ASTM B796-20

Standard Test Method for Nonmetallic Inclusion Content of Ferrous Powders Intended for Powder Forging (PF) Applications

SIGNIFICANCE AND USE
4.1 The extensive porosity present in pressed and sintered ferrous materials masks the effect of inclusions on mechanical properties. In contrast, the properties of material powder forged to near full density are strongly influenced by the composition, size, size distribution, and location of nonmetallic inclusions.  
4.2 The test for nonmetallic inclusions in powder forged steels is useful as the following:  
4.2.1 Characteristic to classify or differentiate one grade of powder from another.  
4.2.2 Means of quality comparison of powders intended for powder forging, lot to lot.  
4.3 Significant variations in nonmetallic inclusion content will occur if:  
4.3.1 The powder used to form the test specimen does not meet powder forging quality standards for nonmetallic inclusion content.  
4.3.2 Processing of the powder forged test specimen has been carried out under conditions that do not permit oxide reduction or allow oxidation of the test specimen, or both.
SCOPE
1.1 This test method covers a metallographic method for determining the nonmetallic inclusion level of ferrous powders intended for powder forging (PF) applications.  
1.2 The test method covers repress powder forged test specimens in which there has been minimal lateral material flow (  
1.3 This test method is not suitable for determining the nonmetallic inclusion level of powder forged test specimens that have been forged such that the core region contains porosity. At the magnification used for this test method, residual porosity is hard to distinguish from oxide inclusions. Too much residual porosity makes a meaningful assessment of the inclusion population impossible.  
1.4 The test method may be applied to materials that contain manganese sulfide (admixed or prealloyed), provided the near neighbor separation distance is changed from 30 μm to 15 μm.
Note 1: The test method may be applied to powder forged parts where there has been a greater amount of material flow provided:
The near neighbor separation distance is changed, or
The inclusion sizes agreed between the parties are adjusted for the amount of material flow.  
1.5 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.6 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.  
1.7 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-Mar-2020
• ICS: 77.040.99 - Other methods of testing of metals
• Technical Committee: B09 - Metal Powders and Metal Powder Products
• Drafting Committee: B09.11 - Near Full Density Powder Metallurgy Materials

Relations

• Replaces: ASTM B796-14 - Standard Test Method for Nonmetallic Inclusion Content of Ferrous Powders Intended for Powder Forging (PF) Applications
• Effective Date: 01-Apr-2020
• Refers: ASTM E768-99(2010) - Standard Guide for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel
• Effective Date: 01-Nov-2010
• Refers: ASTM E3-01(2007)e1 - Standard Guide for Preparation of Metallographic Specimens
• Effective Date: 01-Jul-2007
• Refers: ASTM E3-01(2007) - Standard Guide for Preparation of Metallographic Specimens
• Effective Date: 01-Jul-2007
• Refers: ASTM E768-99(2005) - Standard Guide for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel
• Effective Date: 01-May-2005
• Refers: ASTM E768-99(2004) - Standard Guide for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel
• Effective Date: 01-Nov-2004
• Refers: ASTM E3-01 - Standard Practice for Preparation of Metallographic Specimens
• Effective Date: 10-Apr-2001
• Refers: ASTM E3-95 - Standard Practice for Preparation of Metallographic Specimens
• Effective Date: 10-Apr-2001
• Refers: ASTM E768-99 - Standard Practice for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel
• Effective Date: 10-Apr-1999
• Referred By: ASTM B848/B848M-21 - Standard Specification for Powder Forged (PF) Ferrous Materials
• Effective Date: 01-Apr-2020

Overview

ASTM B796-20 establishes a standard test method for determining the nonmetallic inclusion content of ferrous powders specifically intended for powder forging (PF) applications. Developed by ASTM International, this standard provides a metallographic approach to accurately assess the size, distribution, and frequency of nonmetallic inclusions in powder forged steels processed to near full density. Nonmetallic inclusions can significantly influence the mechanical properties and consistency of powder forged parts, making this measurement critical for material quality assurance and process control in high-performance applications.

Key Topics

• Scope of Application

  • Targets ferrous powders used for powder forging with near full density and minimal lateral material flow (<1%).
  • Not suitable for specimens with core porosity, as porosity can obscure inclusions at the magnification used.

