1、 WORLDWIDE ENGINEERING STANDARDS Test Procedure GMW16844 Retained Austenite Reference Photomicrographs and Test Method for Nodular Cast Iron Camshafts Copyright 2012 General Motors Company All Rights Reserved September 2012 Originating Department: North American Engineering Standards Page 1 of 4 1 S
2、cope This procedure is for determining and rating the level of retained austenite present in the hardened case of nodular (ductile) cast iron camshafts. The camshaft material grade is specified from GMW10. Retained austenite is a microstructural phase resulting from a heat and quench hardening opera
3、tion. It is soft and unstable and is often undesirable in high-precision machine components such as camshafts. A series of 4 photomicrographs of nodular cast iron with progressive levels of retained austenite are used for evaluation. This visual reference method is preferred over quantitative measur
4、ement methods such as x-ray diffraction and image analysis due to the high investment costs and sample size requirements. Note: Nothing in this standard supercedes applicable laws and regulations. Note: In the event of conflict between the English and domestic language, the English language shall ta
5、ke precedence. 1.1 Purpose. The intent of this document is to provide a standardized method of preparing and evaluating metallographic samples for determining the amount of retained austenite in the microstructure, and to rate it on a scale of 0 to 4. 1.2 Foreword. Not applicable. 1.3 Applicability.
6、 This document describes the specific procedures for sectioning hardened camshaft lobes for analysis of retained austenite. However, the basic principle and analysis can be applied to any case hardened cast iron material with similar microstructures. 2 References Note: Only the latest approved stand
7、ards are applicable unless otherwise specified. 2.1 External Standards/Specifications. ASTM 6-8 ASTM E3 2.2 GM Standards/Specifications. GMW10 GMW16547 2.3 Additional References. High resolution photomicrographs of the 4 retained austenite levels used by this document are available from the GMPT cam
8、shaft materials engineer. 3 Resources 3.1 Facilities. Not applicable. 3.2 Equipment. 3.2.1 Test Equipment. 3.2.1.1 A cutting machine that will section nodular cast iron without producing excessive heat that would cause microstructural changes in the material. 3.2.1.2 Metallographic preparation equip
9、ment (mounting press, polishing wheels, etc.) 3.2.1.3 Nital etchant (2% nitric acid, remainder methanol or ethanol). Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWI
10、DE ENGINEERING STANDARDS GMW16844 Copyright 2012 General Motors Company All Rights Reserved September 2012 Page 2 of 4 3.2.1.4 Metallograph capable of 200x total magnification. 3.3 Test Vehicle/Test Piece. 3.3.1 Test Material. Nodular cast iron with a nodularity of at least 80% (per GMW16547), nodul
11、e size between ASTM 6-8, minimum nodule count of 250/mm2, and hardened to produce a microstructure of martensite (80% or higher) can be evaluated by this procedure. 3.4 Test Time. Not applicable. 3.5 Test Required Information. Not applicable. 3.6 Personnel/Skills. Not applicable. 4 Procedure 4.1 Pre
12、paration. 4.1.1 Summary of Test Method. A polished and etched section of the hardened zone is produced showing contrast between retained austenite and the surrounding martensite. 4.1.2 Test Sample Preparation. A section should be taken from the area of the hardened lobe with the highest tendency for
13、 retained austenite. In most cases, this would be at the nose of the lobe. The cutting should be performed carefully as to prevent tempering of the part, which can lower the amount of retained austenite. Standard metallurgical sample preparation procedures should be followed. Reference ASTM E3 for m
14、ore details. The etching time should be controlled to produce a good contrast between the martensite matrix and the retained austenite. A higher amount of untempered martensite will require a slightly longer etch time. 4.2 Conditions. 4.2.1 Environmental Conditions. Not applicable. 4.2.2 Test Condit
15、ions. Deviations from the requirements of this standard shall have been agreed upon. Such requirements shall be specified on component drawings, test certificates, reports, etc. 4.3 Instructions. The test samples can be examined either in-situ using a metallograph, or micrographs can be produced ele
16、ctronically or on physical media. The microstructure shall be examined at 200x, which is the same magnification as the comparison photomicrographs in Appendix A. The photomicrographs in Appendix A are at 200x scale when printed full size on standard 8.5 in x 11 in paper. A total area of 1 mm2 is to
17、be compared. This generally translates to 10 different fields of view when evaluated at a magnification of 200x. The area examined shall be within 0.5 mm from the outside surface of the lobe. If the sample is from an unground camshaft lobe, compensate for the extra grind stock of 1.5 mm to 2 mm from
18、 the outside edge of the sample. 5 Data 5.1 Calculations. Not applicable. 5.2 Interpretation of Results. Not applicable. 5.3 Test Documentation. 5.3.1 Evaluation and Rating. The comparison rating of all examined areas shall be averaged and rounded up to the next highest level. 5.3.2 Report. A rating
19、 level between 0 and 4 is used to define the amount of retained austenite in the microstructure of the sample. Level 0 defines a microstructure with no visible retained austenite at 200x magnification. There shall be no mid-point levels such as 3.5, etc. All fractional values shall be rounded up to
20、the next integer. The only acceptable levels are: 0, 1, 2, 3, and 4. 6 Safety This standard may involve hazardous materials, operations, and equipment. This standard does not propose to address all the safety problems associated with its use. It is the responsibility of the user of this standard to
21、establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WO
22、RLDWIDE ENGINEERING STANDARDS GMW16844 Copyright 2012 General Motors Company All Rights Reserved September 2012 Page 3 of 4 7 Notes 7.1 Glossary. Not applicable. 7.2 Acronyms, Abbreviations, and Symbols. GSSLT Global Subsystem Leadership Team 8 Coding System This standard shall be referenced in othe
23、r documents, drawings, etc., as follows: Test to GMW16844 9 Release and Revisions This standard was originated in July 2012. It was first approved by the Non Ferrous Metals and Castings GSSLT in September 2012. It was first published in September 2012. Issue Publication Date Description (Organizatio
24、n) 1 SEP 2012 Initial publication. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16844 Copyright 2012 General Motors Company All Rights Reserved September 2012 Page 4 of 4 Appendix A Figure A1: Level 1 Figure A2: Level 2 Figure A3: Level 3 Figure A4: Level 4 Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
