ASTM A561-71(1999)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:A 561–71 (Reapproved 1999)
Standard Practice for
Macroetch Testing of Tool Steel Bars
This standard is issued under the fixed designation A 561; 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 4.1.4 Cut specimens to expose a transverse section of the
bar; however, the test is occasionally performed on a longitu-
1.1 This practice for macroetch testing has been found to be
dinal section.
a useful and reliable method for evaluating the quality of tool
4.1.5 Specimens may be taken from one or both ends of a
steel bars. It is used as a quality control and inspection test to
bar. Each bar may be sampled, or a few typical specimens may
reveal by deep acid etching the macrostructure in specimens
be tested as representative of a large number of bars.
cut from bars and to show the presence of such conditions as
pipe, cracks, porosity, segregation, or foreign material. The
5. Specimen Preparation
etched surface is generally examined visually, but magnifica-
5.1 In all cutting and grinding operations on the specimen,
tion up to about 103 is occasionally employed.
care must be excercised to avoid heating the surface to an
2. Apparatus excessively high temperature. Specimens are cut from bars by
sawing, machining, abrasive wheel cutting, or other means.
2.1 Etching Containers—Macroetching may be performed
Cutting should be controlled to prevent smearing the cut face
in a vessel of borosilicate glass, porcelain, corrosion-resistant
and masking the structure.
metals, or some other acid-resisting material.
5.1.1 The “as-cut” surface of a specimen may be sufficiently
3. Reagent
smooth to reveal the defects for which the examination is
conducted. No additional surface preparation may then be
3.1 Etching Reagent—A solution of equal volumes of con-
necessary.
centrated hydrochloric acid (HCl, sp gr 1.19) and water is
5.1.2 Additional surface preparation may be required to
commonly used for macroetching tool steels. This solution
remove cutting marks and to allow details to be revealed by
must be used under a ventilating hood because HCl is volatile
etching. In such circumstances, machining, grinding, or pol-
and the fumes are corrosive and irritating, although nontoxic.
ishing may be necessary. Generally, the degree of surface
The solution may be reused within limits. With use, the
smoothness required is greater the finer the detail that must be
concentration of dissolved iron and other metals increases and
resolved. When the action of the etchant is drastic, a coarser
the acidity of the solution decreases retarding the etching
surface finish may be used.
action. Spent solution shall be replaced with fresh solution, not
5.1.3 The surface must be free of adhering grease and oil.
replenished with concentrated acid.
There should be no scale or oxide on the surface which will be
4. Sampling
examined after etching.
4.1 The selection of specimens for macroetch testing must
6. Procedure
be done with care for interpretations to be of value.
6.1 Temperature for Macroetching—Etching characteristics
4.1.1 Specimens are usually cut from hot-rolled annealed
are influenced markedly by the temperature of the etchant.
bars, but may be cut from machined or ground bars if the bars
Thus, the reagent temperature should be controlled for macro-
are to be finish machined or ground.
etching if comparative results are desired. Tool steels are
4.1.2 Thespecimenshouldbelocatedatasufficientdistance
generally macroetched at about 160°F (71°C).At this tempera-
from the end of the bar to avoid end effects.
1 1
ture, the etching reaction is vigorous and solution losses
4.1.3 For ease in handling, use specimens ⁄4 to ⁄2 in. (6.35
through evaporation are not excessive. The solution may be
to 12.7 mm) thick.
heated on a gas or electric hot plate, by an acid-proof
immersion heater, or by steam.
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
6.2 Etching Time—The etching time should be sufficiently
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
long to completely reveal the structure in the specimen, yet
A01.29 on Tool Steel.
should not be so long as to develop artifacts such as etch pits
Current edition approved Oct. 25, 1971. Published December 1971. Originally
published as A 561 – 66. Last previous edition A 561 – 66. or to obscure or obliterate the structure. Generally, etching
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