1、 Manufacturing StandardsFord Motor Company199506 CARBONITRIDING AND W-HT4-2HARDENINGEngineering Standards e.g., inmulti-zoned furnaces, it is recommended that the MINIMUM gap spacingbe equivalent to one zone-length. It should be noted that a greatergap may be necessary.Manufacturing StandardsFord Mo
2、tor Company199506 CARBONITRIDING AND W-HT4-2HARDENINGEngineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 3 of 11Material from different steel mill heats, hot mill schedules, ormelts which require different austenitizing, quenching, or temperingtimes and/or tempera
3、tures 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: Atmospheres suitable for carbonitridingnormally consist of an endothermic gas or a nitrogen-base gas ornitrogen-methanol blend*
4、as a carrier with additions of ammonia anda hydrocarbon gas (such as methane CH4 or propane C3H8). Theatmosphere or salt bath shall provide a carbonitriding potential toproduce a surface carbon concentration (refer to Para. 4.13) of 0.70- 0.95% in production parts. The gas atmosphere must be circula
5、tedin the furnace chamber. For optimum control, the carrier gasgenerally should be slightly carburizing and be of sufficient volumeto ensure a positive pressure in the furnace chamber. Hydrocarbonadditions should be made to develop the required carbon potential ofthe atmosphere, the volume of the ad
6、dition being dependent upon thecondition of the furnace, the temperature, the nature of the parts,etc., and may be varied throughout a process cycle to achieveoptimum results. Ammonia additions must be adequate to develop thenecessary case hardenability to ensure the required surface hardnessbut lim
7、ited to minimize the formation of retained austenite.| * 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
8、is feasible.| 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.When the process for which a furnace is being used is to be changed,the furnace atmosphere
9、MUST be purged, as per W-HTX-1 or W-HTX-12.4.5 MOLTEN SALT BATH: The bath may be of the conventional sodiumcyanide/sodium chloride-type or the activated cyanide-type. Thecyanide content of the sodium cyanide-chloride mixture should not beallowed to fall below 25% for medium carbon steels.The concent
10、ration of proprietary-activated carbonitriding baths mustbe maintained as recommended by the salt supplier. The bath must becontrolled to produce a surface carbon concentration (refer to Para.4.13) of 0.70 to 0.95% in production parts.Manufacturing StandardsFord Motor Company199506 CARBONITRIDING AN
11、D W-HT4-2HARDENINGEngineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 4 of 114.6 TEMPERATURE: Carbonitriding temperatures shall be controlled within+/- 5C (+/- 10 F) of the set point, as evidenced by continuousrecording pyrometers. Greater temperature deviations i
12、n Zone 1 of amulti-zoned furnace are acceptable due to the loading conditions,provided that Zone 2 temperatures are not affected, and that partquality, function, and performance are also not affected.4.7 TIME: For optimum control, it is desirable that constant conditionsof furnace (or salt bath) loa
13、ding, carbon potential, and temperatureare maintained and that time is the main process parameter varied toachieve the specified case depth.4.8 QUENCHING: At time of quench, the parts shall be at a temperaturesuch that detrimental transformation products are not formed. Directquenching is preferred.
