ASTM B650-23

Standard Specification for Electrodeposited Engineering Chromium Coatings on Ferrous Substrates

ABSTRACT
This specification covers the requirements for electrodeposited chromium coatings (sometimes referred to as functional or hard chromium) applied to ferrous alloy substrates for engineering applications, particularly for increasing wear, abrasion, fretting, and corrosion resistance; for reducing galling or seizing, and static and kinetic friction; and for building up undersize or worn parts. Coatings shall be classified according to their thickness. Coatings shall be sampled, tested, and shall conform accordingly to specified requirements as to appearance, stress relief and hydrogen embrittlement treatment, thickness (to measured either by microscopical, magnetic, coulometric, or X-ray spectrometry method), adhesion (to be assessed either by bend, file, heat and quench, or push test), porosity (to be examined either by ferroxyl, neutral salt spray, or copper sulfate test), workmanship, and packaging.
SCOPE
1.1 This specification covers the requirements for electrodeposited chromium coatings applied to ferrous alloys for engineering applications.  
1.2 Electrodeposited engineering chromium, which is sometimes called “functional” or “hard” chromium, is usually applied directly to the basis metal and is much thicker than decorative chromium. Engineering chromium is used for the following:  
1.2.1 To increase wear and abrasion resistance,  
1.2.2 To increase fretting resistance,  
1.2.3 To reduce static and kinetic friction,  
1.2.4 To reduce galling or seizing, or both, for various metal combinations,  
1.2.5 To increase corrosion resistance, and  
1.2.6 To build up undersize or worn parts.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2023
• ICS: 25.220.40 - Metallic coatings
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.03 - Engineering Coatings

Relations

• Replaces: ASTM B650-95(2023) - Standard Specification for Electrodeposited Engineering Chromium Coatings on Ferrous Substrates
• Effective Date: 01-Nov-2023
• Refers: ASTM B117-19 - Standard Practice for Operating Salt Spray (Fog) Apparatus
• Effective Date: 01-Nov-2019
• Referred By: ASTM B765-03(2023) - Standard Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
• Effective Date: 01-Nov-2023
• Referred By: ASTM B851-04(2020) - Standard Specification for Automated Controlled Shot Peening of Metallic Articles Prior to Nickel, Autocatalytic Nickel, or Chromium Plating, or as Final Finish
• Effective Date: 01-Nov-2023
• Referred By: ASTM B177/B177M-11(2021) - Standard Guide for Engineering Chromium Electroplating
• Effective Date: 01-Nov-2023
• Referred By: ASTM F1007-18(2022) - Standard Specification for Pipeline Expansion Joints of the Packed Slip Type for Marine Application
• Effective Date: 01-Nov-2023

Overview

ASTM B650-23: Standard Specification for Electrodeposited Engineering Chromium Coatings on Ferrous Substrates establishes requirements for applying electrodeposited (electroplated) chromium coatings-commonly known as "hard" or "functional" chromium-onto ferrous alloys. Unlike decorative chromium plating, these engineering coatings are applied in greater thickness and aim to enhance the performance and longevity of critical steel components. Adherence to ASTM B650-23 ensures improved wear, abrasion, fretting resistance, and corrosion protection, as well as reduced friction and galling, alongside potential restoration of worn or undersized parts.

Key Topics

Chromium Plating for Engineering Use

ASTM B650-23 covers various technical aspects relevant to the electrodeposition of hard chromium on steel and iron substrates, including:

• Coating Classes: Coatings are classified by thickness to suit different engineering requirements, from light wear resistance and friction reduction to significant build-up for salvage applications.
• Testing & Quality Requirements: The standard specifies comprehensive sampling and testing methods, addressing:
  • Coating thickness (measured via microscopical, magnetic, coulometric, or X-ray spectrometric methods)
  • Adhesion (evaluated through bend, file, heat and quench, or push tests)
  • Porosity (verified using ferroxyl, neutral salt spray, or copper sulfate tests)
  • Workmanship and coating appearance
  • Stress relief and hydrogen embrittlement treatments to ensure safety and structural integrity
• Significant Surfaces: Only surfaces accessible by a 20-mm ball (unless otherwise specified) are generally required to meet the controlled thickness criteria.

