1、Designation: F 1941M 05METRICStandard Specification forElectrodeposited Coatings on Threaded Fasteners Metric1This standard is issued under the fixed designation F 1941M; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis specification covers the coating of steel metric screw threaded fasteners by electrodeposition.The properties of
3、 the coatings shall conform to the ASTM standards for the individual finishes listed.Coating thickness values are based on the tolerances for M series metric threads having thefollowing tolerance positions: 6g and 4g6g for external threads, and 6H for internal threads. Thecoating must not cause the
4、basic thread size to be transgressed by either the internal or externalthreads. The method of designating coated threads shall comply with ASME B1.13M.With normal methods for depositing metallic coatings from aqueous solutions, there is a risk ofdelayed failure due to hydrogen embrittlement for case
5、 hardened fasteners and fasteners having ahardness 40 HRC or above. Although this risk can be managed by selecting raw materials suitable forthe application of electrodeposited coatings and by using modern methods of surface treatment andpost heat-treatment (baking), the risk of hydrogen embrittleme
6、nt cannot be completely eliminated.Therefore, the application of a metallic coating by electrodeposition is not recommended for suchfasteners.1. Scope1.1 This specification covers application, performance anddimensional requirements for electrodeposited coatings onthreaded fasteners with metric scre
7、w threads. It specifiescoating thickness, supplementary chromate finishes, corrosionresistance, precautions for managing the risk of hydrogenembrittlement and hydrogen embrittlement relief for high-strength and surface-hardened fasteners. It also highlights thedifferences between barrel and rack pla
8、ting and makes recom-mendations as to the applicability of each process.1.2 The following precautionary statement pertains to thetest method portion only, Section 9, of this specification: Thisstandard does not purport to address all of the safety concerns,if any, associated with its use. It is the
9、responsibility of the userof this standard to establish appropriate safety and healthpractices and determine the applicability of regulatory limita-tions prior to use.2. Referenced Documents2.1 ASTM Standards:2B117 Practice for Operating Salt Spray (Fog) ApparatusB 487 Test Method for Measurement of
10、 Metal and OxideCoating Thickness by Miocroscopical Examination of aCross SectionB 499 Test Method for Measurement of Coating Thicknessby the Magnetic Method: Nonmagnetic Coatings on Mag-netic Basis MetalsB 504 Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric MethodB
11、 567 Test Method for Measurement of Coating Thicknessby the Beta Backscatter MethodB 568 Test Method for Measurement of Coating Thicknessby X-Ray SpectrometryB 659 Guide for Measuring Thickness of Metallic andInorganic Coatings1This specification is under the jurisdiction of ASTM Committee F16 onFas
12、teners and is the direct responsibility of Subcommittee F16.03 on Coatings onFasteners.Current edition approved May 1, 2005. Published May 2005. Originallyapproved in 2000. Last previous edition approved in 2000 as F 1941M 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orco
13、ntact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E 376 Practice for M
14、easuring Coating Thickness byMagnetic-Field or Eddy-Current (Electromagnetic) Exami-nation MethodsF 606 Test Methods for Determining the Mechanical Prop-erties of Externally and Internally Threaded Fasteners,Washers, and RivetsF 1470 Guide for Fastener Sampling for Specified Mechani-cal Properties a
15、nd Performance InspectionF 1624 Test Method for Measurement of Hydrogen Em-brittlement Threshold in Steel by the Incremental StepLoading TechniqueF 1940 Test Method for Process Control Verification toPrevent Hydrogen Embrittlement in Plated or CoatedFasteners2.2 ASME Standard:3B1.13M Metric Screw Th
16、reads - M Profile2.3 National Aerospace Standard (AIA):4NASM-1312-5 Fast Test Method - Method 5: Stress Dura-bility2.4 IFI Standard:5IFI-142 Hydrogen Embrittlement Risk Management3. Terminology3.1 Definitions:3.1.1 local thicknessmean of the thickness measurements,of which a specified number is made
17、 within a reference area.3.1.2 minimum local thicknesslowest local thicknessvalue on the significant surface of a single article.3.1.3 reference areaarea within which a specified numberof single measurements are required to be made.3.1.4 significant surfacesignificant surfaces are areaswhere the min
18、imum thickness to be met shall be designated onthe applicable drawing or by the provision of a suitably markedsample. However, if not designated, significant surfaces shallbe defined as those normally visible, directly or by reflection,which are essential to the appearance or serviceability of thefa
19、stener when assembled in normal position, or which can bethe source of corrosion products that deface visible surfaces onthe assembled fastener. Figs. 1 and 2 illustrate significantsurfaces on standard externally threaded and internallythreaded fasteners.4. Classification4.1 Coating MaterialThe coat
