Quote Originally Posted by BlacknTan View Post
O1 is a very common alloy of Oil Hardening Tool Steel... Probably the most common. When taken to the limits of it's range on the Rockwell scale, it can be quite brittle. ...
It's also a steel that people neglect to consider can be hardened to Bainite with a still decent hardness. The brittleness is not much of a factor at that point. It's not something incredibly easy to do but can be done with rather ordinary shop equipment.