Method of Making Surface-Hardened Metal Shot

Author:  Yoshio Miyasaka et. al
Source:  US Patent 6,018,854
Doc ID:  2023012
Year of Publication:  2000
Abstract:  
When a shot having a hardness equal to or higher than a ferrous or nonferrous metal shot material is blasted against the surface of the metal shot material at a blasting speed of 80 m/s or above, the collision causes heat to be generated only in portions of the metal shot material against which the shot has collided. The temperature is raised in the vicinity of the surface of the metal shot material. Alternatively, the metal shot material may be blasted against a metal body having a hardness at least equal to that of the temperature of the metal shot material. In either case, the temperature in the vicinity of the surface of the metal shot material is increased to or above an A3 transformation temperature when the material is ferrous and is increased to or above a recrystallization temperature when the material is nonferrous. Subsequently, the metal shot material is quickly cooled. As a result, the metallurgical structure of the surface layer 20μ deep from the surface of the metal shot material is refined such that a highly hardened and tough structure is obtained. Part of the metal shot material and the shot is recovered and the recovered metal shot material and the shot are reblasted against unrecovered metal shot material and the shot, repeatedly.