Applications

Practical Value of ASTM B650-23

The use of ASTM B650-23 is essential for industries where component durability, reduced maintenance, and performance reliability are crucial. Typical applications include:

• Automotive and Aerospace Engineering: Enhancing wear and corrosion resistance of shafts, gears, pistons, and hydraulic rods.
• Heavy Equipment Manufacturing: Restoring worn or undersized steel components, thereby extending equipment life.
• Machinery Repair and Maintenance: Providing an economical solution to salvage high-value ferrous parts with precise dimensional control.
• Reducing Friction and Preventing Galling: Critical for moving parts operating under load or in hostile environments.

Implementing hard chromium coatings according to ASTM B650-23 supports regulatory compliance requirements and customer mandates, especially for components supplied to government or defense agencies.

Related Standards

Several ASTM standards and industry practices support or are referenced within ASTM B650-23:

• ASTM B117: Salt Spray (Fog) Testing for corrosion resistance validation
• ASTM B177, B183, B242, B320: Guidelines for preparing ferrous alloys before electroplating
• ASTM B487, B499, B504, B568: Methods for measuring coating thickness
• ASTM B571: Adhesion testing procedures
• ASTM B849, B850: Treatments to reduce hydrogen embrittlement in plated steel
• MIL-S-13165: Shot peening process for fatigue life improvement

Aligning processes with these related standards ensures best practices in electroplating, sampling, inspection, and component performance, helping manufacturers and engineers achieve reliable results with engineering chromium coatings.

