I have a .02 thk X 1.5 long X .375 wide flat spring. Cold Rolled Steel, SAE1095, Blued and Tempered, Zinc Plate per ASTM B633 [link by ed. to spec at TechStreet] , Type III. It is fastened at one end and flexes approx. .25 in. (static flex) I have experienced breakage usually a day or two after installation but with no other breakage during installation or weeks after installation. I suspect hydrogen embrittlement. If these parts are not baked, how long would I have to wait before I was certain the parts will not have a latent failure?Dean S. Cowles
- Redmond, WA
Hi Dean ,
One of the insidious things about Hydrogen embrittlement is that once the part has been treated in a pickling , cleaning ,phosphating , plating or other process involving the release of hydrogen on the workpiece then embrittlement WILL occur at some time after the part has been loaded . There is some thought that the degree of loading is in some way proportional to the time taken to fracture but there is no real conclusive evidence to back this up yet that I am aware of . The chance of failure can be lessened( not completely eliminated ) by baking after treatment according to the appropriate standard (ASTM or Mil Spec ) or other standard , this treatment must be performed as soon as possible after plating ( usually within 4 hours ) , and there is some evidence of a correlation between the time taken to get the parts into the relief heat treatment vessel and the effectiveness of the heat treatment (if dwell time between plating & relief is more than 8 hours Forget it ! )
I suggest that you investigate Mechanical Plating , I have worked with it for a long time ( about 20 years ) and have not seen any failures in plated fasteners ( Fully loaded ) in that time ( Hardnesses up to 60 Rockwell C )
- Victoria Australia
The standard tests for hydrogen embrittlement are typically no more than 200 hours. This interval, however, is at stress near the yield strength. At lower stress, failure could take longer.
Could you use a proof test at 75% of ultimate tensile strength to screen for hydrogen embrittlement. This approach is used for critical fasteners, for example.
Some metallurgical investigation to confirm the hydrogen embrittlement failure mode may also be in order. You could spend a lot of effort to combat hydrogen embrittlement that does not exist.
Dean, Go with John's recommendation on mechanical. Call Waterbury Conn for information on the process. Rayray delorey
cambridge, ontario, canada
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