1、Designation:B87496(Reapproved 2013)Standard Specification forChromium Diffusion Coating Applied by Pack CementationProcess1This standard is issued under the fixed designation B874;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the y
2、ear 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.Scope1.1 This specification covers the requirements for chromiumdiffusion of metals by the pack cementation method.Packdiffus
3、ion employs the chemical vapor deposition of a metalwhich is subsequently diffused into the surface of a substrate athigh temperature.The material to be coated(substrate)isimmersed or suspended in a powder containing chromium(source),a halide salt(activator),and an inert diluent such asalumina(fille
4、r).When the mixture is heated,the activatorreacts to produce an atmosphere of chromium halides whichtransfers chromium to the substrate for subsequent diffusion.The chromium-rich surface enhances corrosion,thermalstability,and wear-resistant properties.1.2 This standard does not purport to address a
5、ll 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 of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2B374 Terminology Relati
6、ng to ElectroplatingB487 Test Method for Measurement of Metal and OxideCoating Thickness by Microscopical Examination ofCross SectionB602 Test Method for Attribute Sampling of Metallic andInorganic CoatingsB697 Guide for Selection of Sampling Plans for Inspectionof Electrodeposited Metallic and Inor
7、ganic CoatingsB762 Test Method of Variables Sampling of Metallic andInorganic CoatingsC664 Test Methods for Thickness of Diffusion CoatingD3951 Practice for Commercial PackagingE766 Practice for Calibrating the Magnification of a Scan-ning Electron MicroscopeE1077 Test Methods for Estimating the Dep
8、th of Decarbur-ization of Steel SpecimensF1330 Guide for Metallic Abrasive Blasting to Descale theInterior of Pipe3.Terminology3.1 Definitions used in this specification are in accordancewith Terminology B374.3.2 Definitions of Terms Specific to This Standard:3.2.1 diffusion coatinga diffusion coati
9、ng is one producedby causing an element to react with or diffuse into,or both,thesurface of a metallic substrate,thus,chemically altering thesurface of the substrate.3.2.2 retortscontainers in which powder and parts arepacked for processing.They can be constructed of carbon,stainless,or high alloys
10、and fabricated in all shapes and sizesto accommodate parts being processed.3.2.3 significant surfaceareas that are essential to theserviceability or function of the article.These surfaces must beidentified on a drawing or marked-up sample of product.Areascan fall into one of three categories as foll
11、ows:3.2.4 coating requiredthese surfaces must be in accor-dance with all quality requirements of this specification.3.2.5 no coating requiredthese surfaces are areas whereno coating is allowed due to a number of reasons includingdimensional,fabrication,and welding,as well as others.Materials used fo
12、r masking are commercially available.3.2.6 optionalthese surfaces do not require coating,but atthe same time do not require masking.4.Classification4.1 There are four classes of chromium diffusion defined bybase(basis)metal category.4.1.1 Class ICarbon steel.4.1.2 Class IILow-alloy steels.4.1.3 Clas
13、s IIIStainless steels.4.1.4 Class IVNickel-based alloys.1This specification is under the jurisdiction of ASTM Committee B08 onMetallic and Inorganic Coatings and is the direct responsibility of SubcommitteeB08.03 on Engineering Coatings.Current edition approved Dec.1,2013.Published December 2013.Ori
14、ginallyapproved in 1996.Last previous edition approved in 2008 as B874 96(2008).DOI:10.1520/B0874-96R13.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Doc
15、ument Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.Ordering Information5.1 In order to make the application of this specificationcomplete,the purchaser shall supply the following informationto the vend
16、or through a purchase order and drawings:5.1.1 Title,ASTM designation number,and date of issue ofthis specification.5.1.2 Deposit by classification(see Section 4).5.1.3 Composition and metallurgical condition of substrateto be coated.5.1.4 Location of significant surfaces(see 3.2.3).5.1.5 Samples for destructive metallurgical test(see 8.1).5.1.6 Any post heat treatment required.5.1.7 Acceptance inspection procedure to be used(seeSection 9).5.1.8 Any requirement for certification(see Section 11).
