ASTM B177-01(2006)e1

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Endorsed by American
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Designation:B177–01 (Reapproved 2006) Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
Standard Guide for
Engineering Chromium Electroplating
This standard is issued under the fixed designation B177; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
´ NOTE—Warning notes in 7.2.1, 7.2.2, and 7.2.3 were editorially updated in April 2006.
1. Scope B254 Practice for Preparation of and Electroplating on
Stainless Steel
1.1 This guide provides information about the deposition of
B281 Practice for Preparation of Copper and Copper-Base
chromium on steel for engineering uses. This is sometimes
Alloys for Electroplating and Conversion Coatings
called “functional” or “hard” chromium and is usually applied
B320 Practice for Preparation of Iron Castings for Electro-
directlytothebasismetalandisusuallythickerthandecorative
plating
deposits.
B322 Guide for Cleaning Metals Prior to Electroplating
1.2 This guide is not intended as a standardized procedure,
B481 Practice for Preparation of Titanium and Titanium
but as a guide for obtaining smooth, adherent coatings of
Alloys for Electroplating
chromium of a desired thickness while retaining the required
B487 Test Method for Measurement of Metal and Oxide
physical and mechanical properties of the base metals. Speci-
CoatingThicknessbyMicroscopicalExaminationofCross
fied chromium electrodeposits on ferrous surfaces are defined
Section
in Specification B650.
B499 Test Method for Measurement of Coating Thick-
1.3 This standard does not purport to address all of the
nessesbytheMagneticMethod:NonmagneticCoatingson
safety concerns, if any, associated with its use. It is the
Magnetic Basis Metals
responsibility of the user of this standard to establish appro-
B504 Test Method for Measurement of Thickness of Me-
priate safety and health practices and determine the applica-
tallic Coatings by the Coulometric Method
bility of regulatory limitations prior to use.
B507 Practice for Design ofArticles to Be Electroplated on
2. Referenced Documents Racks
B558 Practice for Preparation of NickelAlloys for Electro-
2.1 ASTM Standards:
plating
B183 Practice for Preparation of Low-Carbon Steel for
B568 Test Method for Measurement of Coating Thickness
Electroplating
by X-Ray Spectrometry
B242 Guide for Preparation of High-Carbon Steel for Elec-
B571 Practice for Qualitative Adhesion Testing of Metallic
troplating
Coatings
B244 TestMethodforMeasurementofThicknessofAnodic
B578 Test Method for Microhardness of Electroplated
Coatings onAluminum and of Other Nonconductive Coat-
Coatings
ings on Nonmagnetic Basis Metals with Eddy-Current
B602 Test Method for Attribute Sampling of Metallic and
Instruments
Inorganic Coatings
B253 Guide for Preparation of Aluminum Alloys for Elec-
B630 Practice for Preparation of Chromium for Electroplat-
troplating
ing with Chromium
B650 Specification for Electrodeposited Engineering Chro-
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and mium Coatings on Ferrous Substrates
Inorganic Coatings and is the direct responsibility of Subcommittee B08.08.01 on
B697 Guide for Selection of Sampling Plans for Inspection
Engineering Coatings.
of Electrodeposited Metallic and Inorganic Coatings
Current edition approved April 1, 2006. Published April 2006. Originally
B762 Test Method of Variables Sampling of Metallic and
approved in 1955. Last previous edition approved in 2001 as B177 – 01. DOI:
10.1520/B0177-01R06E01.
Inorganic Coatings
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
B849 Specification for Pre-Treatments of Iron or Steel for
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Reducing Risk of Hydrogen Embrittlement
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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B177–01 (2006)
B850 Guide for Post-Coating Treatments of Steel for Re- with Specification B849 may be baked at a lower temperature
ducing the Risk of Hydrogen Embrittlement but not less than 130°C for a minimum period of 8 h. Shorter
B851 Specification forAutomated Controlled Shot Peening times at higher temperatures may be used, if the resulting loss
of Metallic Articles Prior to Nickel, Autocatalytic Nickel, in surface hardness is acceptable.
