1、 WORLDWIDE ENGINEERING STANDARDS Material Specification GMW25 Mechanical Properties and Material Requirements for Externally Threaded Fasteners Copyright 2012 General Motors Company All Rights Reserved August 2012 Originating Department: North American Engineering Standards Page 1 of 8 1 Scope This
2、specification defines the mechanical and material requirements for externally threaded fasteners sized M39 and smaller. This specification is based on ISO 898-1. However, only property class described in this document shall be used. 1.1 Material Description. The fasteners applicable to this specific
3、ation are formed from wire steel and heat treated by quench and tempering, as required by the property class. The chemical composition, internal cleanliness of the steel, mechanical properties, microstructure, and other physical properties are described in this document. 1.2 Symbols. Not applicable.
4、 1.3 Typical Applications. This specification applies to bolts, screws, SEMS (bolts with washer assembly), threaded plugs, and studs. 1.4 Remarks. 1.4.1 GM does not allow new release of fasteners with property class 9.8. The properties listed are for reference for legacy parts only. 1.4.2 Property c
5、lass 12.9 fasteners shall be released only after consultation and approval from GM Fastener and Materials Engineers. Usage of property class 12.9 (underlined grade) is not permitted. 1.4.3 The scope of ISO 898-1 does not include threaded plugs. For the purpose of this specification, a threaded plug
6、can be considered a very short bolt. 2 References Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. ISO 898-1 ISO 16047 ISO 898-2 SAE J422 ISO 6157-1 SAE/USCAR-8 ISO 6157-3 2.2 GM Standards/Specifications. GMW3059 2.3 Additiona
7、l References. GM parts drawing 24502102. TMC003 Material Safety Data Sheet guidance documents (available at ). 3 Requirements Fasteners manufactured to this specification shall meet the requirements and test methods of ISO 898-1 unless otherwise specified in this document. Note: Fasteners with modif
8、ied material or mechanical properties outside of specified range for the base property class shall not have the property class identified on the head of the fastener. 3.1 Test Reporting. Table A3 lists the tests required to be performed and reported for Production Part Approval Process (PPAP) and al
9、so for each production lot. When requested, other requirements described in this standard shall be produced by the fastener supplier. 3.2 Steel Chemistry. Fasteners to this standard shall be made of steel conforming to the chemical composition requirements specified in Table A1. 3.2.1 In addition to
10、 the chemistry requirements, the supplier must ensure that the selected grade of steel has sufficient hardenability to produce a heat treated microstructure of minimum 90% martensite before tempering. 3.3 Steel Inclusions. The inclusion rating of steel shall not exceed 3-O (oxide) or 4-S (silicate)
11、as per SAE J422. Note: This requirement is for referee purpose only. 3.4 Mechanical Properties. Parts shall meet the mechanical requirements specified in Table A2 when tested per ISO 898-1. Note: In the case of special bolts and screws with alternative configurations, such as drilled heads, which ma
12、ke the heads weaker than the threaded section, tensile strength requirements may not be met. Supplier is required to run tensile test of the special head fasteners for information purposes. This test result, including the failure mode, shall be Provided by IHSNot for ResaleNo reproduction or network
13、ing permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW25 Copyright 2012 General Motors Company All Rights Reserved August 2012 Page 2 of 8 included in PPAP submission. Short bolts/screws (length smaller than 2.5 diameters) are excluded from tensile test. 3.4.1 In the case
14、of property class 8.8 SEMS where the washer and bolt is heat treated as an assembly, the maximum surface and core hardness of the bolt may reach a maximum of 36 HRC (354 HV). 3.5 Microstructure. For fasteners with property class 8.8 and higher, the microstructure shall consist of minimum 90% tempere
15、d martensite. 3.6 Decarburization. Fasteners of property class 8.8 shall meet the decarburization limits described in ISO 898-1. 3.7 Surface Discontinuities. 3.7.1 Fasteners of property class 6.8 and below shall meet the requirements of ISO 6157-1. 3.7.2 Fasteners of property classes 8.8 and higher
16、shall meet the requirements of ISO 6157-3. 3.7.3 Discontinuities at thread root caused by usage of serrated thread forming dies are permissible if the depth does not exceed 0.5% of the fasteners nominal diameter. These discontinuities are the in form of scallops at the root and follow contour of thr
17、ead root. 3.7.4 For threaded plugs sized M20 and larger, conformance to ISO 6157-3 section 3.7 shall be met, except the maximum torque value allowed for screwing on a GO-ring gauge is 7 Nm. Note: The surface discontinuity test is applied to parts before any finishing/coating processes. 3.8 Grain Flo
18、w. Grain flow at the head-shank junction of a bolt must follow the contour of the fillet. No end grain exposure is allowed at the filler or adjacent shank area. Grain flow must conform to SAE/USCAR-8. 3.9 Dephosphating. For fasteners with property class 10.9 and 12.9, any phosphate coating must be r
19、emoved prior to heat treatment. A metallographically detectable (500 x magnification) white phosphorous enriched layer is not permitted. Note: The metallographic test is for referee purpose only. 3.10 Retempering Test. To test the effectiveness and stability of the tempering operation, take 3 hardne
20、ss measurements on parts before and after retempering. The retempering temperature is 10 C below the minimum production tempering temperature. The retempering time is 30 minutes. The mean average hardness readings before and after retempering shall not differ by more than 20 Vickers hardness points.
