1、Designation: A 799/A799M 04Standard Practice forSteel Castings, Stainless, Instrument Calibration, forEstimating Ferrite Content1This standard is issued under the fixed designation A 799/A799M; the number immediately following the designation indicates the yearof original adoption or, in the case of
2、 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*1.1 This practice covers the procedure for calibration ofinstruments to be used for estimating th
3、e ferrite content of themicrostructure of cast stainless steels by magnetic response ormeasurement of permeability. This procedure covers bothprimary and secondary instruments.1.1.1 A primary instrument is one that has been calibratedusing National Institute of Standards and Technology-StandardRefer
4、ence Material (NIST-SRM) thickness coating standards.It is a laboratory tool to be used with test specimens. Someprimary instruments may be used to directly measure the ferritecontent of castings.1.1.2 A secondary instrument is one that has been calibratedby the use of secondary standards that have
5、been measured bya calibrated primary instrument. Secondary instruments are tobe used to directly measure the ferrite content of castings.1.2 The values stated in either inch-pound units or SI unitsare to be regarded separately as standard. Within the text, theSI units are shown in brackets. The valu
6、es stated in eachsystem are not exact equivalents; therefore, each system mustbe used independently of the other. Combining values from thetwo systems may result in nonconformance with the specifi-cation.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with
7、 its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 941 Terminology Relating to Steel, Stainless Steel, Re-lated Alloy
8、s, and FerroalloysB 499 Test Method for Measurement of Coating Thick-nesses by the Magnetic Method: Nonmagnetic Coatings onMagnetic Basis MetalsE 562 Practice for Determining Volume Fraction by Sys-tematic Manual Point Count2.2 NIST Standard:NIST-SRM Coating Thickness StandardsNOTE 1The specific coa
9、ting thickness standards previously refer-enced in this practice are no longer available. Similar ones are nowavailable from NIST.3. Terminology3.1 Definitions: The definitions in Terminology A 941 areapplicable to this standard.3.2 Definitions of Terms Specific to This Standard:3.2.1 ferrite, nthe
10、body-centered cubic microconstituentin stainless steel.3.2.2 ferrite percentage, na value designating the ferritecontent of stainless steels.3.2.2.1 DiscussionThe Steel Founders Society ofAmerica (SFSA) has assigned ferrite percentages to the seriesof NIST coating thickness standards3. This assignme
11、nt wasbased on the magnetic attraction for a standard magnet by thecoating standards when compared with the magnetic attractionof the same magnet by a series of cast stainless steels whoseferrite content had been determined by an accurate metallo-graphic point count. A similar assignment based on ma
12、gneticpermeability was also established. Algebraic equations havenow been derived from a plot of the thickness of thesestandards and the assigned ferrite percentages. By the use ofthese equations, any primary instrument will have its calibra-tion traceable to the SFSAs instruments or any other calib
13、ratedinstrument and thus afford comparable reproducible ferritepercentages. It also allows traceability to NIST.3.2.3 secondary standards, na piece of cast stainless steelwhose ferrite percentage has been determined by a calibratedprimary instrument.1This practice is under the jurisdiction of ASTM C
14、ommittee A01 on Steel,Stainless Steel, and Related Alloys and is the direct responsibility of SubcommitteeA01.18 on Castings.Current edition approved March 1, 2004. Published April 2004. Originallyapproved in 1982. Last previous edition approved in 1992 as A 799/A 799M 92(2002).2For referenced ASTM
15、standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Aubrey, L.S., Weiser, P.F., Pollard, W.J., and Schoefer, E.A., “Ferrite Measure-m
16、ent and Control in Cast Duplex Stainless Steels,” Stainless Steel Castings, ASTMSTP 756, ASTM, 1982, p 126.1*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.3.2.3.1 Disc
17、ussionSecondary statements are used to cali-brate secondary instruments (see Calibration of SecondaryInstruments).4. Significance and Use4.1 The amount of ferrite present in an austenitic stainlesssteel has been shown to influence the strength, toughness andcorrosion resistance of this type of cast
18、alloy. The amount offerrite present tends to correlate well with the magneticpermeability of the steel. The methods described in thisstandard cover calibration practice for estimating ferrite by themagnetic permeability of the steel. The practice is inexpensiveto use over large areas of the cast par
19、t and is non-destructive.4.2 This practice has been used for research, alloy develop-ment, quality control, and manufacturing control.4.2.1 Many instruments are available having different de-signs, and different principles of operation. When the probe isplaced on the material being investigated, a c
20、losed magneticcircuit is formed allowing measurement of the magneticpermeability. When calibrated with standards having knownferrite content, this permeability indicates the ferrite content ofthe material being analyzed. The estimated ferrite content isread from a calibrated dial or from a digital-r
