ASTM B242-99(2014)
(Guide)Standard Guide for Preparation of High-Carbon Steel for Electroplating
Standard Guide for Preparation of High-Carbon Steel for Electroplating
ABSTRACT
This guide outlines the standard procedure for establishing and maintaining a preparatory cycle for electroplating on high carbon steel producing minimal hydrogen embrittlement and maximal adhesion of the electrodeposited metal. The reagents needed for this method are technical grade hydrochloric acid, nitric acid, sulfuric acid, and water. Steel substrates shall conform to required hardness, hydrogen embrittlement, and surface oxidation characteristics, and quality. Proper preplating treatments such as precleaning, stress relief treatment, mechanical treatment, electrolytic anodic cleaning, hydrochloric acid treatment, treatment for smut removal, anodic acid etching, and electropolishing shall be performed. Coating adhesion and embrittlement shall be tested.
SCOPE
1.1 This guide is intended as an aid in establishing and maintaining a preparatory cycle for electroplating on high-carbon steel (Note 1) producing a minimum of hydrogen embrittlement and maximum adhesion of the electrodeposited metal. For the purpose of this guide, steels containing 0.35 % of carbon or more, and case-hardened low-carbon steel, are defined as high-carbon steels. There is no generally recognized definite carbon content dividing high from low-carbon steels for electroplating purposes.
Note 1: Electroplating of plain high-carbon steel introduced problems not found in similar operations on low-carbon steel. During the cleaning and electroplating cycle, high-carbon steel differs from low-carbon steel in regard to its greater tendency to become embrittled and the greater difficulty in obtaining maximum adhesion of the electrodeposit. The preparation of low-carbon steel for electroplating is covered in Practice B183.
1.2 This guide does not apply to the electroplating of alloy steel. For methods of chromium electroplating directly on steel see Guide B177.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety problems 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. For a specific hazards statement, see 3.1.
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Designation: B242 − 99(Reapproved 2014) Endorsed by American
Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
Standard Guide for
Preparation of High-Carbon Steel for Electroplating
This standard is issued under the fixed designation B242; 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.
1. Scope B183 Practice for Preparation of Low-Carbon Steel for
Electroplating
1.1 This guide is intended as an aid in establishing and
B849 Specification for Pre-Treatments of Iron or Steel for
maintaining a preparatory cycle for electroplating on high-
Reducing Risk of Hydrogen Embrittlement
carbon steel (Note 1) producing a minimum of hydrogen
B850 Guide for Post-CoatingTreatments of Steel for Reduc-
embrittlement and maximum adhesion of the electrodeposited
ing the Risk of Hydrogen Embrittlement
metal. For the purpose of this guide, steels containing 0.35 %
of carbon or more, and case-hardened low-carbon steel, are
3. Reagents
defined as high-carbon steels. There is no generally recognized
definite carbon content dividing high from low-carbon steels
3.1 PurityofReagents—Allacidsandchemicalsusedinthis
for electroplating purposes.
practice are technical grade.Acid solutions are based upon the
following assay materials:
NOTE 1—Electroplating of plain high-carbon steel introduced problems
Hydrochloric acid (HCl) 31 mass %, density 1.16 g/mL
not found in similar operations on low-carbon steel. During the cleaning
andelectroplatingcycle,high-carbonsteeldiffersfromlow-carbonsteelin Nitric acid (HNO ) 67 mass %, density 1.40 g/mL
regard to its greater tendency to become embrittled and the greater
Sulfuric acid (H SO ) 93 mass %, density 1.83 g/mL
2 4
difficulty in obtaining maximum adhesion of the electrodeposit. The
(Warning—Dilute sulfuric acid by slowly adding it to the
preparation of low-carbon steel for electroplating is covered in Practice
approximateamountofwaterrequiredwithrapidmixing.After
B183.
cooling, bring the mixture to exact volume.)
1.2 This guide does not apply to the electroplating of alloy
3.2 Purity of Water—Use ordinary industrial or potable
steel. For methods of chromium electroplating directly on steel
water for preparing solutions and rinsing.
see Guide B177.
1.3 The values stated in SI units are to be regarded as
4. Nature of Steel
standard. No other units of measurement are included in this
standard. 4.1 Hardness—High hardness is a major cause of cracking
of the steel during or after electroplating. The recommended
1.4 This standard does not purport to address all of the
maximum hardness range for classes of products depends on
safety problems associated with its use. It is the responsibility
their geometry and service requirements (Note 2). Parts hard-
of the user of this standard to establish appropriate safety and
ened by heat treatment should be inspected before electroplat-
health practices and determine the applicability of regulatory
ing for the presence of cracks by a suitable method, such as
limitations prior to use. For a specific hazards statement, see
magnetic or fluorescent powder inspection.