21、 Note: This requirement is for referee purpose only. 3.11 Torsional Yield Test. This test procedure is only applicable to parts drawings specifying a torsional yield requirement. This procedure may be used in place of the requirements on GM part drawing 24502102. 3.11.1 The following characteristics
22、 will be determined and reported: Torsional yield load Ultimate strength Angular ductility 3.11.2 The test equipment and fixtures shall meet the following requirements: Load cell with 0.3% (full scale) accuracy and minimum capacity 130% of the average peak load of fastener to be tested. Torque trans
23、ducer with 0.3% (full scale) accuracy and minimum capacity 130% peak torque of fastener to be tested. Angle transducer accurate to 1 degree of angular rotation. Data acquisition system capable of recording load versus angle and load versus torque measurements. Plain HL washer and plain test nut per
24、ISO 16047 or other suitable part as agreed to by GM fastening engineer. The washer and nut shall be degreased in solvent within 2 h of performing this test. Torque chatter and thread stripping will invalidate the test. 3.11.3 Test Procedure. a. Test a minimum of 12 parts randomly selected from each
25、production lot. b. Install test bolt onto test fixture, shimming as necessary to duplicate the clamp length from actual application (obtained from fastener engineer). The head of the bolt shall bear against the test washer. The test washer shall be restrained from turning during tightening. Finger a
26、ssemble the bolt approximately 2 threads into the test nut. c. Using the electric tool, tighten at 20 to 100 rpm spindle speed until bolt reaches ultimate strength. d. During tightening, load, torque, and angle of the bolt is recorded continuously a minimum of 1 data point per degree rotation. 3.11.
27、4 Calculations: a. Ultimate Strength - The highest load measured during the test. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW25 Copyright 2012 General Motors Company All Rights Reserved August 2012 Page 3 of
28、 8 b. Torsional Yield Point (load) - Determine the slope of the elastic (linear) portion of the Load-angle plot between 80% and 30% of ultimate strength. Draw a line with the same slope, but offset 30 degrees to the right. The intersection of this line with the load-angle plot is the Torsional Yield
29、 Point. c. Angular Ductility The angle of turn from the Torsional Yield Point to the Ultimate Strength. See Figure A1 in Appendix A for an illustration of the calculations. 3.11.5 For parts with torsional yield requirements, the tensile and hardness test results can deviate from the values in Table
30、A2. However, the supplier shall maintain a tensile strength range of 110 MPa and hardness range of 4 points HRC. For example: Hardness 36.0 to 40.0. 4 Manufacturing Process 4.1 Heading Practice. Methods other than forging are permitted only by special agreement. 4.1.1 Property class 4.6 may be hot o
31、r cold headed at the option of the supplier. 4.1.2 Property classes 4.8 to 12.9 bolts and screws in nominal thread diameters M20, and in product lengths 150 mm shall be cold headed. Larger diameter and longer lengths may be cold or hot headed at the option of the supplier. 4.2 Threading Practice. Fa
32、steners sizes M20 and lengths 150 mm shall be roll threaded unless otherwise agreed upon. Threading practice for fasteners of all other sizes shall be at the option of the supplier. 4.3 Heat Treatment. 4.3.1 Property classes 4.8, 5.6, 5.8 and 6.8 bolts and screws shall be stress relieved at 470 C mi
33、nimum temperature to assure the soundness of the head to shank junction. 4.3.2 Property class 8.8 and higher bolts, screws and studs shall be austenitized and quenched to obtain a structure of 90% minimum martensite in the core of the threaded section and tempered at a minimum temperature of 425 C.
