| This study examined the degree and the avoidable conditions of the intergranular sensitization on the commercial stainless steel(STS 304, 304L, 316, 316L) in the temperature range of 450℃ to 850℃. The electrochemical potentiokinetic reactivation test was used in detecting the degree of sensitization of STS 304, 304, 316 and 316L in an electrolyte which contained sulfuric acid with KSCN as an additive. On the isothermal sensitization process, the chief variables choosed the sensitizing temperatures (580, 650, 750, 800℃) and time of the isothermal hold (0.5, 1.0, 10, 24, 72 hr). In the case of isothermal heat treatment, the degree of sensitization was increased with the heat treating time as 580℃ and 650℃. but the degree of sensitization was derreased by long heat treating time at 730℃ and 800℃, because of a self-healing of the chromiume depleted zone. The degree of sensitization was reduced as the carbon content in the austenitic stainless steel decreased. The molybdenum in the austenitic stainless s eel increased the intergranular corrosion resistance. As continuously cooled from 1050℃ to 450℃, STS 304, 304L, and 316 were not sensitized at cooling rates faster than 5, 0.4, and 0.25℃/sec, respectively. as continuously cooled from different annealing temperature under constant cooling rate, the degree of sensitization was extremely served at 900℃ but decreased above 950℃. |
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