ASTM F2078-2008 Standard Terminology Relating to Hydrogen Embrittlement Testing.pdf

1、Designation: F 2078 08Standard 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 in

2、 parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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)generallycaused by hydrogen introduced into the steel from theenvironment after exposure to an externally applied stress.DISCUSSIONEmbrittlement as a result of hydrogen introduced intosteel from external sources wh

11、ile under stress. Tests are conducted in anenvironment. Found in plated parts that cathodically protect the metalfrom corroding. Generates hydrogen at the surface of the metal.Produces a clean, intergranular fracture surface and is not reversible.For the subtle differences between IHE and EHE see Ta

12、ble X1.1.(STP 962) (STP 543)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 of external sources of highpressure hydrogen gas; cracking

13、 initiates on the outersurface.heat treatmentheating and cooling processes that producemetallurgical changes in the metallic alloy which alter themechanical properties and microstructure of the metal.1This terminology standard is under the jurisdiction of ASTM Committee F07on Aerospace and Aircraft

14、and is the direct responsibility of Subcommittee F07.04on Hydrogen Embrittlement.Current edition approved Feb. 15, 2008. Published March 2008. Originallyapproved in 2001. Last previous edition approved in 2007 as F 207807.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontac

15、t ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.hydrogen-assisted stress

16、 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 by absorption of hydrogen incombination with stress, eit

17、her 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 susceptibility ratio (Hsr)the ratio of the thresh-old for the ons

18、et of hydrogen-assisted cracking to the tensilestrength of the material.internal hydrogen embrittlement (IHE)hydrogen em-brittlement caused by absorbed atomic hydrogen from anychemical process that introduces hydrogen into the steelbefore exposure to an externally applied stress.DISCUSSIONEmbrittlem

19、ent results from the formation of microc-racks with time and is often referred to as “time-delayed embrittle-ment.” Once microcracks have been formed, ductility can not berestored. Tests are generally conducted in air. This type of embrittle-ment is referred to as the classic type of hydrogen embrit

20、tlement insteel, although IHE has also been observed in a wide variety of othermaterials including nickel base alloys and austenitic stainless steelsprovided that they are severely charged with hydrogen. For steels, IHEis most severe at room temperature. The problem primarily results fromelectroplat

21、ing. Other sources of hydrogen are the processing treatmentssuch as melting and pickling. For the subtle differences between IHEand EHE see Table X1.1. (STP 543)notched tensile strength (NTS)the maximum nominal (netsection) stress that a notched tensile specimen is capable ofsustaining. (E 1823)proc

22、essa defined event or sequence of events 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 ex

23、ternalforces.sharp-notch strengththe 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 app

24、lied stress. (C 904)stressthe resistance 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 experimenta

25、lprocedures that give equivalent values, 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

26、 excludes intercrystalline or transcrystalline 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 sing

27、ularity) fora particular mode in a 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 s

28、liding in the crack plane and in the 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 materi

29、alproperty that is measured by the 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 th

30、eeffect; the lowest load at which subcritical 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

31、and abovewhich, time-delayed fracture 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 increm

32、entally increasing load underdisplacement 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

33、crack initiationsth-IHEthreshold stresstest conducted in airgeometrydependentsth-EHEthreshold stresstest conducted in a specifiedenvironmentgeometry dependentKstress-intensity factorKththreshold stress intensityKtstress concentration factorKIsccthreshold stress intensity for stress corrosion crackin

34、gKIHEthreshold stress intensity for IHEKEHEthreshold stress intensity for EHERsbratio of specimen crack strength to yield strength inbendingF2078082Rnsbratio of specimen notched strength to yield strength inbendingththresholdSththreshold stress4.3 Abbreviations:EACenvironmentally assisted crackingEH

35、Eenvironmental hydrogen embrittlementGHEgaseous hydrogen embrittlementHASChydrogen-assisted stress crackingHSChydrogen stress crackingHsrhydrogen susceptibility ratioIHEinternal hydrogen embrittlementHEhydrogen embrittlementNFS(B)notched fracture strength in bendingNFS(T)notched fracture strength in

36、 tensionNTSnotched tensile strengthISLincremental step loadISLththreshold from an incremental step-load testRAreduction of areaRHEreaction hydrogen embrittlementSCCstress corrosion crackingSCEsaturated calomel electrodeSLTsustained load testANNEX(Mandatory Information)A1. DEFINITIONS OF SYMBOLIC EXP

37、RESSIONSA1.1 The following abbreviations 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)

38、 a notched, high-strengthstructural 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 servi

39、ce under cathodic chargingconditions 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 c

40、oncentration becausethe tests are 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) = f

41、racture strength (tension), ksi; 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; calcul

42、ated from themeasured fracture or 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 test

43、s are performed at arate that allows 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

44、in air in either tension or bend.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 environ

45、ment of -1.2V versus SCE in eithertension 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 muc

46、h moresensitive to microstructure 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 ten

47、sion or bend at a given cathodicpotential 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 environm

48、ent of -1.2V versus SCE.F2078083APPENDIX(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

49、, ASTM, West Conshohocken, PA, 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. 39, 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 En