ASTM F1624-12(2018)

Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique

SIGNIFICANCE AND USE
5.1 This test method is used for research, design, service evaluation, manufacturing control, and development. This test method quantitatively measures stress parameters that are used in a design or failure analysis that takes into account the effects of environmental exposure including that which occurs during processing, such as plating (8) (ASTM STP 962).  
5.2 For plating processes, the value of σth-IHE is used to specify quantitatively the maximum operating stress for a given structure or product.  
5.3 For quality control purposes, an accelerated test is devised that uses a specified loading rate, which is equal to or lower than the loading rate necessary to determine the threshold stress (see 8.1).  
5.4 For fasteners, the value of σth-IHE is used to specify quantitatively the maximum stress during installation and in service to avoid premature failure caused by residual hydrogen in the steel as a result of processing.  
5.5 For fasteners, the value of σth-EHE is used to specify quantitatively the maximum stress during installation and in service to avoid failure from hydrogen absorbed during exposure to a specific environment.  
5.6 To measure the relative susceptibility of steels to hydrogen pickup from various fabrication processes, a single, selected, discriminating rate is used to rank the resistance of various materials to hydrogen embrittlement.  
5.7 Annex A1 describes the application of this standard test method to hydrogen embrittlement testing of fasteners.
SCOPE
1.1 This test method establishes a procedure to measure the susceptibility of steel to a time-delayed failure such as that caused by hydrogen. It does so by measuring the threshold for the onset of subcritical crack growth using standard fracture mechanics specimens, irregular-shaped specimens such as notched round bars, or actual product such as fasteners (2) (threaded or unthreaded) springs or components as identified in SAE J78, J81, and J1237.  
1.2 This test method is used to evaluate quantitatively:  
1.2.1 The relative susceptibility of steels of different composition or a steel with different heat treatments;  
1.2.2 The effect of residual hydrogen in the steel as a result of processing, such as melting, thermal mechanical working, surface treatments, coatings, and electroplating;  
1.2.3 The effect of hydrogen introduced into the steel caused by external environmental sources of hydrogen, such as fluids and cleaners maintenance chemicals, petrochemical products, and galvanic coupling in an aqueous environment.  
1.3 The test is performed either in air, to measure the effect if residual hydrogen is in the steel because of the processing (IHE), or in a controlled environment, to measure the effect of hydrogen introduced into the steel as a result of the external sources of hydrogen (EHE) as detailed in ASTM STP 543.  
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
Note 1: The values stated in metric units may not be exact equivalents. Conversion of the inch-pound units by appropriate conversion factors is required to obtain exact equivalence.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2018
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: F07 - Aerospace and Aircraft
• Drafting Committee: F07.04 - Hydrogen Embrittlement

Relations

• Replaces: ASTM F1624-12 - Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique
• Effective Date: 01-Nov-2018
• Refers: ASTM F519-23 - Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• Effective Date: 01-Dec-2023
• Refers: ASTM E1681-23e1 - Standard Test Method for Determining Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials
• Effective Date: 01-May-2023
• Refers: ASTM F519-18 - Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• Effective Date: 01-Nov-2018
• Refers: ASTM F519-17a - Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• Effective Date: 01-Dec-2017
• Refers: ASTM F519-17 - Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• Effective Date: 01-Mar-2017
• Refers: ASTM A574-16 - Standard Specification for Alloy Steel Socket-Head Cap Screws
• Effective Date: 01-Oct-2016
• Refers: ASTM G5-14 - Standard Reference Test Method for Making Potentiodynamic Anodic Polarization Measurements
• Effective Date: 01-Nov-2014
• Refers: ASTM A490-14a - Standard Specification for Structural Bolts, Alloy Steel, Heat Treated, 150 ksi Minimum Tensile Strength (Withdrawn 2016)
• Effective Date: 01-Sep-2014
• Refers: ASTM A490-14 - Standard Specification for Structural Bolts, Alloy Steel, Heat Treated, 150 ksi Minimum Tensile Strength
• Effective Date: 01-Aug-2014
• Refers: ASTM F606-14 - Standard Test Methods for Determining the Mechanical Properties of Externally and Internally Threaded Fasteners, Washers, Direct Tension Indicators, and Rivets
• Effective Date: 01-Jul-2014
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM F519-13 - Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• Effective Date: 01-Dec-2013
• Refers: ASTM F606-13 - Standard Test Methods for Determining the Mechanical Properties of Externally and Internally Threaded Fasteners, Washers, Direct Tension Indicators, and Rivets
• Effective Date: 01-Nov-2013
• Refers: ASTM E1681-03(2013) - Standard Test Method for Determining Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials
• Effective Date: 15-Oct-2013

