ASTM E381-98
(Test Method)Standard Method of Macroetch Testing Steel Bars, Billets, Blooms, and Forgings
Standard Method of Macroetch Testing Steel Bars, Billets, Blooms, and Forgings
SCOPE
1.1 Macroetching, which is the etching of specimens for macrostructural examination at low magnifications, is a frequently used technique for evaluating steel products such as bars, billets, blooms, and forgings.
1.2 Included in this method is a procedure for rating steel specimens by a graded series of photographs showing the incidence of certain conditions. The method is limited in application to bars, billets, blooms, and forgings of carbon and low alloy steels.
1.3 A number of different etching reagents may be used depending upon the type of examination to be made. Steels react differently to etching reagents because of variations in chemical composition, method of manufacture, heat treatment and many other variables. Establishment of general standards for acceptance or rejection for all conditions is impractical as some conditions must be considered relative to the part in which it occurs.
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. See the specific precautionary statement in 5.3.
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Designation: E 381 – 98
Standard Method of
Macroetch Testing Steel Bars, Billets, Blooms, and
Forgings
This standard is issued under the fixed designation E 381; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 3. Terminology
1.1 Macroetching, which is the etching of specimens for 3.1 Definitions—For definitions of terms used in this
macrostructural examination at low magnifications, is a fre- method, see Terminology E 7.
quently used technique for evaluating steel products such as 3.2 Definitions of Terms Specific to This Standard:
bars, billets, blooms, and forgings. 3.2.1 Terminology Applicable Only to Ingot Cast Product:
1.2 Included in this method is a procedure for rating steel 3.2.1.1 splash—a nonuniform etch pattern where
specimens by a graded series of photographs showing the irregularly-shaped areas exhibit a different etch contrast than
incidence of certain conditions. The method is limited in surrounding areas. Splash is normally associated with molten
application to bars, billets, blooms, and forgings of carbon and steel which solidifies and oxidizes during initial pouring and
low alloy steels. which is not completely redissolved by the remaining molten
1.3 A number of different etching reagents may be used steel.
depending upon the type of examination to be made. Steels 3.2.1.2 butt tears—subsurface cracks normally parallel to
react differently to etching reagents because of variations in the surface of the ingot mold wall.
chemical composition, method of manufacture, heat treatment 3.2.1.3 flute cracks—cracks perpendicular to the surface of
and many other variables. Establishment of general standards the ingot mold wall which may, or may not, extend to the
for acceptance or rejection for all conditions is impractical as surface of the product.
some conditions must be considered relative to the part in 3.2.1.4 burst—a single or multi-rayed crack normally lo-
which it occurs. cated at the center of the wrought product.
1.4 This standard does not purport to address all of the 3.2.2 Definitions Applicable Only to Continuously Cast
safety concerns, if any, associated with its use. It is the Products:
responsibility of the user of this standard to establish appro- 3.2.2.1 chill zone—rapidly cooled metal with a fine struc-
priate safety and health practices and determine the applica- ture at the surface of the product which is normally continuous
bility of regulatory limitations prior to use. See the specific around that surface.
precautionary statement in 5.3. 3.2.2.2 chill zone crack—any crack which is located par-
tially or completely in the chill zone and may extend to the
2. Referenced Documents
surface of the product.
2.1 ASTM Standards: 3.2.2.3 diagonal crack—a crack which lies completely or
E 7 Terminology Relating to Metallography
partially in the diagonal regions of a non-round product where
E 340 Test Method for Macroetching Metals and Alloys adjacent columnar or dendritic growth patterns intersect.
E 1180 Practice for Preparing Sulfur Prints for Macrostruc-
3.2.2.4 subsurface crack—a crack perpendicular to and just
tural Examination beneath the chill zone.
2.2 ASTM Adjuncts:
3.2.2.5 mid-radius crack—a crack perpendicular to the
Photographs for Rating Macroetched Steel (3 plates) surface of the product located approximately halfway between
the surface and center of the product.
3.2.2.6 center crack—a crack with an aspect ratio (length/
width) of approximately 3 or greater located at, or near, the
This method is under the jurisdiction of ASTM Committee E-4 on Metallog-
center of the product.
raphy, and is the direct responsibility of Subcommittee E04.01 on Sampling,
Specimen Preparation, and Photography.
3.2.2.7 star crack—a star-shaped or multi-rayed crack at the
Current edition approved October 10, 1998. Published December 1998. Origi-
center of the product.
nally published as E 381 – 68. Last previous edition E 381 – 94.