14、 Delayed quenching that formsaustenite-decomposition products which degrade the parts isspecifically prohibited.Quenching systems must have provisions for maintaining both maximumand minimum quenchant temperatures specified in the process. Forcedflow-through ducted agitation, or equivalent, must be
15、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 hardness and the amount of distortion| which can be tolerated. Quenching media and quench operating| paramet
16、ers other than those herein described are not permissible| unless authorized by the affected Ford Supplier Technical Assistant| (STA) and/or Quality/Engineering Team.Note: In any of the quenching methods, parts must be cooled to alow enough temperature prior to tempering so that no furtherdetrimenta
17、l transformation of the austenite to fresh martensite willoccur upon cooling the parts to room temperature following thetempering operation. A process factor which will contribute to theneed for lowering the temperature of the parts (following quenchingprior to tempering) is the use of a carbon pote
18、ntial in excess ofthe range prescribed under Para. 4.4, Furnace Environment.This 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 subsequ
19、ent sludging of the oil.Manufacturing StandardsFord Motor Company199506 CARBONITRIDING AND W-HT4-2HARDENINGEngineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 5 of 114.8.1 OIL QUENCH: Quench directly into a suitable, well-agitated oilmaintained at a temperature of
20、 45-80C (110-180F).4.8.2 HOT OIL QUENCH: Quench directly into a well-agitated oil attemperatures of 80-175C (180-350F).4.8.3 MARQUENCHING: Quench directly into a well-agitated oil ormolten salt in the temperature range 175-260C (350-500F). Theestablishment of the actual marquenching temperature must
21、 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-TYPE CARBONITRIDING FURNACE,MUST NOT HAVE A FULLY-ENCLOSED QUENCH. TH
22、E 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 CANNOT BE TOO STRONGLYEMPHASIZED THAT THIS METHOD IS NOT TO BE US
23、ED FOR DIRECTQUENCHING FROM LIQUID CARBURIZING SALTS CONTAINING CYANIDE.SHOULD THIS PROCESS BE USED WITH A LIQUID CARBONITRIDINGOPERATION, IT IS ABSOLUTELY NECESSARY THAT AN INTERMEDIATE HIGHTEMPERATURE NEUTRAL SALT BATH BE UTILIZED TO WASH OFF THECARBONITRIDING SALTS BEFORE ENTERING THE MARQUENCHIN
24、G(OXIDIZING) SALT.4.8.4 | 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 Technical Assistant (STA)| and/or Quality/Engineering Team. Exposu
25、re of the quench media| to the austenitizing furnace atmosphere must be avoided to| prevent addition of excessive moisture to the carbonitriding| environment.CAUTION: Special attention must be given to assuring that thequenchant is used within the appropriate temperature andconcentration ranges that
26、 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 CARBONITRIDING AND W-HT4-2HARDENINGEngineering Standards & Print
27、ed copies are uncontrolled.Systems Engineering (ESSE) Page 6 of 114.8.5 | BRINE/CAUSTIC QUENCHANTS: A brine or caustic quenchant with| appropriate agitation may be satisfactory for certain| applications in which a quench that is faster than oil is| required. However, prior written concurrence is req
28、uired from| the affected Ford Supplier Technical Assistant (STA) and/or| Quality/Engineering Team. Exposure to the quench media to the| carbonitriding furnace atmosphere must be avoided to prevent| the addition of excessive moisture to the carbonitriding| environment.4.9 TEMPERING: Immediately after
29、 carbonitriding, hardening, andwashing, the parts must be tempered in a recirculated or forcedair-type furnace or liquid bath at 150-200C (300-400F) for one hourminimum at heat or to the appropriate higher temperature/longertime to obtain the hardness specified on the Engineering print.Tempering at
30、260-370C (500-700F) is not permitted unlessspecifically agreed upon. Where dimensional stability of the partis critical, the thermal treatment for stabilization should bespecified on the Engineering print.| CAUTION: The parts should be tempered as soon as possible after| quenching and washing, with
31、specific delay times established by the| affected Ford Supplier Technical Assistant (STA) and/or| Quality/Engineering Team and documented in the control plan. Carbon| steels containing more than 0.40% carbon, alloy steels containing| more than 0.35% carbon, or parts with sharp corners, holes,| reces
32、ses, or abrupt changes in cross-section thickness or which have| a significant portion of the cross-section enriched with carbon from| the carbonitriding process may require more restrictive delay times| or other restrictive practices to preclude cracking.4.10 MICROSTRUCTURE: The microstructure of t
