ASTM B874-96(2018)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: B874 − 96 (Reapproved 2018)
Standard Specification for
Chromium Diffusion Coating Applied by Pack Cementation
Process
This standard is issued under the fixed designation B874; 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 B697 Guide for Selection of Sampling Plans for Inspection
of Electrodeposited Metallic and Inorganic Coatings
1.1 This specification covers the requirements for chromium
B762 Test Method of Variables Sampling of Metallic and
diffusion of metals by the pack cementation method. Pack
Inorganic Coatings
diffusion employs the chemical vapor deposition of a metal
C664 Test Methods for Thickness of Diffusion Coating
which is subsequently diffused into the surface of a substrate at
D3951 Practice for Commercial Packaging
high temperature. The material to be coated (substrate) is
E766 Practice for Calibrating the Magnification of a Scan-
immersed or suspended in a powder containing chromium
ning Electron Microscope
(source), a halide salt (activator), and an inert diluent such as
E1077 Test Methods for Estimating the Depth of Decarbur-
alumina (filler). When the mixture is heated, the activator
ization of Steel Specimens
reacts to produce an atmosphere of chromium halides which
F1330 Guide for Metallic Abrasive Blasting to Descale the
transfers chromium to the substrate for subsequent diffusion.
Interior of Pipe
The chromium-rich surface enhances corrosion, thermal
stability, and wear-resistant properties.
3. Terminology
1.2 This standard does not purport to address all of the
3.1 Definitions used in this specification are in accordance
safety concerns, if any, associated with its use. It is the
with Terminology B374.
responsibility of the user of this standard to establish appro-
3.2 Definitions of Terms Specific to This Standard:
priate safety, health, and environmental practices and deter-
3.2.1 diffusion coating—a diffusion coating is one produced
mine the applicability of regulatory limitations prior to use.
by causing an element to react with or diffuse into, or both, the
1.3 This international standard was developed in accor-
surface of a metallic substrate, thus, chemically altering the
dance with internationally recognized principles on standard-
surface of the substrate.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
3.2.2 retorts—containers in which powder and parts are
mendations issued by the World Trade Organization Technical
packed for processing. They can be constructed of carbon,
Barriers to Trade (TBT) Committee.
stainless, or high alloys and fabricated in all shapes and sizes
to accommodate parts being processed.
2. Referenced Documents
3.2.3 significant surface—areas that are essential to the
2.1 ASTM Standards:
serviceability or function of the article. These surfaces must be
B374 Terminology Relating to Electroplating
identified on a drawing or marked-up sample of product. Areas
B487 Test Method for Measurement of Metal and Oxide
can fall into one of three categories as follows:
Coating Thickness by Microscopical Examination of
3.2.4 coating required—these surfaces must be in accor-
Cross Section
dance with all quality requirements of this specification.
B602 Test Method for Attribute Sampling of Metallic and
3.2.5 no coating required—these surfaces are areas where
Inorganic Coatings
no coating is allowed due to a number of reasons including
dimensional, fabrication, and welding, as well as others.
This specification is under the jurisdiction of ASTM Committee B08 on
Materials used for masking are commercially available.
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
B08.03 on Engineering Coatings.
3.2.6 optional—these surfaces do not require coating, but at
Current edition approved June 1, 2018. Published June 2018. Originally
the same time do not require masking.
approved in 1996. Last previous edition approved in 2013 as B874 – 96 (2013).
DOI: 10.1520/B0874-96R18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 4. Classification
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
4.1 There are four classes of chromium diffusion defined by
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. base (basis) metal category.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B874 − 96 (2018)
4.1.1 Class I—Carbon steel. 6.5 Post-Cleaning—Retorts should be allowed to cool suf-
ficiently before opening. When parts are removed from retorts,
4.1.2 Class II—Low-alloy steels.
residual pack mix is removed from surfaces by a supplier-
4.1.3 Class III—Stainless steels.
approved method.
4.1.4 Class IV—Nickel-based alloys.
6.6 Post-Straightening—Long tubes may have distortion
5. Ordering Information
due to the high temperature of process. Use rotary straightener
or hydraulic press to restore straightness and ovality.
