Effects of Surface Finishing and High Vacuum Environment on Surface- and Interior-Originating Fatigue Properties of High Strength Steel.

Abstract

Uniaxial tension fatigue tests were carried out in air and high vacuum environments using pieces made of high strength steel (SNCM 439) with various finishing conditions. Based on the results of fatigue tests and the data arranged by the initial stress intensity factor range (ΔKini), (i) effects of surface finishing and high vacuum environment on surface- and interior-originating fatigue properties, (ii) effects of high vacuum and inner environment of materials on the growth limit of the fatigue crack, were considered. The following results were obtained; (1) Interior-originating fractures were not affected by surface finishing conditions and surrounding environments. (2) The shape of the "Duplex S-N curve" depended on surface finishing conditions and surrounding environments. (3) Fatigue lives of surface-originating fractures in high vacuum and interior-originating fractures were much longer than surface-originating fractures in air. Surface cracks in high vacuum and interior cracks of materials grew from smaller defects whoseΔKini were lower than the growth limit of surface cracks in air. A lower growth limit of fatigue cracks and a longer fatigue life of interior-originating fractures were inferred from the effects of the inner environment of materials, which were similar to those of high vacuum environment.