ASTM E381-01(2006)
(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: E381 − 01(Reapproved 2006)
Standard Method of
Macroetch Testing Steel Bars, Billets, Blooms, and
Forgings
This standard is issued under the fixed designation E381; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 2.2 ASTM Adjuncts:
Photographs for Rating Macroetched Steel (3 plates)
1.1 Macroetching, which is the etching of specimens for
macrostructural examination at low magnifications, is a fre-
3. Terminology
quently used technique for evaluating steel products such as
bars, billets, blooms, and forgings. 3.1 Definitions—For definitions of terms used in this
method, see Terminology E7.
1.2 Included in this method is a procedure for rating steel
3.2 Definitions of Terms Specific to This Standard:
specimens by a graded series of photographs showing the
incidence of certain conditions. The method is limited in 3.2.1 Terminology Applicable Only to Ingot Cast Product:
3.2.1.1 splash—a nonuniform etch pattern where
application to bars, billets, blooms, and forgings of carbon and
low alloy steels. irregularly-shaped areas exhibit a different etch contrast than
surrounding areas. Splash is normally associated with molten
1.3 A number of different etching reagents may be used
steel which solidifies and oxidizes during initial pouring and
depending upon the type of examination to be made. Steels
which is not completely redissolved by the remaining molten
react differently to etching reagents because of variations in
steel.
chemical composition, method of manufacture, heat treatment
3.2.1.2 butt tears—subsurface cracks normally parallel to
and many other variables. Establishment of general standards
the surface of the ingot mold wall.
for acceptance or rejection for all conditions is impractical as
3.2.1.3 flute cracks—cracks perpendicular to the surface of
some conditions must be considered relative to the part in
the ingot mold wall which may, or may not, extend to the
which it occurs.
surface of the product.
1.4 This standard does not purport to address all of the
3.2.1.4 burst—a single or multi-rayed crack normally lo-
safety concerns, if any, associated with its use. It is the
cated at the center of the wrought product.
responsibility of the user of this standard to establish appro-
3.2.2 Definitions Applicable Only to Continuously Cast
priate safety and health practices and determine the applica-
Products:
bility of regulatory limitations prior to use. See the specific
3.2.2.1 chill zone—rapidlycooledmetalwithafinestructure
precautionary statement in 5.3.
at the surface of the product which is normally continuous
around that surface.
2. Referenced Documents
3.2.2.2 chill zone crack—any crack which is located par-
2.1 ASTM Standards:
tially or completely in the chill zone and may extend to the
E7Terminology Relating to Metallography
surface of the product.
E340Test Method for Macroetching Metals and Alloys
3.2.2.3 diagonal crack—a crack which lies completely or
E1180Practice for Preparing Sulfur Prints for Macrostruc-
partially in the diagonal regions of a non-round product where
tural Evaluation
adjacent columnar or dendritic growth patterns intersect.
3.2.2.4 subsurface crack—a crack perpendicular to and just
This method is under the jurisdiction of ASTM Committee E04 on Metallog-
beneath the chill zone.
raphy and is the direct responsibility of Subcommittee E04.01 on Specimen
3.2.2.5 mid-radius crack—a crack perpendicular to the sur-
Preparation.
faceoftheproductlocatedapproximatelyhalfwaybetweenthe
Current edition approved Oct. 1, 2006. Published October 2006. Originally
approved in 1968. Last previous edition approved in 2001 as E381–01. DOI: surface and center of the product.
10.1520/E0381-01R06.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from ASTM Headquarters. Order Adjunct: ADJE038101 (Plate I),
the ASTM website. ADJE038102 (Plate II), and ADJE038103 (Plate III).
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E381 − 01 (2006)
3.2.2.6 center crack—a crack with an aspect ratio (length/ internal (shrinkage) forces result in the separation of crystal-
width) of approximately 3 or greater located at, or near, the lites so as to permit solute rich liquid to refill the gap as it
center of the product. forms.
3.2.2.7 star crack—astar-shapedormulti-rayedcrackatthe
4. Significance and Use
center of the product.
