1、Designation: B 935 05Standard Guide forSteam Treatment of Ferrous Powder Metallurgy (P/M)Materials1This standard is issued under the fixed designation B 935; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide is intended as an aid in establishing andmaintaining a procedure for the steam treatment, also referredto as steam blac
3、kening, of sintered ferrous P/M materials andthe appropriate use and evaluation of these materials. Addi-tional information concerning the effect of this process onferrous P/M material properties is contained in Appendix X1.1.2 This standard does not purport to address all of thesafety concerns, if
4、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. Summary of Guide2.1 A normal sequence of steps is: (1) preheat the load; (2)introduce a
5、superheated steam-rich atmosphere; (3) heat theload to the processing temperature and maintain the tempera-ture for the duration of the processing cycle; and (4) cool theload to a temperature suitable for handling. This process willproduce a layer of black iron oxide (magnetite) on the surfaceof the
6、 parts and on the surfaces of the interconnected porosityby the reaction.3Fe 1 4H2O gas!Fe3O41 4H2gas!3. Significance and Use3.1 The performance and quality of steam-treated materialsdepends upon the surface cleanliness of the material prior tosteam treatment and the adequacy of the processing. Stea
7、mtreatment can be used as a decorative coating, producing ablue-gray to a blue-black appearance. It can reduce thesusceptibility of ferrous P/M materials to further oxidation andcorrosion, thus providing better shelf life. More significantly,improvements in apparent hardness, compressive strength,we
8、ar 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.Stea
9、m treatment is also used to seal parts or provide a basematerial for additional coatings. Steam treated ferrous P/Mmaterials are used in many industries, including automotive,marine, home appliances and lawn and garden applications.4. Apparatus4.1 The material can be processed in either a batch-type
10、furnace 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 must meet thesame criteria described in the following procedure section
11、.When both batch and continuous furnaces are operated to meetthe same processing times, temperatures, and atmosphere, theresults should be similar.5. Procedure5.1 Place the load in the furnace and heat in air until thetemperature of the entire load is above 100C (212F) withoutexceeding 430C (800F).5
12、.2 Once the load is preheated, introduce superheated steaminto the furnace until all of the air is purged from the furnaceor processing zone. This steam atmosphere must be maintaineduntil the processing cycle is complete.NOTE 1The temperature of the parts must be in excess of 100C(212F) before the s
13、uperheated steam is introduced. If it is not, water willcondense on the parts and rust spots will form. The temperature must notexceed 430C (800F) before the superheated steam is introduced or theparts will be covered with a smooth even coating of rust caused by air inthe furnace atmosphere.5.3 Rais
14、e the temperature of the furnace to the processingtemperature of between 430C (800F) and 590C (1100F)while maintaining the atmosphere of superheated steam.NOTE 2The processing temperature depends on the desired proper-ties. Lower temperatures result in deeper oxide penetration while highertemperatur
15、es produce a thicker surface oxide layer.NOTE 3Processes that decrease the amount or the size of theinterconnected porosity such as copper infiltration, grinding, vibratoryfinishing, sizing, machining, burnishing, shot peening, or polishing willreduce the effectiveness of the steam treatment by limi
16、ting the ability ofsteam to penetrate the part. Increasing the density reduces the pore size,which reduces penetration unless sufficiently large porosity is available to1This guide is under the jurisdiction of ASTM Committee B09 on Metal Powderand Metal Powder Products and is the direct responsibili
17、ty of Subcommittee B09.05on Structural Parts.Current edition approved Oct. 1, 2005. Published October 2005.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.maintain a pathway for the steam. Copper infiltration also coats thesurface of
18、 iron particles with copper, which prevents steam from reactingwith the iron and decreases the effectiveness of steam treatment as asurface treatment.5.4 Hold the load at the processing temperature for 30 to120 min depending on the desired properties. Steam treatmentbuilds an oxide layer on pore sur
19、faces and gradually restrictsthe access of the steam to the interior of the part. Highertemperature causes the metal to be more reactive, producing athicker surface layer and limiting the penetration of the oxideinto the part. Lower temperature produces deeper penetrationwith a thinner surface layer
