ASTM B276-21

Standard Test Method for Apparent Porosity in Cemented Carbides

SIGNIFICANCE AND USE
4.1 Cemented carbide materials may contain small voids that, depending on the application, may affect the performance of the product. To assist users in specifying the maximum acceptable level of porosity, this test method illustrates a broad range of porosity levels for each of three porosity types. This test method is not intended to be used as a specification, but the levels shown here may be cited in specifications written by producers and users of cemented carbides.
SCOPE
1.1 This test method specifies procedures for the metallographic determination of apparent porosity in cemented carbides.  
Note 1: The term “apparent porosity” is construed to mean all microstructures observed on a properly prepared, unetched surface, including structures resulting from uncombined carbon, non-metallic inclusions, etc., as well as true, inherent porosity.  
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, health, and environmental 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.

General Information

• Status: Published
• Publication Date: 31-Aug-2021
• ICS: 77.160 - Powder metallurgy
• Technical Committee: B09 - Metal Powders and Metal Powder Products
• Drafting Committee: B09.06 - Cemented Carbides

Relations

• Refers: ASTM B665-19 - Standard Guide for Metallographic Sample Preparation of Cemented Tungsten Carbides
• Effective Date: 01-Nov-2019
• Refers: ASTM B243-18 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Oct-2018
• Refers: ASTM B243-16 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Jul-2016
• Refers: ASTM B243-13 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Nov-2013
• Refers: ASTM B665-08(2012) - Standard Guide for Metallographic Sample Preparation of Cemented Tungsten Carbides
• Effective Date: 01-Oct-2012
• Refers: ASTM B243-12 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Jul-2012
• Refers: ASTM B243-11 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Nov-2011
• Refers: ASTM B243-10 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Jan-2010
• Refers: ASTM B243-09a - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Dec-2009
• Refers: ASTM B243-09 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Jan-2009
• Refers: ASTM B665-08 - Standard Guide for Metallographic Sample Preparation of Cemented Tungsten Carbides
• Effective Date: 01-Nov-2008
• Refers: ASTM B243-08a - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Mar-2008
• Refers: ASTM B243-08 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Feb-2008
• Refers: ASTM B243-06 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Nov-2006
• Refers: ASTM B243-05b - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Oct-2005

Overview

ASTM B276-21 is a standard test method developed by ASTM International for determining the apparent porosity in cemented carbides through metallographic techniques. Cemented carbides, also known as hardmetals, are highly valued in demanding applications due to their exceptional hardness and wear resistance. However, the presence of porosity or voids within these materials can impact performance and longevity.

This standard provides users with a systematic approach to evaluating and reporting apparent porosity levels. Although not intended to serve as a product specification itself, ASTM B276-21 can be referenced in specifications by producers and users to define acceptable porosity thresholds for cemented carbides.

Key Topics

• Definition of Apparent Porosity: Encompasses all microstructural voids observed on a properly prepared, unetched surface, including those due to uncombined carbon, non-metallic inclusions, and inherent porosity.
• Metallographic Procedures: Describes sample preparation, use of a metallographic microscope (up to 200× magnification), and evaluation techniques to observe and quantify porosity.
• Porosity Types and Classification: Porosity is classified into different types based on pore size and origin, such as:
  • Type A: Pores ≤10 μm
  • Type B: Pores >10 to ≤25 μm
  • Larger pores: >25 μm, further sub-categorized by size range
  • Type C: Porosity resulting from uncombined carbon
• Comparison with Reference Micrographs: The observed microstructures are compared against standard photomicrographs to grade porosity levels, ensuring consistent and objective assessment.
• Reporting Requirements: User reports must reference this test method, detail the specimen, results, and any occurrences that may affect the findings.