20、ing material shall be se-lected and designated in accordance with Table 1.4.2 Coating ThicknessThe coating thickness shall beselected and designated in accordance with Table 2.4.3 Chromate FinishThe chromate finish shall be selectedand designated in accordance with Table 3.5. Ordering Information fo
21、r Electroplating5.1 When ordering threaded fasteners to be coated byelectrodeposition in accordance with this specification, thefollowing information shall be supplied to the electroplater:5.1.1 The desired coating, coating thickness and the chro-mate finish, or the classification codes as specified
22、 in Tables1-3. (For example, Fe/Zn 5C denotes yellow zinc plated with aminimum thickness of 5 m on significant surfaces.)5.1.2 The identification of significant surfaces (optional).5.1.3 The requirement, if any, for stress relief before elec-troplating, in which case the stress-relief conditions mus
23、t bespecified.5.1.4 The requirements, if any, for hydrogen embrittlementrelief by heat treatment (baking) stating the tensile strength orsurface hardness of the fasteners and/or baking time andtemperature.NOTE 1Fasteners with a specified maximum hardness of 34 HRC andbelow have a very low susceptibi
24、lity to hydrogen embrittlement and donot require baking.3Available from American Society of Mechanical Engineers (ASME), 345 E.47th Street, New York, NY 10017.4Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.5Available fro
25、m Industrial Fasteners Institute (IFI), 1717 East 9th Street, Suite1105, Cleveland, OH 441142879.NOTE 1Black dot () indicates test surface.FIG. 1 Significant surfaces on Externally Threaded FastenersNOTE 1Black dot () indicates test surface.FIG. 2 Significant surfaces on Internally Threaded Fastener
26、sTABLE 1 Designation of Common Coating MaterialsCoating Designation Coating TypeFe/Zn ZincFe/Cd CadmiumFe/Zn-Co Zinc Cobalt AlloyFe/Zn-Ni Zinc Nickel AlloyFe/Zn-Fe Zinc Iron AlloyTABLE 2 Designation of Coating ThicknessNOTE 1The conversion factor from microns to inch is 3.94 3 105(for example, 5 m =
27、 0.0002 in.).Thickness Designation Minimum Thickness m33558812 12F 1941M 0525.1.5 The requirements, if any, for the type of electroplatingprocess (barrel-plating or rack-plating). See Section 10 andAppendix X1.5.1.6 The designation of coated thread class shall complywith ASME B1.13M.6. Requirements6
28、.1 Coating RequirementsThe electrodeposited coating asordered shall cover all surfaces and shall meet the followingrequirements:6.1.1 The coating metal deposit shall be bright or semi-bright unless otherwise specified by the purchaser, smooth, finegrained, adherent and uniform in appearance.6.1.2 Th
29、e coating shall be free of blisters, pits, nodules,roughness, cracks, unplated areas, and other defects that willaffect the function of the coating.6.1.3 The coating shall not be stained, discolored or exhibitany evidence of white or red corrosion products.6.1.3.1 Slight discoloration that results f
30、rom baking, drying,or electrode contact during rack-plating, or all of these, as wellas slight staining that results from rinsing shall not be cause forrejection.6.2 Corrosion ResistanceCoated fasteners, when testedby continuous exposure to neutral salt spray in accordance with9.3, shall show neithe
31、r corrosion products of coatings (whitecorrosion) nor basis metal corrosion products (red rust) at theend of the test period. The appearance of corrosion productsvisible to the unaided eye at normal reading distance shall because for rejection, except when present at the edges of thetested fasteners
32、. Refer to Annex A1 for neutral salt sprayperformance requirements for zinc, zinc alloy and cadmiumcoatings.6.3 ThicknessThe coating thickness shall comply withrequirements of Table 2 when measured in accordance with9.1.6.3.1 Restrictions on Coating ThicknessThis specificationimposes minimum local t
33、hickness requirements at significantsurfaces in accordance with Table 2. Thick or thin localthickness in a location other than a significant surface shall notbe a cause for rejection. However the following restrictionsapply:6.3.1.1 Minimum coating thickness at low current densityareas, such as the c
34、enter of a bolt or recesses, must be sufficientto provide for adequate chromate adhesion.6.3.1.2 External ThreadsMaximum coating thickness athigh current density threaded tips must provide for basic(tolerance position h) GO thread gauge acceptance. Therefore,the thread after coating is subject to ac
35、ceptance using a class 6hGO gauge for plated 6g class external threads and 4h6h GOgauge for plated 4g6g class external threads respectively.6.3.1.3 Internal ThreadsMaximum coating thickness ofinternal threads must provide for basic (tolerance position H)Go thread gauge acceptance. Therefore, the thr
36、ead after coatingis subject to acceptance using a class 6H GO gauge for 6Hclass internal threads.6.3.1.4 Surfaces such as threads, holes, deep recesses, basesof angles, and similar areas on which the specified thickness ofdeposit cannot readily be controlled, are exempted fromminimum thickness requi
37、rements unless they are speciallydesignated as not being exempted. When such areas are subjectto minimum thickness requirements, the purchaser and themanufacturer shall recognize the necessity for either thickerdeposits on other areas or special racking.6.3.2 Applicability to M Series Threads:6.3.2.