34、4.3.3 SEMS bolt and washer may be heat treated separately. See section 3.4.1 for exceptions. 4.3.4 For fasteners with property class 10.9 or higher, the phosphate coating used for wire drawing or parts forming must be removed completely before quench and temper heat treatment. 5 Rules and Regulation
35、s 5.1 Legal Regulations. All materials must satisfy applicable laws, rules, regulations and recommendations valid in the country of usage. 5.2 Language. In the event of conflict between the English and domestic language, the English language shall take precedence. 5.3 Inspection and Rejection. Sampl
36、es of components or materials released to a GM material specification shall be tested for conformity with the requirements of this material specification and approved by the responsible Engineering department prior to commencement of delivery of bulk supplies. A new approval must be received for any
37、 changes, e.g., properties, manufacturing process, location of manufacture, etc. If not otherwise agreed, all testing and documentation normally required for initial release must be completed. It is the responsibility of the supplier to inform the customer in a timely manner, without solicitation, a
38、nd to include documentation of all modifications of materials and/or processes and to apply for a new release. If not otherwise agreed, all release tests shall be repeated and documented by the supplier prior to commencement of delivery of non-conforming bulk supplies. In individual cases, a shorter
39、 test can be agreed to between the responsible Engineering department and the supplier. 5.4 Material Safety Data Sheets/Safety Data Sheets (MSDS/SDS). For new product submissions, or when a change in chemical composition of an existing product has occurred, a complete copy of the Material Safety Dat
40、a Sheet/Safety Data Sheet must be submitted in compliance with the Globally Harmonized System of Classification and Labeling of Chemicals (GHS) requirements or other country-specific MSDS/SDS requirements. In addition, product MSDS/SDS submissions must be in compliance with specific country General
41、Motors TMC003 Material Safety Data Sheet/Safety Data Sheet guidance documents where available. 5.5 All materials supplied to this standard must comply with the requirements of GMW3059, Restricted and Reportable Substances for Parts. 6 Approved Sources The appropriate GM Materials Engineering departm
42、ent(s) must confirm material as meeting the requirements of this specification. Any test data sheets of material submitted to General Motors for Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW25 Copyright 2012 G
43、eneral Motors Company All Rights Reserved August 2012 Page 4 of 8 such confirmation (e.g., during Production Part Approval Process (PPAP) under this material specification must list all properties and must apply corresponding test methods of this material specification. 7 Notes 7.1 Glossary. Product
44、ion Lot: A batch of finished products as shipped to the customer. This batch shall have the same raw material (wire) heat number, and processed in one continuous heat treatment cycle. 7.2 Acronyms, Abbreviations, and Symbols. Cr Chromium GHS Globally Harmonized System of Classification and Labeling
45、of Chemicals HRC Rockwell Hardness HV Vickers Hardness Mn Manganese Mo Molybdenum MSDS Material Safety Data Sheet Ni Nickel Nm Newton meter (torque) PPAP Production Part Approval Process rpm rotation per minute SDS Safety Data Sheet SEMS Bolt with washer assembly Wt % Weight percentage 8 Coding Syst
46、em This standard shall be referenced in other documents, drawings, etc., as follows: Fastener material per GMW25, 8.8 Fastener bolt, stud, etc. GMW25 This specification. 8.8 The property class specified. 9 Release and Revisions This standard originated in April 1999. It was first approved by the Fas
47、tening Materials Team in April 1999. It was first published in September 1999. Issue Publication Date Description (Organization) 1 SEP 1999 Initial publication. 2 DEC 2003 Revised paragraphs 1, 1.4,7, Table 2 and added paragraph 8.2. 3 AUG 2012 Rewritten to add 9.8 and 12.9 property class; revised t
48、o harmonize with the updated revision of ISO 898-1. Added new materials and other requirements. (Ferrous Metals Global Subsystem Leadership Team) Cross Reference of Replaced Specifications Standard No. Replaced Specifications GMW25 GM500M, GM255M, GM337M (GMNA) EDS-T-4601, EDS-T-4603, EDS-T-4604 (GM
49、 Korea) Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW25 Copyright 2012 General Motors Company All Rights Reserved August 2012 Page 5 of 8 Appendix A Figure A1: Illustrated Torsional Yield Definitions (Reference Section 3.11) Provided by IHSNot for ResaleNo reproduction or networking permitted without license from
