Can the chromate conversion process cause hydrogen embrittlement

[WillCole]

Hello,

I have received a bit of conflicting advice about a chromate conversion coating applied over mechanically plated parts. One source says there is hydrogen embrittlement risk, the other say there is no concern. I would be interested in any additional opinions or information.

Thanks!

 

[swall]

It is unlikely that you would get embrittlement. Conversion coatings, such as phosphate and chromate generally are self-relieving as long as the parts are not put into service right after coating. Usually, a 24 hour interval is satisfactory for the parts to self relieve. One of my former employers DID require embrittlement relief after electro plating and before chromate, but it was noted that the corrosion resistance of the coating would be degraded due to the degradation of the chromate from the 350F baking temperature. The final answer is that it all depends on the tensile strength level of the steel you are working with. One way to check out the susceptibility of your particular part(s) would be to run the ASTM F-519 test.

 

[TVP]

The chromate conversion coating process is not a source of hydrogen embrittlement, only electroplating, acid cleaning, and other processes using concentrated acids, etc. Industry standards that describe hydrogen embrittlement and the necessary processing procedures included IFI-142, SAE/USCAR-5, SAE AMS2759/9, ASTM B49 and B850, and ISO 9587 and 9588. Here are some useful links:

bbs.6jc.cn/pdf/usa/IFI%20142-97.pdf

http://surtec.com/TB/TB08E.pdf

 

[WillCole]

I understand about the risks from electroplating. The question has been with chromate on mechanical plated parts. With mechanical plating the surface layer is more porous and I am guessing there is where the debate was stemming from.

 

[kmenke]

WillCole, unfortunately a number of failures get attributed to hydrogen embrittlement unjustly or without further investigating the true cause so you may struggle finding conclusive evidence certain processes do not have a risk. We have been using ASTM B695 (mechanical galv) for split lock washers and have tested pretty extensively using the ASTM F1940 test method using coatings from various coaters with and without a chromate conversion coating. We have not found there to be a risk for failure from internal hydrogen embrittlement with or without the chromate conversion coating.