Work hardening, sensitization, and potential effects on the susceptibility to crack initiation of 316L stainless steel in BWR environment

After CBB testing, the structure and composition of surface oxide films on austenitic stainless steels in high-temperature water were examined by changing the metallurgical conditions in alloys and the concentration of dissolved oxygen and dissolved hydrogen in high-temperature water. SEM, X-ray diffraction, and Auger electron spectroscopy revealed that the water chemistry played a major role in the formation of the oxide film and in the crack initiation. The oxide film is composed of an outer layer formed with hematite and magnetite and an inner layer corresponding to the transition oxide/substrate, which is Cr-rich and Ni-rich. Dissolved hydrogen conditions reduced the thickness of the oxide and increased its nickel content. Dissolved oxygen conditions promoted the formation of numerous and bigger cracks compared with dissolved hydrogen conditions. Environmental conditions are preponderant compared with metallurgical conditions. (author)