1、Designation: F 2078 08aStandard Terminology Relating toHydrogen Embrittlement Testing1This standard is issued under the fixed designation F 2078; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number i
2、n parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This terminology covers the principal terms, abbrevia-tions, and symbols relating to mechanical methods for hydro-gen embrittlement testing, wh
3、ich are present in more than oneof the standards under the jurisdiction of ASTM CommitteeF07 onAerospace andAircraft. These definitions are publishedto encourage uniformity of terminology in product specifica-tions.2. Referenced Documents2.1 ASTM Standards:2C 904 Terminology Relating to Chemical-Res
4、istant Non-metallic MaterialsD 4848 Terminology Related to Force, Deformation andRelated Properties of TextilesE6 Terminology Relating to Methods of Mechanical Test-ingE8 Test Methods for Tension Testing of Metallic MaterialsE 631 Terminology of Building ConstructionsE 1823 Terminology Relating to F
5、atigue and Fracture Test-ingF 109 Terminology Relating to Surface Imperfections onCeramicsF 1624 Test Method for Measurement of Hydrogen Em-brittlement Threshold in Steel by the Incremental StepLoading TechniqueG15 Terminology Relating to Corrosion and CorrosionTesting3. Significance and Use3.1 The
6、terms used in describing hydrogen embrittlementhave precise definitions. The terminology and its proper usagemust be completely understood to communicate and transferinformation adequately within the field.3.2 The terms defined in other terminology standards, arerespectively identified in parenthese
7、s following the definition.4. Terminology4.1 Definitions:bakingheating to a temperature, not to exceed 50F (27.8C)below the tempering or aging temperature of the metal oralloy, in order to remove hydrogen before embrittlementoccurs by the formation of microcracks.DISCUSSIONNo metallurgical changes t
8、ake place as a result ofbaking.brittlesee brittleness.brittlenessthe tendency of a material to break at a very lowstrain, elongation, or deflection, and to exhibit a cleanfracture surface with no indications of plastic deformation.(E 631)crackline of fracture without complete separation. (F 109)crac
9、k strengththe maximum value of the nominal stress thata cracked specimen is capable of sustaining. (E 1823)ductilesee ductility.ductilitythe ability of a material to deform plastically beforefracturing. (E6)embrittlesee embrittlement.embrittlementthe severe loss of ductility or toughness, orboth, of
10、 a material, usually a metal or alloy. (G15)environmental hydrogen embrittlement (EHE)hydrogenembrittlement caused by hydrogen introduced into a steel/metallic alloy from an environmental source coupled withstress either residual or externally applied.DISCUSSIONProduces a clean intergranular fractur
11、e and is notreversible. For the subtle differences between EHE and IHE, see TableX1.1.environmentally assisted cracking (EAC)see stress cor-rosion cracking.fracture strengththe normal stress at the beginning offracture.gaseous hydrogen embrittlement (GHE)a distinct form ofEHE caused by the presence
12、of external sources of highpressure hydrogen gas; cracking initiates on the outersurface.1This terminology standard is under the jurisdiction of ASTM Committee F07on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.04on Hydrogen Embrittlement.Current edition approved July
13、1, 2008. Published July 2008. Originally approvedin 2001. Last previous edition approved in 2008 as F 207808.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the sta
14、ndards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.heat treatmentheating and cooling processes that producemetallurgical changes in the metallic alloy which alter themechanical properties
15、and microstructure of the metal.hydrogen-assisted stress cracking (HASC)crack growth asa result of the presence of hydrogen, which can be either IHEor EHE and sometimes is referred to as hydrogen stresscracking (HSC).hydrogen embrittlement (HE)a permanent loss of ductilityin a metal or alloy caused
16、by absorption of hydrogen incombination with stress, either an externally applied or aninternal residual stress.hydrogen embrittlement reliefsee baking.hydrogen-induced stress crackingsee hydrogen-assistedstress cracking.hydrogen stress crackingsee hydrogen-assisted stresscracking.hydrogen susceptib
17、ility ratio (Hsr)the ratio of the thresh-old for the onset of hydrogen-assisted cracking to the tensilestrength of the material.internal hydrogen embrittlement (IHE)hydrogen em-brittlement caused by absorbed atomic hydrogen into thesteel/metallic alloy from an industrial hydrogen emittingprocess cou
18、pled with stress, either residual or externallyapplied.DISCUSSIONFor the subtle differences between IHE and EHE seeTable X1.1.notched tensile strength (NTS)the maximum nominal (netsection) stress that a notched tensile specimen is capable ofsustaining. (E 1823)processa defined event or sequence of e