5.1 In order to make the application of this specification
complete, the purchaser shall supply the following information
6.7 Visual Inspection—Inspect in accordance with 7.3.
to the vendor through a purchase order and drawings:
6.8 Marking and Packaging—To be defined by the pur-
5.1.1 Title, ASTM designation number, and date of issue of
chaser in the purchase order. Parts processed for the U.S.
this specification.
government and military, including subcontract, shall be pack-
5.1.2 Deposit by classification (see Section 4).
aged in accordance with Practice D3951.
5.1.3 Composition and metallurgical condition of substrate
to be coated.
7. Coating Requirements
5.1.4 Location of significant surfaces (see 3.2.3).
7.1 Diffusion Thickness—The following are minimums for
5.1.5 Samples for destructive metallurgical test (see 8.1).
the different classes of materials based on standard process
5.1.6 Any post heat treatment required.
parameters. Thicker coatings require special processing and
5.1.7 Acceptance inspection procedure to be used (see
must be called out for in the purchase order if required.
Section 9).
Class Minimum, in.
5.1.8 Any requirement for certification (see Section 11).
Class I (carbon) 0.003
Class II (low alloys) 0.003
Class III (stainless steels) 0.002
6. Processing Requirements
Class IV (nickel base alloys) 0.001
6.1 Substrate Preparation—The metal to be chromized shall
7.2 Decarburization—For certain Class I and Class II
be free of flaws and defects that will be detrimental to the
materials, the maximum depth of decarburization to be defined
coating. Thorough cleaning is essential to ensure satisfactory
by the purchaser.
diffusion. Materials used for cleaning should not damage the
7.3 Chromium Content—The outer 15 % of coating shall
base metal. Oils, dirt, grease, and stains must be removed.
contain a minimum of 20 % (by weight) chromium.
When blasting is also required, use aluminum oxide (90 to 220
mesh) at 60 to 80 psi from 4 to 6 in. standoff. (Refer to Guide
7.4 Appearance—The diffusion zone shall be nonporous
F1330.)
and adherent to the base metal and shall have a uniform surface
free from objectionable imperfections. Minor variations in
6.2 Materials:
color and surface appearance shall be considered acceptable,
6.2.1 Masteralloy with 50 to 100 % Pure Chromium —Sold
providing the requirements of 7.1 and 7.2 are met (see 8.7).
under a number of trade names, in various mesh sizes.
Percentage in mix depends on material being processed.
8. Test Methods
6.2.2 Activator—Most commonly used is ammonium
chloride, but many othe
...

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: B874 − 96 (Reapproved 2013) B874 − 96 (Reapproved 2018)
Standard Specification for
Chromium Diffusion Coating Applied by Pack Cementation
Process
This standard is issued under the fixed designation B874; 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 specification covers the requirements for chromium diffusion of metals by the pack cementation method. Pack diffusion
employs the chemical vapor deposition of a metal which is subsequently diffused into the surface of a substrate at high temperature.
The material to be coated (substrate) is immersed or suspended in a powder containing chromium (source), a halide salt (activator),
and an inert diluent such as alumina (filler). When the mixture is heated, the activator reacts to produce an atmosphere of chromium
halides which transfers chromium to the substrate for subsequent diffusion. The chromium-rich surface enhances corrosion,
thermal stability, and wear-resistant properties.
1.2 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.3 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:
B374 Terminology Relating to Electroplating
B487 Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section
B602 Test Method for Attribute Sampling of Metallic and Inorganic Coatings
B697 Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
B762 Test Method of Variables Sampling of Metallic and Inorganic Coatings
C664 Test Methods for Thickness of Diffusion Coating
D3951 Practice for Commercial Packaging
E766 Practice for Calibrating the Magnification of a Scanning Electron Microscope
E1077 Test Methods for Estimating the Depth of Decarburization of Steel Specimens
F1330 Guide for Metallic Abrasive Blasting to Descale the Interior of Pipe
3. Terminology
3.1 Definitions used in this specification are in accordance with Terminology B374.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 diffusion coating—a diffusion coating is one produced by causing an element to react with or diffuse into, or both, the
surface of a metallic substrate, thus, chemically altering the surface of the substrate.
