SNCM439鋼の応力腐食割れき裂成長に及ぼす結晶粒径の影響とフラクタル特性

概要

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Stress corrosion cracking tests were conducted in 3.5% NaCl solution by using SNCM439 steel specimens which have three different prior-austenite grain sizes, d=12, 78 and 172μm. The fracture surfaces obtained were analyzed from a viewpoint of fractal geometry The results obtained are summarized as follows: (1) The crack growth rate, da/dt, increased with increasing the stress intensity factor, K, and with decreasing prior-austenite grain size,d. (2) The grain boundary fracture area, φ, decreased with increasing K. At a given K level, φ increased with increasing d. (3) The profiles of stress corrosion cracks had the character of fractal. The relevant fractal dimension, D, was about 1.05 in the region c where the intergranular cracking was predominant, while it was aout 1.10 in the region b where the mixed feature of intergranular and transgranular cracking appeared. (4) The fractal analysis explained the dependence of da/dt on d.
1991-08-15