超微細フェライト-セメンタイト組織鋼の疲労特性に及ぼす強化機構の影響(力学特性)

概要

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Fatigue tests were conducted using a series of ultrafine ferrite-cementite steels with the ferrite grain size below 1μm in order to investigate the effects of precipitation, solid solution and dislocation strengthening on the fatigue properties. Some steels contained 0.15% of carbon and others 0.45% to investigate the effects of precipitation strengthening since the carbon addition increased the number of cementite particle in case of the ultrafine ferrite-cementite steels. 0.1% of phosphorus was added to some steels to discuss the effects of solid solution strengthening. The effects of dislocation strengthening were investigated by comparing the as-rolled steels with the annealed versions. As the result, tensile strength of the prepared ultrafine ferrite-cementite steels ranged from 721 to 1048MPa. All of the prepared ultrafine ferrite-cementite steels showed high fatigue strength and the fatigue limit ratios (fatigue limit/tensile strength) exceeded 0.5. The fatigue strength of the ultrafine ferrite-cementite steels was higher than that of ferrite-pearlite steels, and as high as that of tempered martensite steels. In conclusion, all of the above strengthening mechanisms effectively improved the fatigue strength of the ultrafine ferrite-cementite steels. The reasons why the ultrafine ferrite-cementite steels stably showed high fatigue strength would be because the microstructures were not only ultrafine but also uniform.
2006-01-01