Annual Book of ASTM Standards, Vol 03.01.
Available from ASTM Headquarters. Order Adjunct: ADJE038101 (Plate I),
ADJE038102 (Plate II), and ADJE038103 (Plate III).
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 381
3.2.2.8 scattered porosity—multiple round or irregularly- magnifications (usually <103).
shaped pores uniformly distributed about the central portion of 4.2 Macroetching will show: (1) variations in structure such
the product.
as grain size, dendrites, and columnar structure; (2) variations
3.2.2.9 white band—a light etching continuous band(s) in chemical composition such as segregation, coring, and
parallel to the surface of the product usually located between
banding; and, (3) the presence of discontinuities such as laps,
the one-quarter and three-quarter radius position, normally seams, cracks, porosity, bursts, pipe. and flakes.
associated with electromagnetic stirring.
4.3 When, in accordance with the requirements of the
3.2.2.10 columnar grains—a coarse structure of parallel, inquiry, contract, order or specifications, forgings, billets,
elongated grains formed by unidirectional growth during
blooms, etc., are to be produced subject to macroetch testing
solidification. and inspection, the manufacturer and the purchaser should be
3.2.3 Conditions Applicable to Both Ingot and Continuously
in agreement concerning the following: (1) the stage of
Cast Product: manufacture at which the test shall be conducted; (2) the
3.2.3.1 nonmetallic inclusions—nonmetallic particles
number and locations of the sections to be examined; (3) the
trapped in the steel or the voids resulting when inclusions are necessary surface preparation prior to etching of the specimen;
dissolved by the macroetchant.
(4) the etching reagent, temperature, and time of etching; and,
3.2.3.2 pattern—a dark etching band, usually rectangular or (5) the type, size, number, location, and orientation of condi-
square, enclosing the central portion of the cross section, tions that are to be considered injurious.
normally visible only in wrought product. In ingot cast product, 4.4 When not specified, the procedures of the test may be
it is sometimes called ingotism or ingot pattern.
selected by the manufacturer to satisfy the requirements of the
3.2.3.3 pipe or center void—a single large cavity located at,
governing specification.
or near, the center of the product.
4.5 When agreed upon by purchaser and producer, sulfur
3.2.3.4 center unsoundness—multiple round or irregularly-
printing of as cast-sections, if continuously cast, is an accept-
shaped voids concentrated at the center of the product.
able alternative to macroetching. Sulfur printing shall be
3.2.3.5 dark center—a dark etching area at the center of the
performed in accordance with Practice E 1180. Examination
product. Dark center is solid material and should not be
and rating of specimens shall be in accordance with Sections
confused with center unsoundness.
10 and 11 of this (E 381) standard.
3.2.3.6 pinholes—small pores which lie at, or just beneath,
4.6 Steel from ingots shall be examined according to pro-
the surface of the product.
cedures described in Section 9. Continuously cast steel blooms
3.2.3.7 mold slag—inclusions which are normally associ-
and billets, in the as cast condition, shall be examined
ated with entrapped fused mold powder and are normally
according to the procedures described in Sections 10 and 11.
located at, or just beneath, the surface of the product. They are
With reductions over a 3:1 area ratio, wrought product from
usually found in continuously cast or bottom poured products.
continuously cast steel may be examined according to Section
3.2.3.8 flakes—short discontinuous internal cracks attrib-
9.
uted to stresses produced by localized transformation and
hydrogen solubility effects during cooling after hot working. In 5. Reagents
an etched transverse section, they appear as short, tight
5.1 The most common reagent for macroetching iron and
discontinuities which are usually located in the midway to
steel is a 1:1 mixture, by volume, of concentrated hydrochloric
center location of the section. They are also known as shatter
acid (HCl) and water. The hydrochloric acid need not be
cracks or hairline cracks.
reagent grade. Commercial quality hydrochloric acid (also
3.2.3.9 gassy—irregularly-shaped voids which may, or may
known as muriatic acid) is satisfactory. The etching solution
not, be uniformly distributed throughout the cross section.
should be clear and free from scum. It should be hot, 70 to
These may be located anywhere from the near surface region of
80°C (160 to 180°F). The reagent should be used under a fume
the product to the center of the product, depending on the
hood, or some other means of carrying off the corrosive fumes
source and severity of the condition.
must be provided. The solution may be heated without serious
3.2.3.10 dendritic—a “tree-like” pattern with branches (pri-
change in concentration. The etching solution may be reused if
mary, secondary, and tertiary arms) due to compositional
it has not become excessively contaminated or weakened.
differences that arise during solidification. For a specific
NOTE 1—The addition of hydrogen peroxide (H O ) may be necessary
2 2
composition, a weak dendritic structure is associated with a
in order to provide sufficient reaction to properly etch some types of
low superheat while a strong dendritic structure is associated
product. This should be added to an etching bath that is operating at room
with a high superheat during casting. Compositional differ-
temperature.
ences also influence the clarity of the dendrites.
