H₂SO₄-NaCl水溶液中における304鋼の粒界腐食速度に及ぼす予ひずみの影響

抄録

The effect of prestraining on intergranular corrosion rate was studied to clarify the relationship between the preferential dissolution of grain boundary and the dislocation density for 423 K prestrained 304 stainless steel in H₂SO₄-NaCl solution.
The intergranular corrosion was not observed on solution treated specimen but was observed on prestrained specimens in 1.0 kmol/m³ H₂SO₄-0.2 kmol/m³ NaCl solution at −330 mV(vs S.C.E.). Localized intergranular corrosion was especially observed in 2.5% prestrained specimen. The amount of strain in the grain interior was 10.1% determined by an image analysis computer for 6.8% prestrained specimen. The intergranular corrosion rate and the dissolution rate for austenite were determined from the slopes of curves plotting the depth of intergranular corrosion or dissolution as a function of time. These rates were found to increase with increasing prestrain, that is, the dislocation density in the specimen. The dislocation density in the grain boundary for the prestrained specimen was predicted from the relationship between the dissolution rate of austenite and the dislocation density by using the intergranular corrosion rate for the grain interior. The dislocation density in the grain boundary was increased with increasing the amount of strain and was indicated higher values than the dislocation density in the grain interior. These changes of dislocation density in the grain boundary and the grain interior for the amount of strain were corresponded to the reported result of the dislocation density which was determined by using transmission electron microscopy.
It is considered that the intergranular corrosion is induced by the preferential dissolution due to the dislocation pile-ups to the grain boundary in this material.