高強度鋼のSCCき裂進展に及ぼす応力繰返し速度・波形効果と粒界・粒内破面の自動判別

概要

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Software for the automatic extraction of intergranular failures from a mixed mode of inter-granular and transgranular ones is developed based upon computer image processing and pattern recongnition techniques. Without human assistance, calculations of intergranular fracture area fractions can be done quickly and accurately by computing co-occurrence matrices. Using this technique, the influences of stress cycle frequency on dynamic SCC crack growth, and those of stress wave form on cyclic SCC crack growth are investigated in a high-strength steel, 300M (σ_B=1310 MPa) , sentitive to hydrogen embrittlement type SCC. At higher stress cycle frequencies of f≧30 Hz, threshold values, K_<DSCC>, are smaller than the static SCC threshold, K_<ISCC>. However, at lower stress cycle frequencies of f≦5 Hz, the repassivation of oxide films becomes dominant, resulting in an increase in K_<DSCC> up to K_<ISCC>. Threshold values for cyclic SCC crack growth are independent of stress wave form, including superimposed waves. At intermediate stress intensity factor ranges, however, crack growth rates increase with increasing stress rise time. In the case of a superimposed wave, a negative pulse wave with a superposition of small vibratory stresses, crack growth rates are much accelerated by promoted dissolution at the crack tips.
一般社団法人日本機械学会の論文
1988-04-25