Applications

The ASTM B276-21 standard is crucial for a variety of industries that rely on cemented carbides or hardmetals, including:

• Tool Manufacturing: Helps tooling and cutting manufacturers assess porosity in carbide inserts, bits, and dies, which is critical for ensuring consistent tool life and performance.
• Powder Metallurgy: Enables producers to verify quality and control the manufacturing process of cemented tungsten carbides and related materials.
• Quality Control Laboratories: Provides a repeatable method for inspecting incoming materials or finished components to meet internal or customer requirements.
• Specification Development: Assists end-users and manufacturers in developing and referencing maximum allowable porosity criteria in procurement and quality assurance documentation.
• Failure Analysis: Supports engineers in determining whether excessive porosity contributed to a product’s failure or underperformance.

Related Standards

Users of ASTM B276-21 may also find the following standards relevant:

• ASTM B243: Terminology of Powder Metallurgy - Provides definitions associated with powder metallurgy and related materials.
• ASTM B665: Guide for Metallographic Sample Preparation of Cemented Tungsten Carbides - Offers detailed procedures for sample preparation, essential for accurate porosity assessment.
• ISO 4499-4:2016: Hardmetals - Metallographic Determination of Microstructure - Part 4: Characterisation of Porosity, Carbon Defects, and Eta-phase Content - An international standard for similar assessments, aiding harmonization across borders.

---

Keywords: ASTM B276, cemented carbides, apparent porosity, hardmetals, powder metallurgy, metallographic test method, porosity classification, quality control, carbide tool inspection, standard reference micrographs, tungsten carbide, manufacturing standards.

