ASTM A799/A799M-04(2009)
(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.
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.
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.
Contact ASTM International (www.astm.org) for the latest information.
Designation: A799/A799M – 04 (Reapproved 2009)
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 nessesbytheMagneticMethod:NonmagneticCoatingson
Magnetic Basis Metals
1.1 This practice covers the procedure for calibration of
E562 Test Method for Determining Volume Fraction by
instruments to be used for estimating the ferrite content of the
Systematic Manual Point Count
microstructure of cast stainless steels by magnetic response or
2.2 NIST Standard:
measurement of permeability. This procedure covers both
NIST-SRM Coating Thickness Standards
primary and secondary instruments.
1.1.1 A primary instrument is one that has been calibrated
NOTE 1—The specific coating thickness standards previously refer-
using National Institute of Standards andTechnology-Standard
enced in this practice are no longer available. Similar ones are now
available from NIST.
Reference Material (NIST-SRM) thickness coating standards.
It is a laboratory tool to be used with test specimens. Some
3. Terminology
primaryinstrumentsmaybeusedtodirectlymeasuretheferrite
3.1 Definitions: The definitions in Terminology A941 are
content of castings.
applicable to this standard.
1.1.2 Asecondary instrument is one that has been calibrated
3.2 Definitions of Terms Specific to This Standard:
by the use of secondary standards that have been measured by
3.2.1 ferrite, n—the body-centered cubic microconstituent
a calibrated primary instrument. Secondary instruments are to
in stainless steel.
be used to directly measure the ferrite content of castings.
3.2.2 ferrite percentage, n—a value designating the ferrite
1.2 The values stated in either inch-pound units or SI units
content of stainless steels.
are to be regarded separately as standard. Within the text, the
3.2.2.1 Discussion—The Steel Founders’ Society of
SI units are shown in brackets. The values stated in each
America (SFSA) has assigned ferrite percentages to the series
system are not exact equivalents; therefore, each system must
of NIST coating thickness standards . This assignment was
be used independently of the other. Combining values from the
based on the magnetic attraction for a standard magnet by the
two systems may result in nonconformance with the specifi-
coating standards when compared with the magnetic attraction
cation.
of the same magnet by a series of cast stainless steels whose
1.3 This standard does not purport to address all of the
ferrite content had been determined by an accurate metallo-
safety concerns, if any, associated with its use. It is the
graphic point count. A similar assignment based on magnetic
responsibility of the user of this standard to establish appro-
permeability was also established. Algebraic equations have
priate safety and health practices and determine the applica-
now been derived from a plot of the thickness of these
bility of regulatory limitations prior to use.
standards and the assigned ferrite percentages. By the use of
2. Referenced Documents
these equations, any primary instrument will have its calibra-
tiontraceabletotheSFSA’sinstrumentsoranyothercalibrated
2.1 ASTM Standards:
instrument and thus afford comparable reproducible ferrite
A941 Terminology Relating to Steel, Stainless Steel, Re-
percentages. It also allows traceability to NIST.
lated Alloys, and Ferroalloys
3.2.3 secondary standards, n—a piece of cast stainless steel
B499 Test Method for Measurement of Coating Thick-
whose ferrite percentage has been determined by a calibrated
primary instrument.
1 3.2.3.1 Discussion—Secondary statements are used to cali-
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel and RelatedAlloys and is the direct responsibility of Subcommittee brate secondary instruments (see Calibration of Secondary
A01.18 on Castings.
Instruments).
Current edition approved Oct. 1, 2009. Published January 2010. Originally
approved in 1982. Last previous edition approved in 2004 as A799/A799M – 04.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
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-04R09. STP 756, ASTM, 1982, p 126.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
A799/A799M – 04 (2009)
4. Significance and Use 5.2.1 Newer versions of this instrument have a single-point
probe while older versions have a two-point probe as the
4.1 The amount of ferrite present in an austenitic stainless
sensingdevice.Whenthisprobeisplacedonthematerialbeing
steel has been shown to influence the strength, toughness and
investigated, a closed magnetic circuit is formed and energized
corrosion resistance of this type of cast alloy. The amount of
by a low-frequency magnetic field. The voltage induced in the
ferrite present tends to correlate well with the magnetic
probe coil by this field is a measure of the permeability. When
permeability of the steel. The methods described in this
calibrated with standards having known ferrite content, this
standard cover calibration practice for estimating ferrite by the
permeability indicates the ferrite content of the material being
magnetic permeability of the steel. The practice is inexpensive
analyzed. The estimated ferrite content is read from a cali-
to use over large areas of the cast part and is non-destructive.
brated dial or from a digital-readout dial.
4.2 This practice has been used for research, alloy develop-
5.3 One secondary instrument consists of a balance arm that
ment, quality control, and manufacturing control.
has a rod-shaped magnet attached to one end. The opposite
4.2.1 Many instruments are available having different de-
end is counterweighted to balance the magnet.
signs, and different principles of operation. When the probe is
5.3.1 This arm with its magnet and counterweight is en-
placed on the material being investigated, a closed magnetic
closed in a transparent box. The top face of this container has
circuit is formed allowing measurement of the magnetic
a threaded hole directly over the magnet. Into this hole are
permeability. When calibrated with standards having known
screwed-marked inserts that have metal plates on their bottom
ferrite content, this permeability indicates the ferrite content of
face. These plates have different strengths of attraction for the
the material being analyzed. The estimated ferrite content is
magnet.
read from a calibrated dial or from a digital-readout dial.
5.3.2 In use, the bottom end of the magnet is touched to the
Followthemanufacturer’sinstructionsforpropercalibrationof
material being investigated. The other end of the magnet is in
the instrument.
contact with the metal plate on the bottom of the insert. The
4.3 Since this practice measures magnetic attraction and not
container is then raised. If the material being measured has a
ferrite directly, it is subject to all of the variables that affect
greater attraction for the magnet than does the plate on the
magnetic permeability, such as the shape, size, orientation, and
bottom of the insert, the magnet will be pulled away from the
composition of the ferrite phase. These in turn are affected by
insert.Ifnot,themagnetwillpullawayfromthematerialbeing
thermal history. Ferrite measurements by magnetic methods
measured.Theinsertbuttonsarechangeduntiltheonesthatare
have also been found to be affected by the surface finish of the
just weaker and also stronger than the material being investi-
material being analyzed.
gated 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
6. Calibration
the material being tested.
6.1 Calibrate primary instruments that use magnetic attrac-
5.1.2 The spring is then wound until the force of the coiled
tion as criterion as follows:
spring overcomes the magnetic attraction of the magnet for the
6.1.1 When calibrating magnetic instruments, make sure
material being tested, causing the magnet to break contact and
there is no magnetic material within the area that could affect
the lever arm to rise.
the calibration. This includes beneath the surface on which the
5.1.3 The amount of force that the coiled spring has
instrument rests.
developed is determined from a marked dial securely attached
6.1.2 Magnet—Use weighted standard No. 2 magnet for
to the shaft that is used to coil or uncoil the spring.
measurement of ferrite content of cast stainless steel.
5.1.3.1 A weighted number 2 is used with this instrument,
6.1.3 Zeroing—Before calibra
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