It really depends on if there is a resulting rolling texture.
If there is then it depends on the alloy and residual stress.
Remember, residual stresses are in the opposite direction to the last deformation. In many materials this would imply that cracking in the x-y plane (delamination of the z) is most likely.
Thanks you ED! If there are rolling marks, will be the SCC along the rolling direction since the cracking could initialize from the texture? Would you mind taking a look at the attached picture to see if the longitudinal cracks are SCC. The transverse marks were ground with 30 grit, the cracks existed before polish.
I suspected the recent road salt caused SCC, but some thought it was not SCC, who claimed the cracks would have been orientated transverse to the rolling direction.
This is a high thermal expansion alloy with Mn up to 70%. The slab was cogged from 16x10 to 13x5, no other stress. cracks were observed at billet conditioning.
I doubt that SCC is involved, unless they exposed it a chemical that they shouldn't have.
More likely to be either hot working at too high or low of a temperature, or perhaps interganular oxidation damage (this is notorious in high Mn alloys).
This alloy is very very susceptible to SCC, maybe the worst I have ever met at strip (but I didnot have a chance to see SCC samples at earlier stage). Unless it is not annealed, our process is to send to next operation immediately at any step. A cold rolled coil can develop substantial cracks sitting overnight even at a humid atmosphere!
Indeed it is notorious for oxidation, and we do a full grind/polish before cogging. so oxidation damage is less likely.
Did the picture give any hints that they were not likely SCC?
Up to 70% Mn? What kind of alloy is that? (Rhetorical question, I know).
Anyway, I also wonder why you know this would be SCC. There are other mechanisms that are consistent with the cracking shown. You need to do a real failure analysis with an experienced lab, either in-house or contract. Looks like there is some proprietary information that you cannot share with the forum that would acutally help this discussion. You'll be able to really understand this issue by work performed by someone experienced who you can also share all of the background with.
I donot have direct evidence to say it is SCC, or it is not SCC. It is a quick question, needs further investigation for sure. Given the weather condition, and the nature of this alloy, SCC was my first suspicion.
Thanks for input!
In suceptible aluminum alloys, I've found SCC primarily oriented in the grain-elongation direction [as-rolled/extruded/forged axis]; VS fatigue cracks which are usually transverse to the local tensile/shear strain-field.
Problem with SCC is that it usually ititiates/propagates at an exposed grain edge [machined-edge/surface-thru grains, drilled/reamed holes, etc...thru the thickness] usually in the ST [short transverse, thru]-in-the-L [long, grain-elongation] direction. HOWEVER, this "common orientation can be trued-on edge by the SCC phenomnea: those same alloys can also be susceptible to SCC in the LT-[transverse]-to-L direction within the metal-laminate/thickness [this is usually described as inner-laminar corrosion] which appears to splinter-off layers of metals.
NOTE. SCC usually does not initiate in thin wrought materials...or zones on/adjacent-to wrought surfaces in thicker materials... due to localized compression stresses caused by the cold-working effects from the wrough processing.
Other alloys, specifically titanium and steel alloys included, have different SCC forms/conditions, depending on alloy/HT state, wrought-method, induced or inherent material defects, extent of machining [exposing grain-ends], etc.
Regards, Wil Taylor
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