1、Designation: F 1940 07aStandard Test Method forProcess Control Verification to Prevent HydrogenEmbrittlement in Plated or Coated Fasteners1This standard is issued under the fixed designation F 1940; the number immediately following the designation indicates the year oforiginal adoption or, in the ca
2、se of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure to prevent, to theextent possible, internal hydrogen
3、embrittlement (IHE) offasteners by monitoring the plating or coating process, such asthose described in Specifications F 1137 and F 1941. Theprocess is quantitatively monitored on a periodic basis with aminimum number of specimens as compared to qualifying eachlot of fasteners being plated or coated
4、. Trend analysis is used toensure quality as compared to statistical sampling analysis ofeach lot of fasteners. This test method consists of a mechanicaltest for the evaluation and control of the potential for IHE thatmay arise from various sources of hydrogen in a plating orcoating process.1.2 This
5、 test method consists of a mechanical test, con-ducted on a standard specimen used as a witness, for theevaluation and control of the potential for IHE that may arisefrom various sources of hydrogen in a plating or coatingprocess.1.3 This test method is limited to evaluating hydrogeninduced embrittl
6、ement due only to processing (IHE) and notdue to environmental exposure (EHE, see Test MethodF 1624).1.4 This test method is not intended to measure the relativesusceptibility of steels to either IHE or EHE.1.5 This test method is limited to evaluating processes usedfor plating or coating ferrous fa
7、steners.1.6 This test method uses a notched square bar specimenthat conforms to Test Method F 519, Type 1e, except that theradius is increased to accommodate the deposition of a largerrange of platings and coatings. For the background on TestMethod F 519 testing, see publications ASTM STP 5432andAST
8、M STP 962.3The stress concentration factor is at a Kt=3.1 6 0.2. The sensitivity is demonstrated with a constantimposed cathodic potential to control the amount of hydrogen.Both the sensitivity and the baseline for residual hydrogen willbe established with tests on bare metal specimens in air.1.7 Th
9、e sensitivity of each lot of specimens to IHE shall bedemonstrated. A specimen made of AISI E4340 steel heattreated to a hardness range of 50 to 52 HRC is used to producea “worst case” condition and maximize sensitivity to IHE.1.8 The test is an accelerated (#24 h) test method tomeasure the threshol
10、d for hydrogen stress cracking, and is usedto quantify the amount of residual hydrogen in the specimen.The specimen undergoes sustained load and slow strain ratetesting by using incremental loads and hold times underdisplacement control to measure a threshold stress in anaccelerated manner in accord
11、ance with Test Method F 1624.1.9 In this test method, bending is used instead of tensionbecause it produces the maximum local limit load tensile stressin a notched bar of up to 2.3 times the yield strength asmeasured in accordance with Test Method E8. A fastener thatis unintentionally exposed to ben
12、ding on installation may attainthis maximum local tensile stress.1.10 The values stated in inch-pound units are to be re-garded as standard. The values given in parentheses aremathematical conversions to SI units that are provided forinformation only and are not considered standard.1.11 This standar
13、d does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM
14、 Standards:4D 1193 Specification for Reagent WaterE4 Practices for Force Verification of Testing MachinesE8 Test Methods for Tension Testing of Metallic MaterialsE18 Test Methods for Rockwell Hardness of MetallicMaterialsE29 Practice for Using Significant Digits in Test Data to1This test method is u
15、nder the jurisdiction of ASTM Committee F16 onFasteners and is the direct responsibility of Subcommittee F16.93 on QualityAssurance Provisions for Fasteners.Current edition approved Sept. 1, 2007. Published September 2007. Originallypublished as approved in 1998. Last previous edition approved in 20
16、07 asF 1940 07.2Hydrogen Embrittlement Testing, ASTM STP 543, American Society forTesting and Materials, 1974.3Hydrogen Embrittlement; Prevention and Control, ASTM STP 962, AmericanSociety for Testing and Materials, 1985.4For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact
17、 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.Determine Conformance wit
18、h SpecificationsE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 1823 Terminology Re
19、lating to Fatigue and Fracture Test-ingF 519 Test Method for Mechanical Hydrogen Embrittle-ment Evaluation of Plating/Coating Processes and ServiceEnvironmentsF 1137 Specification for Phosphate/Oil and Phosphate/Organic Corrosion Protective Coatings for FastenersF 1624 Test Method for Measurement of
20、 Hydrogen Em-brittlement Threshold in Steel by the Incremental StepLoading TechniqueF 1941 Specification for Electrodeposited Coatings onThreaded Fasteners (Unified Inch Screw Threads (UN/UNR)G5 Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization Measurements2.2 SA
