1、Designation: B 650 95 (Reapproved 2002)Standard Specification forElectrodeposited Engineering Chromium Coatings onFerrous Substrates1This standard is issued under the fixed designation B 650; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, the year of 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This specificat
3、ion covers the requirements for electrode-posited chromium coatings applied to ferrous alloys for engi-neering applications.1.2 Electrodeposited engineering chromium, which is some-times called “functional” or “hard” chromium, is usuallyapplied directly to the basis metal and is much thicker thandec
4、orative chromium. Engineering chromium is used for thefollowing:1.2.1 To increase wear and abrasion resistance,1.2.2 To increase fretting resistance,1.2.3 To reduce static and kinetic friction,1.2.4 To reduce galling or seizing, or both, for various metalcombinations,1.2.5 To increase corrosion resi
5、stance, and1.2.6 To build up undersize or worn parts.1.3 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 practices and determine the applica-bility o
6、f regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:B 117 Practice for Operating Salt Spray (Fog) Apparatus2B 177 Guide for Engineering Chromium Electroplating3B 183 Practice for Preparation of Low-Carbon Steel forElectroplating3B 242 Guide for Preparation of High-Carbon
7、Steel forElectroplating3B 320 Practice for Preparation of Iron Castings for Electro-plating3B 374 Terminology Relating to Electroplating3B 487 Test Method for Measurement of Metal and OxideCoating Thicknesses by Microscopical Examination of aCross Section3B 499 Test Method for Measurement of Coating
8、 Thick-nesses by the Magnetic Method: Nonmagnetic Coatings onMagnetic Basis Metals3B 504 Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric Method3B 507 Practice for Design of Articles to Be Electroplated onRacks3B 568 Test Method for Measurement of Coating Thicknessby
9、 X-Ray Spectrometry3B 571 Practice for Qualitative Adhesion Testing of MetallicCoatings3B 602 Test Method for Attribute Sampling of Metallic andInorganic Coatings3B 697 Guide for Selection of Sampling Plans for Inspectionof Electrodeposited Metallic and Inorganic Coatings3B 762 Test Method of Variab
10、les Sampling of Metallic andInorganic Coatings3B 849 Specification for Pre-Treatments of Iron or Steel forReducing the Risk of Hydrogen Embrittlement3B 850 Guide for Post-Coating Treatments of Steel for Re-ducing Risk of Hydrogen Embrittlement3D 3951 Practice for Commercial Packaging4E 8 Test Method
11、s for Tension Testing of Metallic Materials5F 1459 Test Method for Determination of the Susceptibilityof Metallic Materials to Gaseous Hydrogen Embrittlement62.2 Other Standard:MIL-S-13165 Shot Peening of Metal Parts73. Terminology3.1 Definitions:3.1.1 significant surfacesall surfaces upon which a d
12、e-posit of controlled thickness is required.3.1.1.1 DiscussionWhen a controlled deposit is requiredin holes, corners, recesses, and similar areas, special racking,auxiliary anodes or shielding, or both, will be necessary. With1This specification is under the jurisdiction of ASTM Committee B08 onMeta
13、llic and Inorganic Coatingsand is the direct responsibility of SubcommitteeB08.08.01on Engineering Coatings.Current edition approved Nov. 10, 1995. Published January 1996. Originallypublished as B 650 78. Last previous edition B 650 93e1.2Annual Book of ASTM Standards, Vol. 03.023Annual Book of ASTM
14、 Standards, Vol 02.05.4Annual Book of ASTM Standards, Vol 15.09.5Annual Book of ASTM Standards, Vol 03.01.6Annual Book of ASTM Standards, Vol 15.03.7Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.1Copyright ASTM Inter
15、national, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the best practices there will be areas where a controlled depositis impossible.3.2 Definitions used in this specification are in accordancewith Terminology B 374.4. Classification4.1 Electrodeposited chromi
16、um coatings in accordance withthis specification are classified by the thickness of the coatingas follows:Class No. Chromium Thickness, m Typical Application1 2.5 to 25 reduce friction; anti-galling, lightwear resistance2 25 as specified buildup to dimension specified forsalvage or as required for s
17、everewear resistance4.2 Unless otherwise specified by suitably marked drawingsor samples, only those surfaces that can be touched with a20-mm diameter ball shall be considered significant. In holes,corners, recesses, and other areas where a controlled depositcannot be obtained under normal electropl
18、ating conditions, thethickness of the deposit may be that which results from controlon the significant surfaces.5. Ordering Information5.1 The purchaser shall exercise the desired options of thisstandard. Ordering documents shall specify the followinginformation:5.1.1 Title, ASTM designation, and is
19、sue date of this speci-fication,5.1.2 Alloy and metallurgical condition of the product to bechromium plated,5.1.3 Ultimate tensile strength of the material to be plated,5.1.4 Heat treatment required for stress relief and whether ithas been performed or is required,5.1.5 The significant surfaces if d
20、ifferent from the 20-mmball rule (see 3.1.1),5.1.6 Thickness of the deposit or class (see 4.1),5.1.7 Control record requirements,5.1.8 Preproduction test specimens, if required,5.1.9 Sampling plan, if different from that specified in TestMethod B 602 (see Section 8),5.1.10 The number of test specime
21、ns for destructive testing(see 7.1),5.1.11 Thickness, adhesion, porosity, and hydrogen em-brittlement tests required (see Section 6),5.1.12 Whether separate test specimens will be used (see 7.1and 7.5),5.1.13 Where required, any special requirements for partsthat are subsequently ground to size,5.1.
