Cutting edges of the orthodontic instruments are made up of
Because of their high yield strength and hardness, martensitic stainless steels are used for surgical and cutting instruments. 
The austenitic stainless steels are the most corrosion-resistant of the three major types and are the stainless steels used for orthodontic wires, endodontic instruments, and crowns in pediatric dentistry.
Ferritic Stainless Steels: These alloys provide good corrosion resistance at a low cost, when high strength is not required. They cannot be hardened by heat treatment or readily work-hardened. Consequently, they have little application in dentistry.
Ref: Phillip’s 12th edition page 406
Austenitic carbon steel
Martensitic carbon steel
Ferritic carbon steel
Cementite carbon steel