45039

Hydrogen Embrittlement During Stripping Process  

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My company has low carbon (1022) heat treated fasteners that have been electroplated with yellow zinc dichromate. Our customer wishes to a different coating in place of the electroplated yellow zinc dichromate. If the fasteners are stripped using a low temperature hydrochloric acid bath to remove the electroplate, what potential is there to induce hydrogren embrittlement if the fasteners are not baked after the stripping process? If hydrogen embrittlement can be induced in the stripping process, what processes are available that would eliminate this hydrogen embrittlement potential?

Greg LeCompte
Product Designer - Bryan, OH, USA

As soon as you say fasteners, you are in another world from conventional plating.
1022 is normally not heat treat hardened to a high hardness. Different industries have different hardnesses where they demand de-embrittlement. Strip will certainly induce embrittlement. Typically, if it is below Rc 36 , it is not de-embrittle treated. The Rc will depend on your customer's call out.
The treatment is typically 2-4 hours at temperature in an oven at 375F.

James Watts
- Navarre, Florida

Yes, stripping can induce hydrogen embrittlement. However if done quickly and removed from the acid as soon as stripped, there may be no problem. Hydrogen embrittlement can be relieved by baking @ 375F for four hours, but is usually necessary only if the parts are RC 39 or harder, which 1022 probably isn't.

Jeffrey Holmes, CEF - Spartanburg, SC, USA

Exposure to HCl acid will create potential for hydrogen embrittlement. Baking is the required method for embrittlement relief. Standards such as ASTM B 850 or SAE/USCAR-5 should be referenced regarding embrittlement relief procedures.

Toby Padfield
Automotive module supplier - MI, USA

Good afternoon:

Just wanted to let you know that there are many heat treated fasteners made from 1022 that require baking. The two types of fasteners that come to mind are self drilling screws per SAE J 78 and tapping screws per SAE J 933. These screws, in addition to having a core hardness typically mid 30s HRC are also given a shallow case.

Steve Bizub
- St Louis, MO

Mr. Bizub,
I didn´t know the carbon level in a 1022 steel was enough to reach that hardness. More so inside, for there is also the cooling rate issue. Could it be the case treatment you mentioned alters its chemical analysis rendering something that is not 1022 anymore? Or could it be due to some work hardening effect?

Guillermo Marrufo
Monterrey, NL, Mexico

Good afternoon, Mr. Marrufo:

Many of these fasteners have a small major diameter. A fairly fast oil quench will harden out 1022 Si killed fine grained fasteners if they are #12 or smaller. Above that diameter, 1022 Si killed coarse grained steel is often used to give added hardenability. The self drilling, tapping, and thread rolling screws typically have a case only about 0.004-0.010" deep, depending on the major diameter of the screw. There is no work hardening effect; they are fully austenitized when they drop into the oil quench.

Steve Bizub
- St Louis, MO

Have you considered an ammonium nitrate stripping process instread of acid? Seems that should not induce hydrogen embrittlement therefore you need not wory about bake?

Douglas A. Hahn
- Saint Charles, Missouri