13Crステンレス鋼の腐食疲労破面について

抄録

Fractographic analysis and surface observations were carried out by SEM to clarify the corrosion fatigue behavior of 13Cr stainless steel. Rotating bending fatigue tests with a speed of 3400rpm were conducted up to 10⁹ cycles in 0.03% NaCl aqueous solution.
Samll corrosion pits were found at the initiation region of fracture surface. The depth of these corrosion pits was 10∼20μm and was almost constant notwithstanding stress amplitude, which confirms the previous results⁵⁾ that the depth of corrosion pits is 10∼20μm and is almost constant notwithstanding NaCl contents (3∼3×10^-3%) in aqueous solution. Intercrystalline fracture was predominant in the propagation region. The percentage of intercrystalline fractures increased with decreasing stress amplitude. In the neighbourhood of the initiation region, the number of intercrystalline fractures was fewer than that in the propagation region. Corrosion pits and subcracks accompanied with corrosion pits were observed on the surface near the fracture path. Cracks were also seen on the surface of unbroken specimens subjected to the bending of more than 10⁹ cycles. It is considered that Cl^- concentration at the bottom of corrosion pits is one of the predominant factors to affect the corrosion fatigue behavior of 13Cr stainless steel in aquous solution containing Cl^-.