低温焼入による鋼の材質の変化について : 第8報鋼の時効硬化能と切欠疲労強度

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Having studied the fatigue strength of the low-temperature quenched carbon steel, we found that the strain-age hardening of ferrite played an important role in preventing the fatigue failure. It is natural that the high strength of hard material, which have great resistance against slip, should have high fatigue resistance, because the first stage of fatigue failure appears to proceed by particularly fine slips in individual crystals. But this criterion seems to be not always correct on the notch fatigue strength of the low-temperature quenched steel. The notch fatigue strength of the low-temperature quenched steels is greater, in spite of their low strength and hardness, than that of tempered ones, because of their high age-hardening power. Even though fine slips are produced by comparatively low repeated-stresses in the low-temperature quenched steel, whose ferrite has a high age-hardening power, the slipped region should be strengthened by strain-aging, and may endure the higher repeated-stress without fracture. This tendency is more remarkable in the sharp notched specimen, since the aging phenomenon is markedly accelerated by the high localized stress at the root of notch. The notch endurance limit of carbon steel for rotary bending fatigue was calculated on the basis of the strain-age hardening of ferrite, and the following formula was obtained, log(0.25-0.058α_k)+0.77log(1/η-1)=0.05ΔH_<max>-(2.04-0.169α_k), where α_k is the geometrical stress concentration factor, η is the notch sensitivity index, and ΔH_<max> is the age-hardening power of the ferrite and defined as the maximum increase in hardness caused by quench-aging at 100℃. Using the above formula, the notch fatigue limit of carbon steel can be calculated without the fatigue test, when the α_k, ΔH_<max> and also σ_w' (the endurance limit of plane specimen) are given. A fairly good agreement between the calculated and the observed endurance limlt is obtained. This agreement proves that the above theory is almost correct.
社団法人日本材料学会の論文
1959-02-15

低温焼入による鋼の材質の変化について : 第8報鋼の時効硬化能と切欠疲労強度

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低温焼入による鋼の材質の変化について : 第8報 鋼の時効硬化能と切欠疲労強度

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低温焼入による鋼の材質の変化について : 第8報鋼の時効硬化能と切欠疲労強度