22、14 Where required, the base metal finish in terms ofcenter line average (CLA) or arithmetic average (AA), and5.1.15 Where required, dimensional tolerances allowed forthe specified coating thickness or class.5.2 The manufacturer of the parts to be electroplated shallprovide the electroplating facilit
23、y with test specimens (seeSection 7) to be electroplated for conformance tests as re-quested for preparation, control, inspection, and lot acceptanceunless other arrangements have been made between the pur-chaser and the electroplating facility.6. Coating Requirements6.1 The appearance of the chromi
24、um coating on the signifi-cant surfaces of the product shall be smooth and free of visualdefects such as blisters, pits, roughness, cracks, burned depos-its, uncoated areas, or macrocracking of the deposit that isvisible without magnification. The boundaries of electroplatingthat cover only a portio
25、n of the surface shall, after finishing asindicated on the drawing, be free of beads, nodules, jaggededges, or other irregularities that will interfere with thefunctioning of the plated part. Imperfections and variations thatarise from surface conditions of the basis metal (scratches,pores, roll mar
26、ks, inclusions, etc.) and that persist in the finishdespite the observance of good metal finishing practices shallnot be cause for rejection.NOTE 1Applied finishes generally perform better in service when thesubstrate over which they are applied is smooth and free of torn metal,inclusions, pores, an
27、d other defects. It is recommended that the specifi-cations covering the unfinished product provide limits for these defects. Ametal finisher can often remove defects through special treatments such asgrinding, polishing, abrasive blasting, chemical treatments, and elec-tropolishing, which are not n
28、ormal in the treatment steps preceding theapplication of the finish and will add to the cost. When they are desired,they are the subject of a special agreement between the purchaser and theseller.6.2 In cases where design for maximum fatigue life is aconsideration the parts should be shot peened (se
29、e MIL-S-13165C) or given an alternate mechanical treatment to com-pressively stress the surface.6.3 Stress Relief Treatment (See headnote at the beginningof this specification.):6.3.1 All steel parts having an ultimate tensile strength of1000 MPa (150 000 psiapproximately 32 HRC) or greater,that may
30、 contain residual stress caused by various fabricationoperations such as machining, grinding, straightening, or coldforming, will require one of the stress relief heat treatmentsprescribed in Specification B 849 prior to electroplating. In allcases, the duration of heat treatment shall commence from
31、 thetime at which the whole of each part attains the specifiedtemperature.6.3.1.1 The treatment selected, of necessity, must be basedupon experience with the part or empirical test data. Therefore,Class SR-0 treatment is provided for parts that the purchaserwishes to exempt from treatment. However,
32、many, if not most,steels with a tensile strength in excess of 1000 MPa willbecome embrittled when plated with chromium. The stressrelief and hydrogen embrittlement relief treatments are essen-tial for the safe performance of chromium plated itemsfabricated from those steels. Selection of Class SR-0
33、or ER-0requires thorough knowledge of the embrittlement susceptibil-ity of the specific steel employed. When the purchaser specifiesClass SR-0 or ER-0, the purchaser assumes sole responsibilityfor any embrittlement failure of the part. The relative suscep-tibility of a steel can be determined by sub
34、jecting it to the DiskRupture Test of Test Method F 1459. When no stress relieftreatment is specified by the purchaser then Class SR-1 shall beapplied.6.3.2 Parts having surface hardened areas that would sufferan unacceptable reduction in hardness by treatment in accor-dance with Specification B 849
35、 shall be heat-treated at a lowerB 6502temperature but not less than 130C for a minimum period of8 h. This treatment is applicable for parts made of steel with anactual tensile strength below 1400 MPa. The purchaser mayrequire that the heat-treatment temperature shall not reduce thesurface hardness.
