Hard Chrome and fatigue

[Dougt115]

I need some wisdom.

I have a part that is 17-4 H900 stainless steal that was hard chrome coated, and electro-polished. The problem is that they coated my threads too. I have removed the chrome from the threads but I am trying to determine if there is residual degradation of my part fatigue life from the chroming?

The threads were not supposed to be coated, they screwed up! The company that did it states that there is no residual effects... but I know chroming can decrease endurance by as much as 50%. Did the chrome removal restore my endurance? If not how much did it decrease (%)?

Thanks

 

[metengr]

How did you remove the hard chrome plating from the threads? There is literature that supports your statement that the fatigue life will be lower for a steel substrate having hard chrome plating because of the residual tensile stress induced on the surface by the hard chrome plate. Removal should eliminate the residual stress. I say should because the method of removal can affect the surface roughness of the steel and fatigue life.

 

[tbuelna]

Dougt115-

17-4PH in an H900 cond. is susceptible to hydrogen embrittlement as a result of electroplating processes. As long as your parts were processed carefully, including hydrogen embrittlement relief treatment, there should be no detrimental effect on fatigue properties.

You can refer to AMS2759/9 for more details on hydrogen embrittlement relief.

Hope that helps.
Terry

 

[TVP]

Good answers from both metengr & tbuelna. Final results will depend greatly on how the plating was removed and whether or not an embrittlement relief treatment was used.

 

[Maui]

In order to prevent a recurrence of this problem in the future, I would recommend updating your part drawing to include a stop-off coating prior to plating if you have not already done so. This should ensure that this information is properly communicated to your plater.

Maui

http://www.EngineeringMetallurgy.com