it is %26-30 Cr and %1 Mo it is hard as cast and not mashiable it is used for parts under sever abrasion and errosion for example salary pumps and grinding balls there is standard ASTM A532 for these types
in my experiance as you are hardening a thin part you shoud cool it alitelbeat slower or austenitize it in lower temperatur so you will have less retained austenite and more hardness.