3.1.
NOTE 2—Some examples of parts and Rockwell hardness ranges are as
2. Referenced Documents
follows:
2.1 ASTM Standards:
Rockwell Hard-
B177 Guide for Engineering Chromium Electroplating ness Range
Springs C45 to C48
Spring washers C45 to C53
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
Small instrument parts C52 to C55
Inorganic Coatingsand is the direct responsibility of Subcommittee B08.02 on Pre
Parts to be chromium electroplated C57 to C62
Treatment.
for engineering use
Current edition approved Nov. 1, 2014. Published November 2014. Originally
4.2 Hydrogen Embrittlement—Difficulties resulting from
approvedin1949.Lastpreviouseditionapprovedin2009asB242 – 99(2009).DOI:
10.1520/B0242-99R14.
hydrogen embrittlement increase with increasing hardness,
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
whether produced by heat treatment or cold work. Difficulties,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
during or after electroplating of hardened high-carbon steel
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. parts, may in some cases be minimized without material
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B242 − 99 (2014)
change in hardness by baking before final pretreatment. For a 5.3 Pretreatment Time—All processing steps involving hy-
listing of such hydrogen embrittlement relief bake cycles, drogen generation must be designed to operate for a minimum
length of time, to avoid hydrogen embrittlement of the high-
consult Guide B850.
carbon steel.
4.3 Surface Oxidation—In order that subsequent treatments
5.4 Control—All pretreatment steps should be carried out
be facilitated, every reasonable precaution should be taken
with solutions that are maintained in good working condition
throughouttheprocessingtolimitoxidationorscaleformation.
by control of composition and contaminants, and used under
In particular cases pre-electroplating with copper to a mini-
conditions of time, temperature and current density specified to
mum thickness of 13 µm may assist in maintaining a preferred
meet the requirement of the work being processed.
surface through the heat treatment.Anonoxidizing atmosphere
should be maintained in the furnace. This copper shall be
5.5 Pretreatment Cycle Design—Depending upon the re-
removed prior to the regular electroplating cycle. Care should quirements for the particular high-carbon steel parts to be
be used in oil-quenching parts heat treated in a salt bath, to
electroplated, a minimum cycle should be selected from the
prevent the charring effect that can be caused by salt-bath generalstepslistedin5.1.Differentclassesofmaterialsrequire
drag-out. Proper lead-bath quenching results in only slight selected process steps combined into pretreatment cycles of
oxidation. greater or less complexity according to the condition and
properties of the material. The minimum number of steps
4.4 Steel Quality—The quality of the steel should be char-
necessary to accomplish the electroplating satisfactorily is
acteristic of the requirement of the product and the electroplat-
recommended.
ing operation. The steel should be free of injurious surface
defects, and of at least average cleanliness.
6. Preliminary Pretreatment Procedures
6.1 Application—Degreasing and mechanical surface treat-
5. Preparation of Steel, General
ment are necessary only where the high-carbon steel parts are
5.1 Preparatory Treatments—A wide variety of surface contaminated to such an extent that otherwise the burden
imposed on the pretreatment cycle would impair its efficiency,
conditions are encountered in high-carbon steel articles to be
electroplated. The surface may require the removal of one or increase its complexity, and tend to prevent the attainment of
the required quality of the deposit. The overall cost of the
more of the following contaminants: grease, oil or drawing
electroplating process is usually reduced by using the prelimi-
compounds, burned-in oil scale, light to heavy treatment scale,
nary treatments where applicable. Oil, grease, dirt, drawing
permeable oxide films, emery and fine steel particles resulting
compounds, burnt-in oil, heavy scale, and emery and steel
fromthegrindingoperation.Theremovalofsuchcontaminants
particles are typical of the gross contaminants encountered.
is accomplished by one or more of the following pretreatment
procedures where applicable:
6.2 Precleaning—Solvent-degreasing with clean solvent,
5.1.1 Substantial removal of oil, grease, and caked-on dirt
spray-washing, or emulsion-cleaning, followed by electrolytic
by precleaning before the part enters the electroplating cycle
or soak-alkali cleaners are recommended.The former types are
(applicable in all cases). preferred to reduce the burden on the alkali treatments.