Overview

ASTM F1624-12(2018) is the internationally recognized standard test method for measuring the hydrogen embrittlement threshold in steels using the Incremental Step Loading Technique. Developed by ASTM, this method delivers a quantitative assessment of steel’s susceptibility to hydrogen-induced delayed failure. The procedure uses fracture mechanics specimens, notched round bars, and actual product items such as fasteners or springs to determine the threshold for subcritical crack growth as a function of environmental exposure and material properties.

Hydrogen embrittlement can occur during manufacturing processes like plating or from in-service exposure to hydrogen sources. This standard provides an accelerated protocol for determining threshold stress or stress intensity, facilitating timely and informed design, quality control, and failure analysis.

Key Topics

• Hydrogen Embrittlement in Steel: Understanding time-delayed failure due to the introduction of hydrogen either during processing or from environmental exposure.
• Incremental Step Loading Technique: A method for progressively increasing load to determine the onset of subcritical crack growth, reducing the number of specimens and total test time compared to other methods.
• Threshold Stress and Intensity Factors: Quantitative metrics such as threshold stress (σth) and threshold stress intensity factor (KI) for both internally stored hydrogen (IHE) and environmental hydrogen (EHE).
• Applicability to Different Specimens: Protocols for standard fracture mechanics specimens, irregular shapes, and real-world components, especially fasteners as addressed in the annex.
• Test Environments: Procedures in air (for IHE) and in controlled hydrogen-charging environments (for EHE).
• Loading Profiles: Specific incremental loading strategies based on steel hardness, optimizing sensitivity and test duration.

Applications

The ASTM F1624-12(2018) standard is widely used across industries where steel components are at risk of hydrogen embrittlement, particularly in:

• Research and Development: Comparing the susceptibility of different steel grades or heat treatments to hydrogen embrittlement to optimize materials selection.
• Design and Failure Analysis: Quantifying maximum allowable stresses in components, such as fasteners, to prevent time-delayed hydrogen-assisted cracking.
• Manufacturing and Quality Control: Establishing acceptance criteria for steel products after processing, especially those subjected to electroplating, surface treatments, or other operations where hydrogen uptake is possible.
• Service Evaluation: Monitoring steel parts exposed to aggressive service environments, including fluids, chemicals, or cathodic protection systems.
• Fasteners and Springs: Specifying maximum installation and service stresses to avoid premature failure due to residual or environmentally absorbed hydrogen.
• Coating and Plating Evaluation: Assessing the risk of hydrogen embrittlement introduced by various fabrication and coating processes, both for bare and coated steel components.

Related Standards

Many referenced and related standards further enhance the practical applicability of ASTM F1624-12(2018):

• ASTM E1681: Test Method for Determining Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials
• ASTM F519: Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• ASTM E399: Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIC of Metallic Materials
• ASTM E8: Test Methods for Tension Testing of Metallic Materials
• SAE J78, J81, J1237: Standards for self-drilling tapping screws and thread rolling screws relevant to fastener testing
• ASTM STP 543 & ASTM STP 962: Technical publications on hydrogen embrittlement testing and prevention

Other standards such as ANSI/ASME B18.18 series relate to inspection and quality assurance for fasteners, supporting comprehensive quality control programs in accordance with ASTM F1624-12(2018).

