ASTM B177-93

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
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Designation: B 177 – 93 Endorsed by American
Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Guide for
Chromium Electroplating on Steel for Engineering Use
This standard is issued under the fixed designation B 177; 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.
1. Scope B 602 Test Method for Attribute Sampling of Metallic and
Inorganic Coatings
1.1 This standard provides information about the deposition
B 630 Practice for Preparation of Chromium for Electro-
of chromium on steel for engineering uses. This is sometimes
plating with Chromium
called “functional” or “hard” chromium and is usually applied
B 650 Specification for Electrodeposited Engineering Chro-
directly to the basis metal and is much thicker than decorative
mium Coatings on Ferrous Surfaces
deposits.
B 697 Guide for Selection of Sampling Plans for Inspection
1.2 This specification is not intended as a standardized
of Electrodeposited Metallic and Inorganic Coatings
procedure, but as a guide for obtaining smooth, adherent
B 762 Test Method of Variables Sampling of Metallic and
coatings of chromium of a desired thickness while retaining the
Inorganic Coatings
required physical and mechanical properties of the steel base.
2.2 Military Standard:
Requirements for chromium electrodeposits on ferrous sur-
MIL-S-13165B Shot Peening of Metal Parts
faces are defined in Specification B 650.
1.3 This standard does not purport to address all of the
3. Nature of Steel
safety problems, if any, associated with its use. It is the
3.1 High Strength Steel—Since steel of high strength is
responsibility of the user of this standard to establish appro-
susceptible to cracking, the tensile strength of the steel should
priate safety and health practices and determine the applica-
not exceed 1000 MPa (150 000 psi) or a hardness of 32 HRC
bility of regulatory limitations prior to use.
unless the steel has been stress-relieved (3.4). Before electro-
2. Referenced Documents plating, heat-treated parts should be examined for cracks by
suitable techniques such as the fluorescent dye or magnetic
2.1 ASTM Standards:
powder methods. It is important that the hardness of the steel
B 183 Practice for Preparation of Low-Carbon Steel for
base be sufficient to withstand the service load without defor-
Electroplating
mation and consequent stress fracturing of the chromium
B 242 Practice for Preparation of High-Carbon Steel for
deposit.
Electroplating
3.2 Smoothness—The smoothness of the steel surface to be
B 322 Practice for Cleaning Metals Prior to Electroplating
electroplated should be adequate to meet the requirements of
B 487 Test Method for Measurement of Metal and Oxide
the finished product. Chromium electrodeposits do not exhibit
Coating Thicknesses by Microscopical Examination of a
leveling, and consequently the surface roughness of the elec-
Cross Section
trodeposit will always be greater than that of the substrate. Any
B 499 Test Method for Measurement of Coating Thick-
mechanical operations that can result in grinding checks or
nesses by the Magnetic Method: Nonmagnetic Coatings on
2 glazing of the steel are detrimental and should be eliminated.
Magnetic Basis Metals
The required surface smoothness may be obtained by suitable
B 504 Test Method for Measurement of Thickness of Me-
2 chemical, mechanical, or electrochemical procedures. Depend-
tallic Coatings by the Coulometric Method
ing upon the thickness of the electrodeposit and the smoothness
B 507 Practice for Design of Articles to Be Electroplated on
2 required of the electrodeposit, grinding of the electrodeposit
Racks
may be required.
B 571 Test Methods for Adhesion of Metallic Coatings
3.3 Fatigue Considerations—Cracking that can occur in
B 578 Test Method for Microhardness of Electroplated
chromium electrodeposits either as a function of the plating
Coatings
bath chemistry, the plating conditions, or both, or as a result of
grinding of the electrodeposit can lead to a reduction in the
This guide is under the jurisdiction of ASTM Committee B-8 on Metallic and
fatigue life of the electroplated part. If this is a design
Inorganic Coatings and is the direct responsibility of Subcommittee B08.08 on
Engineering Coatings.
