1、Designation: F2328M 14F2328M 17Standard Test Method forDetermining Decarburization and Carburization in Hardenedand Tempered Threaded Steel Bolts, Screws, Studs, andNuts (Metric)1This standard is issued under the fixed designation F2328M; the number immediately following the designation indicates th
2、e year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers procedures for measuring,
3、 classifying, and determining the presence of decarburization andcarburization in the threaded section of hardened and tempered metric steel bolts, screws, studs, nuts and similar parts which havebeen heated to facilitate fabrication or to modify their mechanical properties. This test method is not
4、intended to address productswhich are intentionally carburized to achieve specific results.1.2 Two routine methods are described for measuring the limits of and determining the presence of decarburization orcarburization; the Optical Method and the Microindentation Method 1. Either method is appropr
5、iate for routine examinations. TheMicroindentation Method 2 shall be considered the referee method.1.3 For the purpose of these tests, there are five classes of hardened and tempered steel products for which specificmeasurements must be made with respect to their physical properties.1.4 The values s
6、tated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safet
7、y and health practices and determine the applicability of regulatorylimitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standar
8、ds, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2A574M Specification for Alloy Steel Socket-Head Cap Screws (Metric) (Withdrawn 2015)3E3 Guide for Preparation of Metallographic SpecimensE384 Te
9、st Method for Microindentation Hardness of MaterialsF835M Specification for Alloy Steel Socket Button and Flat Countersunk Head Cap Screws (Metric) (Withdrawn 2015)3F912M Specification for Alloy Steel Socket Set Screws (Metric) (Withdrawn 2015)3F1789 Terminology for F16 Mechanical Fasteners3. Termin
10、ology3.1 Definitions:3.1.1 carburizationprocess or result of increasing the carbon content of the surface layers of the steel fastener product.3.1.2 decarburizationin accordance with Terminology F1789, is a loss of carbon from the surface layer of the fastener,normally associated with heat treatment
11、.3.1.3 gross decarburizationalso known as complete decarburization, is characterized by a sufficient carbon loss to show onlyclearly defined ferrite grains.1 This test method is under the jurisdiction of ASTM Committee F16 on Fasteners and is the direct responsibility of Subcommittee F16.01 on Test
12、Methods.Current edition approved Aug. 1, 2014Sept. 1, 2017. Published September 2014September 2017. Originally approved in 2004. Last previous edition approved in 2014as F2328M 07F2328M 14.(2014). DOI: 10.1520/F2328M-14.10.1520/F2328M-17.2 For referencedASTM standards, visit theASTM website, www.ast
13、m.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard is referenced on www.astm.org.This document is not an ASTM standard
14、 and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases on
15、ly the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.4 partial decarb
16、urizationcharacterized as a loss of carbon sufficient to cause a lighter shade of tempered martensite thanthat of the immediately adjacent base metal, but as being of insufficient carbon loss to show clearly defined ferrite grains.4. Significance and Use4.1 Decarburization and carburization are two
17、surface conditions created, either intentionally or unintentionally, as with apre-existing condition created during the rod rolling process, the rod/wire annealing process, or while heat treating threaded steelproducts. Too much of either will adversely affect the safety and performance of the threa
18、ded product. Therefore, limits have beenestablished for four different product groups: the harder and greater the tensile strength of the product, the more susceptible tofailure the product becomes if these limits are exceeded.4.2 When testing to a particular product specification that lists the dim
19、ensions and microindentation data to be used, that datashall take precedence over the tables in this test method.4.3 There are only two viable methods available to detect these deficiencies: either by the visual method or the microindentationmethod. Both methods are used for routine inspections when
20、 evaluations are conducted at a single location on the product sample.Because an evaluation at a specific location may not be representative of the whole part, the referee method employs themicroindentation method taken as an average of evaluations conducted on four adjacent threads. This procedure