19、vents in plating orcoating that may include pretreatments and posttreatments.reaction hydrogen embrittlement (RHE)irreversible em-brittlement caused by the reaction of hydrogen with metal toform a stable hydride.residual stressstress in a metal in the absence of externalforces.sharp-notch strengthth
20、e maximum nominal (net section)stress that a sharply notched specimen is capable of sustain-ing. (E 1823)straindeformation of a material caused by the application ofan external force. (D 4848)strain ratethe rate of relative length deformation with timedue to an applied stress. (C 904)stressthe resis
21、tance to deformation developed within amaterial subjected to an external force. (D 4848)stress concentration factor (kt)the ratio of the greateststress in the region of a notch or other stress concentrator, asdetermined by the theory of elasticity or by experimentalprocedures that give equivalent va
22、lues, to the correspondingnominal stress. (E 1823)stress corrosion cracking (SCC)a cracking process thatrequires the simultaneous action of a corrodent and sustainedtensile stress.DISCUSSIONThis excludes corrosion-reduced sections that fail byfast fracture. It also excludes intercrystalline or trans
23、crystalline corro-sion, which can disintegrate an alloy without either applied or residualstress (G15). In essence the process of SCC and EAC are equivalent.stressintensity factor, Kthe magnitude of the mathemati-cally ideal cracktip stress field (stress field singularity) fora particular mode in a
24、homogeneous linearelastic body.(E 1823)DISCUSSIONKI=for a Mode I (opening mode) loading condition thatdisplaces the crack faces in a direction normal to the crack plane.KII=for a Mode II (sliding mode) loading condition where the crackfaces are displaced in shear sliding in the crack plane and in th
25、e primarycrack propagation direction.KIII=for a Mode III (tearing mode) loading condition where the crackfaces are displaced in shear tearing in the crack plane but normal to theprimary crack propagation direction.susceptibility to hydrogen embrittlementis a materialproperty that is measured by the
26、threshold stress intensityparameter for hydrogen induced stress cracking, KIscc,KIHE,or KEHE, which is a function of hardness and microstructure.threshold (th)a point, separating conditions that will pro-duce a given effect, from conditions that will not produce theeffect; the lowest load at which s
27、ubcritical cracking can bedetected.threshold stress (sth)a stress below which no hydrogenstress cracking will occur and above which time-delayedfracture will occur.threshold stress intensity (Kth)a stress intensity belowwhich no hydrogen stress cracking will occur and abovewhich, time-delayed fractu
28、re will occur.time-delayed embrittlementsee internal hydrogen em-brittlement.4.2 Symbols:Papplied loadPccritical load required to rupture a specimen using acontinuous loading ratePicrack initiation load for a given loading and environmentalcondition using an incrementally increasing load underdispla
29、cement controlPththreshold load in which Piis invariant with respect toloading rate; Pthis the basis for calculating the thresholdstress or the threshold stress intensitysapplied stresssnetnet stress based on area at minimum diameter of notchedround barsistress at crack initiationsth-IHEthreshold st
30、resstest conducted in airgeometrydependentsth-EHEthreshold stresstest conducted in a specifiedenvironmentgeometry dependentKstress-intensity factorKththreshold stress intensityKtstress concentration factorKIsccthreshold stress intensity for stress corrosion crackingKIHEthreshold stress intensity for
31、 IHEKEHEthreshold stress intensity for EHERsbratio of specimen crack strength to yield strength inbendingF 2078 08a2Rnsbratio of specimen notched strength to yield strength inbendingththresholdSththreshold stress4.3 Abbreviations:EACenvironmentally assisted crackingEHEenvironmental hydrogen embrittl
32、ementGHEgaseous hydrogen embrittlementHASChydrogen-assisted stress crackingHSChydrogen stress crackingHsrhydrogen susceptibility ratioIHEinternal hydrogen embrittlementHEhydrogen embrittlementNFS(B)notched fracture strength in bendingNFS(T)notched fracture strength in tensionNTSnotched tensile stren
33、gthISLincremental step loadISLththreshold from an incremental step-load testRAreduction of areaRHEreaction hydrogen embrittlementSCCstress corrosion crackingSCEsaturated calomel electrodeSLTsustained load testANNEX(Mandatory Information)A1. DEFINITIONS OF SYMBOLIC EXPRESSIONSA1.1 The following abbre
34、viations and symbols are in-cluded as separate sections in this standard because theyevolved specifically from tests conducted on fasteners, whichinherently have all of the ingredients necessary to createhydrogen embrittlement problems.A1.2 Fasteners are generally (1) a notched, high-strengthstructu
