Believe it or not, I've had a few cores come in with broken cranks, my latest was a 2012 6.7, with well under 100k, that broke on the arm between 5 and 6.
I had one 5.9 a couple years ago that broke across a rod journal, tore up the rod bearing, tossed the rod, then the crank wedged apart, splitting the block, breaking 3 main caps and blowing the side out of the block.
It was a stone stock 305 horse 2003 6 speed engine.
I think Cummins
CR cranks are extremely hard and sometimes surface fracture, then it spreads, which is why knowing how to properly machine them is such a critical step.
They are so hard, that I've had them come in totally rusty, from sitting outside for a year and they only needed to be cut .010-010.
Mark.