• Test Method Fundamentals

  • Utilizes metallographic techniques: core sections are cut, prepared, and polished for microscopic examination.
  • Inclusions are measured and counted using the maximum Feret’s diameter and a “near neighbor separation” criterion (typically 30 μm, 15 μm for manganese sulfide-containing steels).
  • Inclusions are categorized by size and the number of inclusions per 100 mm² is reported.

• Significance and Use

  • Aids in classifying powder grades, enabling differentiation and quality comparison between powder lots.
  • Essential for detection of variations resulting from powder quality or inappropriate forging conditions, such as lack of oxide reduction.

• Reporting and Precision

  • Results are reported by inclusion size ranges: ≥30 μm and <100 μm, ≥100 μm and <150 μm, and ≥150 μm.
  • Recognizes potential measurement uncertainty and emphasizes the necessity for repeatability and reproducibility in testing processes.

Applications

ASTM B796-20 is widely applied in industries where powder forging technology is essential for manufacturing near-net shape ferrous components. Practical uses include:

• Automotive components: Assessment of steel powder cleanliness for parts requiring high structural integrity.
• Industrial machinery: Quality assurance for gears, bearings, and other critical forged parts.
• Material suppliers: Batch certification and lot-to-lot quality comparison of ferrous powders.
• Research and development: Materials research focusing on the impact of inclusion content on mechanical properties.

Proper use of this test method ensures:

• Improved reliability in powder forged steel parts.
• Minimization of failure risks associated with nonmetallic inclusions.
• Enhanced process control for powder metallurgy and forging operations.

Related Standards

For optimal implementation and complementary processes, consider the following related ASTM standards:

• ASTM E3 - Guide for Preparation of Metallographic Specimens: Provides instructions for specimen preparation applicable to this test method.
• ASTM E768 - Guide for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel: Offers methodologies relevant for inclusion detection.
• ASTM B09 - Series of standards on Metal Powders and Powder Metallurgy Products: Encompasses broader aspects of powder metallurgy quality control.

Summary

By specifying a clear metallographic procedure for nonmetallic inclusion assessment, ASTM B796-20 supports manufacturers and quality professionals in maintaining consistent quality and performance in powder-forged ferrous components. Adoption of this standard fosters robust quality assurance, supports international trade through compliance with recognized procedures, and underpins safe, reliable application of powder metallurgy products across key industries. For up-to-date methodologies, always reference the latest official ASTM standard document.

