EVALUATION OF TOUGHNESS DETERIRATION BY AN ELECTROCHEMICAL METHOD IN AN ISOTHERMALLY-AGED N-CONTAINING AUSTENITIC STAINLESS STEEL

This work shows the evaluation of the cryogenic toughness deterioration by means of an electrochemical method in a N-containing austenitic stainless steel aged at temperatures of 700, 800 and 900 degrees C for times from 10 to 1000 minutes. The aging process at 700 and 800 degrees C caused the decrease in the Charpy V-Notch impact energy at -196 degrees C because Of the intergranular precipitation of carbides. The scanning electron microscope fractographs of the Charpy V-Notch test specimens showed the presence of intergranular brittle fracture. The degree of sensitization was determined by the ratio of the maximum density current generated by the reactivation scan to that of the anodic scan, I(r)/I(a) using the double-loop electrochemical potentiokinetic reactivation test. The Charpy V-Notch impact energy decreased with the increase in the I(r)/I(a) ratio. This relation enables to estimate the deterioration of cryogenic toughness because of the thermal aging in this type of steel.