1、 Manufacturing StandardsFord Motor Company198611 AUSTEMPERING HT2-7Engineering Standards depending upon the alloy content,the maximum cross-section that can be austempered will vary accordingly).(a) to achieve improved mechanical properties (higher ductility or notchtoughness for a specified high ha
2、rdness), and/or(b) to reduce the risk of cracking or distortion.3. REQUIREMENTS:Note: A control plan as referenced in this standard is defined inQuality System Standard Q-101, Appendix A.3.1 PROCESS: Austenitizing of the part prior to quenching in a :- continuous muffle or radiant tube furnace or- m
3、olten salt bath or- fluidized bed ( if approved by the affected Ford SQA or Qualityactivity and documented in the control plan).(The continuous muffle or radiant tube furnace is the preferredmethod of heat treatment).The heating facilities must be able to heat the parts uniformly inthe range of 815-
4、950 C (1500-1750 F). There shall also be facili-ties for quenching (Para. 3.6).3.2 LOADING: The loading practice shall be as follows:- Components must be thoroughly cleaned of oils, die lubricants,and related materials prior to introduction to the austenitizingfurnace.- The parts shall be suitably l
5、oaded to assure that every part isadequately heated during austenitizing and is properly exposedto the quenchant.- With any continuous process there shall be adequate spacingbetween lots which require different austenitizing, quenching, ortempering times or temperatures to ensure that lot is process
6、edas necessary to attain the specified metallurgical properties.3.3 FURNACE ENVIRONMENT: Furnace atmospheres suitable for austemperingnormally consist of a carries gas (endothermic or nitrogen-base or anitrogen-methanol blend*) with additions of a hydrocarbon gas (suchas methane (CH4) or propane (C3
7、H8). The gas atmosphere must becirculated in the furnace chamber and be of sufficient volume to en-sure a positive pressure in the furnace. A neutral furnace atmosphereManufacturing StandardsFord Motor Company198611 AUSTEMPERING HT2-7Engineering Standards & Printed copies are uncontrolled.Systems En
8、gineering (ESSE) Page 2 of 7carbon potential shall be utilized for the grade of steelinvolved. No ammonia shall be added to austempering furnace atmos-pheres nor shall there be an ammonia line connected to the unit.* It is essential that nitrogen-methanol furnace atmospheres beblended so that the mo
9、le ratio of the nitrogen to methanol is twoto one in order that CO2, dew point, or oxygen potential controlis feasible. Consequently, such atmospheres are permitted onlywhen specifically authorized by the affected Ford SQA or Qualityactivity and are documented in the control plan.3.4 AUSTENITIZING T
10、EMPERATURE: The temperature shall be controlledwithin +/- 5C (+/- 10F) of the set point, as evidenced by continuousrecording pyrometers.3.5 AUSTENITIZING TIME: The parts shall be held for such time to assurethat the parts have been completely austenitized.Note: Certain alloy steels may require extra
11、 holding time to as-sure adequate carbon dissolution in the austenite.3.6 QUENCHING: The parts shall be at a temperature at least 25C (45F)above the upper critical temperature (Ac 3 ) for hypoeutectoid steelsand at least 25C (45F) above the Acm for hypereutectoid steels atthe time of the quench.3.6.
12、1 Quench systems must have provisions for maintaining both maximum andminimum temperatures of the quenchant. Forced agitation must be providedin the quench system to assure uniformity of temperature and efficiency ofquench. The temperature of the quenchant shall be controlled within +/- 5F(+/- 10C)
13、ofset point, as evidenced by continuous monitoring pyrometers.3.6.2 Molten salt is an acceptable quenching media for austempered parts. Moistureadditions to the salt bath to achieve faster quench rates are not permissibleunless prior approval is granted by the affected Ford SQA or Quality Controlact
14、ivityand documented in the control plan.3.6.3 To assure proper quenching, parts shall not be stacked together whenentering the quenching media.3.6.4 Direct quenching is preferred. Delayed quenching that forms austeniticdecomposition products which degrade the parts is specifically prohibited.(Refer
15、to Par. 3.8)3.6.5 Parts shall be held in the quenching medium for sufficient time to assurecomplete transformation to bainite. The minimum times for specific gradesand quench temperatures are listed in Chart no. 1.Manufacturing StandardsFord Motor Company198611 AUSTEMPERING HT2-7Engineering Standard
16、s & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 3 of 73.6.6 Use of quenchant temperatures below the “martensite start” temperature ofthe steel may be used only with prior approval of the affected Ford SQA orQuality activity and are documented in the control plan. Quench immersion
