ASTM E340-00(2006)
(Test Method)Standard Test Method for Macroetching Metals and Alloys
Standard Test Method for Macroetching Metals and Alloys
SCOPE
1.1 These test procedures describe the methods of macro- etching metals and alloys to reveal their macrostructure.
1.2 The values stated in inch-pound units are to be regarded as the standard. The SI equivalents of inch-pound units may be approximate.
1.3 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. For specific warning statements, see 6.2, 7.1, 8.1.3, 8.2.1, 8.8.3, 8.10.1.1, and 8.13.2.
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Standards Content (Sample)
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Designation: E340 − 00(Reapproved 2006)
Standard Test Method for
Macroetching Metals and Alloys
This standard is issued under the fixed designation E340; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope and ferrite banding, coring, inclusions, and depth of carburiza-
tion or decarburization. The information provided about varia-
1.1 These test procedures describe the methods of mac-
tions in chemical composition is strictly qualitative but the
roetching metals and alloys to reveal their macrostructure.
location of extremes in segregation will be shown. Chemical
1.2 The values stated in inch-pound units are to be regarded
analyses or other means of determining the chemical compo-
as the standard.The SI equivalents of inch-pound units may be
sition would have to be performed to determine the extent of
approximate.
variation. Macroetching will also show the presence of discon-
1.3 This standard does not purport to address all of the
tinuities and voids, such as seams, laps, porosity, flakes, bursts,
safety concerns, if any, associated with its use. It is the
extrusion rupture, cracks, etc.
responsibility of the user of this standard to establish appro-
3.1.3 Other applications of macroetching in the fabrication
priate safety and health practices and determine the applica-
of metals are the study of weld structure, definition of weld
bility of regulatory limitations prior to use. For specific
penetration, dilution of filler metal by base metals, entrapment
warning statements, see 6.2, 7.1, 8.1.3, 8.2.1, 8.8.3, 8.10.1.1,
of flux, porosity, and cracks in weld and heat affected zones,
and 8.13.2.
etc. It is also used in the heat-treating shop to determine
location of hard or soft spots, tong marks, quenching cracks,
2. Referenced Documents
case depth in shallow-hardening steels, case depth in carbur-
2.1 ASTM Standards:
ization of dies, effectiveness of stop-off coatings in
E3 Guide for Preparation of Metallographic Specimens
carburization, etc. In the machine shop, it can be used for the
E381 Method of Macroetch Testing Steel Bars, Billets,
determination of grinding cracks in tools and dies.
Blooms, and Forgings
3.1.4 Macroetchingisusedextensivelyforqualitycontrolin
3. Significance and Use
the steel industry, to determine the tone of a heat in billets with
respect to inclusions, segregation, and structure. Forge shops,
3.1 Applications of Macroetching:
in addition, use macroetching to reveal flow lines in setting up
3.1.1 Macroetching is used to reveal the heterogeneity of
the best forging practice, die design, and metal flow. For an
metals and alloys. Metallographic specimens and chemical
example of the use of macroetching in the steel forging
analyses will provide the necessary detailed information about
industry see Method E381. Forging shops and foundries also
specific localities but they cannot give data about variation
use macroetching to determine the presence of internal faults
from one place to another unless an inordinate number of
and surface defects.The copper industry uses macroetching for
specimens are taken.
control of surface porosity in wire bar. In the aluminum
3.1.2 Macroetching, on the other hand, will provide infor-
industry, macroetching is used to evaluate extrusions as well as
mation on variations in (1) structure, such as grain size, flow
the other products such as forgings, sheets, etc. Defects such as
lines, columnar structure, dendrites, etc.; (2) variations in
chemical composition as evidenced by segregation, carbide coring, cracks, and porthole die welds are identified.
4. Sampling
This test method is under the jurisdiction of ASTM Committee E04 on
MetallographyandisthedirectresponsibilityofSubcommitteeE04.01onSpecimen
4.1 As in any method of examination, sampling is very
Preparation.
important. When macroetching is used to solve a problem, the
Current edition approved Oct. 1, 2006. Published October 2006. Originally
ε1
problemitselflargelydictatesthesourceofthesampleastothe
approved in 1968. Last previous edition approved in 2000 as E340 – 00 . DOI:
10.1520/E0340-00R06.
