Structural analysis and intergranular corrosion tests of AISI 316L steel

Pure AISI 316L steel is investigated after solution heat treatment (1050°C/H₂O) and structural sensitization (650°C). Two quite different intergranular corrosion tests are used to determine the degree of structural sensitization due to the precipitation of secondary phases along the grain boundaries (mainly the M₂₃C₆ and σ-phase): the oxalic acid etch test and the electrochemical potentio-kinetic reactivation test. Generally, the dissolution of chromium-rich carbides (M₂₃C ₆) is provoked by oxalic acid etch tests, whereas the chromium-depleted zones, in the vicinity of chromium-rich carbides (M ₂₃C₆), are attacked by electrochemical potentio-kinetic reactivation tests. Both intergranular corrosion tests are used to determine the maximum degree of structural sensitization. Thus structural analysis by carbon replicas reveals the Laves phase, and both the M₂₃C₆ and (Cr,Mo)_x(Fe,Ni)_y phases. The results of intergranular corrosion tests are related to the findings of the structural analysis.