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: B796 − 20
Standard Test Method for
Nonmetallic Inclusion Content of Ferrous Powders Intended
for Powder Forging (PF) Applications
This standard is issued under the fixed designation B796; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This test method covers a metallographic method for
determiningthenonmetallicinclusionlevelofferrouspowders
2. Referenced Documents
intended for powder forging (PF) applications.
2.1 ASTM Standards:
1.2 The test method covers repress powder forged test
E3Guide for Preparation of Metallographic Specimens
specimens in which there has been minimal lateral material
E768Guide for Preparing and Evaluating Specimens for
flow (<1%). The core region of the powder forged test
Automatic Inclusion Assessment of Steel
specimen shall contain no porosity detectable at 100×.
3. Summary of Test Method
1.3 This test method is not suitable for determining the
nonmetallic inclusion level of powder forged test specimens
3.1 A section representing the core region is cut from the
that have been forged such that the core region contains
powder forged test specimen, parallel to the direction of
porosity. At the magnification used for this test method,
forging, to obtain a rectangular section that is mounted for
residual porosity is hard to distinguish from oxide inclusions.
metallographic grinding and polishing.
Too much residual porosity makes a meaningful assessment of
3.2 The polished sample is examined microscopically at a
the inclusion population impossible.
magnification of 100× and a note made of inclusions larger
1.4 Thetestmethodmaybeappliedtomaterialsthatcontain
than a predetermined size.
manganese sulfide (admixed or prealloyed), provided the near
3.3 The maximum Feret’s diameter is used to determine
neighbor separation distance is changed from 30 µm to 15 µm.
inclusion size. A Feret’s diameter is a caliper diameter as
NOTE1—Thetestmethodmaybeappliedtopowderforgedpartswhere
illustrated in Fig. 1.
there has been a greater amount of material flow provided:
3.4 The fragmented nature of some inclusions means that
The near neighbor separation distance is changed, or
The inclusion sizes agreed between the parties are adjusted for the
theirsizedeterminationissomewhatcomplicated.Theconcept
amount of material flow.
of near neighbor separation is used in determining inclusion
size. If an inclusion is within a certain distance of its neigh-
1.5 Units—The values stated in SI units are to be regarded
asstandard.Nootherunitsofmeasurementareincludedinthis boring particles, it is considered a member of an inclusion
cluster or agglomerate. Detected features within 30 µm of one
standard.
another are considered part of the same inclusion.The concept
1.6 This standard does not purport to address all of the
is illustrated schematically in Fig. 2.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.5 The nonmetallic inclusion level of the test specimen is
priate safety, health, and environmental practices and deter- reported as the number of inclusions per 100 mm greater than
mine the applicability of regulatory limitations prior to use.
or equal to the predetermined size.
1.7 This international standard was developed in accor-
4. Significance and Use
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
4.1 The extensive porosity present in pressed and sintered
Development of International Standards, Guides and Recom-
ferrous materials masks the effect of inclusions on mechanical
properties.Incontrast,thepropertiesofmaterialpowderforged
This test method is under the jurisdiction of ASTM Committee B09 on Metal
Powders and Metal Powder Products and is the direct responsibility of Subcom-
mittee B09.11 on Near Full Density Powder Metallurgy Materials. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2020. Published June 2020. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1988. Last previous edition approved in 2014 as B796–14. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/B0796-20. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B796 − 20
determines the features that will be resolved, and all detected features are
included in the assessment of inclusion size.
6. Test Specimen Preparation
6.1 Mix the powder that is intended for use in a powder
forgingapplicationwithanappropriateamountofgraphiteand
lubricant.
6.2 Press a cylindrical compact to a specified green density
and heat the compact to the desired forging temperature using
a furnace with a suitable reducing gas atmosphere.
6.3 Transfer the heated cylindrical compact to a pre-heated
die in a fast-acting press and repress forge the cylinder.
6.4 The relationship between the diameter of the green
compact and the diameter of the forging die shall be such that
the lateral flow during the repress forging operation is < 1%.
FIG. 1 Schematic Illustration of Feret’s Diameter
7. Sampling
7.1 A metallographic sample shall be removed from the
powder forged test specimen, austenitized, and quenched.
7.2 Thepolishedsurfaceofthesampletobeexaminedshall
be not less than 350 mm in area. Multiple sections are
permitted in order to obtain the necessary area for measure-
ment.
7.3 The polished surface shall be parallel to the direction of
forging, that is, parallel to the direction of travel of the forging
punch, and shall represent the core region of the test specimen
as illustrated in Fig. 3.
FIG. 2 Schematic Illustration of the “Near Neighbor” Concept
and Maximum Feret’s Diameter
8. Procedure
8.1 Preparation of Specimens—In polishing the specimens,
to near full density are strongly influenced by the composition,
it is highly important that a clean polish be obtained and that
size, size distribution, and location of nonmetallic inclusions.
the inclusions not be pitted, dragged, or obscured. It is
recommended that the procedures described in Guide E3 and
4.2 The test for nonmetallic inclusions in powder forged
steels is useful as the following: Guide E768 be followed. Automate
...

