1、Designation: F2328M 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 the year of
2、original 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,classifyi
3、ng, and determining the presence of decarburizationand carburization in the threaded section of hardened andtempered metric steel bolts, screws, studs, nuts and similarparts which have been heated to facilitate fabrication or tomodify their mechanical properties. This test method is notintended to a
4、ddress products which are intentionally carburizedto achieve specific results.1.2 Two routine methods are described for measuring thelimits of and determining the presence of decarburization orcarburization; the Optical Method and the MicroindentationMethod 1. Either method is appropriate for routin
5、e examina-tions. The Microindentation Method 2 shall be considered thereferee method.1.3 For the purpose of these tests, there are five classes ofhardened and tempered steel products for which specificmeasurements must be made with respect to their physicalproperties.1.4 The values stated in SI unit
6、s are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health pract
7、ices and determine the applica-bility of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and
8、 Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2A574M Specification for Alloy Steel Socket-Head CapScrews (Metric) (Withdrawn 2015)3E3 Guide for Preparation of Metallographic SpecimensE384 Test Method for
9、Microindentation Hardness of Mate-rialsF835M Specification for Alloy Steel Socket Button and FlatCountersunk Head Cap Screws (Metric) (Withdrawn2015)3F912M Specification for Alloy Steel Socket Set Screws(Metric) (Withdrawn 2015)3F1789 Terminology for F16 Mechanical Fasteners3. Terminology3.1 Definit
10、ions:3.1.1 carburizationprocess or result of increasing thecarbon content of the surface layers of the steel fastenerproduct.3.1.2 decarburizationin accordance with TerminologyF1789, is a loss of carbon from the surface layer of the fastener,normally associated with heat treatment.3.1.3 gross decarb
11、urizationalso known as completedecarburization, is characterized by a sufficient carbon loss toshow only clearly defined ferrite grains.3.1.4 partial decarburizationcharacterized as a loss ofcarbon sufficient to cause a lighter shade of tempered marten-site than that of the immediately adjacent base
12、 metal, but asbeing of insufficient carbon loss to show clearly defined ferritegrains.4. Significance and Use4.1 Decarburization and carburization are two surface con-ditions created, either intentionally or unintentionally, as with1This test method is under the jurisdiction of ASTM Committee F16 on
13、Fasteners and is the direct responsibility of Subcommittee F16.01 on Test Methods.Current edition approved Sept. 1, 2017. Published September 2017. Originallyapproved in 2004. Last previous edition approved in 2014 as F2328M 14. DOI:10.1520/F2328M-17.2For referenced ASTM standards, visit the ASTM we
14、bsite, 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.3The last approved version of this historical standard is referenced onwww.astm.org.*A Summary of Changes sect
15、ion appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on
16、 Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1a pre-existing condition created during the rod rolling process,the rod/wire annealing process, or while heat treating threadedste
17、el products. Too much of either will adversely affect thesafety and performance of the threaded product. Therefore,limits have been established for four different product groups:the harder and greater the tensile strength of the product, themore susceptible to failure the product becomes if these li
18、mitsare exceeded.4.2 When testing to a particular product specification thatlists the dimensions and microindentation data to be used, thatdata shall take precedence over the tables in this test method.4.3 There are only two viable methods available to detectthese deficiencies: either by the visual
19、method or the microin-dentation method. Both methods are used for routine inspec-tions when evaluations are conducted at a single location on theproduct sample. Because an evaluation at a specific locationmay not be representative of the whole part, the referee methodemploys the microindentation met
20、hod taken as an average ofevaluations conducted on four adjacent threads. This proceduresignificantly reduces random test variables when compared totesting on a single thread.4.4 Specifying this test method does not specify or implythat testing shall be for either decarburization or carburizationalo
21、ne or for both conditions. When either test method isperformed, both conditions will be apparent and shall bereported. For example, if an order is placed to test fordecarburization and none is found but the presence of decar-burization is detected, it shall be reported on the test report thatcarburi
22、zation was found.5. Class of Decarburization5.1 Class DeterminationThese measurements by Classare predicated upon their relationship between the height (H) ofthe external thread at its maximum boundary, disregarding anysurface coating, and N, which is the minimum thread height inthe non-decarburized
23、 zone (see Figs. 1-3). The dimensions forN and H are listed in Table 2 for each Class. Dimension G(Table 1 and Fig. 1) represents the maximum depth of gross orcomplete decarburization.NOTE 1Refer to the product standard for specific requirements. Whenlimits are not specified, use Table 1 as a sugges
24、ted reference.6. Preparation6.1 The use of either the optical or microindentation hard-ness method requires the finished product to be longitudinallycross-sectioned, approximately through the threaded axis, andmounted for grinding and polishing in any suitable mediumwhich will provide edge retention
25、 of the specimen. This shallbe performed in accordance with good metallographic practice.See Practice E3.7. Evaluation by the Optical Method7.1 Etch the mounted specimen (Section 6)ina2to4%nital or picral solution to exhibit the microstructure. Examinethe specimen at 100X magnification using a metho
26、d capable ofmeasuring distances to at least 0.001 in. resolution. The widthof any light-etching band of martensite defines the depth ofdecarburization. Compare the image with Fig. 1 for themaximum limits for G by taking a measurement on a lineperpendicular to the flank of the thread midway between t