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: B276 − 21
Standard Test Method for
Apparent Porosity in Cemented Carbides
This standard is issued under the fixed designation B276; 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* 3. Terminology
1.1 This test method specifies procedures for the metallo- 3.1 Definitions—Definition of powder metallurgy terms can
graphic determination of apparent porosity in cemented car-
be found in Terminology B243.
bides.
4. Significance and Use
NOTE 1—The term “apparent porosity” is construed to mean all
microstructures observed on a properly prepared, unetched surface,
4.1 Cemented carbide materials may contain small voids
including structures resulting from uncombined carbon, non-metallic
that, depending on the application, may affect the performance
inclusions, etc., as well as true, inherent porosity.
of the product. To assist users in specifying the maximum
1.2 This standard does not purport to address all of the
acceptable level of porosity, this test method illustrates a broad
safety concerns, if any, associated with its use. It is the
range of porosity levels for each of three porosity types. This
responsibility of the user of this standard to establish appro-
test method is not intended to be used as a specification, but the
priate safety, health, and environmental practices and deter-
levels shown here may be cited in specifications written by
mine the applicability of regulatory limitations prior to use.
producers and users of cemented carbides.
1.3 This international standard was developed in accor-
dance with internationally recognized principles on standard-
5. Interferences
ization established in the Decision on Principles for the
5.1 Lack of adequate pressure on the specimen during
Development of International Standards, Guides and Recom-
polishing may result in material being torn from the surface of
mendations issued by the World Trade Organization Technical
the specimen. This condition may be erroneously interpreted as
Barriers to Trade (TBT) Committee.
porosity.
2. Referenced Documents
6. Apparatus
2.1 ASTM Standards:
6.1 A metallographic microscope permitting observation
B243 Terminology of Powder Metallurgy
and measurement up to a magnification of 200×.
B665 Guide for Metallographic Sample Preparation of Ce-
mented Tungsten Carbides
6.2 Equipment for the metallographic preparation of test
specimens.
2.2 ISO Standard:
ISO 4499-4:2016 Hardmetals — Metallographic Determina-
tion of Microstructure — Part 4: Characterisation of 7. Specimen Preparation
Porosity, Carbon Defects and Eta-phase Content
7.1 Where possible, specimens should be metallographi-
cally mounted in a plastic material, so that they can be polished
without rounding the edges. Larger specimens may be polished
This test method is under the jurisdiction of ASTM Committee B09 on Metal without mounting. When the specimens are too large, they
Powders and Metal Powder Products and is the direct responsibility of Subcom-
shall be sectioned using a diamond cut-off wheel or by
mittee B09.06 on Cemented Carbides.
fracturing (appropriate safety precautions shall be utilized
Current edition approved Sept. 1, 2021. Published February 2022. Originally
when fracturing a specimen). The area selected for examina-
approved in 1954. Last previous edition approved in 2015 as B276 – 05(2015). DOI:
10.1520/B0276-21.
tion should represent, as nearly as possible, the entire cross
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
section.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
7.2 The specimen shall be prepared for metallographic
the ASTM website.
examination. A suitable procedure is described in Guide B665.
Available from International Organization for Standardization (ISO), ISO
The surface to be examined shall be unetched and free of
Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Switzerland, https://www.iso.org. grinding and polishing marks.
*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
B276 − 21
8. Procedure count by the area examined (see A1.3) to obtain the number of
2 2
“B” pores/cm . If this number is less than 70 pores/cm ,
8.1 Pore size shall be defined as the maximum dimension of
designate this as B00-#, where # is the number of “B”
the pore. Make special reference to the presence of cracks and
pores/cm so obtained. If the number is greater than or equal to
slits, as well as nonmetallic inclusions.
70 pores/cm , designate this as B02. If no “B” pores are
8.2 Classification of Type “A” and “C” apparent porosity is
observed, designate this as B00-0.
based entirely on comparison of the microstructures found with
8.2.2.2 If the number of “B” pores appears to be greater than
the illustrations in Figs. 1-3 with due consideration to the
that represented by B02, with consideration to the relationship
difference in field of view of the microscope or micrographs
of area between the illustrations in Fig. 4 and that observed in
compared to the area of the illustrations. This can be accom-
the microscope (see A1.4), classify the “B” porosity as B04,
plished by scanning the specimen surface under the microscope
B06, or B08 with reference to the illustrations in Fig. 4. If the
at the appropriate magnification, and noting which of the
porosity is not uniform over the area of the test-piece section
illustrations most nearly represents the fields observed. The
being examined, identify the location of the section, for
operator should take particular care to ensure that the scale
example, as top, bottom, edge, rim (case), core, and so forth.
markers represented in the field of view of the microscope or
8.2.3 Count and report pores larger than 25 μm as the
printed micrographs are as close as possible to those on the
number of pores per cm . Choose the size ranges as follows:
illustrations in the figures. This will minimize any differences
>25 to ≤75 μm, >75 to ≤125 μm, and over 125 μm.
due to slight variability in magnification as a result of calibra-
8.2.4 Classify porosity resulting from uncombined carbon
tion or duplication/printing of images. Choose an area fully
as Type C (see Fig. 2 and Fig. 3 and examine at a magnification
representative of the specimen surface for comparison with the
of 100 or 200×). Report the porosity level by reference to the
illustrations.
appropriate illustration with consideration to the relationship of
area between the illustrations in Fig. 2 and Fig. 3 and that
NOTE 2—The illustrations in Figs. 1-4 represent only a portion of the
obser
...