4.1 Macroetching is used in the steel industry because it is
3.2.2.8 scattered porosity—multiple round or irregularly-
shaped pores uniformly distributed about the central portion of a simple test that will provide information about the relative
homogeneity of the sample.The method employs the action of
the product.
an acid or other corrosive agent to develop the macrostructural
3.2.2.9 white band—a light etching continuous band(s) par-
characteristics of a suitably prepared specimen. The name
allel to the surface of the product usually located between the
implies that the etched surface is examined visually, or at low
one-quarter and three-quarter radius position, normally associ-
magnifications (usually <10×).
ated with electromagnetic stirring.
3.2.2.10 columnar grains—a coarse structure of parallel,
4.2 Macroetchingwillshow:(1)variationsinstructuresuch
elongated grains formed by unidirectional growth during
as grain size, dendrites, and columnar structure; (2) variations
solidification.
in chemical composition such as segregation, coring, and
3.2.3 Conditions Applicable to Both Ingot and Continuously
banding; and, (3) the presence of discontinuities such as laps,
Cast Product:
seams, cracks, porosity, bursts, pipe. and flakes.
3.2.3.1 nonmetallic inclusions—nonmetallic particles
4.3 When, in accordance with the requirements of the
trapped in the steel or the voids resulting when inclusions are
inquiry, contract, order or specifications, forgings, billets,
dissolved by the macroetchant.
blooms, etc., are to be produced subject to macroetch testing
3.2.3.2 pattern—a dark etching band, usually rectangular or
and inspection, the manufacturer and the purchaser should be
square, enclosing the central portion of the cross section,
in agreement concerning the following: (1) the stage of
normallyvisibleonlyinwroughtproduct.Iningotcastproduct,
manufacture at which the test shall be conducted; (2) the
it is sometimes called ingotism or ingot pattern.
number and locations of the sections to be examined; (3) the
3.2.3.3 pipe or center void—a single large cavity located at,
necessary surface preparation prior to etching of the specimen;
or near, the center of the product.
(4) the etching reagent, temperature, and time of etching; and,
3.2.3.4 center unsoundness—multiple round or irregularly-
(5) the type, size, number, location, and orientation of condi-
shaped voids concentrated at the center of the product.
tions that are to be considered injurious.
3.2.3.5 dark center—a dark etching area at the center of the
4.4 When not specified, the procedures of the test may be
product. Dark center is solid material and should not be
selected by the manufacturer to satisfy the requirements of the
confused with center unsoundness.
governing specification.
3.2.3.6 pinholes—small pores which lie at, or just beneath,
4.5 When agreed upon by purchaser and producer, sulfur
the surface of the product.
printing of as cast-sections, if continuously cast, is an accept-
3.2.3.7 mold slag—inclusions which are normally associ-
able alternative to macroetching. Sulfur printing shall be
ated with entrapped fused mold powder and are normally
performed in accordance with Practice E1180. Examination
located at, or just beneath, the surface of the product.They are
and rating of specimens shall be in accordance with Sections
usually found in continuously cast or bottom poured products.
10 and 11 of this (E381) standard.
3.2.3.8 flakes—short discontinuous internal cracks attrib-
uted to stresses produced by localized transformation and
4.6 Steel from ingots shall be examined according to pro-
hydrogensolubilityeffectsduringcoolingafterhotworking.In
cedures described in Section 9. Continuously cast steel blooms
an etched transverse section, they appear as short, tight
and billets, in the as cast condition, shall be examined
discontinuities which are usually located in the midway to
according to the procedures described in Sections 10 and 11.
center location of the section. They are also known as shatter
With reductions over a 3:1 area ratio, wrought product from
cracks or hairline cracks.
continuously cast steel may be examined according to Section
3.2.3.9 gassy—irregularly-shaped voids which may, or may 9.
not, be uniformly distributed throughout the cross section.
5. Reagents
Thesemaybelocatedanywherefromthenearsurfaceregionof
the product to the center of the product, depending on the
5.1 The most common reagent for macroetching iron and
source and severity of the condition.
steel is a 1:1 mixture, by volume, of concentrated hydrochloric
3.2.3.10 dendritic—a “tree-like” pattern with branches (pri- acid (HCl) and water. The hydrochloric acid need not be
mary, secondary, and tertiary arms) due to compositional
reagent grade. Commercial quality hydrochloric acid (also
differences that arise during solidification. For a specific known as muriatic acid) is satisfactory. The etching solution
composition, a weak dendritic structure is associated with a
should be clear and free from scum. It should be hot, 70 to
low superheat while a strong dendritic structure is associated 80°C(160to180°F).Thereagentshouldbeusedunderafume
with a high superheat during casting. Compositional differ-
hood, or some other means of carrying off the corrosive fumes
ences also influence the clarity of the dendrites.
must be provided. The solution may be heated without serious
3.2.3.11 refilled crack—A defect formed during the solidi- change in concentration.The etching solution may be reused if
fication of continuously cast steel, either external (bulging) or it has not become excessively contaminated or weakened.
