Abstract
Combined effects of Si, P and Cu on stress corrosion cracking (SCC) of high purity 18Cr-14Ni steels in NaCl solutions were examined with 18Cr-14Ni-<0.1Si-yP-zCu steels (A) and 18Cr-14Ni-xSi-0.03P-1Cu steels (B). Repassivation potentials for crevice corrosion, ER, were measured at 80°C. Decreasing P content for A-series steels and increasing Si content for B-series steels made ER values less noble, while Cu content gave no significant effect on ER for both series steels. To predict any sensitivity to SCC for a steel, each SCC test was conducted under applied potential just above ER value determined for each steel. SCC tests in solutions up to 20% in NaCl concentration at 80°C showed that decreasing P content for A-series steels, increasing Si content for B-series steels and 1 or 2% Cu for both series steels were effective to avoid SCC in higher concentration of NaCl solutions. Critical temperature for SCC at and below which a steel would not suffer SCC was determined in 3% NaCl solution. The temperature became higher with decreasing P content and/or increasing Cu content for A-series steels. The critical temperature for the steel TS-8 with 0.006% P and 2% Cu was 130°C, which was markedly higher than that of 50°C for the steel TS-9 corresponding to type 304L steel. The critical temperature for B-series steels increased with increasing Si content, but did not exceed 120°C with Si content up to 2%.