---

Keywords: ASTM B650-23, chromium plating standard, electrodeposited engineering chromium, hard chromium coatings, ferrous substrates, wear resistance, corrosion resistance, friction reduction, hydrogen embrittlement, thickness measurement, adhesion testing.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B650 − 23
Standard Specification for
Electrodeposited Engineering Chromium Coatings on
Ferrous Substrates
This standard is issued under the fixed designation B650; 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 U.S. Department of Defense.
1. Scope B177 Guide for Engineering Chromium Electroplating
B183 Practice for Preparation of Low-Carbon Steel for
1.1 This specification covers the requirements for electrode-
Electroplating
posited chromium coatings applied to ferrous alloys for engi-
B242 Guide for Preparation of High-Carbon Steel for Elec-
neering applications.
troplating
1.2 Electrodeposited engineering chromium, which is some-
B320 Practice for Preparation of Iron Castings for Electro-
times called “functional” or “hard” chromium, is usually
plating
applied directly to the basis metal and is much thicker than
B374 Terminology Relating to Electroplating
decorative chromium. Engineering chromium is used for the
B487 Test Method for Measurement of Metal and Oxide
following:
Coating Thickness by Microscopical Examination of
1.2.1 To increase wear and abrasion resistance,
Cross Section
1.2.2 To increase fretting resistance,
B499 Test Method for Measurement of Coating Thicknesses
1.2.3 To reduce static and kinetic friction,
by the Magnetic Method: Nonmagnetic Coatings on
1.2.4 To reduce galling or seizing, or both, for various metal
combinations, Magnetic Basis Metals
1.2.5 To increase corrosion resistance, and B504 Test Method for Measurement of Thickness of Metal-
1.2.6 To build up undersize or worn parts. lic Coatings by the Coulometric Method
B507 Practice for Design of Articles to Be Electroplated on
1.3 This standard does not purport to address all of the
Racks
safety concerns, if any, associated with its use. It is the
B568 Test Method for Measurement of Coating Thickness
responsibility of the user of this standard to establish appro-
by X-Ray Spectrometry
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use. B571 Practice for Qualitative Adhesion Testing of Metallic
1.4 This international standard was developed in accor-
Coatings
dance with internationally recognized principles on standard-
B602 Guide for Attribute Sampling of Metallic and Inor-
ization established in the Decision on Principles for the
ganic Coatings
Development of International Standards, Guides and Recom-
B697 Guide for Selection of Sampling Plans for Inspection
mendations issued by the World Trade Organization Technical
of Electrodeposited Metallic and Inorganic Coatings
Barriers to Trade (TBT) Committee.
B762 Guide of Variables Sampling of Metallic and Inorganic
Coatings
2. Referenced Documents
B849 Specification for Pre-Treatments of Iron or Steel for
2.1 ASTM Standards:
Reducing Risk of Hydrogen Embrittlement
B117 Practice for Operating Salt Spray (Fog) Apparatus
B850 Guide for Post-Coating Treatments of Steel for Reduc-
ing the Risk of Hydrogen Embrittlement
This specification is under the jurisdiction of ASTM Committee B08 on
D3951 Practice for Commercial Packaging
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
B08.03 on Engineering Coatings.
E8 Test Methods for Tension Testing of Metallic Materials
Current edition approved Nov. 1, 2023. Published December 2023. Originally
[Metric] E0008_E0008M
approved in 1978. Last previous edition approved in 2023 as B650 – 95 (2023).
F1459 Test Method for Determination of the Susceptibility
DOI: 10.1520/B0650-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
of Metallic Materials to Hydrogen Gas Embrittlement
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
(HGE)
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
B650 − 23
2.2 Other Standard: 5.1.12 Whether separate test specimens will be used (see 7.1
MIL-S-13165 Shot Peening of Metal Parts and 7.5),
5.1.13 Where required, any special requirements for parts
3. Terminology
that are subsequently ground to size,
5.1.14 Where required, the base metal finish in terms of
3.1 Definitions:
center line average (CLA) or arithmetic average (AA), and
3.1.1 significant surfaces—all surfaces upon which a de-
5.1.15 Where required, dimensional tolerances allowed for
posit of controlled thickness is required.
the specified coating thickness or class.
3.1.1.1 Discussion—When a controlled deposit is required
in holes, corners, recesses, and similar areas, special racking,
5.2 The manufacturer of the parts to be electroplated shall
auxiliary anodes or shielding, or both, will be necessary. With
provide the electroplating facility with test specimens (see
the best practices there will be areas where a controlled deposit
Section 7) to be electroplated for conformance tests as re-
is impossible.
quested for preparation, control, inspection, and lot acceptance
unless other arrangements have been made between the pur-
3.2 Definitions used in this specification are in accordance
chaser and the electroplating facility.
with Terminology B374.
6. Coating Requirements
4. Classification
6.1 The appearance of the chromium coating on the signifi-
4.1 Electrodeposited chromium coatings in accordance with
cant surfaces of the product shall be smooth and free of visual
this specification are classified by the thickness of the coating
defects such as blisters, pits, roughness, cracks, burned
as follows:
deposits, uncoated areas, or macrocracking of the deposit that
Class No. Chromium Thickness, μm Typical Application
is visible without magnification. The boundaries of electroplat-
1 2.5 to 25 reduce friction; anti-galling, light
ing that cover only a portion of the surface shall, after finishing
wear resistance
as indicated on the drawing, be free of beads, nodules, jagged
2 >25 as specified buildup to dimension specified for
salvage or as required for severe edges, or other irregularities that will interfere with the
wear resistance
functioning of the plated part. Imperfections and variations that
arise from surface conditions of the basis metal (scratches,
4.2 Unless otherwise specified by suitably marked drawings
or samples, only those surfaces that can be touched with a pores, roll marks, inclusions, etc.) and that persist in the finish