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: B796 − 14 B796 − 20
Standard Test Method for
Nonmetallic Inclusion Content of Ferrous Powders Intended
for Powder Forging (PF) Applications
This standard is issued under the fixed designation B796; 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 test method covers a metallographic method for determining the nonmetallic inclusion level of ferrous powders
intended for powder forging (PF) applications.
1.2 The test method covers repress powder forged test specimens in which there has been minimal lateral material flow
(< 1%).(< 1 %). The core region of the powder forged test specimen shall contain no porosity detectable at 100×.
1.3 This test method is not suitable for determining the nonmetallic inclusion level of powder forged test specimens that have
been forged such that the core region contains porosity. At the magnification used for this test method, residual porosity is hard
to distinguish from oxide inclusions. Too much residual porosity makes a meaningful assessment of the inclusion population
impossible.
1.4 The test method may be applied to materials that contain manganese sulfide (admixed or prealloyed)prealloyed), provided
the near neighbor separation distance is changed from 30 μm to 15 μm.
NOTE 1—The test method may be applied to powder forged parts where there has been a greater amount of material flow provided:
The near neighbor separation distance is changed, or
The inclusion sizes agreed between the parties are adjusted for the amount of material flow.
1.5 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.6 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.
1.7 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:
E3 Guide for Preparation of Metallographic Specimens
E768 Guide for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel
3. Summary of Test Method
3.1 A section representing the core region is cut from the powder forged test specimen, parallel to the direction of forging, to
obtain a rectangular section that is mounted for metallographic grinding and polishing.
3.2 The polished sample is examined microscopically at a magnification of 100× and a note made of inclusions larger than a
predetermined size.
This test method is under the jurisdiction of ASTM Committee B09 on Metal Powders and Metal Powder Products and is the direct responsibility of Subcommittee B09.11
on Near Full Density Powder Metallurgy Materials.
Current edition approved Sept. 1, 2014April 1, 2020. Published October 2014June 2020. Originally approved in 1988. Last previous edition approved in 20022014 as
B796 – 07.B796 – 14. DOI: 10.1520/B0796-14.10.1520/B0796-20.
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.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B796 − 20
3.3 The maximum Feret’s diameter is used to determine inclusion size. A Feret’s diameter is a caliper diameter as illustrated
in Fig. 1.
3.4 The fragmented nature of some inclusions means that their size determination is somewhat complicated. The concept of near
neighbor separation is used in determining inclusion size. If an inclusion is within a certain distance of its neighboring particles,
it is considered a member of an inclusion cluster or agglomerate. Detected features within 30 μm of one another are considered
part of the same inclusion. The concept is illustrated schematically in Fig. 2.
3.5 The nonmetallic inclusion level of the test specimen is reported as the number of inclusions per 100 mm greater than or
equal to the predetermined size.
4. Significance and Use
4.1 The extensive porosity present in pressed and sintered ferrous materials masks the effect of inclusions on mechanical
properties. In contrast, the properties of material powder forged to near full density are strongly influenced by the composition,
size, size distribution, and location of nonmetallic inclusions.
4.2 The test for nonmetallic inclusions in powder forged steels is useful as the following:
4.2.1 Characteristic to classify or differentiate one grade of powder from another.
4.2.2 Means of quality comparison of powders intended for powder forging, lot to lot.
4.3 Significant variations in nonmetallic inclusion content will occur if:
4.3.1 The powder used to form the test specimen does not meet powder forging quality standards for nonmetallic inclusion
content.
4.3.2 Processing of the powder forged test specimen has been carried out under conditions that do not permit oxide reduction
or allow oxidation of the test specimen, or both.
5. Apparatus
5.1 Equipment for the metallographic preparation of test specimens.
5.2 A metallographic microscope permitting observation and measurement up to a magnification of 100× using light with a
wavelength of 544 nm (green filter), an objective lens with a magnification of from 8× to 12.5×, and a numerical aperture between
0.16 and 0.20.
NOTE 2—Defining the light optics used is important because this determines the features that will be resolved, and all detected features are included
in the assessment of inclusion size.
6. Test Specimen Preparation
6.1 Mix the powder that is intended for use in a powder forging application with an appropriate amount of graphite and
lubricant.
6.2 Press a cylindrical compact to a specified green density and heat the compact to the desired forging temperature using a
furnace with a suitable reducing gas atmosphere.
6.3 Transfer the heated cylindrical compact to a pre-heated die in a fast-acting press and repress forge the cylinder.
6.4 The relationship between the diameter of the green compact and the diameter of the forging die shall be such that the lateral
flow during the repress forging operation is < 1%.1 %.
FIG. 1 Schematic illustrationIllustration of Feret’s diameter.Diameter
B796 − 20
FIG. 2 Schematic illustrationIllustration of the “near neighbor” concept and maximum Feret’s diameter.“Near Neighbor” Concept and
Maximum Feret’s Diameter
7. Sampling
7.1 A metallographic sample shall be removed from the powder forged test specimen, austenitized, and quenched.
7.2 The polished surface of the sample to be examined shall be not less than 350 mm in area. Multiple sections are permitted
in order to obtain the necessary area for measurement.
7.3 The polished surface shall be parallel to the direction of forging, that is, parallel to the direction of travel of the forging
punch, and shall represent the core region of the test specimen as illustrated in Fig. 3.
8. Procedure
8.1 Preparation of Specimens—In polishing the specimens, it is highly important that a clean polish be obtained and that the
inclusions not be pitted, dragged, or obscured. It is recommended that the procedures described in PracticeGuide E3 and Guide
E768 be followed. Automated grinding and polishing procedures are recommended. Examine specimens in the as-poli
...