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By following ASTM F1624-12(2018), engineers and manufacturers ensure robust, data-driven decisions when evaluating steels for critical applications exposed to hydrogen, helping to mitigate risks, improve reliability, and meet international best practices for hydrogen embrittlement resistance.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F1624 − 12 (Reapproved 2018)
Standard Test Method for
Measurement of Hydrogen Embrittlement Threshold in Steel
by the Incremental Step Loading Technique
This standard is issued under the fixed designation F1624; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Hydrogen embrittlement is caused by the introduction of hydrogen into steel that can initiate
fracture as a result of residual stress or in service when external stress is applied (1). The hydrogen
can be generated during cleaning or plating processes or the exposure of cathodically protected steel
parts to a service environment including fluids, cleaning treatments, or maintenance chemicals that
maycontactthesurfaceofsteelcomponents.Thismethodcanbeusedtorapidlydeterminetheeffects
ofresidualhydrogeninapartcausedbyprocessingorquantifytherelativesusceptibilityofamaterial
under a fixed set of hydrogen-charging conditions.
The combined residual and applied stress above which time-delayed fracture will occur (finite life)
orbelowwhichfracturewillneveroccur(infinitelife)iscalledthethresholdstressorthresholdstress
intensity (K) for precracked specimens. Historically, sustained load time-to-failure tests have been
conductedonnotchedbarstodeterminethethresholdstressfortheonsetofhydrogenstresscracking.
This technique may require 12 to 14 specimens and several high-load capacity machines. For
precrackedspecimens,therun-outtimecanbeaslongasfourtofiveyearsperU.S.Navyrequirements
for low-strength steels at 33 to 35 HRC. In Test Method E1681, more than 10000 h (> one year) are
specified for low-strength steel (< 175 ksi) and 5000 h for high-strength steel (> 175 ksi).
This standard provides an accelerated method to measure the threshold stress or threshold stress
intensityasdefinedinTestMethodE1681fortheonsetofhydrogenstresscrackinginsteelwithinone
weekononlyonemachine.Thespecificapplicationofthisstandardtohydrogenembrittlementtesting
of fasteners is described in Annex A1.
1. Scope 1.2.2 The effect of residual hydrogen in the steel as a result
of processing, such as melting, thermal mechanical working,
1.1 This test method establishes a procedure to measure the
surface treatments, coatings, and electroplating;
susceptibility of steel to a time-delayed failure such as that
1.2.3 Theeffectofhydrogenintroducedintothesteelcaused
caused by hydrogen. It does so by measuring the threshold for
by external environmental sources of hydrogen, such as fluids
the onset of subcritical crack growth using standard fracture
mechanics specimens, irregular-shaped specimens such as and cleaners maintenance chemicals, petrochemical products,
notched round bars, or actual product such as fasteners (2) and galvanic coupling in an aqueous environment.
(threadedorunthreaded)springsorcomponentsasidentifiedin
1.3 The test is performed either in air, to measure the effect
SAE J78, J81, and J1237.
if residual hydrogen is in the steel because of the processing
1.2 This test method is used to evaluate quantitatively:
(IHE), or in a controlled environment, to measure the effect of
1.2.1 The relative susceptibility of steels of different com-
hydrogen introduced into the steel as a result of the external
position or a steel with different heat treatments;
sources of hydrogen (EHE) as detailed in ASTM STP 543.
1.4 Thevaluesstatedininch-poundunitsaretoberegarded
This test method is under the jurisdiction of ASTM Committee F07 on
as standard. The values given in parentheses are mathematical
Aerospace andAircraft and is the direct responsibility of Subcommittee F07.04 on
conversions to SI units that are provided for information only
Hydrogen Embrittlement.
and are not considered standard.
Current edition approved Nov. 1, 2018. Published December 2018. Originally
approved in 1995. Last previous edition approved in 2012 as F1624–12. DOI:
NOTE1—Thevaluesstatedinmetricunitsmaynotbeexactequivalents.
10.1520/F1624-12R18.
Conversion of the inch-pound units by appropriate conversion factors is
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. required to obtain exact equivalence.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1624 − 12 (2018)
