and ductility and toughness are deteriorated.Addi-tionally,N stabilizes so strongly the austenite pha,that N-alloyed austenitic stainless steels can be work hardened to very high strength levels without fear of strain-induced martensite formation.Nitrogen is known to reduce
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Journal of Materials Processing Technology 117(2001)424±430
*
Corresponding author.
0924-0136/01/$±e front matter #2001Elvier Science B.V .All rights rerved.PII:S 0924-0136(01)00804-4
stacking fault energy(SFE)of austenitic stainless steels, especially at low temperatures[4,5,12],resulting in a num-ber of large bene®cial effects on mechanical properties such as strength,impact and fracture toughness,which depend directly on slip mode,deformation twinning and martensitic transformations.Together with temperature,SFE affects primarily the cross-slip behavior of extended dislocations and the strength of obstacles(forest dislocations).In addi-tion,N retards the precipitation of intermetallic phas(s, Laves(Z),R and w pha)as well as M23C6carbides,in which it has low solubility and/or due to its possible retarding effects on Cr and Mo diffusion.The latter mechan-ism,however,has recently been argued bad on possible enhanced diffusion due to incread vacancy concentration [5,12].
Yield and ultimate tensile strengths(YS and UTS)of austenitic stainless steels increa linearly at room tempera-ture with increasing interstitial N content of the steel[1±5,12±14].The YS of N-alloyed
austenitic stainless steels at room temperature is due to solid solution hardening(thermal component,proportional to N1/2)and grain boundary hard-ening(athermal component),when N is in interstitial solid solution[1±5,12±14].The thermal component is weak above 2008C and very strong below ambient temperature.Solid solution hardening is generally bad on the atomic size mis®t of the solute atoms with the austenite crystal lattice. Nitrogen has the greatest effect on YS among interstitial alloying elements.The grain size hardening in N-alloyed austenitic stainless steels is bad on the grain size depen-dence of the YS described by the Hall±Petch equation.The effect of N content on grain boundary hardening increas proportionally as the N content of the steel increas.The effect of N on grain boundary hardening has been explained by the planar dislocation structures obrved in N-alloyed austenitic stainless steels,and thus,by the decreasing effect of N on SFE.Short range ordering has also been considered as a possible explanation for the planar dislocation arrange-ment in N-alloyed austenitic stainless steels.Grain boundary hardening increas therefore with increasing N content of the steel,and is related to the strong af®nity between Cr,Mo and N atoms[1,2,5].
High N austenitic stainless steels exhibit a ductile-to-brittle transition at low temperatures[3,4,12].Brittle-like fracture occurs along{111}-planes,or along annealing twin or grain b
club是什么意思oundaries.TEM examinations have revealed that neither deformation twinning nor e-martensite forma-tion are necessary and obrved planar dislocation structures just below the fracture surface suggest that brittle-like fracture occurs along active slip planes by a slipping-off mechanism[15].It has also been obrved that grain re®ne-ment has little in¯uence on DBTT opposite to ferritic steels. Fe±Cr±Mn±N steels exhibit more signi®cant embrittlement than Fe±Cr±Ni±Mo±N steels.
The low cycle fatigue(LCF)strength of austenitic AISI 316steel has been studied as a function of N content[1±5]. Nitrogen alloying increas fatigue life with N content up to 0.12wt.%,but no further increa was obtained by increas-ing the N content up to0.4wt.%.In general,the fatigue strength has been related to decreasing effect of N on the SFE of the steel.Nitrogen alloying has also been obrved to affect the fatigue crack growth rate and to increa the fatigue threshold value,D K th[2,3].This was related to the combined effect of N and Mo on fatigue strength,which ems to be related to Mo±N pair formation supporting planar dislocation structures more than the low SFE value.It was concluded that in high N-containing austenitic stainless steels(0.6±1.0wt.%N),neither N content nor cold work or strain aging affect signi®cantly the LCF life[2].Also it is obrved that at low temperatures worning fatigue beha-vior can be obtained[4].
