Stress Corrosion Cracking 9310 Material Carburized

[Skillet74]

What are some key contributors of SCC on carburized 9310 material?

Process background:

Copper Plated as a stop off
Carburized to .015" TCD
Copper is stripped after the heat treat

 

[metengr]

Skillet74
Hydrogen induced cracking is a form of SCC, and comes to mind (high residual tensile stresses in the substrate beneath the carburized zone, source of hydrogen and high strength). How is the copper stripped after heat treatment? Also, you need to provide more information to obtain better responses. Like, have you confirmed it is SCC, exact location? When does the cracking occur or when was it observed?

 

[Skillet74]

Meteng:

After heat treatment, the copper plate is removed chemically. Our metallurgical lab has confirmed it is SCC and the location of the fracture was around the circumference of the gear. Their was no evidence of SCC or damage to the mating part. The failure was found in service (aircraft). I hope this information helps. I am just trying to understand what could cause the failure and what to look for in the processing of the part.

 

[metengr]

Skillet74;
Several more questions of interest. Were there any contaminants found or reported by the met lab along the crack surfaces that could relate to service conditions if they confirmed SCC? If not, after the copper is stripped off, is the component given any final nondestructive test to assure no processing problems before entering service? Are you sure these are not quench cracks from heat treatment?

 

[strider6]

copper alloys can suffer SCC in particular environments like ammonia, alkali..
You should define if in the environments there could be some of these chemicals..also you shloud make a chemical an analyis of the damaged part and found if there are some residual of these compounds..

Stress Corrosion Cracking

http://www.npl.co.uk/upload/pdf/stress.pdf

S.

Corrosion Prevention & Corrosion Control

 

[TVP]

You should review some references on the subject of environmentally-assisted cracking (EAC) and stress corrosion cracking (SCC), such as the NPL guide mentioned by strider6 or one of the following documents:

http://ammtiac.alionscience.com/pdf/AMPQ9_1ART02.pdf

http://standards.gsfc.nasa.gov/reviews/xxx-011/01-108.pdf

see Table III-A

http://www.virginia.edu/ms/faculty/critical.pdf

After reviewing these documents, I suggest you discuss with your metallurgical lab the failure mode of this gear using the precise definitions for "stress corrosion cracking", "corrosion fatigue", "hydrogen assisted cracking", etc. If they confirm that it is indeed SCC, then you need to evaluate the sources of the stress and corrosion and try to reduce or eliminate them. Residual stresses due to manufacturing could be a significant part of the problem, and may explain why the mating gear is not similarly affected. Stress measurement using x-ray diffraction is one technique that may be useful in further investigations.

 

[strider6]

this is another good reference:


Material selection for controlling stress-corrosion cracking

http://esamultimedia.esa.int/docs/industry/SME/2004-Training/M&P/Annex2_ECSS_Q_70_36A.pdf

S

Corrosion Prevention & Corrosion Control

 

[Skillet74]

I guess what I was the help I needed was what to look for in regards to each process step:

Heat Treating - What are some of the potential root causes?

Copper Plate / Stop Off - What are some of the potential root causes?

Copper Plating Strip - What are some of the potential root causes?

Please help?

 

[TVP]

Skillet74,

I'm guessing that you didn't really read any of the information that I recommended. If you had, you would understand that Stress Corrosion Cracking (SCC) is a very specific failure mode, with certain implications for your particular design/material/processing/end-use environment. If the gear truly failed due to SCC, then the copper plating/stop-off and plating strip processes had nothing to do with the failure. SCC occurs when a susceptible material (e.g., ferrous alloy) is exposed to a particular chemical species (e.g., Cl ions from seawater) in the presence of high stresses (residual stresses due to abusive machining/grinding, overly aggressive quenching, extremely high operating stress, etc.).