despite the observance of good metal finishing practices shall
20-mm diameter ball shall be considered significant. In holes,
corners, recesses, and other areas where a controlled deposit not be cause for rejection.
cannot be obtained under normal electroplating conditions, the
NOTE 1—Applied finishes generally perform better in service when the
thickness of the deposit may be that which results from control
substrate over which they are applied is smooth and free of torn metal,
on the significant surfaces. inclusions, pores, and other defects. It is recommended that the specifi-
cations covering the unfinished product provide limits for these defects. A
metal finisher can often remove defects through special treatments such as
5. Ordering Information
grinding, polishing, abrasive blasting, chemical treatments, and
5.1 The purchaser shall exercise the desired options of this
electropolishing, which are not normal in the treatment steps preceding the
standard. Ordering documents shall specify the following
application of the finish and will add to the cost. When they are desired,
they are the subject of a special agreement between the purchaser and the
information:
seller.
5.1.1 Title, ASTM designation, and issue date of this
specification, 6.2 In cases where design for maximum fatigue life is a
5.1.2 Alloy and metallurgical condition of the product to be consideration the parts should be shot peened (see MIL-S-
chromium plated, 13165C) or given an alternate mechanical treatment to com-
5.1.3 Ultimate tensile strength of the material to be plated, pressively stress the surface.
5.1.4 Heat treatment required for stress relief and whether it
6.3 Stress Relief Treatment (See headnote at the beginning
has been performed or is required,
of this specification.):
5.1.5 The significant surfaces if different from the 20 mm
6.3.1 All steel parts having an ultimate tensile strength of
ball rule (see 3.1.1),
1000 MPa (150 000 psi—approximately 32 HRC) or greater,
5.1.6 Thickness of the deposit or class (see 4.1),
that may contain residual stress caused by various fabrication
5.1.7 Control record requirements,
operations such as machining, grinding, straightening, or cold
5.1.8 Preproduction test specimens, if required,
forming, will require one of the stress relief heat treatments
5.1.9 Sampling plan, if different from that specified in Test
prescribed in Specification B849 prior to electroplating. In all
Method B602 (see Section 8),
cases, the duration of heat treatment shall commence from the
5.1.10 The number of test specimens for destructive testing
time at which the whole of each part attains the specified
(see 7.1),
temperature.
5.1.11 Thickness, adhesion, porosity, and hydrogen em-
6.3.1.1 The treatment selected, of necessity, must be based
brittlement tests required (see Section 6),
upon experience with the part or empirical test data. Therefore,
Class SR-0 treatment is provided for parts that the purchaser
wishes to exempt from treatment. However, many, if not most,
Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700
Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS. steels with a tensile strength in excess of 1000 MPa will
B650 − 23
become embrittled when plated with chromium. The stress 6.6 Adhesion—The coating shall be sufficiently adherent to
relief and hydrogen embrittlement relief treatments are essen- the basis metal to pass the adhesion test specified (see 7.3).
tial for the safe performance of chromium plated items These tests are, with the possible exception of the heat quench
fabricated from those steels. Selection of Class SR-0 or ER-0 test, all destructive and therefore, in most cases, should be
performed on test panels.
requires thorough knowledge of the embrittlement susceptibil-
ity of the specific steel employed. When the purchaser specifies
NOTE 3—Adhesion may be influenced by the method of pretreating the
Class SR-0 or ER-0, the purchaser assumes sole responsibility
base metal and the type of steel used as a basis metal. Helpful information
for any embrittlement failure of the part. The relative suscep-
is given in Practices B177, B183, B242, and B320.
tibility of a steel can be determined by subjecting it to the Disk
6.7 The coating shall be sufficiently free of pores to pass the
Rupture Test of Test Method F1459. When no stress relief
porosity test specified (see 7.4).
treatment is specified by the purchaser then Class SR-1 shall be
6.8 Workmanship—Adding to (spotting in) or double
applied.
electroplating, unless evidence of a satisfactory bond is
6.3.2 Parts having surface hardened areas that would suffer
established, shall be cause for rejection. Stripping and replating
an unacceptable reduction in hardness by treatment in accor-
is permitted but parts having an ultimate tensile strength
dance with Specification B849 shall be heat-treated at a lower
greater than 1000 MPa or a hardness greater than 32 HRC that
temperature but not less than 130 °C for a minimum period of
are acid stripped shall be rebaked (see 6.3) before plating.
8 h. This treatment is applicable for parts made of steel with an
Baking after stripping is not necessary if the parts are stripped
actual tensile strength below 1400 MPa. The purchaser may
anodically in an alkaline solution.
require that the heat-treatment temperature shall not reduce the
6.9 Supplemental Requirements—If parts are electroplated
surface hardness. Shorter times at higher temperatures may be
used, if the resulting loss of surface hardness is acceptable. and subsequently ground to size, the grinding shall be done
with a proper coolant, never dry, and with a sufficiently light
6.3.3 If stress relief is given after shot peening or other cold
cut to prevent cracking. Macrocracking, visually observed
working processes to introduce beneficial compressive
without magnification after grinding, shall be cause for rejec-
stresses, the temperature shall not exceed 230 °C.
tion.
6.4 Hydrogen Embrittlement Relief:
6.10 Packaging—Part(s) plated for the U.S. Government
6.4.1 Heat treatment appropriate for the tensile strength of
and Military, including subcontracts, shall be packaged in
the electroplated part (see Specification B850) shall be per-
accordance with Practice D3951.
formed to reduce the risk of hydrogen embrittlement. In all
cases, the d
...

