PH Stainless Custom 465 Failure Investigation

[MetalGuy10]

I am conducting a failure investigation on a Custom 465, Carpenter alloy. The alloy is newer, late 1990's so their does not appear to be much case histories on failure investigations.

The investigation is on a tubing type structure that is used to contain fluids up to 10 KSI preasure. The tube has one linear crack, but the rest of the part does not exhibit visible cracks. The part was used for about 36 hours with a max preasure of 6.5 KSI The material is aged at 950 F. The fracutre mode appears to be an intergranular brittle fracture. The microstructure has the appearance of a martinstie lath structure. The failure appears to be on prior austinite grain boundries.

No dents were found near the initation point. The crack starts at the bottom of the cylinder and moves inward, but not completly through the part.

The material could be over aged to increase ductility, but is there a posiblity of making the alloy brittle by too much aging?

Tensile test results: Yield 246.5 KSI, Tensile 263.2 KSI, y/t ratio .93, Elongation(2") 5.5 %. Hardness about 50 HRC

Does any one have any suggestions, references, or other items that should be reviewed during the investigation?

Thanks

 

[EdStainless]

Look at thermo-mechanical history. I have only worked with welded and drawn material. Many time this will involve multiple intermediate anneals. Grain size and the possibility of a grain texture could be factors.

The crack is on the inside surface? If not then why would it have started at a lower stress location.
What sort of pressure cycling did the part see? I don't feel too good using something with this little ductility in a fatigue application (little damage tolerance).

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[TVP]

Can you provide a few more details on the product and the failure? For starters, a picture is worth a thousand words. A macro view of the failure would be a good place to start. Additionally:

1. Is this an open tube, meaning completely cylindrical, or a closed tube, meaning that it has an integral bottom (cup-shaped)?

2. Does the crack start on the OD or ID? Is the orientation axial, circumferential, or radial?

3. How was the tube manufactured? Welded from sheet? Seamless tube process? Forged or extruded?

Overaging may be a possibility, since this obviously has little ductility. Overaging to the point of excessive brittleness should not be a concern if you follow the general guidelines from Carpenter. 1100 F for an hour will definitely reduce the strength and increase the ductility. Regarding your question about references, etc., I would not be concerned about anything specific to Custom 465, but more about failure analysis in general. Do you have access (company library, personal collection, university library, etc.) to ASM HANDBOOK Volume 11 Failure Analysis and Prevention?

 

[CoryPad]

What is the fluid?

 

[unclesyd]

Here are references to work on failure analysis of Carp 465 by D.Dennies, Boeing and D. Wert, Carpenter. You might be able to get copies of the papers from the AIST.org.or MS&T. Another source of information might be through Metadex.
I would certainly involve Carpenter with your problem.

http://www.programmaster.org/PM/PM....t&ParentUNID=06165B70BD3322E78525771800645D3C

http://www.aist.org/10_spa/Steel_Related_Papers_MS

I may still a have a ex-collegue working at Boeing who may be of some help.

 

[metengr]

The tube has one linear crack, but the rest of the part does not exhibit visible cracks.

Did you perform any surface NDT other than a visual examination to determine if only a single crack was present?

 

[metengr]

This could be a hydrogen embrittlement failure, considering the observed crack morphology, strength properties and low ductility.

 

[unclesyd]

Here is the full link to the AIST paper.

http://www.aist.org/10_spa/Steel_Related_Papers_MS_T.pdf

 

[TemperedMartensite]

How was the tube produced? Cartech does not extrude, so I am assuming that this is a bored bar. Was the ID cleaned up?

Was it solution treated and aged prior to boring? I know some companies prefer receiving PH steels in the fully aged condition and then they bore.

246ksi yield is on the high-side for C465 - and 5.5% elongtation is less than expected (AMS 5936 elongation is 10%L and 8%T for the H950). There is a chance that the furnace temperature never reached the set-point - I would check the furnace charts to see if it was aged low - perhaps closer to 900F.

C465 is age sensitive since it is aged only by its titanium addition. Is the chemistry off?

You may want to check out S240 - it is very similar to C465, but it offers a bit better toughness and it uses, Ti, Al, and Cu for its ageing response.

 

[JAWright]

The elongation seems low - you may try reducing the strength through a higher tempering temperature.
The intergranular nature of the crack might imply stress corrosion cracking might be an issue.

Jim

 

[MetalGuy10]

The final cause of the failure was determined to be hydrogen embrittlement.
The part failure fracture was intergranular, but the fracture surfaces on a tensile and charpy test sample from the same part, had a much different fracture pattern (SEM eval). The tensile sample had some cup and cone morphology, and the charpy had a mix structure with shear ductile and cleavage.
Guys, thanks for your input. I did attend the MS&T conference in Houston last October and was able to learn more about Custom 455 and 465.
I do apologize about being vague on some details because of company confidentiality agreements otherwise I would provide more details.
Best Regards and Thanks!