21、eadout dial.Follow the manufacturers instructions for proper calibration ofthe instrument.4.3 Since this practice measures magnetic attraction and notferrite directly, it is subject to all of the variables that affectmagnetic permeability, such as the shape, size, orientation, andcomposition of the
22、ferrite phase. These in turn are affected bythermal history. Ferrite measurements by magnetic methodshave also been found to be affected by the surface finish of thematerial being analyzed.4.4 Magnetic methods should not be used for arbitration ofconflicts on ferrite content except when agreed upon
23、betweenmanufacturer and purchaser.5. Apparatus5.1 One primary instrument that uses magnetic attractionconsists of a spring-loaded balance arm from which a rod-shaped magnet is suspended.4The opposite end of the balancearm from the magnet has counterweights that balance most butnot all of the weight
24、of the magnet.5.1.1 When this instrument is used, the spring load isrelaxed sufficiently to allow the magnet to make contact withthe material being tested.5.1.2 The spring is then wound until the force of the coiledspring overcomes the magnetic attraction of the magnet for thematerial being tested,
25、causing the magnet to break contact andthe lever arm to rise.5.1.3 The amount of force that the coiled spring hasdeveloped is determined from a marked dial securely attachedto the shaft that is used to coil or uncoil the spring.5.1.3.1 A weighted number 2 is used with this instrument,U5-0664W.5.2 Wh
26、en using a Feritscope,5follow the manufacturersinstructions for calibration. When traceability is required,confirm the calibration using the appropriate NIST standards.5.2.1 Newer versions of this instrument have a single-pointprobe while older versions have a two-point probe as thesensing device. W
27、hen this probe is placed on the material beinginvestigated, a closed magnetic circuit is formed and energizedby a low-frequency magnetic field. The voltage induced in theprobe coil by this field is a measure of the permeability. Whencalibrated with standards having known ferrite content, thispermeab
28、ility indicates the ferrite content of the material beinganalyzed. The estimated ferrite content is read from a cali-brated dial or from a digital-readout dial.5.3 One secondary instrument consists of a balance arm thathas a rod-shaped magnet attached to one end.6The oppositeend is counterweighted t
29、o balance the magnet.5.3.1 This arm with its magnet and counterweight is en-closed in a transparent box. The top face of this container hasa threaded hole directly over the magnet. Into this hole arescrewed-marked inserts that have metal plates on their bottomface. These plates have different streng
30、ths of attraction for themagnet.5.3.2 In use, the bottom end of the magnet is touched to thematerial being investigated. The other end of the magnet is incontact with the metal plate on the bottom of the insert. Thecontainer is then raised. If the material being measured has agreater attraction for
31、the magnet than does the plate on thebottom of the insert, the magnet will be pulled away from theinsert. If not, the magnet will pull away from the material beingmeasured. The insert buttons are changed until the ones that arejust weaker and also stronger than the material being investi-gated are f
32、ound.5.3.3 The results of a measurement with this instrument arereported as less than A and greater than B.5.4 NIST-SRM Coating Thickness Standards. These aremild steel plates that are covered by an electroplated copperlayer which in turn is covered by a flash coat of chromium. Thethickness of the c
33、opper coat varies from standard to standardand is certified by NIST. The strength of the magneticattraction of each standard varies with the thickness of thecoating. These are primary standards for calibration.5.5 Other instruments such as the Elcometer7may be used.6. Calibration6.1 Calibrate primar
34、y instruments that use magnetic attrac-tion as criterion as follows:6.1.1 When calibrating magnetic instruments, make surethere is no magnetic material within the area that could affectthe calibration. This includes beneath the surface on which theinstrument rests.6.1.2 MagnetUse weighted standard N
35、o. 2 magnet formeasurement of ferrite content of cast stainless steel.4Magne Gage, produced by Magne Gage Sales and Service Co., Inc., 629 PackerStreet, Avoca, PA 18641; http:/www.magne-.5Feritscope, produced by Fischer Technology, Inc., 750 Marshall Road, Wind-sor, CT 06095; http:/www.fischer-.6Sev
36、ern Gage, Severn Engineering Co., Old Stage Business Park, 555 StageRoad, Unit A, Auburn, AL 36830; http:/.7Elcometer, Elcometer Instruments Ltd., Edge Lane, Manchester, UK M43 6BU;http:/.A 799/A799M 0426.1.3 ZeroingBefore calibration, zero each primary in-strument.6.1.3.1 When zeroing the instrumen
37、t, use the “T”-shapedhandle to lower the spring-loaded balance arm until theplastic-protection cylinder around the magnet is in contact witha nonmagnetic object. The base plate of the unit is satisfactory.6.1.3.2 Turn the large-knurled knob on the central shaftcounter-clockwise to a dead stop.6.1.3.
