オーステナイト系ステンレス鋼の腐食疲労に関する研究 (第5報)

表面圧延と焼ばめの影響

抄録

Surface rolling of the specimen was achieved by pressing screw and three hard rollors having 20mm diameter and 12mm contour radius, screw pressure of 100kg or 150kg being applied.
Fatigue strength was remarkably increased both in the corrosive environments and in air by surface rolling, but the effect was more pronounced in corrosive environments than in air, and in case of stainless steel, much more improvement of endurance was attained for austenitic steel than for ferritic steel both in 5% H₂SO₄ saturated with air at 25°C and in air.
In slightly corrosive environment, even mild steel showed as good improvement as that of austenitic stainless steel, however in highly corrosive environment dangerous downward S-N curves were exhibited.
It was postulated that improved endurance could predominantly be attributed to its suppressing effect against forming of hemispherical corrrosion pit, though residual compressive stress was favorable to prevent spreading fatigue fissures, and this interpretation was supported by micrographic examinations and potential measurements.
As a conclusion, general effects of surface rolling on corrosion fatigue, presumably, involve three ways; firstly in a corrosive environment in which a metal is fully protected by corrosion product or by passive film, more stress concentration would have been resulted which initiated fissures due to more predominant effect of rapid contraction of anodic area than effect of ready decrease of general corrosion, as was pointed out by Gould and Evans, and aggravated endurance would be resulted; secondly if a metal could be freely soluble, stress concentration also could be avoided and prolonged corrosion fatigue life would be temporarily, resulted; thirdly, if a corrosive medium offered marginal property to a metal, effective control against initiation of corrosion pit would be resulted, without causing dangerous stress concentration and the highest protection against corrosion fatigue could be attained.
Inferring from serious damage observed in shrink fitted austenitic stainless steel into hard steel, the same deterioration of corrosion fatigue would be expected in other cases of such cladding or overlaying.