They use to be made of EN8D grade steel - and the ring-gear has been damaged on a couple of these.
To rectify the problem, they are now made from EN19T chromoly steel, and the width of the ring-gear has been increased too.
The EN19T has a significantly higher Brunel number than EN8D [it's much harder basically].
If you still have concerns, it can be heat treated to your specification at cost.
how much is it to heat treat one, I have one of the first ones and want it done, Jim was going to sort it out for me but hes useless.