35、ral element that in service is always torqued to a highpercentage of the fracture strength, (2) chemically cleaned, (3)coated with a sacrificial anodic coating that is generallyelectrochemically deposited producing a hydrogen chargingcondition, and (4) placed in service under cathodic chargingcondit
36、ions when exposed to an aqueous environmentall ofthe conditions necessary to cause classical hydrogen embrittle-ment (IHE) or environmentally induced hydrogen embrittle-ment (EHE).A1.3 Test Methods E8Loading RatesThese results areindependent of any residual hydrogen concentration becausethe tests ar
37、e performed at a rate that does not allow sufficienttime for the diffusion of hydrogen to occur.A1.3.1 Tensile Test Symbols:TS(T) = tensile strength (tension), ksi; calculated from theminimum specified tensile strength (mst) and minor diameterof the fastener.FS(T) = fracture strength (tension), ksi;
38、 calculated from themeasured fracture or ultimate tensile load of the fastener, ornotched or precracked test sample.Rnst= notched strength ratio in tension; calculated fromFS(T)/TS(T).A1.3.2 Bend Test Symbols:YS(B) = TS(T).FS(B) = fracture strength (bend), ksi; calculated from themeasured fracture o
39、r ultimate bend of the fastener, or notchedor precracked test sample.Rnsb= notched strength ratio in bending.A1.4 Test Method F 1624 Loading RatesThese abbrevia-tions are used for the terms for results that are dependent on theresidual hydrogen concentration. The tests are performed at arate that al
40、lows sufficient time for the diffusion of hydrogen tooccur.A1.4.1 ISLincremental step-load test to measure thethreshold stress, which is slow enough to allow for thediffusion of hydrogen to occur.A1.4.2 sth-air(T/B)the threshold stress at a given loadingrate measured in air in either tension or bend
41、.A1.4.3 sth-V(T/B)the threshold stress at a given loadingrate measured at a given cathodic potential in either tension orbend.A1.4.4 sth-H+(T/B)the lower limit of the threshold stress atan invariant loading rate measured in the most aggressivehydrogen charging environment of -1.2V versus SCE in eith
42、ertension or bend.A1.5 Evaluation Parameter:A1.5.1 %FS(T/B)degradation factor = % fracturestrength.A1.5.2 Hsr(T/B)hydrogen susceptibility ratio, a materialproperty that is a function of composition, melting practice,thermomechanical processing, heat treatment, and much moresensitive to microstructur
43、e than Test Methods E8mechanicalproperties.A1.5.3 Hsr(t/b)-IHEthe threshold notched hydrogen suscep-tibility ratio in either tension or bend for internal hydrogenembrittlement, (IHE).A1.5.4 Hsr(t/b)-EHEthe threshold notched hydrogen suscep-tibility ratio in either tension or bend at a given cathodic
44、potential for external or environmental hydrogen embrittle-ment, (EHE).A1.5.5 Hsr(t/b)-1.2Vthe lower limit threshold notched hy-drogen susceptibility ratio in either tension or bend forhydrogen-induced stress cracking in the most aggressive hy-drogen charging environment of -1.2V versus SCE.F 2078 0
45、8a3APPENDIX(Nonmandatory Information)X1. IHE/EHE COMPARISON CHARTBIBLIOGRAPHYThe following documents and publications may provide additional definitions or terminology in the field of hydrogenembrittlement.(1) Raymond, L., Ed., Hydrogen Embrittlement Testing, ASTM STP543, ASTM, West Conshohocken, PA
46、, 1972.(2) Raymond, L., Ed., Hydrogen Embrittlement: Prevention and Con-trol, ASTM STP 962, ASTM, West Conshohocken, PA, 1988.(3) “The Susceptibility of Fasteners to Hydrogen Embrittlement andStress Corrosion Cracking,” Handbook of Bolts and Bolted Joints,Marcel Decker, Inc., New York, 1998, Chap. 3
47、9, p. 723.(4) ASTM Dictionary of Engineering Science or through the ASTM website(www.astm.org).TABLE X1.1 Similarities/Differences Between Internal (IHE) and Environmental (EHE) Hydrogen EmbrittlementAIHE EHETime delay fracture when stressed in air after exposure to environment Time delay fracture i
48、n environment after exposure to stress in airRequires H+critical from processing (plating, acid cleaning) for a given stressabove hydrogen stress cracking thresholdRequires H+critical from environment (cathodic corrosion reaction) for a givenstress above hydrogen stress cracking thresholdPlating, ac
49、id cleaning, and so forth, considered environment in which “corrosionreaction” takes place to generate H+, while stress is below threshold“Corrosion reaction” takes place in environment to generate H+,orotherenvironmental sources of H+, while stress is above thresholdThe only difference between IHE and EHE is the sequence of applying the stress and exposure to hydrogenPhenomenon is the same!Mechanism is the same!Principle difference is sequence of stress and introduction
