ASTM F2078-01
(Terminology)Standard Terminology Relating to Hydrogen Embrittlement Testing
Standard Terminology Relating to Hydrogen Embrittlement Testing
SCOPE
1.1 This terminology covers the principal terms, abbreviations, and symbols relating to mechanical methods for hydrogen embrittlement testing. These definitions are published to encourage uniformity of terminology in product specifications.
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Designation:F2078–01
Standard Terminology Relating to
Hydrogen Embrittlement Testing
This standard is issued under the fixed designation F 2078; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope baking—heating to a temperature at least 50°F below the
tempering or aging temperature of the metal or alloy to
1.1 This terminology covers the principal terms, abbrevia-
remove hydrogen before embrittlement occurs by the forma-
tions, and symbols relating to mechanical methods for hydro-
tion of microcracks.
gen embrittlement testing. These definitions are published to
encourage uniformity of terminology in product specifications.
DISCUSSION—No metallurgical changes take place as a result of
baking. (A 941)
2. Referenced Documents
brittle—the inability of a material to deform plastically before
2.1 ASTM Standards:
fracturing.
A 941 Terminology Relating to Steel, Stainless Steel, Re-
2 crackstrength—themaximumvalueofthenominalstressthat
lated Alloys, and Ferroalloys
a cracked specimen is capable of sustaining. (E 1823)
E 6 Terminology Relating to Methods of Mechanical Test-
3 ductile—the ability of a material to deform plastically before
ing
fracturing. (E 6)
E 8 TestMethodsforTensionTestingofMetallicMaterials
embrittle—to make brittle; that is, to lose ductility.
E 812 Test Method for Crack Strength of Slow Bend,
embrittlement—thelossofductilityortoughnessofametalor
Precracked Charpy Specimens of High-Strength Metallic
3 alloy. (G 15)
Materials
environmental hydrogen embirttlement (EHE)—generally
E 1823 Terminology Relating to Fatigue and Fracture Test-
3 caused by hydrogen introduced into the steel from the
ing
environment after exposure to an externally applied stress.
F 1624 Test Method for Measurement of Hydrogen Em-
brittlement Threshold in Steel by the Incremental Step
DISCUSSION—Embrittlement as a result of hydrogen introduced into
Loading Technique steelfromexternalsourceswhileunderstress.Testsareconductedinan
G 15 Terminology Relating to Corrosion and Corrosion environment. (STP 962)
DISCUSSION—Foundinplatedpartsthatcathodicallyprotectthemetal
Testing
from corroding. Generates hydrogen at the surface of the metal.
Produces a clean, intergranular fracture surface. Not reversible. (The
3. Significance and Use
subtle differences between IHE and EHE are detailed inAppendix X1.)
3.1 The terms used in describing hydrogen embrittlement
(STP 543)
have precise definitions. The terminology and its proper usage
must be completely understood to communicate and transfer environmentally assisted cracking (EAC)—generic, crack
information adequately within the field. growth as a result of exposure to the environment.
3.2 Some of the terms are defined in other terminology fracture strength—the load at the beginning of fracture
standards, which are respectively identified in parentheses during a tension test divided by the original cross-sectional
following the definition. area.
gaseous hydrogen embrittlement (GHE)—a distinct form of
4. Terminology
EHE caused by the presence of external sources of high
4.1 Definitions: pressure hydrogen gas; cracking initiates on the outer
surface.
heat treatment—heating to a temperature that produces met-
This terminology standard is under the jurisdiction of ASTM Committee F07
allurgical changes in the steel that alter the mechanical
on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.04
properties and microstructure of the metal. (A 941)
on Hydrogen Embrittlement.
Current edition approved May 10, 2001. Published July 2001. hydrogen-assistedstresscracking(HASC)—crackgrowthas
Annual Book of ASTM Standards, Vol 01.01.
a result of the presence of hydrogen; it can be either IHE or
Annual Book of ASTM Standards, Vol 03.01.
EHE and sometimes is referred to as hydrogen stress
Annual Book of ASTM Standards, Vol 15.03.
cracking (HSC).