5.2 A second macroetching solution, favored by some as
4. Significance and Use
producing a clearer structure, is composed of concentrated HCl
4.1 Macroetching is used in the steel industry because it is (38 volume %), sulfuric acid, H SO (12 volume %) and water,
2 4
a simple test that will provide information about the relative H O (50 volume %). (See 5.1 with respect to acid quality,
heating, and ventilation.)
homogeneity of the sample. The method employs the action of
an acid or other corrosive agent to develop the macrostructural 5.3 Observe caution in mixing macroetch solutions. The
characteristics of a suitably prepared specimen. The name acids are strong and they can cause serious chemical burns.
implies that the etched surface is examined visually, or at low Add acid slowly to water with stirring. This is especially true
E 381
for sulfuric acid. Mix solutions and macroetch under a fume nuities, such as thermal cracks or flakes, the purchaser may
hood. specify that disks for macroetch inspection be taken a certain
5.4 An ammonium persulfate solution, a 10 to 20 % aque- minimum distance from the ends of the specimen. In the case
ous solution, is used primarily on longitudinal sections to of forgings, depending upon prior agreement, this may be
detect certain types of ghost lines, segregation, flow lines, etc. accomplished by adding excess metal for discard on the ends or
A freshly made solution is necessary for best results. The ends of the forging; or, by forging in multiple lengths and
solution should be swabbed on the finished surface at room removing the test disk between individual pieces when cutting
temperature. Inspection is most effective when done while the up the multiple forging.
piece is still wet.
7. Preparation
5.5 A nitric acid solution, 5 % or 10 % nitric acid in alcohol
7.1 Specimen preparation need not be elaborate. Any
or water, is used to detect local overstraining, grinding cracks,
method of preparing smooth surfaces with a minimum amount
overheated areas, and depth of carburized or decarburized
of cold work should be satisfactory. Disks may be faced on a
surface zones. The use of this reagent necessitates a smooth
lathe or a shaper. The usual procedure is to take a roughing cut,
surface. The reagent is used at room temperature by immersion
then a finishing cut. This will generate a smooth surface and
or swabbing.
remove cold work from prior operations. Sharp tools are
5.6 Many other reagents have been used for special appli-
necessary to produce a good specimen. Grinding, which also
cations. When the use of a reagent other than those described
may be used, is usually conducted in the same manner, using
in 5.2-5.5 is desired, it should be by agreement between the
free-cutting wheels and light feeds. When fine detail must be
purchaser and the manufacturer. (See Test Method E 340 for
other etching solutions.) revealed, the specimen should be prepared with metallographic
grinding papers, or even with a metallographic polish.
6. Sampling
7.2 After specimen preparation, the surface to be etched
6.1 When macroetching is used as an inspection procedure,
should be cleaned. Any grease, oil, or other residue will
sampling should be done at an early stage of manufacture so
produce an uneven attack and must be removed. It may be
that, if the material is inadequate, the minimum amount of
necessary to use solvents to clean the surface. Once cleaned,
unnecessary processing is done (or the processing can be
care should be taken to avoid touching or otherwise contami-
modified to salvage the material). For ingot cast product, the
nating the surface.
specimen is usually taken after ingot breakdown. Billets or 7.3 Large cross sections may be cut into smaller pieces to
blooms going into small sizes are sampled after the initial
facilitate handling and to comply with safety requirements. The
breakdown. Sampling of continuously cast product is usually sectioning of the large specimens should be done so as not to
done in the as-cast condition, or after intermediate or final
disturb the central portion of the section.
processing, depending on size and preference. Random sam-
8. Procedure
pling of the finished product may be performed if the locations
within the cast are not known. 8.1 Macroetching is carried out in containers which must be
6.2 Normally, the specimens are disks cut from the ends of resistant to the attack of the etching reagent. Small pieces may
bars, billets or blooms. Enough material should be discarded be etched in glass or porcelain vessels of the types commonly
before taking the specimen to eliminate any extraneous effects available in laboratories. Larger disks are etched in corrosion-
of rolling such as “fish tails.” Specimens may be cut cold by resistant alloy ve
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