Soak-alkali cleaning is usual for parts that are to be barrel
5.1.2 Mechanical treatment of the surface by tumbling, sand
electroplated. Electrolytic cleaning should always be anodic
or grit blasting, vapor blasting, or grinding (optional).
where the control of embrittlement is a problem.
5.1.3 Final and complete anodic cleaning in an electrolytic
alkali cleaner. 6.3 Stress Relief Treatment—It is recommended that hard-
ened high-carbon steel parts receive a stress-relief bake before
5.1.4 AcidtreatmentinHCltoremovethelasttraceofoxide
the parts are mechanically pretreated or enter the final pretreat-
and scale. This should be avoided for spring temper and
ment cycle, or both. For a listing of typical stress-relief bakes,
case-hardened parts. This treatment also removes residual
consult Specification B849.
traces of lead that may be present following proper lead-bath
quenching.
6.4 Mechanical Treatment—The purpose of mechanical
5.1.5 Smut removal by cyanide dipping or by anodic treat- treatment is to reduce subsequent acid pickling to a minimum.
Where mechanical treatment has been accomplished with
ment in cyanide or alkali.
precision, it is sometimes possible to eliminate acid pickling
5.1.6 Final preparation for electroplating may be accom-
entirely,thusimprovingthecontrolofhydrogenembrittlement.
plished by an anodic etching treatment in H SO (used when-
2 4
When required, mechanical treatment of small parts is best
ever possible in the interest of high yield and adhesion).
effected by tumbling. All scaled and nearly all oil-quenched
5.1.7 Conditioning of the surface to be electroplated may be
materials require mechanical cleaning such as by tumbling
accomplished, where necessary for the electroplating process,
with or without abrasive, or by sand, grit, or vapor blasting.
by a short dip or rinse in a solution equivalent to the
These operations should be carried out so as to avoid severe
electroplating solution without its metallic content.
roughening of the surface with accompanying notch effect.
5.2 Rinsing—Inadequate rinsing after each solution treat-
One resorts to grinding in certain cases where the surface
ment step is the recognized cause of a large portion of smoothness or dimensions of the parts are of critical
electroplating difficulties. Not enough rinsing is characteristic importance, for example, in chromium electroplating for engi-
of most pretreatment cycles. neering use.
B242 − 99 (2014)
7. Final Pretreatment Procedures interfere with adhesion. Inhibitors are of benefit only in special
cases where surface finish and dimensions are of prime
7.1 Application—Final cleaning, oxide removal, and anodic
importance.
acid treatment are fundamental steps required for preparing
high-carbon steel for electroplating. These pretreatment steps
7.5 Treatment for Smut Removal—When the HCl treatment
are designed to assist in the control of hydrogen embrittlement
of the high-carbon steel results in the presence of smut, the
and in securing the maximum adhesion of the electroplated
smut must be removed before the surface is electroplated.
coating.
Light oxides formed on exposure to air after acid treatment
must likewise be removed. This can be done by an anodic
7.2 Electrolytic Anodic Cleaning:
cyanide or alkaline treatment. Air-formed oxide, if not too
7.2.1 All work, except work to be barrel electroplated,
heavy, can be removed by a cyanide dip after the rinse
should preferably be cleaned in an electrolytic anodic alkaline
following the acid treatment. A concentration of 22 g/L of
cleaner. Anodic cleaning is recommended to avoid hydrogen
NaCN is sufficient for the cyanide dip. Where a severe smut
embrittlementthatislikelytoresultfromcathodiccleaning.An
condition exists, it can be eliminated by a ⁄2 to 1-min anodic
exception is barrel work which, because of the work size, is
treatment at 1.5 to 2 A/dm in a solution of a NaCN of the
preferably cleaned by soaking or tumbling in an alkaline
noncritical concentration of 45 g/L used at room temperature.
cleaning solution without the use of current.
An alternative treatment for a somewhat lighter smut condition
7.2.2 The purpose of this cleaning step is to remove
is electrolytic anodic treatment in the noncyanide alkaline
completelythelasttracesofcontaminants.Inallcasesitshould
cleaning solution (6.3) above 70°C, for 15 to 30 s at 2.5 to 5
be preceded by heavy-duty precleaning as covered in 6.2.
A/dm . The current density is not critical.
