Avoidance of Hydrogen Embrittlement of Steel
SAE/USCAR-5 Revision 2
March 2007
ISBN: 978-0-7680-1941-4
SAE/USCAR-5 REVISION 2
Issued 1997-11 Revised 2007-03
AVOIDANCE OF HYDROGEN EMBRITTLEMENT OF STEEL
1. SCOPE:
This standard outlines the conditions that enhance the risk of hydrogen embrittlement of steel and define the relief procedures required to minimize the risk of hydrogen embrittlement. It is intended to control the process. 1.1 Hydrogen embrittlement of steel, which can cause brittle fractures under stress, occurs as a result of the absorption of hydrogen during cleaning, phosphate coating and plating processes. The susceptibility to
hydrogen embrittlement increases with increasing stress (internal or externally applied stress) and increasing material strength. 1.2 Hardness readings in this specification are in Vickers scale. SAE J417 should be referred to for conversion to other scales.
NOTE 1: All references to temperatures relate to part core temperature and not the indicated oven air temperature. Statistical data of verifications in temperature at the center of the oven load and oven temperature shall be established to develop the oven profile. The temperature of parts in a batch type of baking furnace 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 with a calibrated thermocouple in the lowest temperature position, at least once a year. 2. REFERENCES: 2.1 SAE Publications:
Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.
SAE J417 - Hardness Tests and Hardness Number Conversions 3. REQUIREMENTS:
The parts shall be processed in accordance with this specification as applicable to minimize the risk of
hydrogen embrittlement. Specific applications or customer requirements may require processing that goes beyond the requirements of this specification
__________________________________________________________________________________________________________________________________________ The research data, analysis, conclusion, opinions and other contents of this document are solely the product of the authors. Neither SAE International nor the United States Council for Automotive Research (USCAR) certifies the compliance of any products with the requirements of nor makes any representations as to the accuracy of the contents of this document nor to its applicability for purpose. It is the sole responsibility of the user of this document to determine whether or not it is applicable for their purposes.
Copyright © 2007, USCAR Printed in U.S.A.
QUESTIONS REGARDING THIS DOCUMENT: (248) 273-2470 FAX (248) 273-2494 TO PLACE A DOCUMENT ORDER: (724) 776-4970 FAX (724) 776-0790
SAE/USCAR-5 REVISION 2
AVOIDANCE OF HYDROGEN EMBRITTLEMENT OF STEEL
Revised 2007-03
- 2 - 3.1 Cleaning prior to heat treatment:
All parts to be heat treated to a specified hardness (core or surface) greater than 353 HV must be cleaned prior to heat treatment to remove phosphate associated lubricant residues and detrimental contaminants from the surface.
NOTE 2:
The formation of a delta ferrite layer caused by the penetration of phosphorus during the hardening process enhances the possibility of embrittlement.
3.1.1 Acid Cleaning after heat treatment or cold working:
Acid cleaning of parts to be heat treated to a specified hardness (core or surface) greater than 353 HV or highly stressed cold worked parts enhances susceptibility to hydrogen embrittlement, and shall be minimized. If high hardness parts are to be acid cleaned, it is required that a procedure be established for processing the parts that limits the time in the acid bath to a maximum of 10 minutes. Parts which are acid cleaned and subsequently oiled, phosphated, mechanically (non-electrolytically) plated, or electroplated shall follow the requirements of 3.2, 3.3, 3.4, or 3.5, as applicable. All other parts which are acid cleaned shall not be used for 48 hours or alternately these parts shall be baked for 1 hour minimum at 110 °C minimum following cleaning. 3.2 Oiled:
All parts to be heat treated to a specified hardness (core or surface) greater than 353 HV which are acid
cleaned before application of oil shall not be used for 48 hours or alternatively these parts shall be baked for 1 hour minimum at 110 °C minimum after acid cleaning prior to oil application. 3.3 Phosphated:
All parts to be heat treated to a specified hardness (core or surface) greater than 353 HV, which are acid
cleaned and/or phosphate coated shall not be used for 48 hours or alternatively these parts shall be baked for 1 hour minimum at 110 °C minimum following phosphate coating. 3.4 Mechanical Plated:
All parts to be heat treated to a specified hardness (core or surface) greater than 353 HV which are acid
cleaned before mechanical plating shall not be used for 48 hours or alternatively these parts shall be baked for 1 hour minimum at 110 °C minimum following mechanical plating. 3.5 Electroplated:
3.5.1 All parts either hardened or cold worked to a specified hardness (core or surface) greater than 353 HV, when electroplated shall be baked. Within one hour after the electroplating process and before any
supplementary chemical treatment, parts shall be placed in an oven and heating commenced. The parts shall be heated to a part temperature of 200°C minimum and held at this temperature for a minimum of four hours. This temperature range shall be reached within one hour after commencement of heating.
3.5.2 All parts to be heat treated to a specified hardness (core or surface) greater than 390 HV, when
electroplated shall be baked. Within one hour after the electroplating process and before any supplementary chemical treatment, parts shall be placed in an oven and heating commenced. The parts shall be heated to a part temperature of 200°C minimum and held at this temperature for a minimum of eight hours. This temperature range shall be reached within one hour after commencement of heating.
SAE/USCAR-5 REVISION 2
AVOIDANCE OF HYDROGEN EMBRITTLEMENT OF STEEL
Revised 2007-03
- 3 - 3.5.3 Hardened parts which have been tempered or stress relieved at less than 200 °C when electroplated shall be baked for 8 hours minimum at 110°C minimum within 1 hour of plating.
Note 3:
Longer times at heat than those given may be necessary if verification testing detailed in the Control Plan (see para 3.6) indicates a failure risk.
Note 4:
Where tin or Tin alloy electroplated coatings are specified relatively low, (near 200°C ) deembrittlement temperatures and longer times may be necessary to prevent 'Liquid Metal Embrittlement' issues. In these cases the temperature and time shall be agreed between the coater and the end user, (Original Equipment Manufacturer) 3.6 Verification Test:
The control plan shall include a verification test to demonstrate the effectiveness of de-embrittlement, such as SAE/USCAR-7.
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