Abstract
The low-temperature sensitization (LTS) behavior of weld heat-affected zones (HAZ) of stainless steels is very important for predicting their susceptibility to intergranular stress corrosion cracking (IGSCC) in boiling water reactor (BWR) environments during their service life. Studies of LTS were carried out on regular stainless steels such as Types 304, 304L, 316 and 316L, and nuclear grade (NG) stainless steels such as Types 304NG, 316NG and 347NG. The weld HAZ of Type 304 stainless steel was sensitized by low-temperature heat treatment, being susceptible to intergranular corrosion and IGSCC. The LTS of the weld HAZ of Type 304 stainless steel was controlled by chromium diffusion, the activation energy for which was 38. 6 kcal/mol, lower than the value for the base metal. The weld HAZ of Type 316 stainless steel was less susceptible to LTS than 304 stainless steel owing to the effect of molybdenum alloyed in the steel. Types 304NG, 316NG and 347NG stainless steels were practically immune to LTS, because they contained no chromium carbide from welding and subsequent low-temperature heat treatments.
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