ASTM B874-96(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: B 874 – 96 (Reapproved 2003)
Standard Specification for
Chromium Diffusion Coating Applied by Pack Cementation
Process
This standard is issued under the fixed designation B 874; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 3951 Practice for Commercial Packaging
E 3 Practice for Preparation of Metallographic Specimens
1.1 Thisspecificationcoverstherequirementsforchromium
E 766 Practice for Calibrating Magnification of a Scanning
diffusion of metals by the pack cementation method. Pack
Electron Microscope
diffusion employs the chemical vapor deposition of a metal
E 1077 Test Method for Estimating the Depth of Decarbur-
which is subsequently diffused into the surface of a substrate at
ization of Steel Specimens
high temperature. The material to be coated (substrate) is
F 1330 Guide for MetallicAbrasive Blasting to Descale the
immersed or suspended in a powder containing chromium
Interior of Pipe
(source), a halide salt (activator), and an inert diluent such as
alumina (filler). When the mixture is heated, the activator
3. Terminology
reacts to produce an atmosphere of chromium halides which
3.1 Definitions used in this specification are in accordance
transfers chromium to the substrate for subsequent diffusion.
with Terminology B 374.
The chromium-rich surface enhances corrosion, thermal stabil-
3.2 Definitions of Terms Specific to This Standard:
ity, and wear-resistant properties.
3.2.1 diffusion coating—a diffusion coating is one produced
1.2 This standard does not purport to address all of the
by causing an element to react with or diffuse into, or both, the
safety concerns, if any, associated with its use. It is the
surface of a metallic substrate, thus, chemically altering the
responsibility of the user of this standard to establish appro-
surface of the substrate.
priate safety and health practices and determine the applica-
3.2.2 retorts—containers in which powder and parts are
bility of regulatory limitations prior to use.
packed for processing. They can be constructed of carbon,
2. Referenced Documents stainless, or high alloys and fabricated in all shapes and sizes
to accommodate parts being processed.
2.1 ASTM Standards:
3.2.3 significant surface—areas that are essential to the
B 374 Terminology Relating to Electroplating
serviceability or function of the article. These surfaces must be
B 487 Test Method for Measurement of Metal and Oxide
identified on a drawing or marked-up sample of product.Areas
Coating Thickness by Microscopical Examination of a
can fall into one of three categories as follows:
Cross Section
3.2.4 coating required—these surfaces must be in accor-
B 602 Test Method for Attribute Sampling of Metallic and
dance with all quality requirements of this specification.
Inorganic Coatings
3.2.5 no coating required—these surfaces are areas where
B 697 Guide for Selection of Sampling Plans for Inspection
no coating is allowed due to a number of reasons including
of Electrodeposited Metallic and Inorganic Coatings
dimensional, fabrication, and welding, as well as others.
B 762 Test Method of Variables Sampling of Metallic and
Materials used for masking are commercially available.
Inorganic Coatings
3.2.6 optional—these surfaces do not require coating, but at
C 664 Test Methods for Thickness of Diffusion Coating
the same time do not require masking.
4. Classification
This specification is under the jurisdiction of ASTM Committee B08 on
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
4.1 There are four classes of chromium diffusion defined by
B08.08.01 on Engineering Coatings.
base (basis) metal category.
Current edition approved Sept. 10, 2003. Published Sept. 2003. Originally
approved in 1996. Last previous edition approved in 1996 as B 874 – 96.
4.1.1 Class I—Carbon steel.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
4.1.2 Class II—Low-alloy steels.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
4.1.3 Class III—Stainless steels.
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.
B 874 – 96 (2003)
4.1.4 Class IV—Nickel-based alloys. 6.6 Post-Straightening—Long tubes may have distortion
due to the high temperature of process. Use rotary straightener
or hydraulic press to restore straightness and ovality.
5. Ordering Information
6.7 Visual Inspection—Inspect in accordance with 7.3.
5.1 In order to make the application of this specification
6.8 Marking and Packaging—To be defined by the pur-
complete, the purchaser shall supply the following information
chaser in the purchase order. Parts processed for the U.S.
to the vendor through a purchase order and drawings:
government and military, including subcontract, shall be pack-
5.1.1 Title,ASTM designation number, and date of issue of
aged in accordance with Practice D 3951.
this specification.
5.1.2 Deposit by classification (see Section 4).
7. Coating Requirements
5.1.3 Composition and metallurgical condition of substrate
to be coated.
7.1 Diffusion Thickness—The following are minimums for
5.1.4 Location of significant surfaces (see 3.2.3). the different classes of materials based on standard process
5.1.5 Samples for destructive metallurgical test (see 8.1).
parameters. Thicker coatings require special processing and
5.1.6 Any post heat treatment required. must be called out for in the purchase order if required.
5.1.7 Acceptance inspection procedure to be used (see
Class Minimum, in.
Class I (carbon) 0.003
Section 9).
Class II (low alloys) 0.003
5.1.8 Any requirement for certification (see Section 11).
Class III (stainless steels) 0.002
Class IV (nickel base alloys) 0.001
6. Processing Requirements
7.2 Decarburization—For certain Class I and Class II ma-
6.1 Substrate Preparation—The metal to be chromized
terials, the maximum depth of decarburization to be defined by
shall be free of flaws and defects that will be detrimental to the
the purchaser.
coating. Thorough cleaning is essential to ensure satisfactory
7.3 Chromium Content—The outer 15 % of coating shall
diffusion. Materials used for cleaning should not damage the
contain a minimum of 20 % (by weight) chromium.
base metal. Oils, dirt, grease, and stains must be removed.
7.4 Appearance—The diffusion zone shall be nonporous
When blasting is also required, use aluminum oxide (90 to 220
andadherenttothebasemetalandshallhaveauniformsurface
mesh) at 60 to 80 psi from 4 to 6 in. standoff. (Refer to Guide
free from objectionable imperfections. Minor variations in
F 1330.)
color and surface appearance shall be considered acceptable,
6.2 Materials:
providing the requirements of 7.1 and 7.2 are met (see 8.7).
6.2.1 Masteralloy with 50 to 100 % Pure Chromium—Sold
under a number of trade names, in various mesh sizes.
8. Test Methods
Percentage in mix depends on material being processed.
8.1 Special Test Specimens:
6.2.2 Activator—Most commonly used is ammonium chlo-
8.1.1 The permission or the requirements to use special test
ride, but many others are available. Percentage in mix depends
specimens, the number to be used, the material from which
on material and type of
...