Stress corrosion cracking of stainless steels and nickel alloys in high-temperature water

Stress corrosion cracking (SCC) studies in stainless steels and nickel alloys reveal that all grades and conditions are susceptible to SCC in high-temperature water, whether deaerated or aerated, high H-2 or low, theoretical purity water or buffered/contaminated, lower temperature or higher. However, the kinetics of SCC growth vary enormously with stress intensity, yield strength, sensitization, water chemistry, irradiation, temperature, etc. The role of yield strength is especially important because it changes with surface cold work, bulk cold work, weld shrinkage strain, and irradiation hardening; the role of metallurgical strengthening mechanisms, e.g., nitrogen additions or precipitation hardening, may have a similar effect. SCC growth rate measurements were performed in high-temperature water on unsensitized stainless steels (and Alloy 600 [UNS N06600]) of various grades and compositions. Little effect of grade/heat of stainless steel, martensite content, or H-2 fugacity/permeation rate was observed, while large effects were observed for yield strength (cold work), stress intensity factor, corrosion potential, and temperature. A model "stainless steel" containing 5% Si (and elevated Ni and reduced Cr) showed high growth rates and little effect of corrosion potential or stress intensity factor.