O1 is an excellent tool steel for general use, it's relatively inexpensive and fairly easy to machine. O1 is an oil hardened tool steel supplied in the annealed condition. O1 others all characteristics synonymous with tool steels, a decent level of durability as well as wear resistance.
It's a very viable substitute in place of more expensive tool steels were the extra utility would not be utilised. O1 forgoes the corrosion resistance of D series steels, as well as some level of wear resistance.
AISI ASTM A681
BS EN ISO 4957