1、 Manufacturing StandardsFord Motor Company199312 CARBURIZING AND HARDENING W-HT4-1Engineering Standards e.g.,in multi-zoned furnaces, it is recommended that the MINIMUM gapspacing be equivalent to one zone-length. It should be noted that agreater gap may be necessary.Material from different steel mi
2、ll heats, hot mill schedules, ormelts which require different austenitizing, quenching, or temperingtimes and/or temperatures to ensure that a given lot is processed asnecessary to attain the specified metallurgical properties SHALL NOTBE MIXED OR PROCESSED TOGETHER.4.4 FURNACE ENVIRONMENT: Atmosphe
3、res suitable for carburizing normallyconsist of an endothermic gas or a nitrogen-base gas or nitrogen-methanol blend* as a carrier with additions of a hydrocarbon gas(such as methane (CH4) or propane (C3H8). The atmosphere shallprovide a carburizing potential to produce a surface carbonconcentration
4、 (refer to Para. 4.13) of 0.70 - 1.00% in productionparts (0.70 - 0.90% surface carbon concentration for partscontaining over 2% chromium). The gas atmosphere must be circulatedin the furnace chamber. For optimum control, the carrier gasgenerally should be slightly carburizing and be of sufficient v
5、olumeto ensure a positive pressure in the furnace chamber. Hydrocarbonadditions should be made to develop the required carbon potential ofthe atmosphere, the volume of the addition being dependent upon thecondition of the furnace, the temperature, the nature of the parts,etc. and may be varied throu
6、ghout a process cycle to achieve optimumresults.| * It is essential that methanol-generated furnace atmospheres be| blended so that the mole ratio of the nitrogen to methanol is two| to one (nominally 40:60 by volume) in order that CO2, dew point,| oxygen potential, or carbon potential control is fe
7、asible.| Consequently, such atmospheres are permitted only when authorized| by the affected Ford Supplier Technical Assistant (STA) and/or| Quality/Engineering Team and are documented in the control plan.Manufacturing StandardsFord Motor Company199506 CARBURIZING AND HARDENING W-HT4-1Engineering Sta
8、ndards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 4 of 11When the process for which a furnace is being used is to bechanged over to carburize parts, the furnace atmosphere MUST bepurged, as per W-HTX-1 or W-HTX-12.4.5 TEMPERATURE: Carburizing temperatures shall be controlled w
9、ithin+/- 5C (+/- 10F) of the set point, as evidenced by continuousrecording pyrometers.Greater temperature deviations in Zone 1 of a multi-zoned furnaceare acceptable due to the loading conditions, provided that Zone 2temperatures are not affected, and that part quality, function, andperformance are
10、 also not affected.4.6 TIME: For optimum control, it is desirable that constant conditionsof furnace loading, carbon potential, and temperature are maintainedand that time is the main process parameter varied to achieve thespecified case depth.4.7 QUENCHING: At time of quench, the parts shall be at
11、a temperaturesuch that detrimental transformation products are not formed.Direct quenching is preferred. Delayed quenching that formsaustenite-decomposition products which degrade the parts isspecifically prohibited.Quenching systems must have provisions for maintaining both maximumand minimum quenc
12、hant temperatures specified in the process. Forcedflow-through ducted agitation, or equivalent, must be provided inthe quenching system to assure uniformity of temperature andefficiency of quench.| The following quenches have been proven satisfactory, depending on| the required surface and core hard
13、ness and the amount of distortion| which can be tolerated. Quenching media and quench operating| parameters other than those herein described are not permissible| unless authorized by the affected Ford SQE or Quality/Engineering| activity.Note: In any of the quenching methods, parts must be cooled t
14、o a lowenough temperature prior to tempering so that no further detrimentaltransformation of the austenite to fresh martensite will occur uponcooling the parts to room temperature following the temperingoperation. A process factor which will contribute to the need forlowering the temperature of the
15、parts (following quenching prior totempering) is the use of a carbon potential in excess of the rangeprescribed under Para. 4.4, Furnace Environment.Manufacturing StandardsFord Motor Company199506 CARBURIZING AND HARDENING W-HT4-1Engineering Standards & Printed copies are uncontrolled.Systems Engine
16、ering (ESSE) Page 5 of 11This process requires that, for the best and most economicalresults, the oil surface area be covered by a protective atmosphere.This protection will prolong the life of the quenching medium bypreventing oxidation and subsequent sludging of the oil.4.7.1 OIL QUENCH: Quench di
