凹槽效應對AISI 347不銹鋼腐蝕疲勞性質之影響

Notch Effect on the Corrosion Fatigue Properties of AISI 347 Stainless Steel

本研究主旨在探討凹槽效應對AISI 347不銹鋼腐高週腐蝕疲勞性質之影響。實驗結果顯示，AISI 347不銹鋼之不同形狀試棒，在空氣及四種水溶液中之高週疲勞壽命皆有隨應力集中因子的增加而減少之趨勢，而腐蝕環境中之缺口敏感度以純水及鹽水加抑制劑較高。分別比較平滑試棒與半圓形凹槽試棒之各環境間應力–壽命曲線，各曲線有清楚差異，由高至低依序為空氣、鹽水加抑制劑、純水、鹽水與H2SO4水溶液。V形凹槽試棒之應力–壽命曲線圖則分為兩群，空氣與鹽水加抑制劑為一群，而另一群為純水、鹽水及H2SO4水溶液，此現象主要是因V形凹槽試棒的局部酸化程度比半圓形凹槽試棒嚴重所造成。本研究利用最大應力、應力範圍和最大應力體積或最大應力表面積為整合參數，求得一涵蓋凹槽效應之通用疲勞評估模式，對不同環境下之不同形狀試棒的高疲勞壽命有良好的描述性。

The aim of this study is to investigate the influence of notch effect on the high-cycle corrosion fatigue properties of AISI 347 stainless steel in various environments, namely, air, water, NaCl, NaCl plus inhibitor, and H2SO4 solutions. Results showed that the fatigue lives in various specimen geometries tested in air and four aqueous environments were decreased with increasing stress concentration factor, and the fatigue notch sensitivity among the given corrosion environments was higher in water and 3.5% NaCl solution added with inhibitor. For smooth and semi-circular notch specimens, the rank of fatigue strength in all of the given environments took the following order: air > salt water plus inhibitor > water > salt water > sulfuric acid solution. For V-notch specimens, the S-N curves were separated into two groups; i.e., one group with air and 3.5% NaCl plus inhibitor and the other with water, 3.5% NaCl and H2SO4. This was attributed to a greater effect of localized acidification occurring at the root of a V-notch as compared to a smooth shape and semi-circular notch. A parameter incorporating with the maximum stress, stress amplitude and highly stressed volume (or area) was introduced and well correlated with the fatigue life of various specimen geometries in the given environments.