Critical Cooling Rate of 18Cr-8Ni Stainless Steel for Sensitization and Subsequent Intergranular Stress Corrosion Cracking in High Temperature Water

Calculation of critical cooling rates for sensitization occurring in transient metal forming processes of austenitic stainless steel were carried out using isothermal time-temperature-sensitization curves. A series of 18Cr-8Ni stainless steels each containing a different level of carbon were melted and cooled at various rates from a solution annealing temperature. Two types of tests were run on these alloys to evaluate the degree of sensitization. One test was the 10% oxalic acid electrolytic etch test. The other technique was constant strain rate tests which were conducted at a strain rate of 5 x 10−4 minute−1 in aerated high temperature water containing 10 ppm chloride ions. A good correlation was found between both sets of tests results. Dual structures exhibited intergranular cracking. An actual critical cooling rate for sensitization and subsequent intergranular stress corrosion cracking (SCC) was located in the range between two calculated critical cooling rates.