1.5 This standard does not purport to address all of the J1237Metric Thread Rolling Screws
safety concerns, if any, associated with its use. It is the 2.3 ANSI/ASME:
responsibility of the user of this standard to establish appro- B18.18.2MInspection and Quality Assurance for High-
priate safety, health, and environmental practices and deter- Volume Machine Assembly Fasteners, 1987
mine the applicability of regulatory limitations prior to use. B18.18.3MInspection and Quality Assurance for Special
1.6 This international standard was developed in accor- Purpose Fasteners, 1987
dance with internationally recognized principles on standard- B18.18.4MInspection and Quality Assurance for Fasteners
ization established in the Decision on Principles for the for Highly Specialized Engineering Applications, 1987
Development of International Standards, Guides and Recom- 2.4 Related Publications:
mendations issued by the World Trade Organization Technical ASTM STP 543, Hydrogen Embrittlement Testing, 1974
Barriers to Trade (TBT) Committee. ASTM STP 962,Hydrogen Embrittlement: Prevention and
Control, 1985
2. Referenced Documents
3. Terminology
2.1 ASTM Standards:
3.1 Symbols—Termsnotdefinedinthissectioncanbefound
A490Specification for Structural Bolts, Alloy Steel, Heat
in Terminologies F2078 and E6 and shall be considered as
Treated, 150 ksi Minimum Tensile Strength (Withdrawn
applicable to the terms used in this test method.
2016)
3.1.1 P—applied load.
A574SpecificationforAlloySteelSocket-HeadCapScrews
3.1.2 P —critical load required to rupture a specimen using
B602Test Method for Attribute Sampling of Metallic and
c
Inorganic Coatings a continuous loading rate.
E4Practices for Force Verification of Testing Machines
3.1.3 P—crack initiation load for a given loading and
i
E6Terminology Relating to Methods of MechanicalTesting
environmental condition using an incrementally increasing
E8Test Methods for Tension Testing of Metallic Materials
load under displacement control.
[Metric] E0008_E0008M
3.1.4 P —the invariant threshold load. P is the basis for
th th
E29Practice for Using Significant Digits in Test Data to
calculatingthethresholdstressorthethresholdstressintensity.
Determine Conformance with Specifications
3.1.5 P —the threshold load at a specified loading rate.
E399Test Method for Linear-Elastic Plane-Strain Fracture th-n
Toughness K of Metallic Materials
3.1.6 EHE—Environmental Hydrogen Embrittlement —
Ic
E812Test Method for Crack Strength of Slow-Bend Pre-
test conducted in a specified hydrogen-charging environment.
cracked Charpy Specimens of High-Strength Metallic
3.1.7 IHE—Internal Hydrogen Embrittlement — test con-
Materials (Withdrawn 2005)
ducted in air.
E1681Test Method for DeterminingThreshold Stress Inten-
3.1.8 th—threshold — the lowest load at which subcritical
sityFactorforEnvironment-AssistedCrackingofMetallic
cracking can be detected.
Materials
3.2 Irregular Geometry-Type Specimens—test sample other
F519Test Method for Mechanical Hydrogen Embrittlement
than a fracture mechanics-type specimen; examples include a
Evaluation of Plating/Coating Processes and Service En-
notched round bar or fastener.
vironments
3.2.1 σ=applied stress.
F606Test Methods for Determining the Mechanical Proper-
3.2.2 σ =netstressbasedonareaatminimumdiameterof
net
ties of Externally and Internally Threaded Fasteners,
notched round bar or per Test Method E812 for bend speci-
Washers, and Rivets (Metric) F0606_F0606M
mens.
F2078Terminology Relating to Hydrogen Embrittlement
3.2.3 σ =stress at crack initiation.
i
Testing
3.2.4 σ =threshold stress.
th
G5Reference Test Method for Making Potentiodynamic
3.2.5 σ =EHE threshold stress — test conducted in a
th-EHE
Anodic Polarization Measurements
specified hydrogen charging environment — geometry depen-
G129Practice for Slow Strain Rate Testing to Evaluate the
dent.
Susceptibility of Metallic Materials to Environmentally
3.2.6 σ =IHE threshold stress — test conducted in air
th-IHE
Assisted Cracking
— geometry dependent.
3.2.7 FFS=Fast Fracture Strength.
2.2 SAE Standards:
3.2.8 K =EHE threshold stress intensity at a specified
J78Self-Drilling Tapping Screws
th-EHE
J81Thread Rolling Screws loadingrate—testconductedinaspecifiedhydrogencharging
environment — not geometry dependent.
3.2.9 K =IHE threshold stress intensity at a specified
th-IHE