17、rectly into a suitable, well-agitatedoil maintained at a temperature of 45-80C (110-180F).4.7.2 HOT OIL QUENCH: Quench directly into a well-agitated oil attemperatures of 80-175C (180-350F).4.7.3 MARQUENCHING: Quench directly into well-agitated oil or moltensalt in the temperature range 175-260C (35
18、0-500F). Theestablishment of the actual marquenching temperature must bebased on the chemical analysis of the steel being treated,taking into consideration the carbon content variation betweencase and core.MOLTEN SALT MARQUENCHING PRECAUTIONS: THIS METHOD, WHEN USEDIN CONJUNCTION WITH AN ATMOSPHERE-
19、TYPE CARBURIZING FURNACE,MUST NOT HAVE A FULLY-ENCLOSED QUENCH. THE PARTS LEAVING THEFURNACE ATMOSPHERE MUST COME IN CONTACT WITH AIR BEFORE BEINGQUENCHED IN A MARQUENCHING SALT. THIS EXPOSURE IS NECESSARY TOREMOVE EXCESS CARBONACEOUS MATERIAL BEFORE ENTERING THESTRONGLY-OXIDIZING QUENCHING SALT. IT
20、 CANNOT BE TOO STRONGLYEMPHASIZED THAT THIS METHOD IS NOT TO BE USED FOR DIRECTQUENCHING FROM LIQUID CARBURIZING SALTS CONTAINING CYANIDE.SHOULD THIS PROCESS BE USED WITH A LIQUID CARBURIZINGOPERATION, IT IS ABSOLUTELY NECESSARY THAT AN INTERMEDIATE HIGHTEMPERATURE NEUTRAL SALT BATH BE UTILIZED TO W
21、ASH OFF THECARBURIZING SALTS BEFORE ENTERING THE MARQUENCHING(OXIDIZING) SALT.4.7.4 | WATER-SOLUBLE POLYMER QUENCHANTS: Polymer quenchants with| appropriate agitation may be satisfactory for certain| applications. However, prior written concurrence is required| from the affected Ford Supplier Techni
22、cal Assistant (STA)| and/or Quality/Engineering Team.Exposure of the quench media to the austenitizing furnaceatmosphere must be avoided to prevent addition of excessivemoisture to the carburizing environment.CAUTION: Special attention must be given to assuring that thequenchant is used within the a
23、ppropriate temperature andconcentration ranges that are compatible with the part/materialbeing heat treated. Quenching characteristics of somequenchants can change significantly with relatively minorchanges in temperature or concentration.Manufacturing StandardsFord Motor Company199506 CARBURIZING A
24、ND HARDENING W-HT4-1Engineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 6 of 114.8 REHEAT FOR QUENCHING: When subsequent hardening of slowly-cooledcarburized work is required, parts should be uniformly heated in aprotective atmosphere to at least 30C (50F) above t
25、he upper critical(Ac3) of the base material to completely dissolve the carbidenetwork prior to quenching.4.9 TEMPERING: Immediately after carburizing, hardening, and washing,the parts must be tempered in a recirculated or forced air-typefurnace or liquid bath at 150-200C (300-400F) for one hour mini
26、mumat heat or to the appropriate higher temperature/longer time toobtain the hardness specified on the Engineering print. Temperingat 260-370C (500-700F) is not permitted unless specifically agreedupon. Where dimensional stability of the part is critical, thethermal treatment for stabilization shoul
27、d be specified on theEngineering print.| CAUTION: The parts should be tempered as soon as possible after| quenching and washing, with specific delay times established by the| affected Ford Supplier Technical Assistant (STA) and/or| Quality/Engineering Team and documented in the control plan.| Carbon
28、 steels containing more than 0.40% carbon, alloy steels containing| more than 0.35% carbon, or parts with sharp corners, holes, recesses, or| abrupt changes in cross-section thickness or which have a significant| portion of the cross-section enriched with carbon from the carburizing| process may req
29、uire more restrictive delay times or other restrictive| practices to preclude cracking.4.10 MICROSTRUCTURE: The microstructure of the carburized case shallconsist predominately of tempered martensite and must be free fromnetwork carbides. Fine, uniformly-dispersed carbides areacceptable. Non-martens
30、itic transformation products associated withfurnace oxidation and retained austenite will be permitted only ifsuperficial hardness checks equate to the specified hardnessrequirement minimum. When specific restrictions (such as maximumretained austenite) are imposed on the Engineering print or in the
31、control plan, alternative test methods shall be agreed upon.Note: Of specific concern is whether such transformation productsmay have a deleterious effect on part quality, function, andperformance in the end application.Total or partial decarburization must not be present under or withinthe case.Man
32、ufacturing StandardsFord Motor Company199506 CARBURIZING AND HARDENING W-HT4-1Engineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 7 of 11Core microstructure shall demonstrate fully-quenched transformationproducts commensurate with part alloy composition, section s
33、ize, andquenching media. Exceptions to the foregoing core microstructurewill be permitted in instances where, for example, alternativequenching to Para. 4.7 and 4.8 is specified for purposes of grainrefinement.The case and core grain size shall be no larger than ASTM E112size 5 as the result of the