33、he carbonitrided case shallconsist predominately of tempered martensite and must be free fromnetwork carbides. Fine, uniformly-dispersed carbides areacceptable. Non-martensitic transformation products associated withfurnace oxidation and retained austenite will be permitted only ifsuperficial hardne
34、ss checks equate to the specified hardnessrequirement minimum. When specific restrictions (such as maximumretained austenite) are imposed on the Engineering print or in thecontrol plan, alternative test methods shall be agreed upon.Note: Of specific concern is whether such transformation productsmay
35、 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.Manufacturing StandardsFord Motor Company199506 CARBONITRIDING AND W-HT4-2HARDENINGEngineering Standards & Printed copies are uncon
36、trolled.Systems Engineering (ESSE) Page 7 of 114.11 CASE DEPTH MEASUREMENT: Total case, or that distance measuredperpendicularly from the surface of the case down through the zoneof carbon-nitrogen enrichment, shall be considered as the case depthof light case carbonitrided parts with surface-harden
37、ed layers equalto or less than 0.3 mm (0.012 in.).Effective case may be used as a measure of the case depth ofhardened parts when specified. Parts with surface-hardened layersthat are greater than 0.3 mm (0.012 in.) shall be checked foreffective case. Effective case shall never be reported greater t
38、hanthe total carbonitrided depth.In the event that the core hardness on the carbonitrided partexceeds 450 HV or 45 Rc, other techniques such as metallographic,chemical gradient, or a low carbon test bar shall be employed fordetermining effective case depth.The method for measuring effective case dep
39、th 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 depth of a componentdesigned relevant to Vickers hardness values shall be in accordancewith ISO 2639/4970 (as applicable
40、) or as specified on theEngineering print.On parts that are partially ground, specified case depth refers tothe depth on the unground, significant areas only, such as gearteeth, splines, and other surfaces that are subjected to heavyloading or abrasion. When case depth is important on groundsurfaces
41、, it must be indicated appropriately on the Engineeringprint.| Product Engineering, with concurrence of the affected Ford Supplier| Technical Assistant (STA) and/or Quality/Engineering Team, shall| specify the areas where case depth shall be measured and the| specific method of measurement.The maxim
42、um grind stock removal recommended after carbonitriding:Case Depth: Grind Removal:0.000 - 0.30mm (0.000 to 0.012 in.) No grind recommended0.30 - 0.50mm (0.012 to 0.020 in.) 10% of case depth maximum0.50 - 0.90mm (0.020 to 0.035 in.) 15% of case depth maximumCaution should be exercised during any gri
43、nding operation to avoidburning or cracking the part.Manufacturing StandardsFord Motor Company199506 CARBONITRIDING AND W-HT4-2HARDENINGEngineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 8 of 114.12 HARDNESS: The hardness shall be specified and measured using ISO
44、6507/1024/6508 as appropriate, or as specified on the Engineeringprint.| Surface hardness testing with files (refer to SAE J864), where an| indentation hardness test is not specified and/or for purposes of| corroboration, shall only be used if authorized by the affected| Ford Supplier Technical Assi
45、stant (STA) and/or Quality/Engineering| team.4.13 CARBON CONCENTRATION: Surface carbon concentration shall be anaverage of the carbon content in 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.Correl
46、ation must be established between the carbon concentration barand parts processed to a light case depth.4.14 | SUPPLIERS RESPONSIBILITY: The process which has been approved to| meet the requirements of this Manufacturing Standard, shall not be| changed without prior approval of the responsible Ford
47、Motor Company| authority.5. | APPROVAL OF NEW SUPPLIERS: Suppliers approved to this process must be| reviewed by the appropriate Ford Supplier Technical Assistant (STA)| and/or Quality/Engineering Team.6. GENERAL INFORMATION: The information given below is provided forclarification and assistance in
48、 meeting the requirements of thisStandard.Figure 1 and 2 (Iron-Carbon Phase Equilibrium Diagram and Time-Temperature-Transformation Diagrams, respectively) are intended toserve as a general illustration of the processes covered by thisStandard.They are not intended to portray all diagrams of the var
49、ious alloycombinations that may be processed using this Standard.Manufacturing StandardsFord Motor Company199506 CARBONITRIDING AND W-HT4-2HARDENINGEngineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 9 of 117. INDUSTRY STANDARDS ORDERING INFORMATION:| Industry standards referenced in Ford Manufacturing Standards may be| obtained from the following organizations listed below, or from Global| Engineering Documents. Internal Ford Mot
