From the photos below some might draw the conclusion that the failure was inevitable, with there seemingly rust in the wrong spot at the failure point.
Have posted a few here.
From the pictures, the steel looks freshly broken.
Any more information?
Certainly the web and the outer half of the flange look like they just broke.
The inner half of the flange looks darker, possibly suggesting a fatigue failure.
Thank you for posting those images. Did the wagon fail near laverton or Lara?
Here's the same wagon in the consist of 7922V on Friday 28/2 for point of reference. There don't seem to be any cracks on this side of the wagon