Mn-Cr-B ばね鋼の疲労強度に及ぼすオースフォームの影響

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This work has been carried out for the purpose of obtaining more detailed information on the fatigue properties of ausformed Mn-Cr-B spring steel. The fatigue strength and the fracture behavior of the ausformed specimens under completely reversed plane bending stress were compared with those of the conventionally heat-treated specimens tempered to the approximately same hardness. The results obtained are as follows : (1) The endurance limit of the ausformed steel increases by about 8 to 9 percent on the average from that of specimens heat-treated normally. The strength of the former at 10^6 cycles is also higher than that of the latter. (2) The results of fractographic examination of the specimens fractured at higher stress levels show that the fracture surfaces of the conventionally heat treated specimens exhibit the dimple pattern, while the fracture surfaces of the ausformed specimens are mostly occupied by the featureless flat area. This difference in pattern of the fractographs between the conventionally treated specimen and the ausformed specimen suggests that the improvement of the fatigue strength by ausforming is closely related to the decrease in the rate of fatigue crack propagation. (3) The carbides in the ausformed steel are dispersed very densely in comparison with those in the conventionally heat treated specimens, and the endurance limit σ_w is approximately related to the mean-free path of carbide λby the equation : σ_w=σ_<wo>+C λ^<-1/2> As the results of this experiment, σ_<wo>≒8 kg/mm^2 and C≒0.6 (kg/mm^2) mm^<1/2> were obtained.
社団法人日本材料学会の論文
1973-04-15

Mn-Cr-B ばね鋼の疲労強度に及ぼすオースフォームの影響

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