For referenced ASTM standards, visit the ASTM website, www.astm.org, or loading rate — test conducted in air — not geometry depen-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
dent.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
The last approved version of this historical standard is referenced on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
www.astm.org. 4th Floor, New York, NY 10036.
5 7
Available from Society of Automotive Engineers (SAE), 400 Commonwealth Available from ASTM, 100 Barr Harbor Dr., PO Box C700, West
Dr., Warrendale, PA 15096-0001. Conshohocken, PA 19428.
F1624 − 12 (2018)
3.2.10 KI =invariant value of the EHE threshold stress 5.4 For fasteners, the value of σ is used to specify
EHE th-IHE
intensity — test conducted in a specified hydrogen charging quantitatively the maximum stress during installation and in
environment — not geometry dependent — equivalent to servicetoavoidprematurefailurecausedbyresidualhydrogen
KI . in the steel as a result of processing.
EAC
3.2.11 KI =invariant value of the IHE threshold stress
IHE
5.5 For fasteners, the value of σ is used to specify
th-EHE
intensity — test conducted in air — not geometry dependent.
quantitatively the maximum stress during installation and in
3.2.12 KI =invariant value of the threshold stress inten-
SCC
service to avoid failure from hydrogen absorbed during expo-
sity for stress corrosion cracking—test conducted under open
sure to a specific environment.
circuit corrosion potential or freely corroding conditions—not
5.6 Tomeasuretherelativesusceptibilityofsteelstohydro-
geometry dependent.
gen pickup from various fabrication processes, a single,
3.2.13 SCG=Subcritical Crack Growth.
selected, discriminating rate is used to rank the resistance of
4. Summary of Test Method
various materials to hydrogen embrittlement.
4.1 The test method is based on determining the onset of
5.7 AnnexA1 describes the application of this standard test
subcritical crack growth with a step modified, incrementally
method to hydrogen embrittlement testing of fasteners.
increasing,slowstrainratetest(PracticeG129)underdisplace-
ment control (3), (4), (5).
6. Apparatus
4.2 This test method measures the load necessary to initiate
6.1 Testing Machine—Testing machines shall be within the
a subcritical crack in the steel at progressively decreasing
guidelines of calibration, force range, resolution, and verifica-
loadingrates,forspecimensofdifferentgeometryanddifferent
tion of Practices E4.
environmental conditions.
6.2 Gripping Devices—Various types of gripping devices
4.2.1 By progressively decreasing the loading rate, the
shallbeusedineithertensionorfour-pointbendingtotransmit
threshold stress can be determined.
the measured load applied by the testing machine to the test
4.3 Four-point bending is used to maintain a constant
specimen.
momentalongthespecimen.Thisconditionisusedtosimplify
6.3 Test Environment—The test shall be conducted in air or
thecalculationofstressorstressintensityforanirregularcross
anyothersuitablecontrolledenvironmentusinganappropriate
section.
inert container.
4.4 The minimum or invariant value of the stress intensity
6.3.1 Potentiostatic Control—The corrosion potential of the
(KI ,KI ,orKI ) or stress for a given geometry with
SCC IHE EHE
specimen can be controlled with a reference saturated calomel
regardtotheloadingrate,isthethresholdfortheonsetofcrack
electrode (SCE) or equivalent reference electrode such as
growth due to hydrogen embrittlement.
Ag/AgCl in accordance with Test Method G5. The imposed
4.5 In tension (T) and bending (B), the onset of SCG as a potential is typically cathodic, ranging from 0.0 to −1.2 V
result of hydrogen in steel is identified by a concave decrease
versus SCE (V ) in a 3.5 weight percent NaCl solution (9).
SCE
inloadwhileholdingthedisplacementconstant.Atnetsection 8
6.4 Equipment, such as RSL (trademarked), for determin-
yielding or above, a convex load drop is also observed.
ing the onset of SCG with a step modified, incrementally
4.6 The displacement is incrementally increased in tension
increasing, slow strain rate test under displacement control.
or four-point bending and the resulting load is monitored.
While the displacement is held constant, the onset of subcriti- 7. Sampling and Test Specimens
cal crack growth is detected when the load decreases.
7.1 Sampling—For research, design, and service evaluation
4.7 The loading rate must be sufficiently slow to permit
and development, the sampling size depends on the specific
hydrogentodiffuseandinducecrackingthatmanifestsitselfas