or Chromium Plating, or as Final Finish
3.5 Oxidation—All possible precautions should be taken to
F519 Test Method for Mechanical Hydrogen Embrittlement prevent oxidation of the metal surface between the final
Evaluation of Plating/Coating Processes and Service Envi-
operations of mechanical preparation and electroplating, par-
ronments ticularly with steel substrates. Materials such as aluminum and
2.2 Military Standard:
titanium have an inherent oxide film on the surface that can
MIL-S-13165B Shot Peening of Metal Parts only be removed or minimized just prior to the electroplating
process (see 6.1.1 and 6.1.2). When conditions are especially
3. Substrates
unfavorable,definitestepsmustbetakentomeetthisimportant
3.1 Engineering chromium may be plated directly to the requirement, including storage in a noncorrosive environment,
or the use of a suitable coating to exclude air and moisture.
surface of a number of commonly used engineering metals
such as aluminum, nickel alloys, cast iron, steels, copper,
copper alloys, and titanium. The bond strengths of the chro- 4. Racks andAnodes
mium varies with metallic substrate. Nevertheless, if the
4.1 Steel, cast iron, and stainless steel parts to be electro-
procedures cited in the appropriate references are followed, the
platedmayberackedatanyconvenientstageinthepreparatory
bond strength is such that grinding and honing can be con-
process but preferably prior to the final cleaning and etching.
ducted without delamination of the coating.
Aluminum, titanium, and certain nickel alloys may need to
3.2 Smoothness—The smoothness of the material surface to
have cleaning and etching operations done before racking due
be electroplated should be adequate to meet the requirements
to entrapment of cleaning and etching solutions in the plating
of the finished product. Chromium electrodeposits do not
rack which can result in adhesion failures due to seepage
exhibit leveling, and consequently the surface roughness of the
during chromium electroplating.
electrodeposit will always be greater than that of the substrate.
4.2 See Practice B507 for guidance on rack design, but note
Any mechanical operations that can result in grinding checks
that while the general principles of good racking as used in
or glazing of the metal are detrimental and should be elimi-
other electroplating processes apply, the use of much higher
nated. The required surface smoothness may be obtained by
current densities and the desirability of securing coatings of
suitable chemical, mechanical, or electrochemical procedures.
uniform thickness and quality on desired areas require rack
Depending upon the thickness of the electrodeposit and the
constructiondesignsandmethodsthataremuchmoreexacting.
smoothness required of the electrodeposit, grinding of the
Thedesignofracksforchromiumelectroplatingonthevarious
electrodeposit may be required.
base metals previously mentioned for functional use should
3.3 Fatigue Considerations—Cracking that can occur in
provide for the following to the greatest possible extent.
chromium electrodeposits either as a function of the plating
4.2.1 There must be sufficient current-carrying capacity of
bath chemistry or the plating conditions, or both, or as a result
both cathode and anode circuits to all parts of the rack.
of grinding of the electrodeposit can lead to a reduction in the
4.2.2 Theremustbepositiveelectricalcontacttothepartsto
fatigue life of the electroplated part. If this is a design
beelectroplated,totheanodes,andtothetankcontactbusbars.
consideration, the use of mechanical methods such as shot
4.2.3 There must be uniform current distribution on the
peening (see Specification B851 or MIL-S-13165C, or both) or
parts to be electroplated. This often requires anodes of special
autofrettage to compressively stress the surface can increase
shapes conforming to the shape of the part or area to be
the fatigue strength. This should be done after any stress-
electroplated.
relieving heat treatment.
4.2.4 It may be necessary to use thieves, robbers, or guards,
3.4 High-Strength Steel Stress Relief:
which are auxiliary metallic conductors placed near points of
3.4.1 All steel parts having an ultimate tensile strength of
abnormally high current density to attract the current away
1000 MPa (150 000 psi, approximately 32 HRC) or greater,
from such points; and shields, which are parts made of
which may contain residual stress caused by various fabrica-
nonconductive materials and placed to disperse the current in
tion operations such as machining, grinding, straightening, or
areas where it tends to concentrate unduly.
cold-forming, usually will require one of the stress relief bakes
4.2.5 It is important to protect areas that are to remain free
prescribed in Specification B849 prior to electroplating. In all
of any chromium electroplate by the use of masks made of
cases, the duration of the bake shall commence from the time
rigid, nonconductive materials placed against the substrate, or
at which the whole of each part attains the specified tempera-
stop-offs, which are especially compounded nonconductive
ture. This stress relief is essential if hydrogen embrittlement
tapes, waxes, lacquers, or plastics for the protection of such
from subsequent operations is to be avoided.
substrates. Lead and aluminum tapes will provide a sharp line
3.4.2 Parts having surface-hardened areas that would suffer
of demarcation between coated and uncoated areas with a
an unacceptable reduction in hardness by baking in accordance
minimum of buildup.
