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

17-4Ph SS cracking when we strip the hard chrome off

We use hydrochloric acid to strip hard chrome off of 17-4Ph SS. We are now noticing small cracks in the material after the stripping. Any ideas why?

Jamie Black
Plant Superintendent - Arab, Alabama, USA
September 16, 2011

---

Hi, Jamie.

If the cracking is prevalent enough or directional enough, you might try a microscopic cross-section before stripping in order to gain insight as to whether the cracking occurs during plating or during stripping.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 18, 2011

---

First of two simultaneous responses -- September 20, 2011

You can ruin parts using it, but anodically stripping with caustic is used by many. Try it with scrap. Because it generates oxygen rather than hydrogen, it is less likely to crack than with HCl.
It might help to prebake prior to plate and to bake longer after plate.
Can you use a slightly lower Rc. The higher the hardness, the more prone to hydrogen embrittlement you get.
Aviation industry even shotpeens some parts before plate.

James Watts
- Navarre, Florida

The parts have been checked under a smart scope and documented that they are not cracked before or after chrome plating. They only crack when stripped. It's not every part either. It's only a few select parts. We only have this problem with one style part that we produce. This particular part is produced in nine different sizes. We have had the cracking problem with all nine sizes that we run. All nine sizes are the same material and the process in production.

Jamie Black
- Arab, Alabama
Second of two simultaneous responses -- September 21, 2011