7.2.3 The electrolytic anodic cleaner should be used at a
7.6 Anodic Acid Etching:
temperature of 90°C or higher, and at a current density of 5
A/dm or higher, in order that the required degree of cleanli-
7.6.1 The use of an anodic acid etch and subsequent rinse as
ness be obtained in a time period not exceeding 2 min.
final steps in the preparation for electroplating of high-carbon
7.2.4 On removal from the cleaner, the work should be steel is of importance in securing adhesion. Without such an
thoroughlyrinsed,firstwithwaterwarmedto50°C,andthenin
anodic treatment, poor adhesion may occur. The anodic acid
a cold-water spray at room temperature, prior to the acid dip. treatment is capable of removing a small amount of smut
formed by the preceding HCl treatment; more substantial
7.3 Rinsing:
amounts of smut should be removed according to the proce-
7.3.1 The most thorough fresh-water rinsing operation pos-
dures described in 6.5.
sible is mandatory after each processing step if the best results
7.6.2 A150 to 600 mL/L H SO solution used at a tempera-
2 4
in electroplating high-carbon steel are to be obtained. The
ture of not more than 30°C, and preferably below 25°C, is
purpose of rinsing is to eliminate drag-over by complete
effective for anodic etching of high-carbon steel. See Warning
removaloftheprecedingsolutionfromthesurfaceofthework.
in 3.1. The addition of 125 g/L of Na SO (based on the
2 4
Many existing commercial operations are characterized by
anhydrous salt) is of benefit for many steel grades. Anodic
inadequate rinsing.
treatment in this solution for a time usually not exceeding 1
7.3.2 Warm to hot rinses should be used following alkaline
2 2
min at a current density of 16A/dm (range of 10 to 43A/dm )
solutions or where the subsequent processing solution is hot.
is sufficient.Ahigh acid content, high current density, and low
Therinsetemperatureshouldnotbesohighastoinducedrying
temperature (with reference to the ranges specified) will
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B242 − 99 (Reapproved 2009) B242 − 99 (Reapproved 2014) Endorsed by American
Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
Standard Guide for
Preparation of High-Carbon Steel for Electroplating
This standard is issued under the fixed designation B242; 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.
1. Scope
1.1 This guide is intended as an aid in establishing and maintaining a preparatory cycle for electroplating on high-carbon steel
(Note 1) producing a minimum of hydrogen embrittlement and maximum adhesion of the electrodeposited metal. For the purpose
of this guide, steels containing 0.35 % of carbon or more, and case-hardened low-carbon steel, are defined as high-carbon steels.
There is no generally recognized definite carbon content dividing high from low-carbon steels for electroplating purposes.
NOTE 1—Electroplating of plain high-carbon steel introduced problems not found in similar operations on low-carbon steel. During the cleaning and
electroplating cycle, high-carbon steel differs from low-carbon steel in regard to its greater tendency to become embrittled and the greater difficulty in
obtaining maximum adhesion of the electrodeposit. The preparation of low-carbon steel for electroplating is covered in Practice B183.
1.2 This guide does not apply to the electroplating of alloy steel. For methods of chromium electroplating directly on steel see
Guide B177.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety problems 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. For a specific hazards statement, see 3.1.
2. Referenced Documents
2.1 ASTM Standards:
B177 Guide for Engineering Chromium Electroplating
B183 Practice for Preparation of Low-Carbon Steel for Electroplating
B849 Specification for Pre-Treatments of Iron or Steel for Reducing Risk of Hydrogen Embrittlement
B850 Guide for Post-Coating Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement
3. Reagents
3.1 Purity of Reagents—All acids and chemicals used in this practice are technical grade. Acid solutions are based upon the
following assay materials:
Hydrochloric acid (HCl) 31 mass %, density 1.16 g/mL
Nitric acid (HNO ) 67 mass %, density 1.40 g/mL
Sulfuric acid (H SO ) 93 mass %, density 1.83 g/mL
2 4
(Warning—Dilute sulfuric acid by slowly adding it to the approximate amount of water required with rapid mixing. After
cooling, bring the mixture to exact volume.)
3.2 Purity of Water—Use ordinary industrial or potable water for preparing solutions and rinsing.
4. Nature of Steel
4.1 Hardness—High hardness is a major cause of cracking of the steel during or after electroplating. The recommended
maximum hardness range for classes of products depends on their geometry and service requirements (Note 2). Parts hardened by
heat treatment should be inspected before electroplating for the presence of cracks by a suitable method, such as magnetic or
fluorescent powder inspection.
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.02 on Pre
Treatment.
Current edition approved Sept. 1, 2009Nov. 1, 2014. Published December 2009November 2014. Originally approved in 1949. Last previous edition approved in 20042009
ε1
as B242 – 99(2004)(2009). . DOI: 10.1520/B0242-99R09.10.1520/B0242-99R14.