38、3 Rotate the large-knurled knob clockwise until themagnet lifts off the nonmagnetic object and the pivot arm fromwhich the magnet is suspended is parallel to the base plate.Loosen the set screw holding the black dial in position.6.1.3.4 Set the “0” position on the black dial at the indexposition and
39、 tighten the set screw.6.1.4 Determining Black Dial Values for the NIST-SRMThickness StandardsUse the NIST-SRM coating thicknessstandards.6.1.4.1 Insert, one at a time in random order, the variousNIST-SRM coating thickness standards under the plastic pro-tection cylinder. Lower the instrument each t
40、ime until thecylinder contacts the standard.6.1.4.2 If the magnet is attracted to the plate when theplastic protection cylinder is placed in contact with thestandard, rotate the large-knurled knob clockwise slowly untilthe magnet breaks contact with the standard. Record theblack-dial reading.6.1.4.3
41、 If the magnet is not attracted to the plate when theplastic cylinder comes in contact with the standard, push themagnet into contact by using the push rod located over themagnet. If the magnet does not adhere to the standard, turn thelarge-knurled knob counterclockwise a few divisions at a timeunti
42、l the magnet does adhere when it comes in contact with thestandard. When the magnet remains in contact with thestandard, rotate the large knurled knob clockwise slowly untilthe magnet breaks contact with the standard. Record the blackdial reading.6.1.4.4 Repeat 6.1.4.3 several times, more than three
43、, witheach standard moving the standard under the plastic protectioncylinder after each reading. Take the reading in the central areaof the standard. Average the readings.6.1.4.5 Tabulate the black dial readings and the thickness ofthe coatings on the standards.6.1.5 Preparation of Ferrite Percentag
44、e CurveCalculatethe assigned ferrite percentage value for each NIST-SRMcoating thickness used in 6.1.4.3 by using Eq. 1, where F is theassigned ferrite content and T is the coating thickness, and thecoefficients from Table 1. Round the calculated value to thenearest 0.1 % ferrite.F 5 B01B1T1B2T21B3T
45、31B4T4(1)6.1.5.1 Plot on an arithmetic scale the ferrite percentage foreach standard and the black dial reading obtained for thatstandard. This is the calibration curve for the instrument. It isused to designate the ferrite percentage of any sample mea-sured with the instrument.6.2 Calibrate primary
46、 instruments that use magnetic per-meability as criterion as follows:NOTE 2This calibration procedure applies only to the older (pre-1980), analog instruments with the two-point probe. Analog instrumentsmay have iether an analog meter or a digital meter. Newer (post-1980)instruments with digital rea
47、douts or single-point probes must be calibratedusing the procedure given under Calibration of Secondary Instruments.6.2.1 If the instrument has more than one measuring rangeset the instrument to the desired range.6.2.2 Connect the measuring probe to the instrument.6.2.3 ZeroingBring the needle oppos
48、ite “0” on the dial bymeans of the “zero” knob. Be sure the probe is at least 1 ft 305mm away from any magnetic material when this adjustment ismade.6.2.4 Calibration of “End of Range”:6.2.4.1 Apply the sensing probe to an NIST-SRM with2.00-mil 51.0 m coating thickness. Using the “end point”control
49、knob, bring the meter needle opposite “29” on themeter. If a digital readout meter is being used, bring themaximum digital reading to “29.”6.2.4.2 If an NIST-SRM with coating thickness other than2.00-mil 51.0-m is used, determine the meter setting to beused from Table 2. It is recommended that coating thickness of3.25 mil 82.5 m or less be used.6.2.4.3 When measuring ranges are changed, the “zero”setting must be adjusted to “0.”6.2.5 Determining the Meter Readings for the NIST-SRMThickness
