17Cr-11Niステンレス鋼の応力腐食割れ破断寿命の確率分布

抄録

Probability distribution of failure times of stress corrosion cracking of 17Cr-11Ni stainless steel under constant stresses of 5 to 30 kg/mm² in 25%, 35%, and 45% MgCl₂ solutions at their boiling temperature has been analysed by using the Weibull probability paper which is widely used in reliability engineering. Probability distribution of failure times was found to be described as single or composite Weibull distributions. The composite distribution consisting of mode 1 and mode 2 distributions is found at the low stress conditions. Mode 1 is observed at the earlier failure time region and its shape parameter is larger than unity, depending on the stress and temperature examined. On the other hand, the shape parameter of mode 2 which is observed in the latter region of failure times shows almost a constant value of unity. The condition which gives the shape parameter of unity is likely to correspond to a chance failure or random occurence of crack initiation, while the shape parameter larger than unity indicates a wearout failure which seems to correspond to crack propagation. Thus, the type of distribution of failure times is likely to connect with the failure mode, i.e., crack initiation or propagation.