20、.NOTE 4A discussion of sealing method is recommended for partsrequiring additional surface treatments (plating, painting, and so forth).5.5 The oxide produced by steam treatment is slightlyporous, which can allow corrosive material to penetrate tonon-oxidized iron. While the oxide provides improved
21、shelfand handling life by itself, oil impregnation, an oil dip, or rustpreventatives are recommended for applications requiringadditional corrosion protection.6. Interferences6.1 The surface of the material to be steam-treated should befree of contaminants including red rust, soot, and dirt. Steamtr
22、eatment cannot reduce existing rust. Soot and dirt attractmoisture, which causes rust to form during steam treatment.The soot and dirt will remain as surface blemishes after steamtreatment.6.2 Since steam treatment builds an iron oxide layer on thepore surfaces, it tends to restrict access to the no
23、n-oxidizedinterior iron, causing the reaction to slow until further treat-ment has little effect on the thickness of the oxide layer.7. Hazards7.1 Hydrogen is generated as a by-product of the steamtreatment process. This hydrogen must be flushed from thefurnace and air ingress must be prevented. Pri
24、or to opening abatch-type furnace, the furnace should be flushed with nitrogenor an inert gas unless the parts and furnace are cooled to belowthe auto ignition point of hydrogen while still in the steamatmosphere.7.2 Foreign material can interfere with steam treatment andpossibly pose a serious heal
25、th threat. Some chemical com-pounds, for example, chlorinated hydrocarbons, decomposeinto products that cause materials to rust during processing. Allcutting fluids, lubricants, coolants, and so forth should beremoved prior to steam treatment. This may be done during thepreheating stage of the steam
26、 treatment process. However, theeffect of the contaminant and by-products must be consideredto ensure they are compatible with the steam treatment processand do not create a hazardous condition.8. Testing and Evaluation8.1 Fe3O4can be deposited either heavily on the externalpart surface or uniformly
27、 at the surface and in the porosity.Depending on the objective of the steam treatment, themethods used for evaluation may need to be changed.8.2 A simple visual inspection is sufficient for many deco-rative applications. Density or the change in mass measure theamount of Fe3O4formed. Apparent hardne
28、ss gives an indica-tion of the surface condition. Metallographic evaluation isrecommended to determine the extent of oxide penetration.Microindentation and file hardness testing are not recom-mended.8.3 No single test will indicate the effectiveness of steamtreatment for all potential applications.
29、It is recommended thatthe producer and user agree on test procedures to evaluate partsearly in the part development process.8.4 Steam treatment changes the chemical composition andthe mechanical properties of the material. Testing for compli-ance with material specifications should therefore be per-
30、formed prior to steam treatment unless it is agreed that the partis to be tested in the steam-treated condition.9. Keywords9.1 blackening; black oxide; ferrous P/M parts; iron oxide;magnetite; steamAPPENDIX(Nonmandatory Information)X1. TYPICAL PROPERTIES OF STEAM-TREATED MATERIALSX1.1 Table X1.1 sum
31、marizes data for various materials andprocess cycles. Data are included for material in the as-sinteredand for the steam-treated condition (AS = as-sintered;ST = steam-treated). The data should not be taken as a speci-fication or minimum or maximum results that should beexpected from steam treatment
32、.B935052ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rig
33、hts, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional
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35、 Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above
36、address or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).TABLE X1.1 Comparison of Properties Before (AS) and After Steam Treatment (ST)SinteredGradeAUTS % Elongation TRSUnnotchedCharpy ImpactMacro(Apparent) HardnessDensity103psi I
37、n 1 in. 103psi ft-lbf HRB g/cm3AS ST % Chg. AS ST % Chg. AS ST % Chg. AS ST % Chg. AS ST Net Chg. AS ST Net Chg.F-0000-10 20.0 22.2 +11 6.5 1.5 -77 48 58 +21 4.0 2.0 -50 37 86 +49 6.20 6.50 +0.30F-0000-15 19.1 19.8 +4 3.5 0.5 -86 57 75 +32 4.5 2.0 -56 52 89 +37 6.93 7.09 +0.16F-0008-25 30.6 18.1 -41
38、 1.5 0.5 -67 66 64 -3 2.5 1.5 -40 69 107 +38 6.26 6.60 +0.34F-0008-30 39.5 28.0 -29 1.5 0.5 -67 96 102 +6 3.0 2.0 -33 87 109 +22 6.78 6.96 +0.18FC-0208-40 48.0 30.0 -38 1.0 0.5 -50 99 97 -2 3.5 2.0 -43 87 111 +24 6.27 6.53 +0.26FC-0208-50 66.8 57.2 -14 1.5 1.0 -33 138 143 +4 6.5 4.5 -31 95 109 +14 6.85 6.97 +0.12AThe materials listed are sponge iron powder-based, except for the F-0008-30, a water granulated iron powder-based, the FC-0208-50 and F-0000-15 are wateratomized powder-based materials.B935053
