| 摘要 |
PROBLEM TO BE SOLVED: To improve the fatigue characteristics of a steel work by conducting shot peening treatment of the surface of the steel work with fine metal grain in a specific condition. SOLUTION: A shot peening treatment to project fine hard metal grain of 20 to 100μm grain size in the high velocity >=80m/sec making air or the other gas as a carrier is executed onto a valve spring of an engine or a coil spring of a clutch spring, etc., requiring the fatigue characteristics. In this case, the shot peening condition is regulated so that the surface temperature of untreated spring material is set between >=150 deg.C at which the cementite solubility is raised higher than at the room temperature and the temperature at which the restore recrystallization of steel and austenitizing are caused. Or by executing two step shot peeing treatment in advance of this shot peeing treatment, the shot grain of 100μm to 1.0mm is projected and the compression residual stress is added at the position of 0.05mm to 0.5mm depth from the work surface, thus the fatigue characteristics of the steel work is improved further effectively and largely. |