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: B650 − 95 (Reapproved 2023) B650 − 23
Standard Specification for
Electrodeposited Engineering Chromium Coatings on
Ferrous Substrates
This standard is issued under the fixed designation B650; 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 U.S. Department of Defense.
1. Scope
1.1 This specification covers the requirements for electrodeposited chromium coatings applied to ferrous alloys for engineering
applications.
1.2 Electrodeposited engineering chromium, which is sometimes called “functional” or “hard” chromium, is usually applied
directly to the basis metal and is much thicker than decorative chromium. Engineering chromium is used for the following:
1.2.1 To increase wear and abrasion resistance,
1.2.2 To increase fretting resistance,
1.2.3 To reduce static and kinetic friction,
1.2.4 To reduce galling or seizing, or both, for various metal combinations,
1.2.5 To increase corrosion resistance, and
1.2.6 To build up undersize or worn parts.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
B117 Practice for Operating Salt Spray (Fog) Apparatus
This specification is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.03 on
Engineering Coatings.
Current edition approved May 1, 2023Nov. 1, 2023. Published June 2023December 2023. Originally approved in 1978. Last previous edition approved in 20182023 as
B650 – 95 (2018).(2023). DOI: 10.1520/B0650-95R23.10.1520/B0650-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
B650 − 23
B177 Guide for Engineering Chromium Electroplating
B183 Practice for Preparation of Low-Carbon Steel for Electroplating
B242 Guide for Preparation of High-Carbon Steel for Electroplating
B320 Practice for Preparation of Iron Castings for Electroplating
B374 Terminology Relating to Electroplating
B487 Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section
B499 Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic Basis
Metals
B504 Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
B507 Practice for Design of Articles to Be Electroplated on Racks
B568 Test Method for Measurement of Coating Thickness by X-Ray Spectrometry
B571 Practice for Qualitative Adhesion Testing of Metallic Coatings
B602 Guide for Attribute Sampling of Metallic and Inorganic Coatings
B697 Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
B762 Guide of Variables Sampling of Metallic and Inorganic Coatings
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
D3951 Practice for Commercial Packaging
E8 Test Methods for Tension Testing of Metallic Materials [Metric] E0008_E0008M
F1459 Test Method for Determination of the Susceptibility of Metallic Materials to Hydrogen Gas Embrittlement (HGE)
2.2 Other Standard:
MIL-S-13165 Shot Peening of Metal Parts
3. Terminology
3.1 Definitions:
3.1.1 significant surfaces—all surfaces upon which a deposit of controlled thickness is required.
3.1.1.1 Discussion—
When a controlled deposit is required in holes, corners, recesses, and similar areas, special racking, auxiliary anodes or shielding,
or both, will be necessary. With the best practices there will be areas where a controlled deposit is impossible.
3.2 Definitions used in this specification are in accordance with Terminology B374.
4. Classification
4.1 Electrodeposited chromium coatings in accordance with this specification are classified by the thickness of the coating as
follows:
Class No. Chromium Thickness, μm Typical Application
1 2.5 to 25 reduce friction; anti-galling, light
wear resistance
2 >25 as specified buildup to dimension specified for
salvage or as required for severe
wear resistance
4.2 Unless otherwise specified by suitably marked drawings or samples, only those surfaces that can be touched with a 20-mm
diameter ball shall be considered significant. In holes, corners, recesses, and other areas where a controlled deposit cannot be
obtained under normal electroplating conditions, the thickness of the deposit may be that which results from control on the
significant surfaces.
5. Ordering Information
5.1 The purchaser shall exercise the desired options of this standard. Ordering documents shall specify the following information:
5.1.1 Title, ASTM designation, and issue date of this specification,
Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700 Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
B650 − 23
5.1.2 Alloy and metallurgical condition of the product to be chromium plated,
5.1.3 Ultimate tensile strength of the material to be plated,
5.1.4 Heat treatment required for stress relief and whether it has been performed or is required,
5.1.5 The significant surfaces if different from the 20 mm ball rule (see 3.1.1),
5.1.6 Thickness of the deposit or class (see 4.1),
5.1.7 Control record requirements,
5.1.8 Preproduction test specimens, if required,
5.1.9 Sampling plan, if different from that specified in Test Method B602 (see Section 8),
5.1.10 The number of test specimens for destructive testing (see 7.1),
5.1.11 Thickness, adhesion, porosity, and hydrogen embrittlement tests required (see Section 6),
5.1.12 Whether separate test specimens will be used (see 7.1 and 7.5),
5.1.13 Where required, any special requirements for parts that are subsequently ground to size,
5.1.14 Where required, the base metal finish in terms of center line average (CLA) or arithmetic average (AA), and
5.1.15 Where required, dimensional tolerances allowed for the specified coating thickness or class.
5.2 The manufacturer of the parts to be electroplated shall provide the electroplating facility with test specimens (see Section 7)
to be electroplated for conformance tests as requested for preparation, control, inspection, and lot acceptance unless other