Nitrogen alloying,especially of Mo-alloyed austenitic stainless steels,improves the resistance to locali
zed corro-sion,in general,and in some environments resistance to general corrosion[4,5,16].Nitrogen alloying has been obrved to retard localized corrosion initiation and to suppress the growth of the localized corrosion attack effec-tively by an immediate repassivation.This is suggested to be due to formation of NH4 ions(obrved at passive,active and transpassive potentials,but amount decreasing with increasing applied potential)in initiated pits/crevices increasing locally the pH value and enhancing repassivation. During repassivation,N is enriched in the metal/oxide interface,which is incread in magnitude with the increas-ing corrosion potential,and not affecting the passive®lm composition.The in¯uences of N and Mo on corrosion properties of stainless steels are recently been explained by point defect model(PDM)combined with reactive ele-ment effects(REEs)at the®lm/metal interface[5].The bene®cial effect of N on the corrosion resistance of auste-nitic stainless steels can be utilized as long as the solubility limit of N in the steel is not ,as long as N is in interstitial solid solution.As the solubility limit is exceeded, Cr2N precipitates and localized corrosion resistance is dete-riorated.By increasing the Cr,Mo,and especially N contents of an austenitic stainless steel,it is possible to achieve crevice corrosion resistance comparable to that of some Ni-ba alloys.Partial replacement of Mo with W has also been obrved to improve the localized corrosion resistance of austenitic stainless steels[5].The bene®cial effect of Cr, Mo,and N can be utilized even better in P/M-HIP manu-factured austenitic stainless steels,due to their more ho
mo-geneous microstructures as compared to tho of steels manufactured conventionally or via pressurized metallurgy [5,17,18].Nickel-free austenitic stainless steels have been developed with good resistance to localized corrosion due to N alloying.Nitrogen is an austenite stabilizing element like Ni,and can thus instead of Ni ensure a fully austenitic microstructure[4,5].In addition to the direct effects,N also affects the localized corrosion resistance of stainless steels indirectly,via the retarding effect of N on the precipitation of intermetallic phas such as s,w,etc.,which deteriorate the corrosion resistance.
daleyH.HaÈnninen et al./Journal of Materials Processing Technology117(2001)424±430425
Environment nsitive cracking(stress corrosion cracking (SCC),corrosion fatigue(CF),and hydrogen embrittlement (HE))of N-alloyed austenitic stainless steels has been studied very little systematically.However,recent results show a clear bene®cial effect of N alloying on SCC behavior in chloride solutions[5,19],even though in very aggressive environments,the effects of N em to be minor.The ductility loss of high N austenitic stainless steels caud by hydrogen are more pronounced at high N concentrations [20].Hydrogen charging results in further decrea of SFE, but N is stabilizing strongly the austenite structure prevent-ing hydrogen-induced pha transformations[3].Due to attractive interaction between N and H,the H solubility increas with incre
asing N content of the steel. Nitrogen-containing austenitic steels are susceptible to dynamic strain aging(DSA)at elevated temperatures.The phenomenon is due to interactions between diffusing solute atoms and moving dislocations during plastic deformation at temperatures where the solute mobility is suf®cient to lock mobile dislocations[21,22].At lower temperature range of DSAreorientation of nitrogen±vacancy pairs occurs and at high temperature range DSAis related to substitutional atom (e.g.,Cr)diffusion in austenitic stainless steels.High N contents have been obrved to promote this phenomenon so,that its typical temperature region,from200to6508C,is expanded to higher and lower temperatures[22].DSAhas an in¯uence on mechanical properties as it leads to strengthen-ing,but also to a decrea in fracture toughness,ductility, and LCF resistance.Thus,the knowledge of elevated tem-perature behavior from this point of view is esntial in evaluating the potential u of austenitic HNS in power plants or other high temperature long-term applications.The obrved bene®cial effects of N in solid solution on creep resistance of austenitic stainless steels up to10008C[1±5] have to be evaluated bad on the thermal stability of the steels against nitride and condary pha precipitation. Nitrogen alloying improves sliding wear resistance of austenitic stainless steels[3±5,23].The main reason for the increa in wear resistance is the effect of N on increas-ing the initial hardness and the strain-hardening behavior. Metastability of the austenite would further enhance the wear resistance.Strain-induced martensitic transformation
is not possible in alloys having high N content,becau the austenite stability increas due to N alloying.Abrasion resistance depends on the hardness ratio between abrasive and abraded material.Also the nature,shape,grain size and sharpness of the abrasive have an effect on abrasive wear resistance of high N austenitic stainless steels[23,24].Work hardening may increa abrasive wear resistance if the hardness of abraded material is clo to or exceeds that of abrasive.Nitrogen alloying improves the cavitation ero-sion resistance of austenitic stainless steels,as well as DSSs [5,18,23].The main reason for the increa in cavitation erosion resistance of the austenitic stainless steels is the effect of N on their hardness.ANi-free austenitic HNS, 19%Cr±10%Mn±0.5%N,has also a very high abrasion and cavitation erosion resistance®nding applications in mining industry[4,5].In DSS,the cavitation erosion rate is mainly dependent upon the volume and hardness of the austenite pha.When both duplex and austenitic stainless steels are compared,it appears that bulk ,0.2%YS) provides a good correlation with cavitation rate and mar-tensite transformation(Md30)or SFE are less important.The correlation is non-linear.