location on the work piece and the stage of manufacture; for
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
example, when looking for pipe, the sample should represent
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
the top of the ingot, or when looking for bursts or flakes, the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. sample should be taken as soon after hot working as possible.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E340 − 00 (2006)
4.2 When macroetching is used as an inspection procedure, 4.5.5 Machined and Ground Parts—When looking for
sampling ought to be done in an early stage of manufacturing grinding cracks, etc., the surface itself is used as a sample.
so that if the material proves faulty, no wasteful unnecessary Because the machined or ground part is often the finished part,
work is done. However, the sample should not be taken so it may be undesirable to immerse the part in acid. In this case,
early that further working can introduce serious defects. In the other methods such as dye penetrant methods may be more
steel industry, for example, the sample is usually taken after desirable.
ingot breakdown and after most chances of bursts or flakes
5. Preparation
occurring have passed. Billets or blooms going into small sizes
5.1 Sample preparation need not be elaborate. Any method
are sampled after initial breakdown. Material going into
ofpresentingasmoothsurfacewithaminimumamountofcold
forging billets or die blocks is sampled near finish size.
work will be satisfactory. Disks may be faced on a lathe or a
Sampling may be done systematically or on a random basis.
shaper. The usual procedure is to take a roughing cut, then a
4.3 Samples may be cold cut from the source by any
finishcut.Thiswillgenerateasmoothsurfaceandremovecold
convenient fashion; saws and abrasive cutoff wheels are
work from prior operations. Sharp tools are necessary to
particularly effective. The use of torch cutting or hot cutting
produce a good specimen. Grinding is usually conducted in the
should be used only when necessary to cut a sample from a
same manner, using free-cutting wheels and light finishing
large piece. The sample then is sectioned well away from the
cuts. When fine detail is required, the specimen should be
hot-cut surface.An example of permissible use of torch cutting
ground down through the series of metallographic papers (see
is the excising of a piece from a large plate and then cutting a
Methods E3). Where necessary, details are given in the
sample for macroetching 4 to 5 in. (102 to 127 mm) away from
tabulation of procedures.
the torch-cut edge.
5.2 After surface preparation, the sample is cleaned care-
4.4 Some common methods of sampling, listed by source,
fully with suitable solvents. Any grease, oil, or other residue
are as follows:
willproduceunevenattack.Oncecleaned,careshouldbetaken
4.5 Billets, Blooms, and Hot-Rolled Products—Disks are
not to touch the sample surface or contaminate it in any way.
usually cut from these products near the end. Samples cut too
close to the end, however, may have false structures because of 6. Solutions
fish-tailing. Disks from large blooms are sometimes cut into
6.1 The solutions used for macroetching are given in the
smaller pieces for ease in handling.
tables listed under each alloy. In most cases a good grade of
4.5.1 Forgings and Extrusions—Disks cut transverse to the
reagent should be used but need not be chemically pure or of
longdimensionwillshowflakes,bursts,etc.Forgingsmayalso
analytical quality. The so-called technical grades are usually
be cut parallel to the long dimension to show flow lines. In
satisfactory. The solution should be clean and clear, free of
complicated forgings, some thought will have to be given to
suspended particles, scum, etc.
the proper method of cutting so as to show flow lines.
6.2 Caution must be observed in mixing. Many of the
Macroetching of an unprepared specimen will show surface
etchants are strong acids. In all cases, the various chemicals
defects such as shuts, flats, seams, etc. In extrusions, coring
should be added slowly to the water or solvent while stirring.
and coarse grain are more commonly found in the back end of
In the cases where hydrofluoric acid is used, the solution
the extrusion.
should be mixed and used in polyethylene vessels.
4.5.2 Sheets and Plates—Asufficiently large sample should
(Warning—Hydrofluoricacidshouldnotbeallowedtocontact
be taken when looking for surface defects. An ideal length
the skin since it can cause painful serious ulcers if not washed
would be the circumference of the last roll, but this may be
off immediately.)
inconveniently long. Several samples totaling some given
fraction of the circumference can be used; however, there is
7. Procedure
always a chance then that a defect arising from faulty rolls
7.1 Many of the solutions are aggressive and may give off
would not be detected. When seeking information on
irritating and corrosive fumes. Etching should be done in a
laminations, a transverse section is used. In many cases,
well-ventilated room, preferably under a fume hood. The
however, to reduce the size of the specimen, only a section out
solution should be mixed and placed in a corrosion resistant
of the center of the plate may be taken.
