ASTM A799/A799M-92(1997)
(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
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 problems, 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.
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NOTICE: This standard has either been superseded and replaced by a new version or
withdrawn.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: A 799/A799M – 92 (Reapproved 1997) An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practice for
Steel Castings, Stainless, Instrument Calibration, for
Estimating Ferrite Content
This standard is issued under the fixed designation A 799/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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope NIST-SRM Coating Thickness Standards, No. 1321 through
1323, 1357 through 1360, and 1361a through 1364a, (All
1.1 This practice covers the procedure for calibration of
are in sets of three or four standards.)
instruments to be used for estimating the ferrite content of the
microstructure of cast stainless steels by magnetic response or
3. Terminology
measurement of permeability. This procedure covers both
3.1 Definitions:
primary and secondary instruments.
3.1.1 ferrite—the body-centered cubic microconstituent in
1.1.1 A primary instrument is one that has been calibrated
stainless steel castings.
using National Institute of Standards and Technology-Standard
3.1.2 ferrite percentage—a value designating the ferrite
Reference Material (NIST-SRM) thickness coating standards.
content of cast stainless steels. The Steel Founders Society of
It is a laboratory tool to be used with test specimens. Some
America (SFSA) has assigned ferrite percentages to the series
primary instruments may be used to directly measure the ferrite
of NIST coating thickness standards. This assignment was
content of castings.
based on the magnetic attraction for a weighted No. 2 magnet
1.1.2 A secondary instrument is one that has been calibrated
by the coating standards when compared with the magnetic
by the use of secondary standards that have been measured by
attraction of the same magnet by a series of cast stainless steels
a calibrated primary instrument. Secondary instruments are to
whose ferrite content had been determined by an accurate
be used to directly measure the ferrite content of castings.
metallographic point count. Fig. 1 is a plot of the thickness of
1.2 The values stated in either inch-pound units or SI units
these standards and the assigned ferrite percentages. By the use
are to be regarded separately as standard. Within the text, the
of Fig. 1, any primary instrument will have its calibration
SI units are shown in brackets. The values stated in each
traceable to the SFSA’s instruments or any other calibrated
system are not exact equivalents; therefore, each system must
instrument and thus afford comparable reproducible ferrite
be used independently of the other. Combining values from the
percentages. It also allows traceability to NIST.
two systems may result in nonconformance with the specifi-
3.1.3 secondary standards—pieces of cast stainless steel
cation.
whose ferrite percentage has been determined “in house” by a
1.3 This standard does not purport to address all of the
calibrated primary instrument. These are used to calibrate
safety problems, if any, associated with its use. It is the
secondary instruments (see Section 8).
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Significance and Use
bility of regulatory limitations prior to use.
4.1 The amount of ferrite present in an austenitic stainless
2. Referenced Documents steel has been shown to influence the strength, toughness and
corrosion resistance of this type of cast alloy. The amount of
2.1 ASTM Standards:
ferrite present tends to correlate well with the magnetic
B 499 Test Method for Measurement of Coating Thick-
permeability of the steel. The methods described in this
nesses by the Magnetic Method: Nonmagnetic Coatings on
2 standard cover calibration practice for estimating ferrite by the
Magnetic Basis Metals
magnetic permeability of the steel. The practice is inexpensive
E 562 Practice for Determining Volume Fraction by Sys-
3 to use over large areas of the cast part and is non-destructive.
tematic Manual Point Count
4.2 This practice has been used for research, alloy develop-
2.2 NIST Standard:
ment, quality control, and manufacturing control.
4.2.1 Many instruments are available having two-point
This practice is under the jurisdiction of ASTM Committee A-1 on Steel, probes, single-point probes, and differing excitation current
Stainless Steel, and Related Alloysand is the direct responsibility of Subcommittee
A01.18 on Castings.
Current edition approved Dec. 15, 1992. Published June 1993. Originally
published as A 799 – 82. Last previous edition A 799/A 799M – 90. Available from Office of Standard Reference Materials, Chemistry Building,
Annual Book of ASTM Standards, Vol 02.05. Room B 311, National Institute of Standards and Technology, Gaithersburg, MD
Annual Book of ASTM Standards, Vol 03.01. 20899.
A 799/A799M
FIG. 1 Assigned Ferrite Percentages to NIST Coating Thickness Standards
levels. When the probe is placed on the material being 5.1.3.1 A weighted number 2 is used with this instrument,
investigated, a closed magnetic circuit is formed and energized U5-0664W.
by a low-frequency magnetic field. The voltage induced in the 5.2 When using a Feritscope, follow the manufacturer’s
probe coil by this field is a measure of the permeability. When instructions for calibration. When traceability is required,
calibrated with standards having known ferrite content, this confirm the calibration using the appropriate NIST standards
permeability indicates the ferrite content of the material being listed in 2.2.
analyzed. The estimated ferrite content is read from a cali- 5.2.1 This instrument has a two-point probe as the sensing
brated dial or from a digital-readout dial. Follow the manufac- device. When this probe is placed on the material being
turer’s instructions for proper calibration of the instrument. investigated, a closed magnetic circuit is formed and energized
4.3 Since this practice measures magnetic attraction and not by a low-frequency magnetic field. The voltage induced in the
ferrite directly, it is subject to all of the variables that affect probe coil by this field is a measure of the permeability. When
magnetic permeability, such as thermal history. calibrated with standards having known ferrite content, this
4.4 Magnetic methods should not be used for arbitration of permeability indicates the ferrite content of the material being
conflicts on ferrite content except when agreed upon between analyzed. The estimated ferrite content is read from a cali-
manufacturer and purchaser. brated dial or from a digital-readout dial.
5.3 One secondary instrument consists of a balance arm that
5. Apparatus 7
has a rod-shaped magnet attached to one end. The opposite
5.1 One primary instrument that uses magnetic attraction end is counterweighted to balance the magnet.
consists of a spring-loaded balance arm from which a rod- 5.3.1 This arm with its magnet and counterweight is en-
shaped magnet is suspended. The opposite end of the balance
closed in a transparent box. The top face of this container has
arm from the magnet has counterweights that balance most but a threaded hole directly over the magnet. Into this hole are
not all of the weight of the magnet.
screwed-marked inserts that have metal plates on their bottom
5.1.1 When this instrument is used, the spring load is face. These plates have different strengths of attraction for the
relaxed sufficiently to allow the magnet to make contact with
magnet.
the material being tested. 5.3.2 In use, the bottom end of the magnet is touched to the
5.1.2 The spring is then wound until the force of the coiled
material being investigated. The other end of the magnet is in
spring overcomes the magnetic attraction of the magnet for the contact with the metal plate on the bottom of the insert. The
material being tested, causing the magnet to break contact and container is then raised. If the material being measured has a
the lever arm to rise. greater attraction for the magnet than does the plate on the
5.1.3 The amount of force that the coiled spring has bottom of the insert, the magnet will be pulled away from the
developed is determined from a marked dial securely attached insert. If not, the magnet will pull away from the material being
to the shaft that is used to coil or uncoil the spring. measured. The insert buttons are changed until the ones that are
5 6
Magna Gage, produced by Magna Gage Sales and Service, 6417 Chell Rd., Feritscope, produced by Fisher Technology, Inc., Windsor, CT 06708.
Columbia, MD 21044. Severn Gage, Severn Instrument Co., Annapolis, MD.
A 799/A799M
just weaker and also stronger than the material being investi- tection cyl
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