34、carburizing process.4.11 CASE DEPTH MEASUREMENT: Effective case, i.e., the perpendiculardistance from the surface of the carburized area to the point atwhich a Vickers hardness of 550 HV or a Rockwell hardness of 50 Rc(or equivalent) occurs in full hardness structures, shall be used asa measure of c
35、ase depth of hardened parts with surface-hardenedlayers that are greater than 0.3 mm (0.012 in.) unless otherwisespecified. Effective case shall never be reported greater than thetotal carburized depth.In the event that the core hardness on the carburized part exceeds450 HV or 45 Rc, other technique
36、s such as metallographic, chemicalgradient, or a low carbon test bar shall be employed for determiningeffective case depth.Total case, or that distance measured perpendicularly from thesurface of the case down through the zone of carbon-nitrogenenrichment, shall be considered as the case depth of pa
37、rts withsurface-hardened layers equal to or less than 0.3 mm (0.012 in.).The method for measuring effective case depth of a componentdesigned relevant to Rockwell hardness values shall be in accordancewith SAE J423 or as specified on the Engineering print.The method for measuring effective case dept
38、h of a componentdesigned relevant to Vickers hardness values shall be in accordancewith ISO 2639/4970 (as applicable) or as specified on theEngineering print.| Product Engineering, with concurrence of the affected Ford Suppliers| Technical Assistant (STA) and/or Quality/Engineering Team, shall| spec
39、ify the areas where case depth shall be measured and the specific| method of measurement.Unless otherwise specified, case depth is to be measured on ungroundsurfaces.Manufacturing StandardsFord Motor Company199312 CARBURIZING AND HARDENING W-HT4-1Engineering Standards & Printed copies are uncontroll
40、ed.Systems Engineering (ESSE) Page 8 of 114.12 HARDNESS: Unless otherwise specified, the surface and core hardnessshall be checked on the Rockwell C scale (refer to ISO 6508).(Where appropriate, because of case depth/hardness considerations,ISO 1024 may be employed).Surface hardness testing with fil
41、es (refer to SAE J864), where anindentation hardness test is not specified and/or for purposes ofcorroboration, shall only be used if authorized by the affectedFord SQE or Quality/Engineering activity.4.13 CARBON CONCENTRATION: Surface carbon concentration shall be anaverage of the carbon content in
42、 the first 0.05-0.15 mm(0.002-0.006 in.) depth of case. Carbon concentration bars forcontrol of carburizing operations are described in FLTM AA 101-4.4.14 SUPPLIERS RESPONSIBILITY: The process which has been approved tomeet the requirements of this Manufacturing Standard, as provided inthe Ford Qual
43、ity System Standard Q-101 for product application, orby the specifying authority for non-production application, shallnot be changed without prior approval of the responsible Ford MotorCompany authority.5. APPROVAL OF NEW SUPPLIERS: Suppliers approved to this process mustbe reviewed by the appropria
44、te Ford SQE or Quality/Engineeringactivity.6. GENERAL INFORMATION: The information given below is provided forclarification and assistance in meeting the requirements of thisStandard.Figure 1 and 2 (Iron-Carbon Phase Equilibrium Diagram and Time-Temperature-Transformation Diagrams, respectively) are
45、 intended toserve as a general illustration of the processes covered by thisStandard.They are not intended to portray all diagrams of the various alloycombinations that may be processed using this Standard.Manufacturing StandardsFord Motor Company199312 CARBURIZING AND HARDENING W-HT4-1Engineering S
46、tandards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 9 of 117. INDUSTRY STANDARD ORDERING INFORMATION:Industry standard referenced in Ford Manufacturing Standards may beobtained from the following organization listed below, or from GlobalEngineering Documents. Internal Ford Mot
47、or Company activities may obtainindustry standards from Global Engineering Documents directly throughon-line Standards Information System on Multics.Ford Manufacturing StandardsAdistra101 Union StreetPlymouth, MI 48170 USAPhone number: 313-455-0574Global Engineering Documents (All Industry Standards
48、)2805 McGaw AvenueIrvine, CA 92714Phone number: 714-261-1455Fax number: 714-261-7892Phone Toll Free: 1-800-854-7179Society of Automotive Engineers, International (SAE)400 Commonwealth DriveWarrendale, PA 15096-001 USAPhone number: 412-776-4841Manufacturing StandardsFord Motor Company199312 CARBURIZI
49、NG AND HARDENING W-HT4-1Engineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 10 of 11FIGURE 1IRON - CARBON PHASE EQUILIBRIUM DIAGRAMManufacturing StandardsFord Motor Company199312 CARBURIZING AND HARDENING W-HT4-1Engineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 11 of 11FIGURE 2TIME - TEMPERATURE - TRANSFORMATION DIAGRAMS
