Patent ID: 7600556

Claim:
A surface treatment method of a casting die made of a steel material, said method comprising the steps of: applying a first shot peening treatment to at least a cavity surface of said casting die, so that a maximum height of roughness of said casting die is not more than 16 μm, and a compressive residual stress of said casting die is 1000 MPa or larger after the first shot peening and before a sulphonitriding treatment, applying a sulphonitriding treatment after applying said first shot peening treatment, and applying a second shot peening treatment after applying said sulphonitriding treatment to said at least the cavity surface of said casting die, so that a maximum height of roughness of said cavity surface is not more than 8 μm, and the compressive residual stress is larger than 1200 MPa after the second shot peening treatment, wherein each of said shot peening treatments is performed for a time period ranging from 5 seconds to 10 seconds.