ASTM_B_935_-_16.pdf

Designation:B93516Standard Guide forSteam Treatment of Ferrous Powder Metallurgy(PM)Materials1This standard is issued under the fixed designation B935;the number immediately following the designation indicates the year oforiginal 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 guide is intended as an aid in establishing andmaintaining a procedure for the steam treatment,also referredto as steam blackening,of sintered ferrous PM materials andthe appropriate use and evaluation of these materials.Addi-tional information concerning the effect of this process onferrous PM material properties is contained in Appendix X1.1.2 With the exception of the values for density and themass used to determine density,for which the use of the gramper cubic centimetre(g/cm3)and gram(g)units is the long-standing industry practice,the values in inch-pound units are tobe regarded as standard.The values given in parentheses aremathematical conversions to SI units that are provided forinformation only and are not considered standard.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 of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:B243 Terminology of Powder Metallurgy3.Summary of Guide3.1 A normal sequence of steps for batch processing is:(1)preheat the load;(2)introduce a superheated steam-richatmosphere;(3)heat the load to the processing temperature andmaintain the temperature for the duration of the processingcycle;and(4)cool the load to a temperature suitable forhandling.This process will produce a layer of black iron oxide(magnetite)on the surface of the parts and on the surfaces ofthe interconnected porosity by the reaction.3Fe14H2Ogas!Fe3O414H2gas!3.2 For continuous steam treatment,parts are transportedthrough the furnace on a continuous mesh belt,and the thermalprofile of the furnace(temperature settings of the various zonesand the speed of the mesh belt)is set to ensure that parts areclean and at the appropriate temperature before they areexposed to the superheated steam.4.Terminology4.1Definitions of powder metallurgy(PM)terms can befound in Terminology B243.5.Significance and Use5.1 The performance and quality of steam-treated materialsdepends upon the surface cleanliness of the material prior tosteam treatment and the adequacy of the processing.Steamtreatment can be used as a decorative coating,producing ablue-gray to a blue-black appearance.It can reduce thesusceptibility of ferrous PM materials to further oxidation andcorrosion,thus providing better shelf life.More significantly,improvements in apparent hardness,compressive strength,wear characteristics,and some mechanical properties(seeAppendix X1)can be observed due to steam treatment.Thehardness of magnetite(Fe3O4)formed during steam treatmentis typically equivalent to 50 HRC,and when present in sinteredmaterials,their wear resistance can be improved significantly.Steam treatment is also used to seal parts or provide a basematerial for additional coatings.Steam treated ferrous PMmaterials are used in many industries,including automotive,marine,home appliances and lawn and garden applications.6.Apparatus6.1 The material can be processed in either a batch-typefurnace or a continuous belt-type furnace.The furnace must becapable of heating the load,maintaining it at the processingtemperature,and maintaining a steam atmosphere free of airleaks.Both batch type and continuous furnaces shall meet thesame criteria described in the following procedure section.While comparable performance may be obtained from batchand continuous furnaces,the process conditions used may notbe exactly the same.7.Procedure7.1 Batch Processing1This guide is under the jurisdiction of ASTM Committee B09 on MetalPowders and Metal Powder Products and is the direct responsibility of Subcom-mittee B09.05 on Structural Parts.Current edition approved Oct.1,2016.Published October 2016.Originallyapproved in 2005.Last previous edition approved in 2009 as B935 05(2009)1.DOI:10.1520/B0935-16.*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 States1 7.1.1 Place the load in the furnace and preheat in air untilthe temperature of the entire load is above 212 F(100 C)butnot in excess of 800 F(430 C).A temperature of 600 F(315 C)is typically used.7.1.2 Once the load is preheated,introduce superheatedsteam into the furnace until all of the air is purged from thefurnace or processing zone.This steam atmosphere shall bemaintained until the processing cycle is complete.NOTE1The temperature of the parts sha