21、E Standards:AMS 2759 Hot Drawn, Normalized and Tempered SteelBars. UNS G43406 (AISI E 4340)5AMS 3078 Corrosion Preventive Compound, Solvent Cut-back, Cold-Application5AMS 641553. Terminology3.1 Terms and Symbols Specific to This Standard:3.1.1 environmental hydrogen embrittlement (EHE)testconducted
22、in a specified environmentembrittlement causedby hydrogen introduced into steel from external sources.3.1.2 internal hydrogen embrittlement (IHE)test con-ducted in airembrittlement caused by residual hydrogenfrom processing3.1.3 ISLththreshold from an incremental step load test ona plated or process
23、ed specimen.3.1.4 NFS(B)notched fracture strength in air of a barespecimen in bending at loading rates of 50 to 250 ksi/min (350to 1700 MPa/min).3.1.5 NFS(B)F 1624notched fracture strength in air of abare specimen in bending at Test Method F 1624 step loadingrates.3.1.6 processa defined event or seq
24、uence of events thatmay include pretreatments, plating, or coating and posttreat-ments that are being evaluated or qualified.3.1.7 thresholdthe maximum load at the onset of crackingthat is identified by a 5 % drop in load of NSF(B)F 1624underdisplacement control.4. Summary of Test Method4.1 Specimen
25、s of fixed geometry, certified to have been heattreated to a hardness range of 50 to 52 HRC, and which havebeen certified to exhibit sensitivity to embrittlement from traceamounts of residual hydrogen in steel, are processed withactual parts.4.2 An unstressed test specimen is processed in accordance
26、with the plating or coating process being qualified. Thespecimen is then tested under incremental step load to measurethe threshold stress. The loading rate must be slow enough toensure that the threshold stress will be detected if deleteriousamounts of hydrogen are present in “worst case” sensitize
27、dspecimens. Loading rate protocols are defined in 9.2 and TestMethod F 1624.4.3 If the threshold in air of the specimen is $75 %NFS(B)F 1624, then the process is considered as to not producesufficient hydrogen to induce time delayed IHE failures in theplated or coated fasteners. See 9.3 for optional
28、 limits.4.4 If the threshold in air of the specimen is 75 % NFS(B)F 1624threshold used to qualifythe process is specified as a minimum value for individual data.If statistical limits are to be applied, they are to be establishedthrough agreement between the manufacturer and purchaser.11. Report11.1
29、A test report shall be produced upon completion oftesting that bears the following minimum information:11.1.1 A specimen lot acceptance and sensitivity certifica-tion report,11.1.2 Identification of the process line,11.1.3 A description of the plating or coating process,11.1.4 The threshold load, or
30、 percent of notched fracturestrength or notch bend strength of bare specimens, as appro-priate,11.1.5 The time under load, and11.1.6 Disposition of the results.12. Precision and Bias12.1 PrecisionAn interlaboratory test program7was de-signed to estimate the precision of the ISL test as it applies to
31、this test method. The experimental results were entirely gen-erated using notched square bar standard test specimens. Two7Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: F161000.TABLE 4 Minimum Requirements for a Step-Loading Pr
32、ofile forAccelerated (#24 h) Incremental Step Load ThresholdDetermination%NFSF 1624#h (h %NFSF 1624#h (h %NFSF 1624#h (h10 1 1 65 1 8 85 1 1520 1 2 70 1 9 90 1 1630 1 3 72 1 10 95 1 1740 1 4 74 1 11 100 1 1850 1 5 76 1 12 105 1 1955 1 6 78 1 13 110 1 2060 1 7 80 1 14 . . .TABLE 5 Within Laboratory N
33、otch Fracture Strength,NFS(Baseline)Summary of ResultsSQBsTestedNAvg.xStd. DevsMin. Max.95 %Repeat-abilityLimitrStudy 1 37 219.5 6.52 204.4 232.1 18.26Study 2 30 218.5 4.22 210.8 225.9 11.82Average of study averages, x= 219.0Average of study standard deviations, s= 5.37TABLE 6 Precision StatisticsIm
34、posedPotentialFractureStrengthAveragexRepea-tabilityStandardDeviationSrReprod-ucibilityStandardDeviationSR95 %Repeat-abilityLimitr95 %Reprod-ucibilityLimitR-1.2 V 71.22 9.88 9.88 27.66 27.66-1.0 V 85.12 9.70 9.70 27.15 27.15-0.9 V 102.97 10.02 10.02 28.06 28.06-0.8 V 179.33 9.77 12.44 27.35 34.83AIR
35、 221.82 5.81 7.16 16.27 20.06F 1940 07a5testing modes were used; testing in air (that is, no imposedpotential) and testing under potential (for simulated hydrogencharging conditions).12.1.1 Within Laboratory StudyIn this part of the testprogram, a large number of specimens (minimum 30) weretested in
36、 air within 1 laboratory to estimate repeatability withina single laboratory. The time span for testing 30 specimens wasapproximately 8 weeks. This was due to the length of the testcycle, which can be as long as 24 h. Therefore, to detect anysystematic shift in the values generated by the test appar
37、atus,this test was repeated twice in the space of 1 year. Thesummary results of the study are presented in Table 5.The term repeatability limit is used as specified in PracticeE 177.12.1.2 Interlaboratory StudyFour testing facilities8, eachusing a single ISL loading frame, participated in the study.
