Determination of the Degree of Sensitization in AISI 316 Stainless Steel by the Electrochemical Impedance Technique

One of the main problems with stainless steels is their sensitization during fabrication or conditions under which they are utilized. Thus determining the degree of sensitization (DOS) is very crucial. To change the DOS of the specimens، heat treatment was conducted at 500-800 for 24 h. In this paper the Double loop electrochemical potentiokinetic reactivation test (DLEPR) and anodic polarization tests were first conducted at 25 in a 0. 5 molar sulphuric acid containing 0. 01 molar KSCN for AISI 316 sensitized specimens، the potential range related to transpassive region of each specimen was determined. The electrochemical impedance test in the potentials related to this region and in the frequency range 0. 01-100000Hz was performed. The results were indicative of the presence of three different regions namely the anodic dissolution of the passive layer، dissolution of the grain boundaries and the occurrence of pitting corrosion due to the variations in the anodic potential. The healing effect was observed at the temperatures above 600 for this alloy. By performing the Electrochemical Impedance Spectroscopy (EIS) tests in the potentials related to the dissolution of the passive layer at the grain boundaries، the sensitization of the alloys was determined.