3.2.2 retorts—containers in which powder and parts are packed for processing. They can be constructed of carbon, stainless, or
high alloys and fabricated in all shapes and sizes to accommodate parts being processed.
3.2.3 significant surface—areas that are essential to the serviceability or function of the article. These surfaces must be identified
on a drawing or marked-up sample of product. Areas can fall into one of three categories as follows:
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 Dec. 1, 2013June 1, 2018. Published December 2013June 2018. Originally approved in 1996. Last previous edition approved in 20082013 as
B874 – 96 (2008).(2013). DOI: 10.1520/B0874-96R13.10.1520/B0874-96R18.
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
B874 − 96 (2018)
3.2.4 coating required—these surfaces must be in accordance with all quality requirements of this specification.
3.2.5 no coating required—these surfaces are areas where no coating is allowed due to a number of reasons including
dimensional, fabrication, and welding, as well as others. Materials used for masking are commercially available.
3.2.6 optional—these surfaces do not require coating, but at the same time do not require masking.
4. Classification
4.1 There are four classes of chromium diffusion defined by base (basis) metal category.
4.1.1 Class I—Carbon steel.
4.1.2 Class II—Low-alloy steels.
4.1.3 Class III—Stainless steels.
4.1.4 Class IV—Nickel-based alloys.
5. Ordering Information
5.1 In order to make the application of this specification complete, the purchaser shall supply the following information to the
vendor through a purchase order and drawings:
5.1.1 Title, ASTM designation number, and date of issue of this specification.
5.1.2 Deposit by classification (see Section 4).
5.1.3 Composition and metallurgical condition of substrate to be coated.
5.1.4 Location of significant surfaces (see 3.2.3).
5.1.5 Samples for destructive metallurgical test (see 8.1).
5.1.6 Any post heat treatment required.
5.1.7 Acceptance inspection procedure to be used (see Section 9).
5.1.8 Any requirement for certification (see Section 11).
6. Processing Requirements
6.1 Substrate Preparation—The metal to be chromized shall be free of flaws and defects that will be detrimental to the coating.
Thorough cleaning is essential to ensure satisfactory diffusion. Materials used for cleaning should not damage the base metal. Oils,
dirt, grease, and stains must be removed. When blasting is also required, use aluminum oxide (90 to 220 mesh) at 60 to 80 psi from
4 to 6 in. standoff. (Refer to Guide F1330.)
6.2 Materials:
6.2.1 Masteralloy with 50 to 100 % Pure Chromium —Sold under a number of trade names, in various mesh sizes. Percentage
in mix depends on material being processed.
6.2.2 Activator—Most commonly used is ammonium chloride, but many others are available. Percentage in mix depends on
material and type of activity.
6.2.3 Inert Filler—Aluminum oxide or calcined alumina is used and commercially available in numerous mesh sizes.
Percentage in mix depends on material being processed and mesh size being used.
NOTE 1—It is important that both proper equipment is used and time established to guarantee uniform blend of pack mix.
NOTE 2—It is common practice to rejuvenate used mixes by addition of coating elements, alloys, and activators. Chemical analysis of used mixes
facilitates control of critical constituents. Disposal of used mixes must be performed in compliance with environmental regulations.
6.3 Loading—Place pack mix and parts in retorts. Retort size is limited by dimensions of furnace used for processing.
6.4 Furnace Cycle—Parts are heated to a temperature between 1900 and 2400°F depending on base material and pack mix and
held for amount of time needed to produce desired depth of diffusion.
NOTE 3—Due to the high temperature of the process, a positive pressure of an inert gas, usually argon, must be maintained in retorts throughout the
entire furnace cycle.
6.5 Post-Cleaning—Retorts should be allowed to cool sufficiently before opening. When parts are removed from retorts,
residual pack mix is removed from surfaces by a supplier-approved method.
6.6 Post-Straightening—Long tubes may have distortion due to the high temperature of process. Use rotar
...