requirements of the investigator. For manufacturing control,
a degradation in strength (see Pollock (6) and (7)).
loading rates shall be fixed, but statistically significant sam-
pling sizes are used such as Test Methods F606,ANSI/ASME
5. Significance and Use
B18.18.2M, B18.18.3M, or B18.18.4M andTest Method B602
5.1 This test method is used for research, design, service
for fasteners. For other quality assurance tests, the sampling
evaluation, manufacturing control, and development. This test
size shall be in compliance with the requirements of the
methodquantitativelymeasuresstressparametersthatareused
specification.
inadesignorfailureanalysisthattakesintoaccounttheeffects
7.2 Test Specimens—The test specimen should be classified
of environmental exposure including that which occurs during
as either fracture mechanics-type specimens or irregular-
processing, such as plating (8) (ASTM STP 962).
shaped specimens (10).
5.2 For plating processes, the value of σ is used to
th-IHE
specify quantitatively the maximum operating stress for a
given structure or product.
The sole source of supply of the apparatus known to the committee at this time
is Fracture Diagnostics International, 20261 SW Acacia St., Newport Beach, CA
5.3 For quality control purposes, an accelerated test is
92660,http://www.fracturediagnostics.net.Ifyouareawareofalternativesuppliers,
devised that uses a specified loading rate, which is equal to or
please provide this information to ASTM International Headquarters. Your com-
lower than the loading rate necessary to determine the thresh-
ments will receive careful consideration at a meeting of the responsible technical
old stress (see 8.1). committee, which you may attend.
F1624 − 12 (2018)
7.2.1 Fracture mechanics-type specimens are defined in 8.1.4 The load P is the threshold load, which is the load
th-n
standards such as Test Method E399. corresponding to the step before the onset of crack growth for
a specific loading rate.
NOTE2—Themaximumstressusedduringfatigueprecrackingmustbe
8.1.5 Theinvariantthresholdloadfortheonsetofhydrogen
less than 60% of any measured value of load for crack initiation for the
induced stress cracking P , is used to calculate KI ,KI ,
data to be valid.
th EHE SCC
or KI . The invariant threshold load is attained when the
IHE
7.2.2 Irregular geometry-type specimens shall be either
difference between two subsequent threshold loads is less than
specimensasdefinedinstandardssuchasTestMethodF519or
5%of P . The value of P , P ,or P is the
FFS th-EHE th-SCC th-IHE
specimens from product. The product shall be tested either
lowest measured threshold value.
substantially full size or as a machined specimen.
8.1.6 Referencing Fig. 1, the step load testing protocol can
be summarized as follows:
8. Procedure
SN(1)–Baseline: fast fracture test of specimen after plating to
8.1 Determination of Threshold Load (P ):
th
measure P = P . (This ensures that no cracks initiated or
MAX FFS
8.1.1 This test protocol requires that a minimum of three
softening occurred during the plating process)
samplesbetestedtoestablishthethresholdload, P .Loadone
th
For the hardness range of >54 HRC (see Fig. 1)
sample to rupture at a rate consistent with Test Methods E8 to
SN(2)–(20/5/1) @ P = P ;→ P
MAX FFS th-1
establish the fast fracture strength (FFS) or load, P , for a
SN(3)–(20/5/1) @ P = 1.1 × P ;→ P
MAX th-1 th-2
FFS
SN(4)–(20/5/1) @ P = 1.1 × P ;→ P
MAX th-2 th-3
given specimen geometry, (P = P in Fig. 1). This test
FFS c
and if necessary;
provides the baseline reference data.
SN(5)–(20/5/1) @P = 1.1 × P ;→ P
MAX th-3 th-4
8.1.2 The specific load profile depends on the hardness of measures P , P ,or P when ∆P # 5% P
th-EHE th-SCC th-IHE th FFS
the samples within the ranges of ≥33 HRC to 45 HRC; >45
or,
HRC to 54 HRC; and >54 HRC. The notation used for the
For the hardness range of >45 HRC to 54 HRC (see Fig. 2)
incremental step load profile is (# / %P /hrs) where # is the SN(2)–(10/5/1,2) @ P = P ;→ P
MAX FFS th-1
MAX
SN(3)–(10/5/1,2) @ P = 1.1 × P ;→ P
MAX th-1 th-2
number of steps, % P is the percent of the maximum
MAX
SN(4)–(10/5/1,2) @ P = 1.1 × P ;→ P
MAX th-2 th-3
anticipated load at each step, and hrs is the hold time for each
and if necessary;
SN(5)–(10/5/1,2) @ P = 1.1 × P ;→ P
step. For the hardness range of ≥33 HRC to 45 HRC, the
MAX th-3 th-4
measures P , P ,or P when ∆P # 5%P
th-EHE th-SCC th-IHE th FFS
loading profile is (10/5/2,4) or an initial loading profile of 10