Current edition approved Feb. 15, 1993. Published April 1993. Originally
published as B 177 – 55. Last previous edition B 177 – 68 (1984). Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700
Annual Book of ASTM Standards, Vol 02.05. Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
B 177
consideration, the use of mechanical methods such as shot shapes conforming to the shape of the part or area to be
peening (see MIL-S-13165C) or autofrettage to compressively electroplated.
stress the surfaces can increase the fatigue strength. This
4.2.4 It may be necessary to use thieves, robbers, or guards,
should be done after all stress relieving heat treatments.
which are auxiliary metallic conductors placed near points of
3.4 Stress Relief:
abnormally high current density to attract the current away
3.4.1 All steel parts having an ultimate tensile strength of
from such points; and shields, which are parts made of
1000 MPa (150 000 psi—approximately 32 HRC) or greater,
nonconductive materials and placed to disperse the current in
which may contain residual stress caused by various fabrica- areas where it tends to concentrate unduly.
tion operations such as machining, grinding, straightening, or
4.2.5 It is important to protect areas that are to remain free
cold forming, will require one of the following stress reliefheat
of any chromium electroplate by the use of masks made of
treatments (Table 1) prior to electroplating. In all cases, the
rigid, nonconductive materials placed against the substrate, or
duration of the heat treatment shall commence from the time at
stop-offs, which are especially compounded nonconductive
which the whole of each part attains the specified temperature.
tapes, waxes, lacquers, or plastics for the protection of such
This stress relief is essential if hydrogen embrittlement from
substrates. Lead tape will provide a sharp line of demarcation
subsequent operations is to be avoided.
between coated and uncoated areas with a minimum of
3.4.1.1 Parts having surface hardened areas that would
buildup.
suffer an unacceptable reduction in hardness by treatment in
4.2.6 Plugs (conducting and nonconducting) may be used in
accordance with Table 1 shall be heat-treated at a lower
holes not requiring electroplating to produce a sharp edge
temperature but not less than 130°C for a minimum period of
without grooves around the periphery of the holes.
8 h. Shorter times at higher temperatures may be used, if the
4.2.7 It is very important to remember that improperly
resulting loss in surface hardness is acceptable.
applied stop-off materials or poorly designed racks can entrap
3.5 Oxidation—All possible precautions should be taken to
acids that can cause corrosion of the basis metal, contamination
prevent oxidation of the steel surface between the final
of the solutions used in subsequent operations, or both.
operations of mechanical preparation and electroplating. When
4.2.8 Construction materials must be used that are suffi-
conditions are especially unfavorable, definite steps must be
ciently insoluble and noncontaminating to provide the desired
taken to meet this important requirement, including storage in
rack life.
a noncorrosive environment, or the use of a suitable coating to
4.2.9 Components must be placed in such positions that gas
exclude air and moisture.
from the parts, rack, thieves, masks, and anodes escapes freely
and does not become entrapped so as to prevent electroplating
4. Racks and Anodes
on areas that should be electroplated.
4.1 The parts to be electroplated may be racked at any
4.3 Anodes—Lead anodes containing 4 to 6 % antimony, 4
convenient stage in the preparatory process but preferably prior
to 7 % tin, or 1 % silver, or a combination thereof, are
to the final cleaning and etching.
satisfactory. Chemical lead is also satisfactory where hardness
4.2 See Practice B 507 for guidance on rack design, but note
and rigidity are not important. However, it tends to form
that while the general principles of good racking as used in
greater quantities of scale that may fall on the work and cause
other electroplating processes apply, the use of much higher
pitting or roughness. Lead wire used for small anodes should
current densities and the desirability of securing coatings of
contain 0.25 % antimony to obtain the best relationship be-
uniform thickness and quality on desired areas require rack
tween rigidity and ductility in close tolerance areas. Lead
construction designs and methods that are much more exacting.
sheathed steel, copper, or silver may be used when indicated by
The design of racks for chromium electroplating on steel for
the requirement for strength or conductivity. Platinum, plati-
functional use should provide for the following to the greatest
num clad titanium, platinum clad niobium, or even iron, steel
possible extent.
rods, or wire may be used for internal electroplating of small
4.2.1 There must be sufficient current-carrying capacity of
holes, but the latter will contaminate the bath with iron. If the
both cathode and anode circuits to all parts of the rack.
anode contains little or no lead, the reoxidation of trivalent
4.2.2 There must be positive electrical contact to the parts to
chromium to the hexavalent will not take place or will be
be electroplated, to the anodes, and to the tank contact bars.
seriously impaired, which will lead to trivalent buildup in the
4.2.3 There must be uniform current distribution on the
plating solution and poor results.
parts to be electroplated. This often requires anodes of special
4.3.1 Some proprietary baths may require special anodes,
which should be recommended by the supplier.
