ASTM_A_385_-_A_385M_-_17.pdf

Designation:A385/A385M17Standard Practice forProviding High-Quality Zinc Coatings(Hot-Dip)1This standard is issued under the fixed designation A385/A385M;the number immediately following the designation indicates the yearof original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This practice covers the precautions that should be takento obtain high-quality hot-dip galvanized coatings.1.2 Where experience on a specific product indicates arelaxing of any provision,the mutually acceptable change shallbe a matter for agreement between the manufacturer andpurchaser.1.3 This specification is applicable to orders in eitherinch-pound units(as A385)or in SI units(as A385M).Inch-pound units and SI units are not necessarily exactequivalents.Within the text of this specification and whereappropriate,SI units are shown in brackets.Each system shallbe used independently of the other without combining values inany way.1.4 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 Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2A123/A123M Specification for Zinc(Hot-Dip Galvanized)Coatings on Iron and Steel ProductsA143/A143M Practice for Safeguarding Against Embrittle-ment of Hot-Dip Galvanized Structural Steel Products andProcedure for Detecting EmbrittlementA153/A153M Specification for Zinc Coating(Hot-Dip)onIron and Steel HardwareA384/A384M Practice for Safeguarding Against Warpageand Distortion During Hot-Dip Galvanizing of SteelAssembliesA563 Specification for Carbon and Alloy Steel Nuts2.2 American Institute of Steel Construction(AISC)Docu-ments:3Steel Construction Manual3.Steel Selection3.1 The production of a galvanized coating has as its basisthe metallurgical reaction between the steel and the moltenzinc,resulting in the formation of several iron-zinc compoundlayers,forexample,gamma(notalwaysvisiblemicroscopically),delta,and zeta in Fig.1.In addition,a layerof the molten zinc adheres to the surface of the compoundlayers as the steel is withdrawn from the galvanizing bath.Upon solidification,this adherent zinc forms the eta layer.3.2 It is known that the exact structural nature of thegalvanized coating,as typified by Fig.1,may be modified inaccordance with the exact chemical nature of the steel beinggalvanized.Certain elements found in steels are known to havean influence on the coating structure.The elements carbon inexcess of about 0.25%,phosphorus in excess of 0.04%,ormanganese in excess of about 1.3%will cause the productionof coatings different from the coating typified by Fig.1.Theelement with the most significant effect on the galvanizedcoating is silicon.This element has two composition regionsthat can produce thick and dull coatings.The first region issilicon concentration between 0.06%and 0.13%and is knownas the Sandelin region.The second region is silicon concen-tration above 0.25%.When producing or purchasing steels tobe hot-dip galvanized,a good practice is to aim for steels witha silicon concentration target of 0.15%to 0.22%and aminimum of 0.13%and a maximum of 0.25%to avoid boththe Sandelin region and the high silicon region.Recent studieshave shown that even in cases where the silicon and phospho-rous are individually held to desirable limits,a combined effectbetween them can produce a coating as shown in Fig.2,whichtypically would have a mottled or dull gray appearance.Thevalues of silicon in the mill test reports of steel can give an1This practice is under the jurisdiction of ASTM Committee A05 on Metallic-Coated Iron and Steel Products and is the direct responsibility of SubcommitteeA05.13 on Structural Shapes and Hardware Specifications.Current edition approved Sept.1,2017.Published September 2017.Originallyapproved in 1955.Last previous edition approved in 2015 as A385 15.DOI:10.1520/A0385_A0385M-17.2For 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 Document Summary page onthe ASTM website.3Available from American Institute of Steel Construction(AISC),One E.Wacker Dr.,Suite 700,Chicago,IL 60601-2001,http:/www.aisc.org.*A Summary of Changes section 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 Principles for theDevelopment of International Standards,Guides and Recommendations issued by the