Designation: A 561 – 71 (Reapproved 2004)
Standard Practice for
Macroetch Testing of Tool Steel Bars
1
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
1.1 This practice for macroetch testing has been found to be
a useful and reliable method for evaluating the quality of tool
steel bars. It is used as a quality control and inspection test to
reveal by deep acid etching the macrostructure in specimens
cut from bars and to show the presence of such conditions as
pipe, cracks, porosity, segregation, or foreign material. The
etched surface is generally examined visually, but magnifica-
tion up to about 103 is occasionally employed.
2. Apparatus
2.1 Etching Containers—Macroetching may be performed
in a vessel of borosilicate glass, porcelain, corrosion-resistant
metals, or some other acid-resisting material.
3. Reagent
3.1 Etching Reagent—A solution of equal volumes of con-
centrated hydrochloric acid (HCl, sp gr 1.19) and water is
commonly used for macroetching tool steels. This solution
must be used under a ventilating hood because HCl is volatile
and the fumes are corrosive and irritating, although nontoxic.
The solution may be reused within limits. With use, the
concentration of dissolved iron and other metals increases and
the acidity of the solution decreases retarding the etching
action. Spent solution shall be replaced with fresh solution, not
replenished with concentrated acid.
4. Sampling
4.1 The selection of specimens for macroetch testing must
be done with care for interpretations to be of value.
4.1.1 Specimens are usually cut from hot-rolled annealed
bars, but may be cut from machined or ground bars if the bars
are to be finish machined or ground.
4.1.2 The specimen should be located at a sufficient distance
from the end of the bar to avoid end effects.
4.1.3 For ease in handling, use specimens
1
⁄
4
to
1
⁄
2
in. (6.35
to 12.7 mm) thick.
4.1.4 Cut specimens to expose a transverse section of the
bar; however, the test is occasionally performed on a longitu-
dinal section.
4.1.5 Specimens may be taken from one or both ends of a
bar. Each bar may be sampled, or a few typical specimens may
be tested as representative of a large number of bars.
5. Specimen Preparation
5.1 In all cutting and grinding operations on the specimen,
care must be excercised to avoid heating the surface to an
excessively high temperature. Specimens are cut from bars by
sawing, machining, abrasive wheel cutting, or other means.
Cutting should be controlled to prevent smearing the cut face
and masking the structure.
5.1.1 The “as-cut” surface of a specimen may be sufficiently
smooth to reveal the defects for which the examination is
conducted. No additional surface preparation may then be
necessary.
5.1.2 Additional surface preparation may be required to
remove cutting marks and to allow details to be revealed by
etching. In such circumstances, machining, grinding, or pol-
ishing may be necessary. Generally, the degree of surface
smoothness required is greater the finer the detail that must be
resolved. When the action of the etchant is drastic, a coarser
surface finish may be used.
5.1.3 The surface must be free of adhering grease and oil.
There should be no scale or oxide on the surface which will be
examined after etching.
6. Procedure
6.1 Temperature for Macroetching—Etching characteristics
are influenced markedly by the temperature of the etchant.
Thus, the reagent temperature should be controlled for macro-
etching if comparative results are desired. Tool steels are
generally macroetched at about 160°F (71°C). At this tempera-
ture, the etching reaction is vigorous and solution losses
through evaporation are not excessive. The solution may be
heated on a gas or electric hot plate, by an acid-proof
immersion heater, or by steam.
6.2 Etching Time—The etching time should be sufficiently
long to completely reveal the structure in the specimen, yet
should not be so long as to develop artifacts such as etch pits
or to obscure or obliterate the structure. Generally, etching
1
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
A01.29 on Tool Steel.
Current edition approved September 2004. Published January 2005. Originally
published as A 561 – 66. Last previous edition A 561 – 71 (1999).
1
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