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: B276 − 05 (Reapproved 2015) B276 − 21
Standard Test Method for
Apparent Porosity in Cemented Carbides
This standard is issued under the fixed designation B276; 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 Scope*
1.1 This test method specifies procedures for the metallographic determination of apparent porosity in cemented carbides.
NOTE 1—The term “apparent porosity” is construed to mean all microstructures observed on a properly prepared, unetched surface, including structures
resulting from uncombined carbon, non-metallic inclusions, etc., as well as true, inherent porosity.
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:
B243 Terminology of Powder Metallurgy
B665 Guide for Metallographic Sample Preparation of Cemented Tungsten Carbides
2.2 ASTM Adjunct:ISO Standard:
ADJB0276AISO 4499-4:2016 Apparent Porosity (4 prints of 4 photomicrographs each)Hardmetals — Metallographic
Determination of Microstructure — Part 4: Characterisation of Porosity, Carbon Defects and Eta-phase Content
3. Terminology
3.1 Definitions—Definition of powder metallurgy terms can be found in Terminology B243.
4. Significance and Use
4.1 Cemented carbide materials may contain small voids that, depending on the application, may affect the performance of the
product. To assist users in specifying the maximum acceptable level of porosity, this test method illustrates a broad range of
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 B09.06
on Cemented Carbides.
Current edition approved Oct. 1, 2015Sept. 1, 2021. Published October 2015February 2022. Originally approved in 1954. Last previous edition approved in 20102015
as B276 – 91B276 – 05(2010).(2015). DOI: 10.1520/B0276-05R15.10.1520/B0276-21.
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.
Available from ASTM International Headquarters. Order Adjunct No.International Organization for Standardization (ISO), ADJB0276A. ISO Central Secretariat, Chemin
de Blandonnet 8, CP 401, 1214 Vernier, Geneva, Switzerland, https://www.iso.org.
*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
B276 − 21
porosity levels for each of three porosity types. This test method is not intended to be used as a specification, but the levels shown
here may be cited in specifications written by producers and users of cemented carbides.
5. Interferences
5.1 Lack of adequate pressure on the specimen during polishing may result in material being torn from the surface of the specimen.
This condition may be erroneously interpreted as porosity.
6. Apparatus
6.1 A metallographic microscope permitting observation and measurement up to a magnification of 200×.
6.2 Equipment for the metallographic preparation of test specimens.
7. Specimen Preparation
7.1 Where possible, specimens should be metallographically mounted in a plastic material, so that they can be polished without
rounding the edges. Larger specimens may be polished without mounting. When the specimens are too large, they shall be
sectioned using a diamond cut-off wheel or by fracturing (appropriate safety precautions shall be utilized when fracturing a
specimen). The area selected for examination should represent, as nearly as possible, the entire cross section.
7.2 The specimen shall be prepared for metallographic examination. A suitable procedure is described in PracticeGuide B665.The
. The surface to be examined shall be unetched and free of grinding and polishing marks.
8. Procedure
8.1 Pore size shall be defined as the maximum dimension of the pore. Make special reference to the presence of cracks and slits,
as well as nonmetallic inclusions.
8.2 Classification of Type “A” and “C” apparent porosity is based entirely on comparison of the microstructures found with the
illustrations in Figs.Figs. 1-3 1, 3 and 4 of ADJB0276Awith due consideration to the difference in field of view of the microscope
or micrographs compared to the area of the illustrations. This can be accomplished by scanning the specimen surface under the
microscope at the appropriate magnification, and noting which of the illustrations most nearly represents the fields observed. The
operator should take particular care to ensure that the scale markers represented in the field of view of the microscope or printed
micrographs are as close as possible to those on the illustrations in the figures. This will minimize any differences due to slight
variability in magnification as a result of calibration or duplication/printing of images. Choose an area fully representative of the
specimen surface for comparison with the illustrations.
NOTE 2—The illustrations in Figs.Figs. 1-4 1–4 of ADJB0276Arepresent only a portion of the field of view typically observed in modern microscopes.
Typically, the field of view of a microscope is ~6.5× larger than the area in these figures. The exact relationship between the area observed at any given
magnification in the microscope and the area of the illustrations can be determined using the method in Annex A1.
8.2.1 Classify pores ≤10 μm as Type A (see Fig.Fig. 1 1 of ADJB0276Aand examine at a magnification of 200×.200×). Report
the porosity level by reference to the appropriate illustration with consideration to the relationship of area between the illustration
and that observed in the microscope, and designate as A02, A04, A06, or A08. If the level of Type A pores is less than 50 % of
that shown in the illustration for A02, then designate this as A00. If the porosity is not uniform over the area of the test-piece
section being examined, identify the location of the section, for example, as top, bottom, edge, rim (case), core, and so forth.
8.2.2 Classify pores in the range from >10 to ≤25 μm as Type B (see Fig.Fig. 4 2 of ADJB0276Aand examine at a magnification
of 100×.100×).
8.2.2.1 If the number of “B” pores appears to be less than or equal to that represented by B02, with consideration to the
relationship of
...