arrangements have been made between the purchaser and the electroplating facility.
6. Coating Requirements
6.1 The appearance of the chromium coating on the significant surfaces of the product shall be smooth and free of visual defects
such as blisters, pits, roughness, cracks, burned deposits, uncoated areas, or macrocracking of the deposit that is visible without
magnification. The boundaries of electroplating that cover only a portion of the surface shall, after finishing as indicated on the
drawing, be free of beads, nodules, jagged edges, or other irregularities that will interfere with the functioning of the plated part.
Imperfections and variations that arise from surface conditions of the basis metal (scratches, pores, roll marks, inclusions, etc.) and
that persist in the finish despite the observance of good metal finishing practices shall not be cause for rejection.
NOTE 1—Applied finishes generally perform better in service when the substrate over which they are applied is smooth and free of torn metal, inclusions,
pores, and other defects. It is recommended that the specifications covering the unfinished product provide limits for these defects. A metal finisher can
often remove defects through special treatments such as grinding, polishing, abrasive blasting, chemical treatments, and electropolishing, which are not
normal in the treatment steps preceding the application of the finish and will add to the cost. When they are desired, they are the subject of a special
agreement between the purchaser and the seller.
6.2 In cases where design for maximum fatigue life is a consideration the parts should be shot peened (see MIL-S-13165C) or
given an alternate mechanical treatment to compressively stress the surface.
6.3 Stress Relief Treatment (See headnote at the beginning of this specification.):
6.3.1 All steel parts having an ultimate tensile strength of 1000 MPa (150 000 psi—approximately 32 HRC) or greater, that may
contain residual stress caused by various fabrication operations such as machining, grinding, straightening, or cold forming, will
require one of the stress relief heat treatments prescribed in Specification B849 prior to electroplating. In all cases, the duration
of heat treatment shall commence from the time at which the whole of each part attains the specified temperature.
B650 − 23
6.3.1.1 The treatment selected, of necessity, must be based upon experience with the part or empirical test data. Therefore, Class
SR-0 treatment is provided for parts that the purchaser wishes to exempt from treatment. However, many, if not most, steels with
a tensile strength in excess of 1000 MPa will become embrittled when plated with chromium. The stress relief and hydrogen
embrittlement relief treatments are essential for the safe performance of chromium plated items fabricated from those steels.
Selection of Class SR-0 or ER-0 requires thorough knowledge of the embrittlement susceptibility of the specific steel employed.
When the purchaser specifies Class SR-0 or ER-0, the purchaser assumes sole responsibility for any embrittlement failure of the
part. The relative susceptibility of a steel can be determined by subjecting it to the Disk Rupture Test of Test Method F1459. When
no stress relief treatment is specified by the purchaser then Class SR-1 shall be applied.
6.3.2 Parts having surface hardened areas that would suffer an unacceptable reduction in hardness by treatment in accordance with
Specification B849 shall be heat-treated at a lower temperature but not less than 130 °C for a minimum period of 8 h. This
treatment is applicable for parts made of steel with an actual tensile strength below 1400 MPa. The purchaser may require that the
heat-treatment temperature shall not reduce the surface hardness. Shorter times at higher temperatures may be used, if the resulting
loss of surface hardness is acceptable.
6.3.3 If stress relief is given after shot peening or other cold working processes to introduce beneficial compressive stresses, the
temperature shall not exceed 230 °C.
6.4 Hydrogen Embrittlement Relief:
6.4.1 Heat treatment appropriate for the tensile strength of the electroplated part (see Specification B850) shall be performed to
reduce the risk of hydrogen embrittlement. In all cases, the duration of the heat treatment shall commence from the time at which
the whole part attains the specified temperature. See 6.3.1.1 for important embrittlement relief information regarding the selection
of ER-0. When no embrittlement relief treatment is specified by the purchaser then Class ER-1 shall be applied.
6.4.2 Begin the embrittlement relief heat-treatment as soon as practical following the plating process but no longer than 1.5 h.
1.5 h.
6.4.3 Parts or representative specimens shall be tested for compliance in accordance with 7.5.
6.5 Thickness—The thickness of the coating everywhere on the significant surface(s) shall conform to the requirements of the
specified class as defined in Section 3 (see 7.2).
NOTE 2—The coating thickness requirements of this specification are a minimum requirement, that is, the coating thickness is required to equal or exceed
the specified thickness everywhere on the significant surfaces (see 4.1). Variation in the coating thickness from point to point on a coated article is an
inherent characteristic of electroplating processes. Therefore, the coating thickness must exceed the specified value at some point on the significant
surfaces to ensure that the thickness equals or exceeds the specified value at all points. Hence, in most cases, the average coating thickness on an article
will be greater than the specified value; how much greater is largely determined by the shape of the a
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