H<SUB>2</SUB>SO<SUB>4</SUB>-NaCl溶液中におけるα′マルテンサイトと304鋼の溶解速度に及ぼす炭素量の影響

Abstract

Measurement of dissolution rates of prestrained austenite and α′ martensite of 304 stainless steel was done to study a role of carbon during plastic deformation in stress corrosion cracking.The dissolution rate of solution treated austenite of 18Cr-11Ni stainless steel was not affected by carbon contents but that of α′ martensite was decreased with increasing carbon content in a 2.5 kmol/m3 H2SO4-0.4 kmol/m3 NaCl solution. But the dissolution rate of prestrained austenite increased with increasing dislocation density and the dissolution rate of high carbon austenite showed a lower value than that of low carbon austenite at high dislocation density sites. In addition, the dissolution rate of α′ martensite existed on the extended line of the relationship between the dissolution rate and the dislocation density of austenite. Therefore, the preferential dissolution of α′ martensite is attributed to the high density of dislocations. On the other hand, EPMA linear analysis showed that Ni and Cr concentration were not changed but carbon was enriched on the surface of α′ martensite which held high dislocation density after the corrosion test.It is thought that carbon is enriched at the region of high dislocation density and it depresses the dissolution rates of high prestrained austenite and α′ martensite, and, therefore, the decrease of dissolution rates with carbon enrichment at slip steps or crack tips is one of the factors to decrease the stress corrosion cracking susceptibility.