steps at5%of P at each step for a hold time of 2 h,
FFS or,
followedby10stepsat5%ofP ateachstepforaholdtime For the hardness range of$33 HRC to 45 HRC (see Fig. 3)
FFS
SN(2)–(10/5/2,4) @ P = P ;→ P
MAX FFS th-1
of 4 h. Correspondingly, for hardness range of >45 HRC to 54
SN(3)–(10/5/2,4) @ P = 1.1 × P ;→ P
MAX th-1 th-2
HRC, the loading profile is (10/5/1,2) and for >54 HRC, the
SN(4)–(10/5/2,4) @ P = 1.1 × P ;→ P
MAX th-2 th-3
and if necessary;
loading profile is (20/5/1).
SN(5)–(10/5/2,4) @ P = 1.1 × P ;→ P
MAX th-3 th-4
8.1.3 In addition to the specific load profile, the subsequent
measures P , P ,or P when ∆P # 5% P
th-EHE th-SCC th-IHE th FFS
P for each load profile is set to 1.1 times the P of the
MAX th-n
previous test. The purpose of changing the maximum profile
load is to reduce the loading rate and increase the resolution
because each subsequent test sample results in a smaller step
load.
FIG. 1 Schematic of a (20/5/1) Step Loading Profile to Determine FIG. 2 Schematic of a (10/5/1,2) Step Loading Profile to Deter-
Threshold for the Hardness of Steel >54 HRC mine Threshold for the Hardness of Steel >45 HRC to 54 HRC
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*
NOTE 1— See Fig. 5 for calculation of additional increment.
FIG. 3 Schematic of a (10/5/2,4) Step Loading Profile to Deter-
mine Threshold for the Hardness of Steel$ 33 HRC to 45 HRC
FIG. 4 Definition of Crack Initiation Load, P Load and Threshold
I
Load,P
th
8.1.7 Crack growth shall be considered to have occurred if
the measured load on a sample drops by more than the
established accuracy of the test apparatus, while the displace-
ment is held constant, with the exception identified in 8.1.7.1.
8.1.7.1 The threshold is calculated from the load at the last
step to maintain the load for the duration of the step. The
threshold is defined as the stress or stress intensity calculated
from the load at the onset of crack growth. A 5% NFS load
drop is used as an arbitrary guideline for the measurement of
the onset of crack growth and is appropriate for materials with
a rapid crack growth rate. For materials with extremely slow
crack growth rates, a lesser value of load drop should be
utilized that is more consistent with the visual detection of a
load drop.
FIG. 5 Extrapolation Method for Type A Threshold Load Determi-
8.1.7.2 Any load drop depicted as an increasing rate (con- nation
vex) shall be attributed to SCG in the specimen. The load is
defined as the crack initiation load, P(see Fig. 4,TypeA).The
i
8.1.11 Verification of crack growth is obtained by loading
thresholdload,P ,isthestepbeforeinitiationofcrackgrowth.
th
the tested specimen to fracture. Methods such asTest Methods
8.1.8 If the load is maintained for only a fraction of the
E8 or Test Method E399 shall be used. Fractographic analysis
duration of the step (x), prior to SCG, the threshold can be
may be used to verify the existence of subcritical cracking.
estimatedtobeanadditionalincrementabovethelastcomplete
step (y) by a corresponding fractional amount of the step; that
9. Calculations
is, ∆ = (x/y) of 5 % P used in the example in Fig. 5.If
max
9.1 Stress parameters are calculated from the load measure-
cracking begins immediately on reaching the next step (x = 0,
ments in section 8.1.
Fig. 5), then use the previous load as the threshold, P .
th
8.1.9 Anyloaddropdepictedasadecreasingrate(concave)
9.2 The relationship between load and net stress (σ )is
net
shall be attributed to plasticity or creep in the specimen. This
givenasP/A fortensilespecimensandMy/IperTestMethod
net
is not considered crack growth and is not defined as the crack
E812 for bend specimens,
initiation load, P (see Fig. 4, Type B). This behavior only
i
where:
occurs when the stress at the crack tip attains or exceeds the
A = net cross-sectional area,
yield strength of the material. This is not a threshold value. net
M = the applied moment,
8.1.10 The load at the transition from a constant or decreas-
y = the distance from the neutral axis to the stressed
ing rate to an increasing rate (concave to convex) is defined as
ligament, and
the crack initiation load, P (see Fig. 4,Type C).The threshold
i
I = the cross-sectional moment of inertia.
load, P , is the step before initiation of crack growth.
th
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9.3 Theultimatetensilestrength(UTS)perTestMethodsE8 10.2.3 Report the fracture load and any maximum fracture
is given as P /A . stress or
...