Crack in 303 Stainless Steel
Crack in 303 Stainless Steel
(OP)
I am examining the failure of a machined part manufactured from 303 Stainless Steel, and not exactly sure of the cause. Your thoughts would be appreciated. The key points are:-
The part is a banjo type connector from a brake system on a racing car.
The design has been in use for a number of years with no previous problems. I do not know the full history of the actual failed part, but it is believed to be very new and seen limited used.
I have had a look at the fracture and found it propagated along the grain boundaries - from stereomicroscopy & microscopy of polished cross-section.
The crack extends the full thickness of the banjo (it was found due to a fluid leak, but it does not follow any stress concentrations, it simply follows the longitudinal direction of the material.
When new the part had passed a pressure test of three times the normal in-service pressure.
The brake fluid used is a super-dot 4 type.
The hardness of the material is as it should be.
There is no branching of the crack and the part is not under constant tensile loads - therefore I have ruled out SSC.
Mt first throught on looking at the failure was Hydrogen cracking, but I cannot think of the sort of hydrogen.
As I mentioned above your thoughts are appreciated and I thank you in advanced for your assistance.
The part is a banjo type connector from a brake system on a racing car.
The design has been in use for a number of years with no previous problems. I do not know the full history of the actual failed part, but it is believed to be very new and seen limited used.
I have had a look at the fracture and found it propagated along the grain boundaries - from stereomicroscopy & microscopy of polished cross-section.
The crack extends the full thickness of the banjo (it was found due to a fluid leak, but it does not follow any stress concentrations, it simply follows the longitudinal direction of the material.
When new the part had passed a pressure test of three times the normal in-service pressure.
The brake fluid used is a super-dot 4 type.
The hardness of the material is as it should be.
There is no branching of the crack and the part is not under constant tensile loads - therefore I have ruled out SSC.
Mt first throught on looking at the failure was Hydrogen cracking, but I cannot think of the sort of hydrogen.
As I mentioned above your thoughts are appreciated and I thank you in advanced for your assistance.





RE: Crack in 303 Stainless Steel
A guess, how about that the crack, or at least part of it, was pre-existing. Take some new parts and air test them underwater. You might find some leaks that don't show up with fluid until they open up a little more.
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RE: Crack in 303 Stainless Steel
If you look at the fracture you would probably see fatigue beach marks.
http://www.welding-advisers.com/
RE: Crack in 303 Stainless Steel
Under a stereomicroscope I cannot see beach marks, in addition I would normal expect changes in crack direction as is passed geometric features, but there was no deviation even when it reached a sharp raduii. Although I have already planned to take a look at the fracture surface using an SEM tomorrow at the local university hopefully that will yield further information.
RE: Crack in 303 Stainless Steel
RE: Crack in 303 Stainless Steel
RE: Crack in 303 Stainless Steel
RE: Crack in 303 Stainless Steel
Nick
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