1、Designation: B935 16Standard 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
2、 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 blacken
3、ing, 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 de
4、nsity, 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
5、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
6、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 th
7、e 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.3Fe14H2O gas!Fe3O414H2gas
8、!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
9、 areexposed to the superheated steam.4. Terminology4.1 Definitions 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 ade
10、quacy 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 hardn
11、ess, 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
12、 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 proce
13、ssed 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
14、 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 an
15、d 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 thi
16、s standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States17.1.1 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(
17、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.NOTE 1The temperature of the parts shall be in exc
18、ess of 212 F(100 C) before the superheated steam is introduced. If it is not, water willcondense on the parts and rust spots will form. The temperature shall notexceed 800 F (430 C) before all of the air has been purged from thesystem by the superheated steam or the parts will be covered with asmoot
19、h even coating of rust caused by air in the furnace atmosphere.7.1.3 Raise the temperature of the furnace to the processingtemperature of between 800 F (430 C) and 1100 F (590 C)while maintaining the atmosphere of superheated steam.NOTE 2The processing temperature depends on the desired proper-ties.
20、 Lower temperatures result in deeper oxide penetration while highertemperatures produce a thicker surface oxide layer.NOTE 3Processes that decrease the amount or the size of thesurface-connected porosity such as copper infiltration, grinding, vibratoryfinishing, sizing, machining, burnishing, shot p
21、eening, or polishing willreduce the effectiveness of the steam treatment by limiting the ability ofsteam to penetrate the part. Increasing the density reduces the pore size,which reduces penetration unless sufficiently large porosity is available tomaintain a pathway for the steam. Copper infiltrati
22、on also coats thesurface of iron particles with copper, which prevents steam from reactingwith the iron and decreases the effectiveness of steam treatment as asurface treatment.7.1.4 Hold the load at the processing temperature for 30 to120 min depending on the desired properties. Steam treatmentbuil
23、ds an oxide layer on pore surfaces 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 penetratio
24、nwith a thinner surface layer.NOTE 4A discussion of sealing method is recommended for partsrequiring additional surface treatments (plating, painting, and so forth).7.1.5 The oxide produced by steam treatment is slightlyporous, which can allow corrosive material to penetrate tonon-oxidized iron. Whi
25、le the oxide provides improved shelfand handling life by itself, oil impregnation, an oil dip, or rustpreventatives are recommended for applications requiringadditional corrosion protection.7.2 Continuous Processing7.2.1 A pre-heat zone is used to bring the parts up totemperature while at the same t
26、ime burning out any residual oilor fluid and cleaning the parts. The pre-heat is typically set toa temperature of 840 to 930 F (450 to 500 C). Exothermic gasburners are suitable for the pre-heat zone.7.2.2 The temperature in the steam zone of the furnace isgenerally set to a temperature of 800 to 11
27、00 F (430 to590 C). A typical process temperature is 1000 F (540 C).7.2.3 The actual process temperature and the time at tem-perature depend on the desired properties of the steam-treatedparts. Times at temperature in the superheated steam aretypically from 45 minutes to 112 h.8. Interferences8.1 Th
28、e surface of the material to be steam-treated should befree of contaminants including red rust, soot, and dirt. Steamtreatment 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 steamtr
29、eatment.8.2 Since steam treatment builds an iron oxide layer on thepore surfaces, it tends to restrict access to the non-oxidizedinterior iron, causing the reaction to slow until further treat-ment has little effect on the thickness of the oxide layer.9. Hazards9.1 Hydrogen is generated as a by-prod
30、uct of the steamtreatment process. This hydrogen must be flushed from thefurnace and air ingress must be prevented. Prior 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 whi
31、le still in the steamatmosphere.9.2 Foreign material can interfere with steam treatment andpossibly pose a serious health threat. Some chemicalcompounds, for example, chlorinated hydrocarbons, decom-pose into products that cause materials to rust during process-ing. All cutting fluids, lubricants, c
32、oolants, and so forth shouldbe removed prior to steam treatment. This may be done duringthe preheating stage of the steam treatment process. However,the effect of the contaminant and by-products must be consid-ered to ensure they are compatible with the steam treatmentprocess and do not create a haz
33、ardous condition.10. Testing and Evaluation10.1 Fe3O4can be deposited either heavily on the externalpart surface or uniformly at the surface and in the porosity.Depending on the objective of the steam treatment, themethods used for evaluation may need to be changed.10.2 A simple visual inspection is
34、 sufficient for manydecorative applications. Density or the change in mass measurethe amount of Fe3O4formed. Apparent hardness gives anindication of the surface condition. Metallographic evaluationis recommended to determine the extent of oxide penetration.Microindentation and file hardness testing
35、are not recom-mended.10.3 No single test will indicate the effectiveness of steamtreatment for all potential applications. It is recommended thatthe producer and user agree on test procedures to evaluate partsearly in the part development process.10.4 Steam treatment changes the chemical composition
36、and the mechanical properties of the material. Testing forcompliance with material specifications should therefore beperformed prior to steam treatment unless it is agreed that thepart is to be tested in the steam-treated condition.11. Keywords11.1 blackening; black oxide; ferrous PM parts; iron oxi
37、de;magnetite; steamB935 162APPENDIX(Nonmandatory Information)X1. TYPICAL PROPERTIES OF STEAM-TREATED MATERIALSX1.1 Table X1.1 summarizes 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-tre
38、ated). The data should not be taken as a speci-fication or minimum or maximum results that should beexpected from steam treatment.SUMMARY OF CHANGESCommittee B09 has identified the location of selected changes to this standard since the last issue (B93505(2009) that may impact the use of this standa
39、rd.(1) Changed statement of units.(2) Provided separate procedures for batch and continuousprocessing in a revised Section 7.(3) Changed the verbiage in Section 7.1 and added reference toa typical temperature for preheating.(4) Changed “must” to “shall” in Section 7.2 and in Note 1.(5) Changed some
40、of the verbiage in Note 1.ASTM 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 infrin
41、gement of such rights, 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
42、 or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views
43、 known to the ASTM 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
44、 ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-
45、2600; http:/ X1.1 Comparison of Properties Before (AS) and After Steam Treatment (ST)SinteredGradeAUTS % Elongation TRSUnnotchedCharpy ImpactMacro(Apparent) HardnessDensity103psi In 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
46、+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 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 6.7
47、8 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 water atomizedpowder-based materials.B935 163
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