ASTM A799/A799M-04
(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
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 non-destructive.
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’instructions for proper calibration of the instrument.
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.
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 inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification.
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 and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: A799/A799M – 04
Standard Practice for
Steel Castings, Stainless, Instrument Calibration, for
1
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* lated Alloys, and Ferroalloys
B499 Test Method for Measurement of Coating Thick-
1.1 This practice covers the procedure for calibration of
nessesbytheMagneticMethod:NonmagneticCoatingson
instruments to be used for estimating the ferrite content of the
Magnetic Basis Metals
microstructure of cast stainless steels by magnetic response or
E562 Test Method for Determining Volume Fraction by
measurement of permeability. This procedure covers both
Systematic Manual Point Count
primary and secondary instruments.
2.2 NIST Standard:
1.1.1 A primary instrument is one that has been calibrated
NIST-SRM Coating Thickness Standards
using National Institute of Standards andTechnology-Standard
Reference Material (NIST-SRM) thickness coating standards.
NOTE 1—The specific coating thickness standards previously refer-
It is a laboratory tool to be used with test specimens. Some
enced in this practice are no longer available. Similar ones are now
available from NIST.
primaryinstrumentsmaybeusedtodirectlymeasuretheferrite
content of castings.
3. Terminology
1.1.2 Asecondary instrument is one that has been calibrated
3.1 Definitions: The definitions in Terminology A941 are
by the use of secondary standards that have been measured by
applicable to this standard.
a calibrated primary instrument. Secondary instruments are to
3.2 Definitions of Terms Specific to This Standard:
be used to directly measure the ferrite content of castings.
3.2.1 ferrite, n—the body-centered cubic microconstituent
1.2 The values stated in either inch-pound units or SI units
in stainless steel.
are to be regarded separately as standard. Within the text, the
3.2.2 ferrite percentage, n—a value designating the ferrite
SI units are shown in brackets. The values stated in each
content of stainless steels.
system are not exact equivalents; therefore, each system must
3.2.2.1 Discussion—The Steel Founders’ Society of
be used independently of the other. Combining values from the
America (SFSA) has assigned ferrite percentages to the series
two systems may result in nonconformance with the specifi-
3
of NIST coating thickness standards . This assignment was
cation.
based on the magnetic attraction for a standard magnet by the
1.3 This standard does not purport to address all of the
coating standards when compared with the magnetic attraction
safety concerns, if any, associated with its use. It is the
of the same magnet by a series of cast stainless steels whose
responsibility of the user of this standard to establish appro-
ferrite content had been determined by an accurate metallo-
priate safety and health practices and determine the applica-
graphic point count. A similar assignment based on magnetic
bility of regulatory limitations prior to use.
permeability was also established. Algebraic equations have
2. Referenced Documents
now been derived from a plot of the thickness of these
2
standards and the assigned ferrite percentages. By the use of
2.1 ASTM Standards:
these equations, any primary instrument will have its calibra-
A941 Terminology Relating to Steel, Stainless Steel, Re-
tiontraceabletotheSFSA’sinstrumentsoranyothercalibrated
instrument and thus afford comparable reproducible ferrite
1
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
percentages. It also allows traceability to NIST.
Stainless Steel and RelatedAlloys and is the direct responsibility of Subcommittee
3.2.3 secondary standards, n—a piece of cast stainless steel
A01.18 on Castings.
whose ferrite percentage has been determined by a calibrated
Current edition approved March 1, 2004. Published April 2004. Originally
approved in 1982. Last previous edition approved in 1992 as A799/A799M – 92
primary instrument.
(2002).
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Aubrey, L.S., Weiser, P.F., Pollard, W.J., and Schoefer, E.A., “Ferrite Measure-
Standards volume information, refer to the standard’s Document Summary page on ment and Control in Cast Duplex Stainless Steels,” Stainless Steel Castings, ASTM
the ASTM website. DOI: 10.1520/A0799_A0799M-04. STP 756, ASTM, 1982, p 126.
*A Summary of Changes section appears at the end of this standard.
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