17、times must be adequate to assure complete transformation to bainite.3.7 REMOVAL OF QUENCH SALT: Adequate washing and/or rinsing capabilitymust be available to remove salt residue from the parts after saltquenching. The parts shall be subsequently treated to assurefreedom from rusting.3.8 MICROSTRUCT
18、URE: The microstructure shall consist of bainite. Onhypereutectoid steels, fine, uniformly-dispersed carbides within abainite matrix are acceptable.NOTE: The presence of an intermediate transformation structure(such as fine pearlite mixed with bainite) (because of the specifiedsteel chemistry or par
19、t cross-section) is acceptable only uponconcurrence of the affected Ford SQA or Quality activity (anddocumented in the control plan) as well as verification that thepart meets the requirements of the Engineering print.3.9 PROCESS CONTROL: Suppliers utilizing this process standard must be able, bymea
20、ns of their existing process practices and records, to show evidence ofcontrol of the process as per Ford Quality System Standard Q-101.Users of this process are referred to Ford Manufacturing StandardW-HTX-1 (for parts with heat treat characteristics denoted as Con-trol Item ( ) characteristics or
21、for part with Engineering prints deno-ted as “Must conform to Q-101, Appendix E“ or “Must conform toQ-101, Appendix F“) or to W-HTX-12 (for heat treated parts notcovered by W-HTX-1) in which control practices are outlined.3.9.1 The suppliers utilizing this process must have a defined process forFord
22、 parts which shall include furnace loading rates, austenitizing timesand temperatures, quench salt immersion times and temperatures, and relatedpertinent parameters.3.9.2 The salt immersion time actually employed shall be traceable for each batchof parts processed for Ford Motor Company.3.9.3 On aus
23、temper units which utilize a “standard“ time for parts in the quenchsalt (i.e. the salt bath belt speed remains constant for all parts regardlessof steel grade or salt temperature), the following must be in effect:A permanent sign stating the minimum allowable temperature for the specific grades ofs
24、teel processed must be located adjacent to the salt bath temperature indicator.Example: (Assuming that 1700 seconds had been selected as the “standard“ time.)Manufacturing StandardsFord Motor Company198611 AUSTEMPERING HT2-7Engineering Standards & Printed copies are uncontrolled.Systems Engineering
25、(ESSE) Page 4 of 7“Attention“! the minimum salt bath temperatures that may beused are as follows:For SAE 1050/1055 325 C* (620 F)*For SAE 1060/1065 305 C (580 F)For SAE 1070/1075 310 C (590 F)For SAE 1080 315 C (600 F)For SAE 1095 315 C (600 F)*Refer to paragraph 3.6.6 with respect to restriction to
26、temperatures above the martensite start.3.9.4 The depth of the salt in the quench tank shall be adequate toassure that all parts remain immersed for the required time.This depth shall be specified by the heat treater and checkedwith sufficient frequency to verify control.4. GENERAL INFORMATION:4.1 C
27、AUTION: Parts processed through an austemper operation will beinherently brittle if the parts are not held in the quench salt foradequate time to assure complete transformation. (Refer to Para.3.6.5).4.2 CHEMICAL ANALYSIS: Steel chemistry is critical to successful aus-tempering. Verification of the
28、steel mill heat analysis by means ofmill certification and actual chemical analysis (specifically carbonand manganese) is strongly recommended. The use of SAE 1095 steel,for instance, for a part for which SAE 1070 is specified couldresult in brittle parts because the salt immersion time specified in
29、the process is inadequate to assure a ductile structure.4.3 The process consists of heating clean parts to a temperature in theaustenitic phase field in either a neutral atmosphere or in aneutral liquid salt bath and holding for adequate time to assurethat the part has been completely austenitized.
30、The parts are thenquenched in a medium (generally salt) having a rate of heat remo-val high enough to prevent the formation of high temperature trans-formation products. Temperatures utilized in the quench are such toachieve the desired hardness while being below that of pearliteformation and above
31、that of martensite formation.Isothermal Transformation Diagrams Illustrating Quench and Tempering and Austempering.Manufacturing StandardsFord Motor Company198611 AUSTEMPERING HT2-7Engineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 5 of 7FIGURE 1 and FIGURE 2Manu
32、facturing StandardsFord Motor Company198611 AUSTEMPERING HT2-7Engineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 6 of 7FIGURE 3IRON - CARBON PHASE EQUILIBRIUM DIAGRAMManufacturing StandardsFord Motor Company198611 AUSTEMPERING HT2-7Engineering Standards & Printed copies are uncontrolled.Systems Engineering (ESSE) Page 7 of 7MINIMUM REQUIRED SALT QUENCH TIMES (SECONDS) TO BE USED DURING AUSTEMPERING