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 the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B242 − 99 (2014)
NOTE 2—Some examples of parts and Rockwell hardness ranges are as follows:
Rockwell Hard-
ness Range
Springs C45 to C48
Spring washers C45 to C53
Small instrument parts C52 to C55
Parts to be chromium electroplated C57 to C62
for engineering use
Rockwell Hard-
ness Range
Springs C45 to C48
Spring washers C45 to C53
Small instrument parts C52 to C55
Parts to be chromium electroplated C57 to C62
for engineering use
4.2 Hydrogen Embrittlement—Difficulties resulting from hydrogen embrittlement increase with increasing hardness, whether
produced by heat treatment or cold work. Difficulties, during or after electroplating of hardened high-carbon steel parts, may in
some cases be minimized without material change in hardness by baking before final pretreatment. For a listing of such hydrogen
embrittlement relief bake cycles, consult Guide B850.
4.3 Surface Oxidation—In order that subsequent treatments be facilitated, every reasonable precaution should be taken
throughout the processing to limit oxidation or scale formation. In particular cases pre-electroplating with copper to a minimum
thickness of 13 μm may assist in maintaining a preferred surface through the heat treatment. A nonoxidizing atmosphere should
be maintained in the furnace. This copper shall be removed prior to the regular electroplating cycle. Care should be used in
oil-quenching parts heat treated in a salt bath, to prevent the charring effect that can be caused by salt-bath drag-out. Proper
lead-bath quenching results in only slight oxidation.
4.4 Steel Quality—The quality of the steel should be characteristic of the requirement of the product and the electroplating
operation. The steel should be free of injurious surface defects, and of at least average cleanliness.
5. Preparation of Steel, General
5.1 Preparatory Treatments—A wide variety of surface conditions are encountered in high-carbon steel articles to be
electroplated. The surface may require the removal of one or more of the following contaminants: grease, oil or drawing
compounds, burned-in oil scale, light to heavy treatment scale, permeable oxide films, emery and fine steel particles resulting from
the grinding operation. The removal of such contaminants is accomplished by one or more of the following pretreatment
procedures where applicable:
5.1.1 Substantial removal of oil, grease, and caked-on dirt by precleaning before the part enters the electroplating cycle
(applicable in all cases).
5.1.2 Mechanical treatment of the surface by tumbling, sand or grit blasting, vapor blasting, or grinding (optional).
5.1.3 Final and complete anodic cleaning in an electrolytic alkali cleaner.
5.1.4 Acid treatment in HCl to remove the last trace of oxide and scale. This should be avoided for spring temper and
case-hardened parts. This treatment also removes residual traces of lead that may be present following proper lead-bath quenching.
5.1.5 Smut removal by cyanide dipping or by anodic treatment in cyanide or alkali.
5.1.6 Final preparation for electroplating may be accomplished by an anodic etching treatment in H SO (used whenever
2 4
possible in the interest of high yield and adhesion).
5.1.7 Conditioning of the surface to be electroplated may be accomplished, where necessary for the electroplating process, by
a short dip or rinse in a solution equivalent to the electroplating solution without its metallic content.
5.2 Rinsing—Inadequate rinsing after each solution treatment step is the recognized cause of a large portion of electroplating
difficulties. Not enough rinsing is characteristic of most pretreatment cycles.
5.3 Pretreatment Time—All processing steps involving hydrogen generation must be designed to operate for a minimum length
of time, to avoid hydrogen embrittlement of the high-carbon steel.
5.4 Control—All pretreatment steps should be carried out with solutions that are maintained in good working condition by
control of composition and contaminants, and used under conditions of time, temperature and current density specified to meet the
requirement of the work being processed.
5.5 Pretreatment Cycle Design—Depending upon the requirements for the particular high-carbon steel parts to be electroplated,
a minimum cycle should be selected from the general steps listed in 5.1. Different classes of materials require selected process steps
combined into pretreatment cycles of greater or less complexity according to the condition and properties of the material. The
minimum number of steps necessary to accomplish the electroplating satisfactorily is recommended.
6. Preliminary Pretreatment Procedures
6.1 Application—Degreasing and mechanical surface treatment are necessary only where the high-carbon steel parts are
contaminated to such an extent that otherwise the burden imposed on the pretreatment cycle would impair its efficiency, increase
B242 − 99 (2014)
its complexity, and tend to prevent the attainment of the required quality of the deposit. The overall cost of the electroplating
process is usually reduced by using the preliminary treatments where applicable. Oil, grease, dirt, drawing compounds, burnt-in
oil, heavy scale, and emery and steel particles are typical of the gross contaminants encountered.