27、hethread crest and root (pitch diameter).7.2 Interpretation of Results:7.2.1 Allowable limits for partial decarburization shall be inaccordance with 3.1.4 and Fig. 1, and the measured values shallbe in accordance with Table 2, when measured in accordancewith the illustrations in Figs. 2 and 3.7.2.2
28、Allowable limits for gross decarburization (G) shall bein accordance with 3.1.3 and the measured values as defined inTable 1. The optical method is the only valid method forevaluating the depth of gross decarburization. Gross decarbur-ization is prohibited in Class 3 and Class 4 products.7.2.3 Carbu
29、rization is identified when the tempered marten-site is a darker shade than the immediately adjacent base metal.If visible evidence of surface carburization is present on thesurface zone, the microindentation hardness method, in accor-dance with Section 8, shall be used.7.2.4 The optical method may
30、not be appropriate for speci-mens with certain coatings, such as zinc, where the coating canaffect the etching process and distort the appearance of the basematerial microstructure. These coatings shall be removed priorto mounting if the coating prevents proper etching. Care mustalso be exercised to
31、 not alter the surface condition of thesubstrate during the coating removal process.7.2.5 If the results of the optical method indicate a possiblenonconformance in the measurement of partial decarburizationor carburization, or are otherwise inconclusive, the microin-dentation hardness method (Sectio
32、n 8) shall be performed afterthe specimens are repolished.8. Evaluation by the Microindentation Hardness Method8.1 Prepare the sample in accordance with Section 6 andperform measurements in accordance with Test Method E384on polished and unetched specimens. Use either a Vickers(136) indenter or a Kn
33、oop indenter with the following loadrequirements:Thread Pitch, mmLoadKnoop (HK) Vickers (HV)Over 0.60 500 gf 300 gf0.45 through 0.60 200 gf 200 gfLess than 0.45 100 gfA100 gfAFIG. 1 Decarburization ZonesF2328M 172ALighter loads shall be used if the size of the part warrants.8.2 Routine Decarburizati
34、on/Carburization Test Method1Measurement:8.2.1 Determine the base metal hardness (Position 1) that isnear the intersection of a plane at the thread root diameter anda perpendicular line bisecting the thread crest. Measurement atPosition 2 is taken on the same thread crest bisector line fromPosition
35、1 to an approximate distance N as determined in Table2 and as specified by the product classification or productspecification. See Figs. 2 and 3.8.2.2 For Class 1, 2, and 5 products, Position 3 hardnessshall be measured at a depth of 0.12 mm from the thread flankat an approximate distance of H/2 as
36、measured from the planeof the thread root diameter (Fig. 2).8.2.3 For Class 3 and Class 4 products, Position 3 hardnessshall be measured at an approximate depth of 0.08 mm fromthe thread flank at an approximate distance of H/2, as measuredfrom the plane of the thread root diameter (Fig. 3).8.2.4 Add
37、itionally, Class 4 products shall have a fourthmeasurement taken in the thread root at a depth of 0.1 h. SeeTable 2 and Fig. 3.8.2.5 Position 3 readings and those described in 8.2.4 shallbe taken on the same or adjacent thread and at the same timeas the readings at positions 1 and 2 using the same h
38、ardnessscale. The long axis of the Knoop indenter shall be alignedapproximately parallel with the thread pitch angle at Position 3.FIG. 2 Position for Microindentation MeasurementsFIG. 3 Microindentation Measurements for Class 3 ProductsTABLE 1 Classes of Decarburization: GuideClass N G max Typical
39、Applications112 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.223 H 0.015 mm For products with a minimum tensile strengthof 1040 MPa or a hardness range of 33 to3
40、9 HRC, or both.334 H none permitted For products with a minimum tensile strengthof 1200 MPa or a minimum specifiedhardness of 37 HRC, or both.434 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 manufa
41、ctured to the ASTMrequirements of Specifications A574M,F835M,orF912M, or both.523 H 0.015 mm For heat treated nuts with a hardness of2438HRCF2328M 1738.3 Interpretation of Results:8.3.1 A decrease of more than 30 hardness points of eitherHK or HV between Position 1 to Position 2 indicates excessived
42、ecarburization and that the part does not conform to thespecification. If a nonconformance is indicated, proceed toreferee test method in 8.4 for verification.8.3.2 An increase of more than 30 hardness points of eitherHK or HV between Position 1 to Position 3 shall be regardedas excessive carburizat
43、ion and the part does not conform to thespecification. If a nonconformance is indicated, proceed toreferee test method in 8.5 for verification.8.4 Decarburization Referee Test Method 2Measurement:8.4.1 Determine the base metal hardness as in 8.2.1 bytaking the average of all Position 1 and Position
44、2 readings, asfirst measured during the routine test, and then on threeadditional adjacent threads. Determine the condition of thespecimen by subtracting the average reading noted at Position2 from the average reading noted at Position 1, in accordancewith 8.3.1.8.4.2 Interpretation of ResultsIf the
45、 average of the fourreadings indicates a decrease of more than 30 points of eitherHK or HV from Position 1 to Position 2, the part does notconform 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 app
46、ropriate, by taking the average of all Position 1and Position 3 readings, as first measured during the routinetest, and then on three additional adjacent threads. Determinethe condition of the specimen by subtracting the averagereading noted at Position 1 from the average reading noted atPosition 3,
47、 as defined in 8.3.2. The threaded section will giveevidence of carburization if the average of the four readingsindicates a positive value.8.5.2 Interpretation of ResultsIf the average of the fourreadings indicates an increase of more than 30 points of eitherHV or HK from Position 1 to Position 3,
48、the part does notconform to the carburization specification limit.9. Precision and Bias9.1 Precision and bias evaluations have not been conductedfor this test method. When such data is available, a precisionand bias section will be added.10. Keywords10.1 carburization; complete decarburization; deca
49、rburiza-tion; gross decarburization; HK; HV; Knoop; microindenta-tion; partial decarburization; tempered martensite; VickersTABLE 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 . . . . . . . . .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
