1、 ENGINEERING MATERIAL SPECIFICATION Date Action Revisions Rev. 04 2016 01 11 Revised See Summary of Revisions G. Weber, NA 2015 05 28 Revised See Summary of Revisions C. Mracna, NA 1987 09 18 Released SM/ER 1209TC J.P.C. Lines EAO Controlled document at www.MATS Copyright 2016, Ford Global Technolog
2、ies, LLC Page 1 of 7 EMBRITTLEMENT AVOIDANCE WSS-M99A3-A 1. SCOPE This specification outlines the conditions that enhance the embrittlement risk of steel components, steel and aluminum fasteners, and cast iron. Mechanisms include hydrogen embrittlement, stress corrosion cracking, intergranular corro
3、sion, and liquid metal embrittlement. The specification identifies requirements intended to minimize that risk. 2. APPLICATION The requirements established by this specification apply to steel fasteners, aluminum fasteners, heat treated cast iron or steel components, and cold worked cast iron or ste
4、el components. Hardness values in this specification are in the Vickers scale. All other readings are for reference only. The specified hardness refers to the hardness on the part drawing or product standard and not the actual part hardness. When hardness is not specified on the part drawing or prod
5、uct standard, parts shall be tested for hardness and the measured hardness shall be used to determine conformance to this standard. 2.1 HYDROGEN EMBRITTLEMENT The risk of hydrogen embrittlement exists for parts: - with high tensile strength or hardness, including surface hardening, - which have, or
6、may absorb diffusible hydrogen, and - are under tensile stress. Hydrogen embrittlement can cause delayed brittle fracture under stress and most often occurs as a result of hydrogen absorption during manufacturing processes such as acid cleaning, electroplating, phosphate coating, and heat treatment.
7、 Hydrogen absorbed during these manufacturing processes can be relieved by baking. Hydrogen absorption can also occur from exposure to corrosive environments where the reduction reaction may produce atomic hydrogen. The susceptibility to embrittlement increases with increasing stress and increasing
8、material strength, particularly for martensitic microstructures. Therefore, attention to the processes used for cleaning, finishing, and heat treatment, as well as the review of the application environment for hardened and cold worked steel components, are crucial in reducing the risk of embrittleme
9、nt. 2.2 STRESS CORROSION CRACKING Hardened steels are susceptible to brittle fracture when exposed to a corrosive environment under a sufficient tensile stress. This failure mode is called stress corrosion cracking (SCC). The higher the yield strength, the more susceptible the material is to SCC. Se
10、nsitivity varies with steel alloy, yield strength, corrosive environment and the applied tensile stress and residual manufacturing stress. ENGINEERING MATERIAL SPECIFICATION WSS-M99A3-A Copyright 2016, Ford Global Technologies, LLC Page 2 of 7 2.3 INTERGRANULAR CORROSION OF ALUMINUM FASTENERS Thread
11、ed aluminum fasteners are susceptible to intergranular corrosion. Care should be taken in designing bolted joints utilizing aluminum fasteners so that critical areas of the fastener are not exposed to corrosive environments. 2.4 LIQUID METAL EMBRITTLEMENT Normally ductile metals can experience crack
12、ing and brittle fracture when they come into contact with liquid metals while subjected to a tensile stress. This failure mode is called liquid metal embrittlement (LME). LME can occur when parts with metallic plating are exposed to temperatures above their melting point during subsequent manufactur
13、ing processes or in use. 3. REQUIREMENTS 3.1 APPROVED SOURCES This specification does not have approved sources. 3.2 CONTROL PLAN Fasteners and components affected by this specification shall have a control plan that includes the requirements of this specification. The control plan shall include ver
14、ification test(s) to demonstrate the effectiveness of the embrittlement relief procedures after electroplating. Verification procedures are not required for acid cleaning, phosphating, or mechanical plating. In cases where the electroplating process does not normally produce embrittlement, it may be
15、 necessary to establish verification tests based on proven methodology. 3.3 RESTRICTIONS ON PART USAGE Due to high tensile stresses involved in fastened joints, all fasteners or threaded components with a maximum specified core or surface hardness greater than 390 HV (39 HRC) shall not be used in cr
16、itical applications where there is a potential for corrosion. Critical applications are determined as those with an FMEA severity rating of 9 or 10 for fractures. Fasteners and components used in non-critical applications where the maximum specified core or surface hardness is greater than 390 HV (3
17、9 HRC) shall not be used where exposed to the potential for corrosion without an appropriate FMEA. The FMEA shall include consideration of cracking mechanisms, such as hydrogen embrittlement, stress corrosion cracking, etc. as possible causes of fracture, as well as the need for corrosion protective