Despite their high strength and the fact that N slows down recovery rate during hot rolling,hot workability of austenitic HNS is good if the amount of hot workability reducing ,S,P,Cu or O is kept low[25].They cau edge cracking of the strip during rolling and affect adverly toughn
ess.Therefore,the steel making process play an important role.Also,the rolling temperature must be lected so that Cr2N formation region is not reached. The strength of austenitic HNS can be greatly improved by cold rolling,if an adequate amount of cold rolling can be performed.YS up to3000MPa can be achieved by cold rolling[1±3].Cold workability at high N contents can be restricted due to the high work hardening rate of the steels, which may cau premature cracking of the strip during cold rolling.At least up to0.50wt.%N,the cold workability of austenitic HNS has been adequate[25].One advantage of high N content is that HNS are stable during deformation and martensite formation can be prevented entirely.This is also a signi®cant design consideration in applications requir-ing fracture control planning,clo-dimensional tolerances and abnce of ferromagnetic pha.
The higher solubility of N in the solid pha of austenite combined with lower temperatures and pressures(atmo-spheric pressure)as well as short diffusion distance make solid-state nitriding of austenitic stainless steel powder an effective method for introducing high N contents compared to the molten route manufacturing of HNS[1±5,26].Flui-dized bed nitriding of inert gas atomized powder is one way to introduce N contents above the solubility limit of N in the melt into metal powder,which is then hot isostatically presd(HIP).Nitrogen contents of the powder batches in ¯uidized bed nitridi
ng depend on nitriding temperature (700±8008C),nitriding time and particle size distribution of the powders as well as on material composition[4,26]. Nitrogen content of the powder particles increas with increasing nitriding temperature and decreasing particle size,which means that the desired N content can be achieved faster.As a disadvantage of the¯uidized bed nitriding, oxygen contents of gas atomized powders increa to 100±500ppm depending on the composition of the metal powder.
The high N austenitic stainless steels have:(i)high YS; UTS and ductility as well as fracture toughness;(ii)high strain hardenability;(iii)high resistance to strain-induced martensite formation;(iv)low magnetic permeability;(v) favorable localized corrosion properties.Bad on various combinations of the excellent properties high N-contain-ing austenitic stainless steels are ud in power generation
426H.HaÈnninen et al./Journal of Materials Processing Technology117(2001)424±430
(e.g.,retaining rings of the generator rotors),cryogenic applications(superconducting magnet housings),pulp and paper industry(grinders,valves),transportation industry (ship building),petrochemical industry(pressure vesls, valves,bolting),etc.[1±5].
apartments
3.Duplex stainless steels
DSSs,which consist of approximately similar amounts of austenite and ferrite are designed to combine the best features of austenitic and ferritic stainless steels.They are at prent ud in a wide range of products such as paper machines and other pulp and paper industry machinery, pressure vesls,pipes and heat exchangers as well as off-shore applications and chemical tankers.Materials lection is usually bad on their high strength with desirable tough-ness,which is combined with excellent thermal properties and corrosion resistance,especially to chloride-induced SCC and intergranular corrosion,allowing often both weight and cost savings of the product.The optimization of DSS for the constructions has resulted in continuous material development related to their alloying,especially with N,and the resulting mechanical,corrosion and wear properties as well as weldability.In developing the proper-ties,characterization of the microstructural changes of DSS after different thermal cycles as well as their in¯uence on the deformation and residual stress of different pha constituents reprents a central rearch need for modern DSS.