6.2 Precleaning—Solvent-degreasing with clean solvent, spray-washing, or emulsion-cleaning, followed by electrolytic or
soak-alkali cleaners are recommended. The former types are preferred to reduce the burden on the alkali treatments. Soak-alkali
cleaning is usual for parts that are to be barrel electroplated. Electrolytic cleaning should always be anodic where the control of
embrittlement is a problem.
6.3 Stress Relief Treatment—It is recommended that hardened high-carbon steel parts receive a stress-relief bake before the parts
are mechanically pretreated or enter the final pretreatment cycle, or both. For a listing of typical stress-relief bakes, consult
Specification B849.
6.4 Mechanical Treatment—The purpose of mechanical treatment is to reduce subsequent acid pickling to a minimum. Where
mechanical treatment has been accomplished with precision, it is sometimes possible to eliminate acid pickling entirely, thus
improving the control of hydrogen embrittlement. When required, mechanical treatment of small parts is best effected by tumbling.
All scaled and nearly all oil-quenched materials require mechanical cleaning such as by tumbling with or without abrasive, or by
sand, grit, or vapor blasting. These operations should be carried out so as to avoid severe roughening of the surface with
accompanying notch effect. One resorts to grinding in certain cases where the surface smoothness or dimensions of the parts are
of critical importance, for example, in chromium electroplating for engineering use.
7. Final Pretreatment Procedures
7.1 Application—Final cleaning, oxide removal, and anodic acid treatment are fundamental steps required for preparing
high-carbon steel for electroplating. These pretreatment steps are designed to assist in the control of hydrogen embrittlement and
in securing the maximum adhesion of the electroplated coating.
7.2 Electrolytic Anodic Cleaning:
7.2.1 All work, except work to be barrel electroplated, should preferably be cleaned in an electrolytic anodic alkaline cleaner.
Anodic cleaning is recommended to avoid hydrogen embrittlement that is likely to result from cathodic cleaning. An exception is
barrel work which, because of the work size, is preferably cleaned by soaking or tumbling in an alkaline cleaning solution without
the use of current.
7.2.2 The purpose of this cleaning step is to remove completely the last traces of contaminants. In all cases it should be preceded
by heavy-duty precleaning as covered in 6.2.
7.2.3 The electrolytic anodic cleaner should be used at a temperature of 90°C or higher, and at a current density of 5 A/dm or
higher, in order that the required degree of cleanliness be obtained in a time period not exceeding 2 min.
7.2.4 On removal from the cleaner, the work should be thoroughly rinsed, first with water warmed to 50°C, and then in a
cold-water spray at room temperature, prior to the acid dip.
7.3 Rinsing:
7.3.1 The most thorough fresh-water rinsing operation possible is mandatory after each processing step if the best results in
electroplating high-carbon steel are to be obtained. The purpose of rinsing is to eliminate drag-over by complete removal of the
preceding solution from the surface of the work. Many existing commercial operations are characterized by inadequate rinsing.
7.3.2 Warm to hot rinses should be used following alkaline solutions or where the subsequent processing solution is hot. The
rinse temperature should not be so high as to induce drying of the steel surface between processing steps. Room temperature rinses
are suitable for use following acid solutions where the solution in the next processing step is cold. In no case should very cold water
be used for rinsing.
7.3.3 The recommended rinsing practice includes the use of an immersion rinse, always followed by a spray rinse of fresh water
at the required temperature. Not using a spray rinsing is an invitation to trouble in the electroplating of high-carbon steel.
7.4 Hydrochloric Acid Treatment—The purpose of the HCl treatment is to remove completely the last trace of oxide from the
surface of the high-carbon steel. The intensity of the HCl treatment should be held to the minimum required by the nature and
amount of oxide present. The use of H SO instead of HCl is not recommended for descaling high-carbon steel because of its
2 4
smut-forming tendency, in spite of the somewhat lowered tendency to rusting of H SO -treated surfaces. The addition of wetting
2 4
agents to the HCl solution is not recommended. Care and caution must be exercised in the use of inhibitors where they are required,
because they sometimes interfere with adhesion. Inhibitors are of benefit only in special cases where surface finish and dimensions
are of prime importance.
7.5 Treatment for Smut Removal—When the HCl treatment of the high-carbon steel results in the presence of smut, the smut
must be removed before the surface is electroplated. Lig
...
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