軟鋼の疲労強度に及ぼす表面加工 (旋削 圧延) の影響

The materials used in machine parts, especially, steels suffer almost always from machining. The effect of this machining on the mechanical properties of materials presents a serious problem, of which reinquiry is urgently required on account of the higher efficiency of machine parts that has been attaind in recent years. Therefore, in this paper the fatigue strength of the turned and the surface-rolled low carbon steels under the various machining conditions was examined, in order to clarify the relation between the fatigue strength and machining conditions, systematically. These results are discussed considering the work hardened surface layer. The main results are as follows:(1) The fatigue strength of the machined specimens increased by 10 to 20% for turning, and by 30 to 130% for surface-rolling, respectively, as compared with that of the annealed specimen.(2) The relation between the fatigue limit and the work hardened surface layer could be represented in the following equation.σ*=σ0[1+K{H(I.V.)}1/n/100], H(I.V.)=∫li0{H(l)-H0}dlwhere, σ* is the fatigue limit of the machined specimen including only the effect of the work hardened surface layer, σ0 is the fatigue limit of the annealed specimen, H(I.V.) is the integrated value of hardness increasing by work hardening, H(l) is Vickers hardness at the depth l from the surface of machined specimen, H0 is Vickers hardness of the annealed specimen, li is the depth of the work hardened surface layer, and K and n are constants depending upon the material, the machining method and the stress concentration factor of the specimen.