21、significantlyreduces random test variables when compared to testing on a single thread.4.4 Specifying this test method does not specify or imply that testing shall be for either decarburization or carburization aloneor for both conditions. When either test method is performed, both conditions will b
22、e apparent and shall be reported. For example,if an order is placed to test for decarburization and none is found but the presence of decarburization is detected, it shall be reportedon the test report that carburization was found.5. Class of Decarburization5.1 Class DeterminationThese measurements
23、by Class are predicated upon their relationship between the height (H) of theexternal thread at its maximum boundary, disregarding any surface coating, and N, which is the minimum thread height in thenon-decarburized zone (see Figs. 1-3). The dimensions for N and H are listed in Table 2 for each Cla
24、ss. Dimension G (Table 1and Fig. 1) represents the maximum depth of gross or complete decarburization.NOTE 1Refer to the product standard for specific requirements. When limits are not specified, use Table 1 as a suggested reference.6. Preparation6.1 The use of either the optical or microindentation
25、 hardness method requires the finished product to be longitudinallycross-sectioned, approximately through the threaded axis, and mounted for grinding and polishing in any suitable medium whichwill provide edge retention of the specimen. This shall be performed in accordance with good metallographic
26、practice. See PracticeE3.7. Evaluation by the Optical Method7.1 Etch the mounted specimen (Section 6) in a 2 to 4 % nital or picral solution to exhibit the microstructure. Examine thespecimen at 100X magnification using a method capable of measuring distances to at least 0.001 in. resolution. The wi
27、dth of anylight-etching band of martensite defines the depth of decarburization. Compare the image with Fig. 1 for the maximum limits forG by taking a measurement on a line perpendicular to the flank of the thread midway between the thread crest and root (pitchdiameter).7.2 Interpretation of Results
28、:7.2.1 Allowable limits for partial decarburization shall be in accordance with 3.1.4 and Fig. 1, and the measured values shallbe in accordance with Table 2, when measured in accordance with the illustrations in Figs. 2 and 3.7.2.2 Allowable limits for gross decarburization (G) shall be in accordanc
29、e with 3.1.3 and the measured values as defined inTable 1. The optical method is the only valid method for evaluating the depth of gross decarburization. Gross decarburization isprohibited in Class 3 and Class 4 products.7.2.3 Carburization is identified when the tempered martensite is a darker shad
30、e than the immediately adjacent base metal. Ifvisible evidence of surface carburization is present on the surface zone, the microindentation hardness method, in accordance withSection 8, shall be used.FIG. 1 Decarburization ZonesF2328M 1727.2.4 The optical method may not be appropriate for specimens
31、 with certain coatings, such as zinc, where the coating can affectthe etching process and distort the appearance of the base material microstructure. These coatings shall be removed prior tomounting if the coating prevents proper etching. Care must also be exercised to not alter the surface conditio
32、n of the substrateduring the coating removal process.FIG. 2 Position for Microindentation MeasurementsFIG. 3 Microindentation Measurements for Class 3 ProductsTABLE 1 Classes of Decarburization: GuideClass N G max Typical Applications1 12 H 0.015 mm For heat treated products which have tensilestreng
33、ths up to 830 MPa and those with aspecified minimum tensile strength of 830MPa or a hardness range of 24 to 34 HRC,or both.2 23 H 0.015 mm For products with a minimum tensile strengthof 1040 MPa or a hardness range of 33 to39 HRC, or both.3 34 H none permitted For products with a minimum tensile str
34、engthof 1200 MPa or a minimum specifiedhardness of 37 HRC, or both.4 34 H none permitted For products with a receased socket drive of aminimum tensile strength of 980 MPa, aspecified hardness range within 38 to 53HRC or manufactured to the ASTMrequirements of Specifications A574M,F835M, or F912M, or
35、 both.5 23 H 0.015 mm For heat treated nuts with a hardness of2438HRCF2328M 1737.2.5 If the results of the optical method indicate a possible nonconformance in the measurement of partial decarburization orcarburization, or are otherwise inconclusive, the microindentation hardness method (Section 8)
