マルチ・マイクロプローブ直流電位差法によるオーステナイト系ステンレス鋼316Lのクリープ余寿命予測

抄録

The present authors have proposed a new DC potential difference method using multi-microprobes and showed that the method can successfully make the residual life prediction for high temperature fatigue of an austenitic stainless steel JIS SUS 316L at high temperatures of 765 to 873 K where multiple-site small cracks cause fatigue fracture. In the present paper, the proposed DC potential difference method was applied to the residual creep life prediction of the stainless steel. Unlike the high temperature fatigue of SUS 316L steel, the standard deviation of the normalized potential difference σ_V did not show remarkable change in creep at 873 K, whereas the average potential difference showed sudden rise at a creep life fraction of t/t_r=0.9. During creep at 948 K, however, the σ_V value showed sudden increase at t/t_r=0.8 as in the case of the fatigue of SUS 316L. These results were brought about by different rupture mechanisms; i.e., creep rupture caused by necking or localized deformation and that by multiple-site cracks. Necking developed rapidly and brought about potential difference increase at the later stage of creep at 873 K, whereas, at 948 K, multiple-site cracking occurred and brought about large spatial variation in electric resistance, and hence the sudden increase in the standard deviation of the potential difference in the later stage of creep. The proposed DC potential difference method can make the residual life prediction either by detecting the onset of sudden increase in the average potential difference in creep where necking is the leading cause of creep rupture or by detecting the onset of sudden increase in the standard deviation of potential difference in creep where multiple-site cracks lead to rupture.