TABLE 1 Stress Relief Treatments
Time (h) 5. Cleaning
Class Temperature (°C) Tensile Strength (Rm) MPa
min
5.1 Parts to be electroplated may be cleaned in accordance
SR-1 200 to 230 24 over 1800
with Practices B 183, B 242 or B 322.
SR-2 190 to 220 24 over 1800
SR-3 200 to 230 18 1401 to 1800
5.2 Mechanical methods of cleaning prior to electroplating,
SR-4 190 to 220 18 1450 to 1800
including abrasive blasting or light grinding, are also suitable.
SR-5 177 to 205 3 1034 or greater
If parts have been shot peened to develop a compressively
SR-6 200 to 230 3 1000 to 1400
SR-7 190 to 220 1 1050 to 1450
stressed surface, it is important to avoid removing that surface
SR-8 130 to 160 8 surface hardened parts# 1400
by excessive grinding.
B 177
6. Etching the plating solution, plating is initiated when the parts are made
cathodic at the end of the etching period using the reversing
6.1 Etching of the steel before electroplating is ordinarily
switch.
desirable to obtain satisfactory adhesion of the chromium to the
7.2 Electroplating Baths—In addition to the following two
steel. To reduce the increase in roughness resulting from
baths, there are various proprietary baths offered that may be
etching, the etching times should be kept as short as is
satisfactory and should be operated in accordance with the
consistent with good adhesion, particularly in the case of
vendor’s instructions.
highly finished surfaces.
7.2.1 This is the most common bath and will deposit
6.2 Anodic Etching in Chromic Acid Solution—The part to
chromium at the approximate rate of 25 μm (0.001 in.) in 80
be electroplated may be anodically etched in a solution of
2 2
min at 31 A/dm (2.0 A/in. ).
approximately the same concentration of chromic acid as the
Chromic Acid (CrO ) 250 g/L
plating solution (for example, 250 g/L (33 oz/gal) at approxi-
Sulfate (SO ) 2.5 to 3.1 g/L
mately the temperature used in plating. There should not be any 2
Ratio CrO to SO 80 to 100
3 4
sulfuric acid present. Enter the tank with the current off and Temperature 55°C (range 40 to 65°C)
2 2
Current density 31 A/dm (2 A/in. )
make the part anodic for 10 s to 2 min at a current density of
2 2
Range 25 to 124 A/dm (1.6 to 8.0 A/in. )
2 2
11 to 32 A/dm (100 to 400 A/ft ). Tank voltage is normally 4
NOTE 1—Many factors influence the choice of current densities. With
to 5 V. There does not have to be rinsing before transfer to the
very great agitation, the highest current density shown is possible with a
plating tank, but the parts should be thoroughly drained to
concomitant decrease in the plating time. As the electrochemical efficiency
prevent spillage of the etching solution.
decreases somewhat with increasing current density and bath temperature,
6.3 Anodic Etching in the Plating Solution—Using the same
the increase in the plating rate is not linear with the increase in the current
times and current density described in 6.2, parts can be etched
density.
in the plating solution itself. A reversing switch should be NOTE 2—Chromium will plate satisfactorily from baths with chromic
acid as dilute as 75 g/L and as concentrated as 500 g/L. The lower
provided to make the part anodic. This process is much simpler
concentrations give increased efficiency but the throwing power, which is
than that in 6.2 and requires one less tank, but has the
always poor, gets worse. The normal high concentration bath is 400 g/L at
disadvantage of contaminating the bath with iron, copper, etc.
the same ratio of chromic acid to sulfate as is used with the common 250
6.4 Anodic Etching in Sulfuric Acid Solution—A sulfuric
g/L bath. The higher concentration bath gives slightly improved throwing
acid (H SO ) solution of 50 to 70 volume % 66 Be H SO may
power and a deposit that is slightly less prone to cracking.
2 4 2 4
be used for etching. The temperature should be kept below
NOTE 3—Warning: The sulfate anion (SO ) is added to the bath as
30°C and preferably below 25°C. The time of treatment is 10 sulfuric acid. The calculated amount should be diluted by adding it to
deionized water prior to adding it to the bath. Face shield, chemical
s to 2 min, and the current density 11 to 54 A/dm (100 to 500
goggles, rubber gloves, and other safety equipment should be used when
A/ft ) at 4 to 6 V. Lead cathodes should be used and the tank
handling sulfuric acid and when making t
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