Abstract
Fatigue tests were conducted for a series of ultrafine grained steels comprising ferrite grains below 1μm. The base ultrafine grained steel contained 0.15% and the C added version contained 0.45% of carbon. 0.1% of phosohorus was added to the P added versions. For each ultrafine grained steels, as-rolled and annealed versions were prepared since the as-rolled version was work-hardened. As the result, tensile strength of the prepared ultrafine grained steels ranged from 721 to 1048 MPa. All of the prepared ultra fine grained steels showed high fatigue strength and the fatigue limit ratios (fatigue limit/tensile strength) exceeded 0.5. The faitigue strength of ultrafine grained steels was higher than that of ferrite-pearlite steels, and as high as that of tempered martensite steels.
