ASTM A799/A799M-10(2020)
(Practice)Standard Practice for Steel Castings, Stainless, Instrument Calibration, for Estimating Ferrite Content
Standard Practice for Steel Castings, Stainless, Instrument Calibration, for Estimating Ferrite Content
SIGNIFICANCE AND USE
4.1 The amount of ferrite present in an austenitic stainless steel has been shown to influence the strength, toughness, and corrosion resistance of this type of cast alloy. The amount of ferrite present tends to correlate well with the magnetic permeability of the steel. The methods described in this standard cover calibration practice for estimating ferrite by the magnetic permeability of the steel. The practice is inexpensive to use over large areas of the cast part and is nondestructive.
4.2 This practice has been used for research, alloy development, quality control, and manufacturing control.
4.2.1 Many instruments are available having different designs and different principles of operation. When the probe is placed on the material being investigated, a closed magnetic circuit is formed allowing measurement of the magnetic permeability. When calibrated with standards having known ferrite content, this permeability indicates the ferrite content of the material being analyzed. The estimated ferrite content is read from a calibrated dial or from a digital readout dial. Follow the manufacturer's instructions for proper calibration of the instrument.
4.3 Since this practice measures magnetic attraction and not ferrite directly, it is subject to all of the variables that affect magnetic permeability, such as the shape, size, orientation, and composition of the ferrite phase. These in turn are affected by thermal history. Ferrite measurements by magnetic methods have also been found to be affected by the surface finish of the material being analyzed.
4.4 Magnetic methods should not be used for arbitration of conflicts on ferrite content except when agreed upon between manufacturer and purchaser.
SCOPE
1.1 This practice covers the procedure for calibration of instruments to be used for estimating the ferrite content of the microstructure of cast stainless steels by magnetic response or measurement of permeability. This procedure covers both primary and secondary instruments.
1.1.1 A primary instrument is one that has been calibrated using National Institute of Standards and Technology-Standard Reference Material (NIST-SRM) thickness coating standards. It is a laboratory tool to be used with test specimens. Some primary instruments may be used to directly measure the ferrite content of castings.
1.1.2 A secondary instrument is one that has been calibrated by the use of secondary standards that have been measured by a calibrated primary instrument. Secondary instruments are to be used to directly measure the ferrite content of castings.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.2.1 Within the text, the SI units are shown in brackets.
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
Relations
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: A799/A799M − 10 (Reapproved 2020)
Standard Practice for
Steel Castings, Stainless, Instrument Calibration, for
Estimating Ferrite Content
This standard is issued under the fixed designationA799/A799M; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice covers the procedure for calibration of
A941 TerminologyRelatingtoSteel,StainlessSteel,Related
instruments to be used for estimating the ferrite content of the
Alloys, and Ferroalloys
microstructure of cast stainless steels by magnetic response or
B499 Test Method for Measurement of Coating Thicknesses
measurement of permeability. This procedure covers both
by the Magnetic Method: Nonmagnetic Coatings on
primary and secondary instruments.
Magnetic Basis Metals
1.1.1 A primary instrument is one that has been calibrated
E562 Test Method for Determining Volume Fraction by
using National Institute of Standards andTechnology-Standard
Systematic Manual Point Count
Reference Material (NIST-SRM) thickness coating standards.
It is a laboratory tool to be used with test specimens. Some 2.2 NIST Standard:
primaryinstrumentsmaybeusedtodirectlymeasuretheferrite NIST-SRM Coating Thickness Standards
content of castings.
NOTE 1—The specific coating thickness standards previously refer-
1.1.2 Asecondary instrument is one that has been calibrated
enced in this practice are no longer available. Similar ones are now
by the use of secondary standards that have been measured by available from NIST.
a calibrated primary instrument. Secondary instruments are to
3. Terminology
be used to directly measure the ferrite content of castings.
3.1 Definitions—The definitions in Terminology A941 are
1.2 The values stated in either SI units or inch-pound units
applicable to this standard.
are to be regarded separately as standard. The values stated in
each system may not be exact equivalents; therefore, each 3.2 Definitions of Terms Specific to This Standard:
system shall be used independently of the other. Combining 3.2.1 ferrite, n—the body-centered cubic microconstituent
values from the two systems may result in nonconformance in stainless steel.
with the standard.
3.2.2 ferrite percentage, n—a value designating the ferrite
1.2.1 Within the text, the SI units are shown in brackets.
content of stainless steels.
3.2.2.1 Discussion—The Steel Founders’ Society of
1.3 This standard does not purport to address all of the
America (SFSA) has assigned ferrite percentages to the series
safety concerns, if any, associated with its use. It is the
of NIST coating thickness standards. This assignment was
responsibility of the user of this standard to establish appro-
based on the magnetic attraction for a standard magnet by the
priate safety, health, and environmental practices and deter-
coating standards when compared with the magnetic attraction
mine the applicability of regulatory limitations prior to use.
of the same magnet by a series of cast stainless steels whose
1.4 This international standard was developed in accor-
ferrite content had been determined by an accurate metallo-
dance with internationally recognized principles on standard-
graphic point count. A similar assignment based on magnetic
ization established in the Decision on Principles for the
permeability was also established. Algebraic equations have
Development of International Standards, Guides and Recom-
now been derived from a plot of the thickness of these
mendations issued by the World Trade Organization Technical
standards and the assigned ferrite percentages. By the use of
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This practice is under the jurisdiction of ASTM Committee A01 on Steel, contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee Standards volume information, refer to the standard’s Document Summary page on
A01.18 on Castings. the ASTM website.
