The authoritative public forum
  for Metal Finishing since 1989
-----

What happens to hardened steel surfaces if not baked for trapped hydrogen?

I'm redesigning 2 hardened steel parts. Each are made of low carbon steel that is nitrited to a high surface hardness (C41 or greater) to make each piece ring like a bell. One piece weighs about 1-1/2 lbs with maybe a square foot overall surface area, the other weighs about 2-1/2 lbs with about 1-1/2 square foot overall surface area.

We have been advised that we need a low temperature bake cycle before RoHS plating to drive out the hydrogen to avoid hydrogen embrittlement.

I understand the threads of fasteners fail due to hydrogen embrittlement, but what happens to a large hardened surface if I don't bake out the hydrogen? Pits? Cracks? Discoloration?

I don't want to loose the ringing qualities of each piece, but can live with some pits, if that is all that happens.

Paul Graham
Product Designer - Chicago, Illinois, USA
2007

Cracking is the problem, not pitting. I seriously doubt it a 375F bake for 4 - 6 hours will affect the bell tone. It will at worst lower your hardness by two points Rc. Your part will be less subject to cracking since it has a "soft" center and that the "hard" layer is not very thick.

James Watts
- Navarre, Florida
2007

---

First of two simultaneous responses --

In order to avoid Hydrogen embrittlement problem, I will suggest to temper it at 170 to 180 oC for about 1 to 1 1/2.00 hrs.

Sudhir Kshirsagar
- Pune, Maharashtra, India
2007

---

Second of two simultaneous responses --

The baking temperature is relatively low. In the worst of the cases you can set up your parts over a fixture (during baking process) in order to keep geometry requirements.

Jose Castellanos
- Minneapolis, MN, USA
2007