滲炭表面硬化した鋼の疲労き裂の進展について

概要

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The rotating bending fatigue tests were performed on the notched carburized steel specimen at room temperature, and their properties of fatigue crack propagation were investigated. Furthermore, the relation between fatigue crack behaviours and microscopic structure was discussed. All the SCM21 specimens were carburized at 930℃, under 0.9% carbon potential atmosphere for 4 hrs, and oil-quenched from 830℃. Tempering was carried out at 180℃ for 2 hrs. The results obtained are as follows. (1) The non-propagating crack was observed at 10^7 cycles in the case of SCM21 carburized steel. The maximum notch radius of ρ=0.1 mm to 0.08 mm was essential for the existence of non-propagating cracks at 10^7 cycles. (2) In the case of ρ=0.08 mm, the crack propagation rate was almost constant or slightly decreasing during a considerable part of its life. That tendency could be understood by considering the distribution of compressive residual stress in the surface layer. (3) In the case of ρ=0.5 mm, the crack propagation rate increased proportionally to the crack length. (4) In the case of ρ=0.08 mm, the fatigue crack initiated at the grain boundary of prior austenite. It propagated along the grain boundaries of prior austenite at a high stress amplitude level and through the grains of prior austenite at a low stress amplitude level.
社団法人日本材料学会の論文
1976-03-15