Annual Book of ASTM Standards, Vol 03.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F2078
hydrogen embrittlement—a permanent loss of ductility in a particular mode in a homogeneous linear–elastic body.
metal or alloy caused by hydrogen in combination with (E 1823)
stress, either an externally applied or an internal residual susceptibility to hydrogen embrittlement—is a material
stress. (G 15) property that is measured by the threshold stress intensity
hydrogen susceptibility ratio (Hsr)—the ratio of the thresh- parameter for hydrogen induced stress cracking, K ,K ,
Iscc IHE
old for the onset of hydrogen assisted cracking to the tensile or K , which is a function of hardness and microstructure.
EHE
strength of the material. threshold(th)—apointseparatingconditionsthatwillproduce
internal hydrogen embrittlement (IHE)—hydrogen em- a given effect from conditions that will not produce the
brittlement caused by absorbed atomic hydrogen from any effect; the lowest load at which subcritical cracking can be
chemical process that introduces hydrogen into the steel detected.
before exposure to an externally applied stress. threshold stress (s )—a stress below which no hydrogen
th
stress cracking will occur and above which time-delayed
DISCUSSION—Embrittlement results from the formation of microc-
fracture will occur; in Test Method F 1624, the threshold is
racks with time and is often referred to as “time-delayed embrittle-
identified as the maximum load at the onset of cracking that
ment.” Once microcracks have been formed, ductility cannot be
cuases a 5 % drop in load of NSF(B) under displace-
restored. Tests are generally conducted in air. (STP 543)
F1624
ment control.
DISCUSSION—This type of embrittlement is referred to as the classic
type of hydrogen embrittlement in steel, although IHE has also been
threshold stress intensity (K )—a stress intensity below
th
observed in a wide variety of other materials including nickel base
which no hydrogen stress cracking will occur and above
alloys and austenitic stainless steels provided that they are severely
which, time-delayed fracture will occur.
charged with hydrogen. (STP 543)
4.2 Symbols:
DISCUSSION—Forsteels,IHEismostsevereatroomtemperature.The
P—applied load
problem primarily results from electroplating. Other sources of hydro-
P —critical load required to rupture a specimen using a
gen are the processing treatments, such as melting and pickling. c
continuous loading rate
(STP 543)
P—crackinitiationloadforagivenloadingandenvironmental
i
notched tensile strength—the maximum nominal (net sec-
condition using an incrementally increasing load under
tion) stress that a notched tensile specimen is capable of
displacement control
sustaining. (E 1823)
P —threshold load in which P is invariant with respect to
th i
process—a defined event or sequence of events in plating or
loading rate; P is the basis for calculating the threshold
th
coating that may include pretreatments and posttreatments.
stress or the threshold stress intensity
reaction hydrogen embrittlement (RHE)—hydrogen can
s—applied stress
react with itself, with the matrix, or with a foreign element
s —netstressbasedonareaatminimumdiameterofnotched
net
in the matrix and form new phases that are usually quite
round bar
stable, and embrittlement is not reversible.
s—stress at crack initiation
i
s —threshold stress—test conducted in air—geometry
DISCUSSION—Quite distinct from the other types in that the hydrogen th-IHE
dependent
may react near the surface or diffuse a substantial distance before it
reacts. (STP 543) s —threshold stress—test conducted in a specified
th-EHE
environment—geometry dependent
sharp-notch strength—the maximum nominal (net section)
R —ratio of specimen crack strength to yield strength in
sb
stress that a sharply notched specimen is capable of sustain-
bending
ing. (E 1823)
R —ratio of specimen notched strength to yield strength in
nsb
stress corrosion cracking (SCC)—a cracking process that
bending
requiresthesimultaneousactionofacorrodentandsustained
K —threshold stress intensity for stress corrosion cracking
Iscc
tensile stress.
K —threshold stress intensity for IHE
IHE
DISCUSSION—This excludes corrosion-reduced sections that fail by
K —threshold stress intensity for EHE
EHE
fa
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