18、 finishes. Carburization of through hardened components is not permitted unless specified on the Engineering Drawing. Unintentional carburization sometimes occurs when hardened components are subjected to a carbon rich atmosphere. In these cases, the surface hardness shall not be more than 30 HV abo
19、ve the measured core hardness. For property class 10.9 fasteners, any increase in hardness at the surface that indicates that the surface hardness exceeds 390 HV (39 HRC) is not acceptable. 3.4 ALUMINUM FASTENER USAGE Externally threaded aluminum fasteners shall be free from intergranular corrosion
20、in the under-head, radius transition, shank and shank-to-thread transition areas and the entire threaded length. ENGINEERING MATERIAL SPECIFICATION WSS-M99A3-A Copyright 2016, Ford Global Technologies, LLC Page 3 of 7 3.4.1 Grain Size (ASTM E112, Comparison Procedure) The average grain size for alum
21、inum fasteners must be Grain Size No. 2.5 or finer (150 micrometers) in the longitudinal direction and Grain Size 4.0 or finer (90 micrometers) in the transverse direction. 3.4.2 Laboratory Evaluation for Intergranular Corrosion (FLTM AB 110-01) All joints using externally threaded aluminum fastener
22、s shall be tested per FLTM AB 110-01 during the Design Validation (DV) phase. No intergranular corrosion (No IGC) or cracking of surface coatings is allowed. 3.4.3 Evaluation after Vehicle Corrosion Testing (CETP 00.00-R-343, FLTM AB 110-01, ISO 6157-3) All aluminum fasteners from vehicles completin
23、g the Total Vehicle Corrosion Test, CETP 00.00-R-343, shall be cross-sectioned after test completion and evaluated using the criteria in FLTM AB 110-01. No intergranular corrosion (No IGC) or cracking of surface coatings is allowed. 3.4.4 All aluminum fasteners shall be evaluated for surface discont
24、inuities per ISO 6157-3. Only allowable discontinuities may be present. 3.5 CLEANING PRIOR TO HEAT TREATMENT All fasteners and components with a maximum specified core or surface hardness greater than 353 HV (35 HRC) must be cleaned prior to heat treatment to remove phosphorus-containing products or
25、 any other detrimental contaminants from the surface. The formation of a white, phosphorus enriched layer caused by penetration of phosphorus during the hardening process is not permissible. Note: This is not applicable to induction hardened components due to the short time at temperature. 3.6 HEAT
26、TREATMENT All heat treatment operations, except embrittlement relief via baking (Section 3.8 Embrittlement Relief), shall be completed prior to plating or phosphate coating. 3.7 CLEANING AFTER HEAT TREATMENT OR COLD WORKING Acid cleaning of fasteners and components which have been heat treated to a
27、specified core or surface hardness greater than 353 HV (35 HRC) or have been highly stressed due to cold working, enhances the susceptibility to hydrogen embrittlement, and shall be minimized. If such fasteners and components are to be acid cleaned, an inhibited acid shall be used and a procedure sh
28、all be established that limits exposure to the acid bath to a maximum of 10 minutes. Fasteners and components that are acid cleaned and subsequently phosphate coated, mechanically plated, or electroplated, shall follow the requirements in section 3.8 Embrittlement Relief Table 1 as applicable. All o
29、ther fasteners and components that are acid cleaned but not subsequently coated or plated, shall not be used for 48 hours, or these parts shall be baked for a minimum of 1 hour at 110 C minimum following cleaning. Note: Inhibited acids have inhibitors added to the acid to reduce the corrosive attack
30、 on the steel and absorption of hydrogen. ENGINEERING MATERIAL SPECIFICATION WSS-M99A3-A Copyright 2016, Ford Global Technologies, LLC Page 4 of 7 3.8 EMBRITTLEMENT RELIEF All references to temperature relate to part core temperature and not oven air temperature. Statistical data of variations in te
31、mperature at the center of the oven and oven temperature shall be established to develop the oven profile. The temperature of parts in a batch type oven shall be monitored with a thermocouple placed in the middle of the load. For continuous bake ovens a temperature trace through the oven must be run
32、 with a calibrated thermocouple in the lowest temperature position according to the frequency listed in the control plan. The part temperature should be reached within 1 hour after commencement of heating. Longer times at heat than those given may be necessary if verification testing detailed in the
33、 Control Plan indicates a failure risk. Table 1: Hydrogen Relief Table Process Specified Hardness (Surface and/or Core) Hydrogen Relief Acid Cleaning (for items not subsequently phosphated, mechanically plated, or electroplated) 353 HV (35 HRC) Within four hours after acid cleaning, bake parts at 11