4.2.6 Plugs (conducting and nonconducting) may be used in
holes not requiring electroplating to produce a sharp edge
AvailablefromStandardizationDocumentsOrderDesk,Bldg.4SectionD,700
Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS. without grooves around the periphery of the holes.
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B177–01 (2006)
4.2.7 It is very important to remember that improperly 6.1.2 Titanium—Like aluminum, titanium has an ever-
applied stop-off materials or poorly designed racks can entrap present tenacious oxide film that must be removed prior to
acids that can cause corrosion of the basis material or contami- plating. Practice B481 offers many ways to prepare titanium
nation of the solutions used in subsequent operations, or both. prior to chromium electroplating.
4.2.8 Construction materials must be used that are suffi- 6.1.3 Nickel Alloys—Several different activation methods
ciently insoluble and noncontaminating to provide the desired
are available in Practice B558 for the preparation of different
rack life.
nickel alloys. The main difficulty with these materials when
4.2.9 Components must be placed in such positions that gas
chromium plating is polarization of the nickel alloy surface
from the parts, rack, thieves, masks, and anodes escapes freely priortoplatingwhichresultsindeactivationofthematerialand
and does not become entrapped so as to prevent electroplating
skip plating.
on areas that should be electroplated.
6.1.4 Copper and Copper Alloys—Practice B281 offers
4.3 Anodes—Lead anodes containing 4 to 6 % antimony, 4
many suitable methods for preparing copper and copper alloys
to 7 % tin, or 1 % silver, or a combination thereof, are
prior to chromium electroplating. In general, only deoxidizing
satisfactory. Chemical lead is also satisfactory where hardness
of the copper or copper alloy surface is necessary for chro-
and rigidity are not important. However, it tends to form great
mium electroplating.
quantities of scale that may fall off on the work and cause
6.1.5 Stainless Steel—Practice B254 offers many suitable
pitting or roughness. Lead wire used for small anodes should
activating procedures for the preparation of stainless steel prior
contain 0.25 % antimony to obtain the best relationship be-
to chromium electroplating. Some stainless steels benefit from
tween rigidity and ductility in close tolerance areas. Lead-
a Woods nickel strike prior to chromium electroplating. Polar-
sheathedsteel,copper,orsilvermaybeusedwhenindicatedby
ized surfaces in high-nickel stainless steels can cause skip
requirements for strength or conductivity. Platinum, platinum-
plating if not properly activated.
clad niobium, or even steel rods or wire may be used for
6.1.6 Cast Iron—Practice B320 offers many suitable proce-
internal electroplating of small holes, but the latter will
dures for activating cast iron prior to chromium electroplating.
contaminatethebathwithiron.Iftheanodecontainslittleorno
In general, anodic etching in the chromium plating solution is
lead, the reoxidation of trivalent chromium to the hexavalent
not recommended. Due to the high carbon content in iron
state will not take place or will be seriously impaired, which
castings, anodic etching leaves a carbon smut on the surface of
will lead to trivalent buildup in the plating solution and poor
the metal which results in poor adhesion of the chromium.
results.
6.2 Chromium plating on steel is among the most common
4.3.1 Some proprietary baths may require special anodes,
combination for engineering purposes. Unique activation pro-
which should be recommended by the supplier.
cedures for steel exist with chromium plating that merit a
separate discussion for successful plating as follows.
5. Cleaning
6.2.1 Etching of the steel before electroplating is ordinarily
5.1 Parts to be electroplated may be cleaned in accordance
desirabletoobtainsatisfactoryadhesionofthechromiumtothe
with Practices B183, B242, B254, B281, B320, B322, B481,
steel. To reduce the increase in roughness resulting from
B558,or B630, or Guide B253.
etching, the etching times should be kept as short as is
5.2 Mechanical methods of cleaning steel prior to electro-
consistent with good adhesion, particularly in the case of
plating, including abrasive blasting or light grinding, are also
highly finished surfaces.
suitable. If parts have been shot-peened to develop a compres-
6.2.2 Anodic Etching in Chromic Acid Solution—The part
sivel
...