E381 − 01 (2006)
NOTE 1—The addition of hydrogen peroxide (H O ) may be necessary
6.3 The macroetch test, as applied to the inspection of steel
2 2
in order to provide sufficient reaction to properly etch some types of
products of this specification, is carried out on slices, usually
product.This should be added to an etching bath that is operating at room
13 to 25 mm ( ⁄2 to 1 in.) in thickness. Disks or specimens are
temperature.
usually cut to reveal a transverse surface, but the requirements
5.2 A second macroetching solution, favored by some as
of the specification, contract, or order may include the prepa-
producingaclearerstructure,iscomposedofconcentratedHCl
ration and examination of a longitudinal surface.
(38volume%),sulfuricacid,H SO (12volume%)andwater,
2 4
6.4 When the test is conducted on single pieces (bar, billet,
H O (50 volume %). (See 5.1 with respect to acid quality,
bloom,etc.),thepurchasermayspecifythatthespecimendisks
heating, and ventilation.)
be cut to represent both ends, or only one end, of the piece.
5.3 Observe caution in mixing macroetch solutions. The
6.5 When the test is conducted on a number of pieces made
acids are strong and they can cause serious chemical burns.
from a heat of steel, the purchaser may require that each piece
Add acid slowly to water with stirring. This is especially true
be individually tested; or, a representative method of sampling
for sulfuric acid. Mix solutions and macroetch under a fume
may be agreed upon by the manufacturer and the purchaser.
hood.
6.6 For the indication of certain internal types of disconti-
5.4 An ammonium persulfate solution, a 10 to 20% aque-
nuities, such as thermal cracks or flakes, the purchaser may
ous solution, is used primarily on longitudinal sections to
specify that disks for macroetch inspection be taken a certain
detect certain types of ghost lines, segregation, flow lines, etc.
minimum distance from the ends of the specimen. In the case
A freshly made solution is necessary for best results. The
of forgings, depending upon prior agreement, this may be
solution should be swabbed on the finished surface at room
accomplishedbyaddingexcessmetalfordiscardontheendsor
temperature. Inspection is most effective when done while the
ends of the forging; or, by forging in multiple lengths and
piece is still wet.
removing the test disk between individual pieces when cutting
5.5 Anitric acid solution, 5% or 10% nitric acid in alcohol
up the multiple forging.
or water, is used to detect local overstraining, grinding cracks,
overheated areas, and depth of carburized or decarburized 7. Preparation
surface zones. The use of this reagent necessitates a smooth
7.1 Specimen preparation need not be elaborate. Any
surface.Thereagentisusedatroomtemperaturebyimmersion
method of preparing smooth surfaces with a minimum amount
or swabbing.
of cold work should be satisfactory. Disks may be faced on a
5.6 Many other reagents have been used for special appli- latheorashaper.Theusualprocedureistotakearoughingcut,
cations. When the use of a reagent other than those described then a finishing cut. This will generate a smooth surface and
in 5.2-5.5 is desired, it should be by agreement between the remove cold work from prior operations. Sharp tools are
purchaser and the manufacturer. (See Test Method E340 for necessary to produce a good specimen. Grinding, which also
other etching solutions.) may be used, is usually conducted in the same manner, using
free-cutting wheels and light feeds. When fine detail must be
6. Sampling revealed,thespecimenshouldbepreparedwithmetallographic
grinding papers, or even with a metallographic polish.
6.1 When macroetching is used as an inspection procedure,
sampling should be done at an early stage of manufacture so 7.2 After specimen preparation, the surface to be etched
that, if the material is inadequate, the minimum amount of should be cleaned. Any grease, oil, or other residue will
produce an uneven attack and must be removed. It may be
unnecessary processing is done (or the processing can be
modified to salvage the material). For ingot cast product, the necessary to use solvents to clean the surface. Once clea
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