Busted my 80, axle shaft opinions?

I think I have figured out why my 436hp truck broke an D80 axleshaft... Does this look like the flange got heated? Maybe by a bad outer bearing going out? Or are these supposed to be blue and discolored?
DSCF2504.jpg

It also looks like there was a hollow spot on the inside of the shaft... you can kinda see where the metal looks kinda rough in the center. Maybe a bad shaft from the factory?
 
The axle shafts are inductioned hardened. This means the shaft is ran through a set of heating coils that rapidly heats up the axle, then almost immediately behind the heating, the axle is quenched. Due to this process the heating coils are very close to the od diameter of the shaft, which means the flange will not fit through the coils. The heat marks you see are where the heat bleed up into the flange before it was quenched.

Usually when an axle breaks at the flange, it means the axle had some post heat treat machining done to it, which removes some of the material that had been hardened by the induction hardening process.

Also I can almost guaranty the axle did not have a hollow spot in it. The ends of the axle are made with a process called "upset forging" The smallest diameter of the shaft in the center of axle, is the diameter of the material that the axle started out as. So basically the spot where your axle broke was subjected to a crap pile of heat and pressure, that would leave no voids in the material.

Hope this helps.
 
OK, I was just curious. I knew that was a good chance that the heat discoloration was from the metal being treated, but I thought I would check on the odd chance it was bearing failure. As for the hollow looking spot I thought it might have just been a result of the breakage, though the metal had a crystalline look to it, kinda like when molten metal cools very slowly. Always the odd chance that it was bad, guess I'll keep looking at the upgraded options.
 
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