ASTM G79-83(1996)e1
(Practice)Standard Practice for Evaluation of Metals Exposed to Carburization Environments (Withdrawn 2005)
Standard Practice for Evaluation of Metals Exposed to Carburization Environments (Withdrawn 2005)
SCOPE
1.1 This practice covers procedures for the identification and measurement of the extent of carburization in a metal sample and for the interpretation and evaluation of the effects of carburization. It applies mainly to iron- and nickel-based alloys for high temperature applications. Four methods are described. MethodA Total Mass Gain MethodB Metallographic Evaluation MethodC Carbon Diffusion Profile MethodD Change in Mechanical Properties
1.2 These methods are intended, within the interferences as noted for each, to evaluate either laboratory specimens or commercial product samples that have been exposed in either laboratory or commercially produced environments.
1.3 No attempt is made to recommend particular test exposure conditions, procedures, or specimen design as these may vary with the test objectives.
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use.
WITHDRAWN RATIONALE
This practice covers procedures for the identification and measurement of the extent of carburization in a metal sample and for the interpretation and evaluation of the effects of carburization. It applies mainly to iron- and nickel-based alloys for high temperature applications.
Formerly under the jurisdiction of Committee G01 on Corrosion of Metals, this practice was withdrawn in August 2005.
General Information
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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e1
Designation: G 79 – 83 (Reapproved 1996)
Standard Practice for
Evaluation of Metals Exposed to Carburization
Environments
ThisstandardisissuedunderthefixeddesignationG 79;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Editorial changes were made throughout in October 1996.
1. Scope E 290 TestMethodforSemi-GuidedBendTestforDuctility
of Metallic Materials
1.1 This practice covers procedures for the identification
G 1 Practice for Preparing, Cleaning, and Evaluating Cor-
and measurement of the extent of carburization in a metal
rosion Test Specimens
sample and for the interpretation and evaluation of the effects
of carburization. It applies mainly to iron- and nickel-based
3. Terminology
alloys for high temperature applications. Four methods are
3.1 Definitions:
described.
3.1.1 carbon potential—the amount of carbon available for
Method A Total Mass Gain
reaction in an environment. This amount depends upon the
Method B Metallographic Evaluation
Method C Carbon Diffusion Profile
chemical balance of the carburizing and decarburizing agents
Method D Change in Mechanical Properties
in the system such as carbon monoxide, hydrogen, carbon
1.2 These methods are intended, within the interferences as dioxide, water vapor, methane, and nitrogen.
noted for each, to evaluate either laboratory specimens or 3.1.2 carburization—the absorption of carbon atoms into a
commercial product samples that have been exposed in either metal surface at high temperatures. The carbon may remain
laboratory or commercially produced environments. dissolved or form metal carbides. This may or may not be
1.3 No attempt is made to recommend particular test expo- desirable.
sure conditions, procedures, or specimen design as these may
METHOD A—TOTAL MASS GAIN
vary with the test objectives.
1.4 This standard does not purport to address all of the
4. Summary of Method
safety concerns, if any, associated with its use. It is the
4.1 This method provides a relatively fast, simple, and
responsibility of the user of this standard to establish appro-
inexpensive technique for comparing material or environmen-
priate safety and health practices and determine the applica-
talvariables.Thetotalmassgainofthesampleduringexposure
bility of regulatory limitations prior to use.
is considered as a first approximation of total carbon pickup.
2. Referenced Documents
5. Significance and Use
2.1 ASTM Standards:
5.1 This method has an advantage over the other three,
E 3 Methods of Preparation of Metallographic Specimens
2 which are destructive single-determination techniques, in that
E 8 Test Methods forTensionTesting of Metallic Materials
successive measurements at selected time intervals can be
E 10 Test Method for Brinell Hardness of Metallic Materi-
2 made without destroying the sample. If unwanted reactions
als
(such as sulfidation and oxidation, which are usually minor
E 18 Test Methods for Rockwell Hardness and Rockwell
2 under intentionally carburizing conditions) are not important, a
Superficial Hardness of Metallic Materials
mass gain plot versus time can provide some additional insight
E 23 Test Methods for Notched Bar Impact Testing of
2 about carburizing rate or intermittent variables, or both.
