Hydrogen Embrittlement Testing

[Schuyler]

We have approximately 400 parts that were manufactured but not embrittlement baked subsequent to nital etch (in accordance with the drawing/specification requirements). The drawing requires that the parts be baked within 8 hours after nital etch. Consensus is the material grain boundaries may be damaged (via hydrogen embrittlement) if the parts are not baked within the prescribed time frame. My question is, is there a test that can be performed on these parts to determine if they have been damaged. A destructive test would be fine, we would just perform the test on a statistical sample (from the 400). Also, can the test be performed on the finished product (not requiring a specific test sample to be machined). If you are aware of a test, is there a specific specification (i.e., ASTM) that applies. The material is 52100 steel.

 

[grampi1]

52100 is highly hardenable and will be subject to hydrogen embrittlement if both hydrogen charged and under stress. Compare tensile elongation/RA and Charpy impact vs one baked out at 800F for 1 hr per inch. Am assuming these are Q&T. Will be more senstive to hydrogen the higher strength/hardness. Looking for property change of 20% or more.

What was the purpose of the Nital etch, how long exposed, how much surface area vs volume?

Etching a single face of a moderately thick component for a short period of time ought not to cause mcuh damage.

 

[Metalguy]

Grampi1,

800 deg. F is likely to be far too high for 52100 if it's used for a bearing part-a very common use for this steel. 375 deg. is the commonly used H bake temp.

Schuyler,

There is a non-destructive (IIRC) H measurement test that can be performed on small parts. You'll need to estimate the time/temps. the parts have been subjected to AFTER the etch. The H is then baked out (at 375 deg F I believe) in a special oven where the H released is measured.

 

[CoryPad]

Schuyler,

ASTM has numerous publications on this subject - go to their website (

http://www.astm.org)

and do a search using hydrogen as a keyword. If you tell us what your parts are, perhaps we can suggest an appropriate test.




Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[brahimi]

ASTM F519 and ASTM F1940 can be applied to any process not just plating. The test method is Incremental Step Load testing. Read the two documents. That is your answer.