Becau of the two-pha structure,where both phas have different mechanical properties,which are tempera-ture-dependent,similar to the coef®cient of thermal expan-sion and Young's modulus,thermal cycling induces plastic deformation and pha-speci®c residual stress in the mat
erial even without any external loading[11,27±29]. There is a large variation in published,measured and calculated values of residual stress caud by different elastic and plastic properties of the two phas as well as stress relaxation by creep and texture effects.In general,it is considered that at room temperature,ferrite pha has higher strength than austenite pha,but at about6008C shows austenite higher high-temperature strength.However,even a minor change in the N content may increa the YS of austenite pha so that it becomes from the softer pha to the harder pha.Austenite has markedly higher coef®cient of thermal expansion in the whole temperature range and shows much slower decrea of Young's modulus as a function temperature.The different temperature cycles result in pha-speci®c residual stressÐferrite slightly under compression and austenite correspondingly under tension at room temperature[28].The experimental values are,however,much lower(<100MPa)that can be predicted from the coef®cients of thermal expansion of both phas using purely elastic models.This suggests that plastic deformation occurs at least locally in both phas during the temperature cycles.With increasing temperature,it has been obrved that the¯ow stress of DSS is clo to that of ferrite at solution-annealing temperatures at a slow strain rate,while it is clo to that of austenite at a high strain rate. This leads to a high strain rate nsitivity of¯ow stress(m-value)with coar grain structure.Microduplex stainless steels show a much larger m-value at a higher strain rate region allowing a superior superplastic behavior of the
steels[30].The microstress,which are always prent in DSS,affect the plastic strain and especially cyclic slip localization causing fatigue crack initiation as well as SCC initiation and growth.
In cyclic loading,plastic deformation occurs more in the austenite pha and cyclic hardening is expected to be related to work hardening in the austenite pha which is associated to two mechanisms in N-alloyed steels.Nitrogen may decrea the SFE value of the austenite and the af®nity between N and Cr/Mo induces short range ordering.Both mechanisms enhance planar slip instead of cross-slip increasing,thus,the strain-hardening rate.In fatigue,crack initiation has been obrved at persistent slip bands in the ferrite pha at low strain amplitudes,occasionally also in the austenite pha at intermediate strain amplitudes and in both phas at high strain amplitudes in0.11±0.18wt.%N DSS[31].On the other hand,in0.07wt.%N DSS just the opposite has been en[32].Alloying DSS with high N contents(up to0.4wt.%N)leads to marked modi®cation in the volume fraction of phas and solid solution hardening of the austenite pha.High N DSSs show a tendency to cyclic softening in fatigue,but the bene®cial effect of N is obrved in aged(4758C embrittled)and in corrosive environments. Plastic deformation in aged,spinodally decompod ferrite is dif®cult by dislocation slip and therefore mechanical twinning takes place.In the LCF region,high N content of austenite and hardening of ferrite decrea the resistance of the microstructural barriers(p
ha boundaries)and result in decrea of fatigue properties,while in high cycle fatigue (HCF)region both N alloying and aging of ferrite improve the fatigue resistance.The effect is,however,much less than obrved in monotonic tensile properties.In high temperature fatigue,DSAexhibits a strong in¯uence in the cyclic behavior of DSS similar to ferritic stainless steels, probably indicating that in the DSAtemperature range,the ferrite pha plays an important role.In CF,both the mechanical and electrochemical coupling between austenite and ferrite phas determine their cyclic deformation res-pon in an environment.Particularly,the N content is affecting both of them.In summary,fatigue life of DSS is strongly determined by the behavior of short cracks and the microstructural barriers,such as austenite/ferrite pha boundaries,which arrest the initiating cracks[11].This means that®ne duplex ,P/M-HIP)is much better from fatigue point of view than coar ,casting).
From corrosion properties point of view,pitting corrosion resistance is regarded to be of crucial importance in DSS
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H.HaÈnninen et al./Journal of Materials Processing Technology117(2001)424±430427
applications.The common way of ranking DSS according to their resistance to pitting corrosion has been the calculation of the PREN value[6±11]:
PREN wt:%Cr 3:3wt:%Mo 16wt:%N
DSS having extraordinary resistance to pitting corrosion and having PREN value exceeding40are termed super-duplex stainless steels.In the two-pha structure,Cr (partitioning ratio1.2)and Mo(1.6)are partitioned to ferrite and Ni(0.65)and N(0.,N is esntially concentrated in austenite)are partitioned to austenite, which results in different PREN values for the two phas [8±11].To obtain equal pitting corrosion resistance for both phas,alloying and lection of annealing temperature can be ud.Nitrogen lowers the partitioning ratio for Cr,Ni, and Mo,but Ni enhances the tendency of element parti-tioning for both Cr and Mo.Increa of the annealing temperature narrows the differences in composition for important alloying elements.Due to partitioning,the ferrite pha has higher PREN value becau of higher Mo and Cr, while the amount of N in austenite is too small to result in a similar PREN.When N content of the steel increas(at around0.4wt.%)austenite has higher PREN than ferrite.If the N content is still incread,PREN of austenite further increas while that of ferrite starts to decrea due to reduced partitioning of Cr and Mo caud by high N activity.Higher N level is not alone bene®cial,but needs to be adjusted by increasing Mo and decreasing Cr contents [8,33,34].