Metallic Materials
E 139 Practice for Conducting Creep, Creep-Rupture, and
6. Interferences
Stress-Rupture Tests of Metallic Materials
6.1 The mass change of a sample may not be entirely the
result of carbon pickup. The environment may contain some
other corroding species, such as oxygen, that may react with
This practice is under the jurisdiction of ASTM Committee G-1 on Corrosion
of Metals and is the direct responsibility of Subcommittee G01.05 on Laboratory
Corrosion Tests.
Current edition approved March 25, 1983. Published June 1983.
2 3
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G79
the metal surface to form corrosion products which also affect this situation is illustrated by comparing the relatively distinct
mass change. This type of data also gives no indication of carburized layer boundary in Fig. 1 with the more diffuse area
carbon distribution within the material which may be of more in Fig. 2. This is particularly true of nominally high carbon-
importance than total pickup. Considering its limitations, this content alloys. In these cases, the depth of carbon penetration
method is best used in combination with at least one of the becomesajudgmentbasedondensityoftheprecipitatedphase.
other methods described in this practice or when considerable
12. Procedure
knowledge and understanding exist as to how materials usually
12.1 Success with this method requires that close attention
perform in the particular conditions of the exposure environ-
be paid to Methods E 3. The sample is first cut so that the final
ment, or both.
viewing axis will be perpendicular to the direction of carbon
7. Procedure diffusion. After polishing, the specimen is usually etched with
a suitable acid mixture to delineate carbides. Some particularly
7.1 This method assumes the use of a sample that can be
useful etchants are listed in Table 1. The sample is viewed at a
readily measured to obtain exposed surface area and weighed
magnification of between 503 and 1003.The depth of carbide
both before and after exposure to obtain mass gain per unit
precipitation is then determined with the microscope’s mea-
surface area, that is, grams per square metre. See Practice G 1.
suring recticle or other system such as a glass screen and
appropriate scale. For example, the sample shown in Fig. 1
8. Discussion of Results
appears to have a carbide precipitation depth of about 0.6 mm.
8.1 The successful application of this technique depends
Carbon penetration may in some cases be very uneven due to
primarily upon the ability to measure small mass changes. All
intergranular or other localized acceleration of diffusion. The
weighing should be done to the nearest 0.1 mg. Section
penetration depth shall thus be taken as at least the average of
thicknessisalsoimportantinordertoapproximatean“infinite”
three measurements each in several areas. Some measure of
solid thus allowing carbon diffusion from one surface to be
variability is also necessary such as a standard deviation or
unaffected by diffusion from any other surface. A minimum
other indication. In all cases preview the entire mounted
section thickness of at least 12 mm is necessary, particularly
specimen prior to measurements so that any areas of nonuni-
with cylindrical samples, for short time exposure in most
formity can be identified. It is helpful to compare photomicro-
carburizingenvironments.Whencalculatingcarburizationrate,
graphs of exposed samples with a standard that has received
it must be assumed that carburization as measured by mass
the same temperature and time exposure but without the
gain is not linear with time.
external carbon potential. Alternatively, if the exposed sample
has a large enough cross section, the surface carbide density
METHOD B—METALLOGRAPHIC EVALUATION
can be compared with the unaffected core area.
9. Summary of Method
13. Discussion of Results
9.1 Thesampleiscut,polished,andetchedtoaccentuatethe
13.1 Comparisons of carbon solubility and mobility indica-
carbide structure. The extent of carbon penetration sufficient to
tions are most accurate and meaningful when the boundary
form insoluble carbides is then measured directly on a magni-
between the carburized and uncarburized areas is uniform and
fied area.
well delineated. When this boundary is vague or highly
variable, results can be misleading. Statistical analysis cannot
10. Significance and Use
necessarilysalvagevaguemeasurements.Itisbesttoavoidthis
10.1 The carbon penetration number refers to the point at
technique unless the measurements can be made easily and
which insoluble carbides are first formed. It does not indicate
unequivocally.
the total depth of carbon penetration. Metallographic measure-
ment of carbon penetration can be used by itself for evaluation
of materials. It can be particularly useful when combined with
total mass gain data to give some indication of the solubility
and mobility of carbon in the exposed material as suggested by
the following:
Mass Pene- Solu-
Gain + tration 5 bility and Mobility
low low low low
low high low high
high low high low
high high high high
11. Interferences
11.1 The major limitation of this method lies in the fact that
it is sometimes very difficult to differentiate visually between
carbides that have formed from carbon diffused into the metal
from the exposure environment and those that formed from
FIG. 1 Microstructure of Carburiz
...
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