36、 Shorter times at higher temperatures may beused, if the resulting loss of surface hardness is acceptable.6.3.3 If stress relief is given after shot peening or other coldworking processes to introduce beneficial compressivestresses, the temperature shall not exceed 230C.6.4 Hydrogen Embrittlement Re
37、lief:6.4.1 Heat treatment appropriate for the tensile strength ofthe electroplated part (see Specification B 850) shall be per-formed to reduce the risk of hydrogen embrittlement. In allcases, the duration of the heat treatment shall commence fromthe time at which the whole part attains the specifie
38、d tempera-ture. See 6.3.1.1 for important embrittlement relief informationregarding the selection of ER-0. When no embrittlement relieftreatment is specified by the purchaser then Class ER-1 shall beapplied.6.4.2 Begin the embrittlement relief heat-treatment as soonas practical following the plating
39、 process but no longer than 1.5h.6.4.3 Parts or representative specimens shall be tested forcompliance in accordance with 7.5.6.5 ThicknessThe thickness of the coating everywhere onthe significant surface(s) shall conform to the requirements ofthe specified class as defined in Section 3 (see 7.2).NO
40、TE 2The coating thickness requirements of this specification are aminimum requirement, that is, the coating thickness is required to equal orexceed the specified thickness everywhere on the significant surfaces (see4.1). Variation in the coating thickness from point to point on a coatedarticle is an
41、 inherent characteristic of electroplating processes. Therefore,the coating thickness must exceed the specified value at some point on thesignificant surfaces to ensure that the thickness equals or exceeds thespecified value at all points. Hence, in most cases, the average coatingthickness on an art
42、icle will be greater than the specified value; how muchgreater is largely determined by the shape of the article (see PracticeB 507) and the characteristics of the electroplating process. In addition,the average coating thickness on articles will vary from article to articlewithin a production lot.
43、Therefore, if all of the articles within a productionlot are to meet the thickness requirement, the average coating thickness forthe production lot as a whole will be greater than the average necessary toensure that a single article meets the requirement. This may not apply toparts that are ground a
44、fter plating.6.6 AdhesionThe coating shall be sufficiently adherent tothe basis metal to pass the adhesion test specified (see 7.3).These tests are, with the possible exception of the heat quenchtest, all destructive and therefore, in most cases, should beperformed on test panels.NOTE 3Adhesion may
45、be influenced by the method of pretreating thebase metal and the type of steel used as a basis metal. Helpful informationis given in Practices B 177, B 183, B 242, and B 320.6.7 The coating shall be sufficiently free of pores to pass theporosity test specified (see 7.4).6.8 WorkmanshipAdding to (spo
46、tting in) or double elec-troplating, unless evidence of a satisfactory bond is established,shall be cause for rejection. Stripping and replating is permittedbut parts having an ultimate tensile strength greater than 1000MPa or a hardness greater than 32 HRC that are acid strippedshall be rebaked (se
47、e 6.3) before plating. Baking after strippingis not necessary if the parts are stripped anodically in analkaline solution.6.9 Supplemental RequirementsIf parts are electroplatedand subsequently ground to size, the grinding shall be donewith a proper coolant, never dry, and with a sufficiently lightc
48、ut to prevent cracking.8Macrocracking, visually observedwithout magnification after grinding, shall be cause for rejec-tion.6.10 PackagingPart(s) plated for the U.S. Governmentand Military, including subcontracts, shall be packaged inaccordance with Practice D 3951.7. Test Methods7.1 Separate Specim
49、ensWhen the coated articles are ofsuch a form as not to be readily adaptable to a test specifiedherein, when destructive tests would unreasonably reduce thenumber or pieces in small lots, when the pieces are toovaluable to be destroyed, and when specified by the purchaser,tests shall be made by the use of separate specimens platedconcurrently with the articles represented. The separate speci-mens shall be of a basis metal equivalent to that of the articlesrepresented. Equivalent basis metal includes chemical compo-sition, grade, condition, and finish of surface prior to