36、shall be performed after thespecimens are repolished.8. Evaluation by the Microindentation Hardness Method8.1 Prepare the sample in accordance with Section 6 and perform measurements in accordance with Test Method E384 onpolished and unetched specimens. Use either a Vickers (136) indenter or a Knoop
37、 indenter with the following load requirements:Thread Pitch, mm LoadKnoop (HK) Vickers (HV)Over 0.60 500 gf 300 gf0.45 through 0.60 200 gf 200 gfLess than 0.45 100 gfA 100 gfAA Lighter loads shall be used if the size of the part warrants.8.2 Routine Decarburization/Carburization Test Method 1Measure
38、ment:8.2.1 Determine the base metal hardness (Position 1) that is near the intersection of a plane at the thread root diameter and aperpendicular line bisecting the thread crest. Measurement at Position 2 is taken on the same thread crest bisector line from Position1 to an approximate distance N as
39、determined in Table 2 and as specified by the product classification or product specification.See Figs. 2 and 3.8.2.2 For Class 1 1, 2, and 25 products, Position 3 hardness shall be measured at a depth of 0.12 mm from the thread flank atan approximate distance of H/2 as measured from the plane of th
40、e thread root diameter (Fig. 2).8.2.3 For Class 3 and Class 4 products, Position 3 hardness shall be measured at an approximate depth of 0.08 mm from thethread flank at an approximate distance of H/2, as measured from the plane of the thread root diameter (Fig. 3).8.2.4 Additionally, Class 4 product
41、s shall have a fourth measurement taken in the thread root at a depth of 0.1 h. See Table 2and Fig. 3.8.2.5 Position 3 readings and those described in 8.2.4 shall be taken on the same or adjacent thread and at the same time as thereadings at positions 1 and 2 using the same hardness scale. The long
42、axis of the Knoop indenter shall be aligned approximatelyparallel with the thread pitch angle at Position 3.8.3 Interpretation of Results:8.3.1 A decrease of more than 30 hardness points of either HK or HV between Position 1 to Position 2 indicates excessivedecarburization and that the part does not
43、 conform to the specification. If a nonconformance is indicated, proceed to referee testmethod in 8.4 for verification.8.3.2 An increase of more than 30 hardness points of either HK or HV between Position 1 to Position 3 shall be regarded asexcessive carburization and the part does not conform to th
44、e specification. If a nonconformance is indicated, proceed to refereetest method in 8.5 for verification.8.4 Decarburization Referee Test Method 2Measurement:TABLE 2 Decarburization Limits per ClassificationNOTE 1All values shown are in millimetres.ThreadPitch, P(mm)ThreadHeight,H (mm)Class 1Hex Hea
45、d,N (min)Class 2Hex Head,N (min)Class 3Hex Head,N (min)Class 4Skt HeadN (min)ThreadHeightH (mm)A0.1 HARoot(mm)0.35 0.202 0.10 0.13 0.15 . . . . . . . . .0.40 0.232 0.12 0.15 0.17 . . . . . . . . .0.45 0.262 0.13 0.17 0.2 . . . . . . . . .0.50 0.307 0.15 0.19 0.22 . . . . . . . . .0.60 0.368 0.18 0.2
46、4 0.27 . . . . . . . . .0.70 0.429 0.21 0.28 0.32 0.322 0.429 0.0430.80 0.491 0.24 0.33 0.37 0.368 0.491 0.0491.00 0.613 0.30 0.41 0.46 0.460 0.613 0.0611.25 0.767 0.38 0.51 0.58 0.575 0.767 0.0771.50 0.920 0.46 0.61 0.69 0.690 0.920 0.0921.75 1.074 0.54 0.72 0.81 0.806 1.074 0.1072.00 1.227 0.61 0.
47、82 0.92 0.920 1.227 0.1232.50 1.534 0.77 1.02 1.15 1.151 1.534 0.1533.00 1.840 0.92 1.23 1.38 1.380 1.840 0.1843.50 2.147 1.07 1.43 1.61 1.610 2.147 0.2154.00 2.454 1.23 1.64 1.84 1.841 2.454 0.2454.50 2.761 . . . . . . . . . 2.071 2.761 0.2765.00 3.068 . . . . . . . . . 2.301 3.068 0.307A For Class
48、 4 product only, in reference to Fig. 3.F2328M 1748.4.1 Determine the base metal hardness as in 8.2.1 by taking the average of all Position 1 and Position 2 readings, as firstmeasured during the routine test, and then on three additional adjacent threads. Determine the condition of the specimen bysu
49、btracting the average reading noted at Position 2 from the average reading noted at Position 1, in accordance with 8.3.1.8.4.2 Interpretation of ResultsIf the average of the four readings indicates a decrease of more than 30 points of either HK orHV from Position 1 to Position 2, the part does not conform to the specification limit.8.5 Carburization Referee Test Method 2Measurement:8.5.1 Determine the base metal hardness as in 8.2.1, 8.2.2, or 8.2.3, as appropriate, by taking the average of all Position 1 andPosition 3 readings, as first measured during the
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