38、With the exception of the number of participating laboratories,four instead of a minimum of six, the study was modeled onPractice E 691.9The study consisted of testing square barspecimens at five different conditions, four at different appliedpotentials, 0.8, -0.9, -1.0, and -1.2 V and one in air. E
39、achlaboratory performed five replicate tests for each condition.The precision statistics are presented in Table 6.The terms repeatability limit and reproducibility limit areused as specified in Practice E 177.12.2 Bias:12.2.1 To eliminate any bias of results as a result ofvariation in the conditions
40、 of specimen manufacture, all thespecimens used for this study were E4340 notched square barspecimens, obtained from a single controlled production lot,manufactured with minimal variation. Therefore, note thatvariance within the specimen population, however minimal,was implicitly considered in the p
41、recision estimates.12.2.2 All of the instruments were subject to normal cali-bration procedures by the equipment manufacturer.Any resultsobtained through obvious error in procedure or equipmentmalfunction were disqualified from the study.12.2.3 This method has no bias because comparative mea-suremen
42、t of hydrogen embrittlement is defined only in terms ofthis test method.12.2.4 Random lot-to-lot bias in the properties of square barspecimens related to raw material or specimen manufacturemay exist. This test method produces a quantitative fractionalmeasure based on the baseline fracture strength
43、of square barspecimens not exposed to hydrogen. Since there is no univer-sally accepted reference or laboratory suitable for determiningthe bias for square bar specimens, no justifiable statement ofbias can be made in relation to the baseline fracture strength ofspecimens. However, lot-to-lot bias f
44、or square bar specimensdoes not affect the test fractional results provided a baselinefracture strength is established for every lot of square barspecimens.13. Keywords13.1 coating; delayed failure; displacement control; EHE;fasteners; hydrogen embrittlement; IHE; incremental step load;loading rate;
45、 plating; steel; thresholdAPPENDIXES(Nonmandatory Information)X1. ALTERNATE SQUARE BAR THRESHOLD DETERMINATION FOR SPECIFIC PRODUCT LOTSX1.1 ScopeX1.1.1 Since embrittlement related to hydrogen content canvary with hardness, actual fasteners made of low-strength steelmight have more tolerance for res
46、idual hydrogen because ofthe process and might not need the rigorous requirement setforth in this standard for threshold. Therefore, adjustments inthreshold requirements can be made for a specific lot offasteners once a correlation is established.NOTE X1.1Note that embrittlement related to hydrogen
47、can also varywith other metallurgical and chemical characteristics of steel and that“low-strength steel” is not always a predictor of more tolerance forresidual hydrogen.X1.1.2 To obtain a correlation between actual productionfasteners from singular lots and specimen threshold levels inthis standard
48、, the threshold level or hydrogen tolerance levelfor the production hardware can be measured using four-pointbending in accordance with Test Method F 1624 as a functionof an applied electrical potential verses a saturated calomelelectrode, (SCE) in a 3.5 % sodium chloride solution. Anexample of four
49、-point bend fixturing used for Test MethodF 1624 testing is shown in Fig. X1.1 in which the tensile stressin bending, sb, at the root of the thread can be computed usingthe following formula:sb5 32 M/pDt3! (X1.1)where:Dt= minimum thread diameter (inch) andM = applied moment (inch-pounds) which = Pb* l.X1.1.3 Once the threshold for the product has been deter-mined as a function of the applied potential, the percentfracture strength for the measured thresholds at each potentialare plotted as shown in Fig. X1.2. A statistical response in thedata must be expected, and
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