Current edition approved March 1, 2020. Published March 2020. Originally Aubrey, L. S., Weiser, P. F., Pollard, W. J., and Schoefer, E. A., “Ferrite
approved in 1982. Last previous edition approved in 2015 as A799/A799M – 10 MeasurementandControlinCastDuplexStainlessSteels,”StainlessSteelCastings,
(2015). DOI: 10.1520/A0799_A0799M-10R20. ASTM STP 756, ASTM International, 1982, p 126.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A799/A799M − 10 (2020)
these equations, any primary instrument will have its calibra- 5.1.2 The spring is then wound until the force of the coiled
tiontraceabletotheSFSA’sinstrumentsoranyothercalibrated spring overcomes the magnetic attraction of the magnet for the
instrument and thus afford comparable reproducible ferrite material being tested, causing the magnet to break contact and
percentages. It also allows traceability to NIST. the lever arm to rise.
5.1.3 The amount of force that the coiled spring has
3.2.3 secondary standards, n—a piece of cast stainless steel
developed is determined from a marked dial securely attached
whose ferrite percentage has been determined by a calibrated
to the shaft that is used to coil or uncoil the spring.
primary instrument.
5.1.3.1 A weighted No. 2 magnet (catalog number J5-
3.2.3.1 Discussion—Secondary statements are used to cali-
0664W) is used with this instrument.
brate secondary instruments (see Calibration of Secondary
Instruments). 5.2 When using a Feritscope, follow the manufacturer’s
instructions for calibration. When traceability is required,
4. Significance and Use confirm the calibration using the appropriate NIST standards.
5.2.1 Newer versions of this instrument have a single-point
4.1 The amount of ferrite present in an austenitic stainless
probe, while older versions have a two-point probe as the
steel has been shown to influence the strength, toughness, and
sensingdevice.Whenthisprobeisplacedonthematerialbeing
corrosion resistance of this type of cast alloy. The amount of
investigated, a closed magnetic circuit is formed and energized
ferrite present tends to correlate well with the magnetic
by a low-frequency magnetic field. The voltage induced in the
permeability of the steel. The methods described in this
probe coil by this field is a measure of the permeability. When
standard cover calibration practice for estimating ferrite by the
calibrated with standards having known ferrite content, this
magnetic permeability of the steel. The practice is inexpensive
permeability indicates the ferrite content of the material being
to use over large areas of the cast part and is nondestructive.
analyzed. The estimated ferrite content is read from a cali-
4.2 This practice has been used for research, alloy
brated dial or from a digital readout dial.
development, quality control, and manufacturing control.
5.3 One secondary instrument consists of a balance arm that
4.2.1 Many instruments are available having different de- 6
has a rod-shaped magnet attached to one end. The opposite
signs and different principles of operation. When the probe is
end is counterweighted to balance the magnet.
placed on the material being investigated, a closed magnetic
5.3.1 This arm with its magnet and counterweight is en-
circuit is formed allowing measurement of the magnetic
closed in a transparent box. The top face of this container has
permeability. When calibrated with standards having known
a threaded hole directly over the magnet. Marked inserts that
ferrite content, this permeability indicates the ferrite content of
have metal plates on their bottom faces are screwed into this
the material being analyzed. The estimated ferrite content is
hole. These plates have different strengths of attraction for the
read from a calibrated dial or from a digital readout dial.
magnet.
Followthemanufacturer’sinstructionsforpropercalibrationof
5.3.2 In use, the bottom end of the magnet is touched to the
the instrument.
material being investigated. The other end of the magnet is in
4.3 Since this practice measures magnetic attraction and not contact with the metal plate on the bottom of the insert. The
container is then raised. If the material being measured has a
ferrite directly, it is subject to all of the variables that affect
magnetic permeability, such as the shape, size, orientation, and greater attraction for the magnet than does the plate on the
bottom of the insert, the magnet will be pulled away from the
composition of the ferrite phase. These in turn are affected by
thermal history. Ferrite measurements by magnetic methods insert.Ifnot,themagnetwillpullawayfromthematerialbeing
measured. The inserts are changed and the test repeated until
have also been found to be affected by the surface finish of the
material being analyzed. the inserts that are just weaker and just stronger than the
material being investigated are found.
4.4 Magnetic methods should not be used for arbitration of
5.3.3 The results of a measurement with this instrument are
conflicts on ferrite content except when agreed upon between
reported as less than A and greater than B.
manufacturer and purchaser.
5.4 NIST-SRM Coating Thickness Standards—These are
mild steel plates that are covered by an electroplated copper
5. Apparatus
layerwhichinturniscoveredbyaflashcoatofchromium.The
5.1 One primary instrument that uses magnetic attraction
thickness of the copper coat varies from standard to standard
consists of a spring-loaded balance arm from which a rod-
and is certified by NIST. The strength of the magnetic
shaped magnet is suspended. The opposite end of the balance
attraction of each standard varies with the thickness of the
arm from the magnet has counterweights that balance most but
coating. These are primary standards for calibration.
not all of the weight of the magnet.
5.5 Other instruments such as the Elcometer may be used.
5.1.1 When this instrument is used, the spring load is
relaxed sufficiently to allow the magnet to make contact with
the material being tested. 5
Feritscope, produced by Fischer Technology,
...
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