tray or dish and brought to the operating temperature. The
4.5.3 Weldments—A disk cut perpendicular to the direction
specimen or specimens should be placed in a tray of stainless
of welding will show weld penetration, heat affected zone,
steel screen or on some non-reactive support. Glass rods often
structure, etc. Careful preparation is usually rewarded with
are placed on the bottom of the acid container and the
highlydetailedstructuresgivingalargeamountofinformation.
specimens laid directly on the rods. When etching is
Welds involving dissimilar metals will produce problems in
completed, remove the specimens from the dish taking great
etching.The best method is to etch the least corrosion-resistant
care not to touch the etched surface. When desmutting is
portion first and the more resistant portion afterwards. Occa-
required, dip the specimen into a second solution.After rinsing
sionally an intermediary etchant may be required. The bound-
the specimen with hot water, blow dry with clean compressed
aries between etched and unetched portion will give an idea of
air.
weld penetration and dilution.
4.5.4 Castings—Cut the specimen to display the defect or 7.2 In the case of large specimens, such as ingot sections,
feature being sought. swabbing may be the only practical method of macroetching.
E340 − 00 (2006)
TABLE 1 Macroetchants for Aluminum and Aluminum Alloys
Alloy Composition Procedure Comments
All NaOH 10 g Immerse sample 5 to 15 min in solution heated to 60 Good general-purpose etchant, can be
H O 100 mL to 70°C (140 to 160°F). Rinse in water, and remove used on almost all aluminum alloys.
smut in strong HNO solution. Rinse and repeat Does not require fine grinding.
etching if necessary.
3XXX HCl (concentrated) 75 mL Mix fresh before using. Use at room temperature. May Used to develop grain structure. May be
4XXX HNO (concentrated) 25 mL be used as immersion etch or swabbed over diluted with 25 % water to slow down
5XXX HF (48 %) 5mL specimen surface. Rinse specimen in warm water and etching. Does not require fine grinding.
6XXX dry.
High Si castings
High purity A1 HCl (concentrated) 45 mL Immerse specimen at room temperature until desired Tucker’s etch. General purpose etch for
1XXX HNO (concentrated) 15 mL contrast is developed. Rinse in warm water and dry. revealing microstructure of both cast and
3XXX HF (48 %) 15 mL wrought aluminum. Does not require fine
4XXX H O 25 mL grinding.
5XXX
6XXX
All except high Si HCl (concentrated) 15 mL Same as above. 1 + 2 Tucker’s. Same as above, but
castings HNO (concentrated) 5mL slower acting.
HF (48 %) 5mL
H O 75 mL
2XXX HCl (concentrated) 15 mL May be used as an immersion etch or swabbed over Flick’s reagent. Best results are obtained
High Cu alloys HF (48 %) 10 mL the specimen surface. When desired contrast is with a ground surface. 180 grit will
H O 90 mL obtained, rinse in water and remove deposits with suffice.
concentrated HNO . Rinse in warm water and dry.
Saturate a large wad of cotton held in stainless steel or nickel are required. If fine detail is required, the machined surface
tongs with the etchant and sweep over the surface of the should be ground using silicon carbide paper lubricated with
specimen.An effort should be made to wet the entire surface as water or kerosine.
soon as possible. After the initial wetting, keep the swab 8.1.3 Several of the solutions used in macroetching react
saturated with solution and frequently sweep over the surface
vigorously with the metal and can overheat the specimen. In
of the specimen to renew the solution. When the structure has these cases the specimen is periodically removed from the
beensuitablydeveloped,rinsethespecimen,eitherwithaswab
solution, cooled in running water, and reimmersed in the
saturated with water, or better still, by pouring water over the
etchant. This procedure is repeated until the desired degree of
specimen.After rinsing with hot water, blow the specimen dry
etching is obtained.
with compressed air. Details of the procedure not discussed
8.1.4 Macroetchants for Aluminum and Aluminum Alloys
here are covered in the sections for the various metals and their
(Table 1).
alloys.
8.2 Beryllium:
7.3 The times given in individual tabulations are only
8.2.1 While beryllium in the massive form is not dangerous,
intended as guides. In fact, the progress of etching should be
beryllium and its compounds in the finely divided state are
closely watched and etching stopped when the preferred
extremely poisonous. (Warning—Before starting any work
structural details have been revealed. Specimens should be
involving beryllium, a review of hazards and plans for han-
etched to develop structure. Generally, a light etch is better
dling should be made.Anumber of references on beryllium are
than a heavy etch; overetching can often lead to misinterpre-
available. Particular mention
...
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