DSS have,in general,better SCC resistance than the single-pha austenitic stainless steels in chlori
de-contain-ing environments.The above-mentioned partitioning of alloying elements in each pha of DSS induces differences in mechanical properties and the electrochemical potential between phas(mechanical and electrochemical coupling). Selective dissolution of less noble pha will then occur near the corrosion potential or preferential attack near the trans-passive region or hydrogen-induced cracking in ferrite at low corrosion potentials can cau SCC initiation[35].SCC propagation in the three potential regions is then occurring depending on mechanical and electrochemical properties of the two phas in either of them depending on the test conditions.
In addition to corrosion,the role of N is also in modern DSS with high Cr and Mo contents to delay the formation of intermetallic phas due to its decreasing effect on the activity of Cr.The intermetallic phas(s,w,p,and R pha)form in the temperature range600±10008C as a result of too slow cooling and have an adver effect on corrosion resistance and toughness[6±11,36],but less or no effect on fatigue properties.In addition to intermetallic phas,for-mation of condary austenite(g2),having lower concentra-tion of Cr,Mo and N than the primary austenite,as well as nitrides and carbides takes place in this temperature range. In the lower temperature range300±5008C,pha paration of ferrite occurs to nanoscale modulated regions(2±10nm)of Cr-rich a0-pha and Fe-rich a-pha via spinodal or nucleation and growth mechanism depending on t
he com-position and temperature or to roughly spherical Ni±Si±Mo-rich G-pha(<10nm)precipitation both in the matrix and on dislocations,which is known as the``4758C embrittle-ment''.The embrittlement of ferrite appears to be due to spinodal decomposition to Cr-and Fe-rich regions rather than G-pha precipitation.There is some evidence that N alloying increas the kinetics of spinodal decomposition due to Cr±N clustering[37]and therefore4758C embrittle-ment of DSS,but also the opposite has been claimed bad on retarding effect of N on Cr diffusion.The deleterious phas occur in annealing during manufacturing or in weld-ing as well as during high temperature rvice[6±11,38].If the ferrite pha is thermally embrittled(ferrite hardness is incread),the monotonic hardening is weakly affected by aging,but the cyclic behavior exhibits a strong Bauschinger effect(related to plastic deformation in compression),esn-tially due to the mismatch of the plastic behavior between the both phas[11].
亲爱的 英文
The favorable properties of DSS are strongly dependent on the austenite/ferrite ratio,which in the ba material is designed to be approximately1:1.The pha balance must be maintained in both the weld metal and the heat-affected zone(HAZ).In welding,the microstructure and properties of the weld metal are controlled by adjusting the®ller metal composition.However,the microstructure of the HAZ is determined by the weld thermal cycle and is,thus,nsitive to variations in welding conditions.In th
e HAZ,at elevated temperatures austenite would progressively transform into ferrite until13008C,but the increasing N content of the steels stabilizes austenite and,thus,helps to keep the ferrite/ austenite ratio in HAZ[8±11,39].Subquent grain growth in the ferrite regime takes place and®nally the decomposi-tion of the ferrite to austenite during cooling occurs being controlled by N diffusion from supersaturated ferrite to reforming austenite.
Nitrogen alloying(at least0.2wt.%N)in DSS makes it also possible to develop cost-ef®cient Ni-free DSS with up to about10wt.%Mn content for engineering applications where high strength and moderate/good corrosion resistance are required,such as reinforcing bars[11,40]. Hydrogen can cau a considerable loss of ductility and toughness in DSS.The source can be in rvice cathodic protection,galvanic coupling to low alloy steel,sour gas or oil with signi®cant amounts of H2S providing high fugacity of hydrogen or hydrogen ingress from welding.The solu-bility of hydrogen in austenite is about1000times that of ferrite,but the diffusivity is much higher in ferrite.Thus, austenite provides a long-term source of hydrogen after exposure and may induce cracking or loss of ductility of ferrite(only about2ppm of hydrogen can embrittle ferrite), while austenite is arresting the propagating cracks by ductile blunting[11].
沉甸甸读音>jumpersThe recently developed higher Cr,Mo and N and lower Ni superduplex stainless steels are more dif®
cult to少儿英语课程顾问
428H.HaÈnninen et al./Journal of Materials Processing Technology117(2001)424±430