34、0C minimum for 1 hour minimum, or the parts shall not be used for 48 hours after acid cleaning. Phosphate Coating 353 HV (35 HRC) Within four hours after coating, bake parts at 110C minimum for 1 hour minimum or the parts shall not be used for 48 hours after coating. Mechanical Plating 353 HV (35 HR
35、C) Within four hours after mechanical plating, bake parts at 110C minimum for 1 hour minimum, or the parts shall not be used for 48 hours after mechanical plating. ENGINEERING MATERIAL SPECIFICATION WSS-M99A3-A Copyright 2016, Ford Global Technologies, LLC Page 5 of 7 Table 1: Hydrogen Relief Table
36、(cont) Electroplating 390 HV (39 HRC) FASTENERS OR THREADED COMPONENTS SHALL NOT BE ELECTROPLATED Non-Threaded Components: Within 1 hour after electroplating and before any supplementary chemical treatments, bake parts at 200C minimum for 8 hours minimum. 353 HV (35 HRC) Within 1 hour after electrop
37、lating and before any supplementary chemical treatments, bake parts at 200C minimum for 4 hours minimum. Electroplating for parts tempered or stress relieved below 230C or for tin or tin alloy platings to avoid liquid metal embrittlement. 353 HV (35 HRC) Within 1 hour after electroplating, bake part
38、s at 140C minimum for 8 hour minimum. 3.9 EXCEPTIONS Exceptions to the embrittlement relief requirements may be made due to factors such as alloy composition, coating thickness, coating type, design, or part size. Consideration should be given to the application, tensile stress, and manufacturing pr
39、ocesses. Investigations into the amount of hydrogen absorption and effectiveness of the embrittlement relief for specific parts may result in different recommended times and temperatures versus the ones listed above. In some cases embrittlement relief may not be necessary. Exceptions shall be author
40、ized by the responsible Functional Chief Engineer and communicated to the appropriate Materials/Fastener Engineering Activity. For fasteners, exception approval shall be documented on Form e1217, Request for Part Number or Drawing Change per FAP03-117. Exceptions agreed to for some Standard Fastener
41、s are shown in the General Requirements section of Ford Worldwide Fastener Standard WX-100. For components, exception approval shall be documented in RQT-002901-008060 (Legacy SDS MA-0114), Embrittlement Avoidance. 3.10 CERTIFICATION Compliance with this standard means that, if parts or fasteners me
42、et the conditions to be potentially susceptible to embrittlement as outlined in this standard, the actions required by this standard are in place. Compliance with the requirements of this specification for parts or fasteners with hardness of 353 HV (35 HRC) or greater, for heavily cold worked parts
43、or fasteners, or for aluminum fasteners shall be certified by completion of the certification form in Appendix 1. The completed form shall be included in PPAP documentation for the part. ENGINEERING MATERIAL SPECIFICATION WSS-M99A3-A Copyright 2016, Ford Global Technologies, LLC Page 6 of 7 4. GENER
44、AL INFORMATION The information given below is provided for clarification and assistance in meeting the requirements of this specification. Contact for questions concerning Engineering Material Specifications. References: ASTM B850 “Post-Coating Treatments of Steel for Reducing the Risk of Hydrogen
45、Embrittlement” ISO 9588 Metallic and Other Inorganic Coatings - Post Coating Treatments of Iron or Steel to Reduce the Risk of Hydrogen Embrittlement. SAE/USCAR-5 “Avoidance of Hydrogen Embrittlement of Steel” ASTM E112 “Standard Test Methods for Determining Average Grain Size” ISO 6157-3 “Fasteners
46、 Surface Discontinuities Bolts, Screws, and Studs for Special Requirements” 5. SUMMARY OF REVISIONS 2016 01 11 Added reference to aluminum fasteners and requirement of measuring hardness in Application Added Sections 2.3 and 2.4 Inserted Aluminum Fastener Usage as Section 3.3, renumbered following s
47、ections Added Section 3.9 Added certification document as Appendix 1 2015 05 28 Added reference to cast iron Align Embrittlement, De-Embrittlement, and Hydrogen Relief Nomenclature Added Qualifying Note to Section 3.3 Updated Requirement Identification in Sec. 3.7 2012 03 20 Revised to include more
48、distinction between parts and fasteners. Added location of documented exceptions for components. 2008 02 06 Completely revised, reformatted and renumbered the document. Application section specifically defines hydrogen embrittlement and stress corrosion cracking. The brittleness statement was moved
49、to the control plan paragraph. Carburization section was added into the restriction on part usage section. The plating/coating method statement was moved to the hydrogen relief table. The de-embrittlement section was aligned with SAE/USCAR 5 and the distinction between core and surface hardness was removed. The temperature and times were aligned with SAE/USCAR 5 and placed in tabular form. The fastener exception sheet was updated from FAF-1217 to FAF03-117-01. ENGINEERING MATERIAL SPECIFICATION WSS-M99A3-A Copyright 2016, Ford Global
