Metal finishing Q&As since 1989

-----

Time limit before baking for hydrogen relief

As a bake inspector for an un-named company I have always been told that a four hour time limit from plating ops. to bake was critical, however some of or spec have recently changed. The specs state that a 8 hour time limit is acceptable. My question is at what time limit form, clean to pickle to plate to I REALLY run the risk of trapping the hydrogen in the part, and is there a spec out there that is really the "GOLD STANDARD"

Nathan Saeger
inspector - Kent, Washington, USA
February 4, 2009

---

First of two simultaneous responses -- February 5, 2009

The "gold standard" depends on the hardness of your metal and the chemical process. Simply stated, the harder it is the sooner it needs to be baked. An example, 4340 with a Rc of 50 needs to be baked a lot faster than 4310 with an Rc of 39.
Chrome plating and cyanide processes also generate more H2 , so need to be baked sooner. Also, the acid etch is possibly the worst generator of H2, so that is also a factor.
So, it depends.
Rules are nice, but they really need to consider the real world.

James Watts
- Navarre, Florida

---

Second of two simultaneous responses --

Nathan,

A good starting point would be AMS2759/9. This gives general rules for de-embrittlement. Be careful though, a lot of specifications have their own de-embrittlement requirements embedded within them.

Add to that a lot of the OEMs that have their own control specifications have their own rules on de-embrittlement.

As a general rule of thumb the quicker in the oven the better. For high strength steels it is generally considered to be within 1 hour, for medium strength steels, 4 hours and for the lower strength steels (say 1100MPa, 36 HRC or similar) it may be extended to 8 hours, I have even seen 12 hours quoted.

Whatever you do the quicker the better, and leaves no doubt then.

Brian Terry
Aerospace - Yeovil, Somerset, UK
February 6, 2009