1、Designation: F2328M 07 (Reapproved 2014)F2328M 14Standard Test Method forDetermining Decarburization and Carburization in Hardenedand Tempered Threaded Steel Bolts, Screws Screws, Studs,and StudsNuts (Metric)1This standard is issued under the fixed designation F2328M; the number immediately followin
2、g the designation indicates the 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 Scope*1.1 This test met
3、hod covers procedures for measuring, 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 itstheir mechanic
4、al properties.This test method is not 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 Microindentat
5、ion Method 1. Either method is appropriate for routine examinations. TheMicroindentation Method 2 shall be considered the referee method.1.3 For the purpose of these tests, there are fourfive classes of hardened and tempered steel products for which specificmeasurements must be made with respect to
6、their physical properties.1.4 The values stated 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 th
7、is standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A574M Specification for Alloy Steel Socket-Head Cap Screws (Metric)E3 Guide for Preparation of Metallographic SpecimensE38
8、4 Test Method for Knoop and Vickers Hardness of MaterialsF835M Specification for Alloy Steel Socket Button and Flat Countersunk Head Cap Screws (Metric)F912M Specification for Alloy Steel Socket Set Screws (Metric)F1789 Terminology for F16 Mechanical Fasteners3. Terminology3.1 Definitions:3.1.1 carb
9、urizationprocess 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.3.1.3 gross decarburizationals
10、o known as complete decarburization, is characterized by a sufficient carbon loss to show onlyclearly defined ferrite grains.3.1.4 partial decarburizationcharacterized as a loss of carbon sufficient to cause a lighter shade of tempered martensite thanthat of the immediately adjacent base metal, but
11、as being of insufficient carbon loss to show clearly 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 Methods.Current edition approved Feb. 1, 2014Aug. 1, 2014. Published March 2014S
12、eptember 2014. Originally approved in 2004. Last previous edition approved in 20132014as F2328M 07(2013).(2014). DOI: 10.1520/F2328M-07R14.10.1520/F2328M-14.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of AST
13、M Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard 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 po
14、ssible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only 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 standardC
15、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Significance and Use4.1 Decarburization and carburization are two surface conditions created, either intentionally or unintentionally, as with apre-existing condition created during th
16、e 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 threaded product. Therefore, limits have beenestablished for four different product groups: the harder and greater the tens
17、ile 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 dimensions and microindentation data to be used, that datashall take precedence over the tables in this test method.4.3 T
18、here 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 evaluations are conducted at a single location on the product sample.Because an evaluation at a specific location may
19、 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 significantlyreduces random test variables when compared to testing on a single thread.4.4 Specifying this test method
20、 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 be apparent and shall be reported. For example,if an order is placed to test for decarburization and none is found but
21、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 by Class are predicated upon their relationship between the height (H) of theexternal thread at its maximum boundary,
22、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 Class. Dimension G (Table 1and Fig. 1) represents the maximum depth of gross or complete decarburization.NOTE 1Refer to t
23、he 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 hardness method requires the finished product to be longitudinallycross-sectioned, approximately through the threaded
24、 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 practice. See PracticeE3.7. Evaluation by the Optical Method7.1 Etch the mounted specimen (Section 6) in a 2 to 4 % ni
25、tal 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 width of anylight-etching band of martensite defines the depth of decarburization. Compare the image with Fig. 1 for the
26、 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:7.2.1 Allowable limits for partial decarburization shall be in accordance with 3.1.4 and Fig. 1, and the measured val
27、ues 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 accordance with 3.1.3 and the measured values as defined inTable 1. The optical method is the only valid method for evaluating
28、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 shade than the immediately adjacent base metal. Ifvisible evidence of surface carburization is present on the surface zone
29、, the microindentation hardness method, in accordance withSection 8, shall be used.7.2.4 The optical method may not be appropriate for specimens with certain coatings, such as zinc, where the coating can affectthe etching process and distort the appearance of the base material microstructure. These
30、coatings shall be removed prior tomounting if the coating prevents proper etching. Care must also be exercised to not alter the surface condition of the substrateduring the coating removal process.FIG. 1 Decarburization ZonesF2328M 1427.2.5 If the results of the optical method indicate a possible no
31、nconformance in the measurement of partial decarburization orcarburization, or are otherwise inconclusive, the microindentation hardness method (Section 8) shall be performed after thespecimens are repolished.FIG. 2 Position for Microindentation MeasurementsFIG. 3 Microindentation Measurements for C
32、lass 3 ProductsTABLE 1 Classes of Decarburization: GuideClass N G max Typical Applications1 12 H 0.015 mm For heat treated products which have tensilestrengths 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 p
33、roducts 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 strengthof 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 t
34、ensile strength of 980 MPa, aspecified hardness range within 38 to 53HRC or manufactured to the ASTMrequirements of Specifications A574M,F835M, or F912M, or both.5 23 H 0.015 mm For heat treated nuts with a hardness of2438HRCF2328M 1438. Evaluation by the Microindentation Hardness Method8.1 Prepare
35、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 indenter with the following load requirements:Thread Pitch, mm LoadKnoop (HK) Vickers (HV)Over 0.60 500 gf 300 gf0.45
36、 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 1Measurement:8.2.1 Determine the base metal hardness (Position 1) that is near the intersection of a plane at the thread root
37、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 determined in Table 2 and as specified by the product classification or product specification.See Figs. 2 and 3.8.2.2
38、For Class 1 and 2 products, Position 3 hardness shall be measured at a depth of 0.12 mm from the thread flank at anapproximate distance of H/2 as measured from the plane of the thread root diameter (Fig. 2).8.2.3 For Class 3 and Class 4 products, Position 3 hardness shall be measured at an approxima
39、te 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 products 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 readin
40、gs 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 axis of the Knoop indenter shall be aligned approximatelyparallel with the thread pitch angle at Position 3.8.3 Interpretatio
41、n 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 conform to the specification. If a nonconformance is indicated, proceed to referee testmethod in 8.4 for verification.8.3.2
42、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 the specification. If a nonconformance is indicated, proceed to refereetest method in 8.5 for verification.8.4 Decarburization
43、Referee Test Method 2Measurement:8.4.1 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 bysubtracting the ave
44、rage 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 spe
45、cification limit.TABLE 2 Decarburization Limits per ClassificationNOTE 1All values shown are in millimetres.ThreadPitch, P(mm)ThreadHeight,H (mm)Class 1Hex Head,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 . . .
46、 . . . . . .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 0.24 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
47、 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 0.82 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 1.61
48、0 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 4 product only, in reference to Fig. 3.F2328M 1448.5 Carburization Referee Test Method 2Measurement:8.5.1 Determine the base metal hardness
49、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 routine test, and then on three additional adjacent threads. Determine the conditionof the specimen by subtracting the average reading noted at Position 1 from the average reading noted at Position 3, as definedin 8.3.2. The threaded section will give evidence of carburization if the average of the four readings indicates a positive value.8.5.2 Interpretation of ResultsIf the average of the four readings indicates an incr