38、1 The applicability of the required coating to M seriesmetric threads is limited by the basic deviation of the threads,and hence limited by the pitch diameter, allowance, andtolerance positions. Refer to Appendix X3 as a guideline forthe tolerances of the various thread sizes and classes and thecoat
39、ing thickness they will accommodate.6.3.2.2 Because of the inherent variability in coating thick-ness by the barrel-plating process, the application of a mini-mum coating thickness of 12 m is not recommended for astandard screw thread by this method due to the fact thatdimensional allowance of many
40、metric threaded fastenersnormally does not permit it. If the size of the fastener is largeenough to economically use the rack-plating process, then thelatter shall be used to obtain this thickness requirement. Ifheavier coatings are required, allowance for the depositbuildup must be made during the
41、manufacture of fasteners.6.3.3 Applicability to Wood Screws and Thread FormingScrewsAny classification code in Table 2 may be applied toscrews that cut or form their own threads.6.4 Hydrogen Embrittlement Relief:6.4.1 Requirement for BakingCoated fasteners made fromsteel heat treated to a specified
42、hardness of 40 HRC or above,case-hardened steel fasteners, and fasteners with captive wash-ers made from hardened steel, shall be baked to minimize therisk of hydrogen embrittlement. Unless otherwise specified bythe purchaser, baking is not mandatory for fasteners withspecified maximum hardness belo
43、w 40 HRC.NOTE 2With proper care many steel fasteners can be plated withoutbaking by correlating process conditions to the susceptibility of thefastener material to hydrogen embrittlement, and by applying adequateprocess control procedures, such as those outlined in X4.2. Test MethodF 1940 is a recog
44、nized verification method for process control to minimizethe risk of hydrogen embrittlement. Upon agreement between the supplierand the purchaser, this test method can be used as a basis for determiningif baking should be mandated in a controlled process environment.6.4.2 Baking ConditionsAt the tim
45、e of publication of thisspecification it was not considered possible to give an exactbaking duration. Eight hours is considered a typical example ofbaking duration. However, upon agreement between the pur-chaser and the manufacturer, baking times between 2 and 24 hat temperatures of 175 to 235C (350
46、 to 450F) are suitabledepending on the type and size of the fastener, geometry,TABLE 3 Designation of Chromate FinishDesignation Type Typical AppearanceA Clear Transparent colorless with slight iridescenceB Blue-bright Transparent with a bluish tinge and slightiridescenceC Yellow Yellow iridescentD
47、Opaque Olive green, shading to brown or bronzeE Black Black with slight iridescenceF Organic Any of the above plus organic topcoatF 1941M 053mechanical properties, cleaning process and cathodic effi-ciency of the electroplating process used. The baking condi-tions shall be selected based on the resu
48、lts of recognizedembrittlement test procedures such as Test Methods F 1940,F 1624, F 606, or NASM 1312-5.6.4.2.1 Bake time and temperatures may require lowering tominimize the risk of solid or liquid metal embrittlementresulting from alloy compositions such as those containing leador from the lower
49、melting point of cadmium 320C (610F) incomparison to zinc 419C (786F).6.4.2.2 Fasteners must be baked within 4 h, preferably 1 hafter electroplating. Baking to relieve hydrogen embrittlementmust be performed prior to the application of the chromatefinish because temperatures above 65C (150F) damage thechromate film thereby negating its performance.6.4.3 Hydrogen Embrittlement TestingHydrogen em-brittlement testing is mandatory for fasteners with a specifiedhardness of 40 HRC or above, unless the electroplating processhas been qualified in acc
