Evaluating Sensitized Chromium Steel Alloys with Induction Infrared Thermography

Abstract

A nondestructive evaluation (NDE) technique is presented that can detect sensitization in welded austenitic stainless steel components for 100% evaluation of in situ parts in real time during production or in service. The sensitization of austenitic stainless steels due to welding or heat treatment has mostly been eliminated by industry standards for manufacturing these alloys that require a carbon content well below the threshold at which sensitization would occur. Such alloys are especially important in naval applications because of their corrosion resistance. However, critical stainless steel components used in naval applications where component failure would be catastrophic are currently not allowed to be fabricated by welding because, until now, there has been no proven, efficient NDE method to verify that each weld in each stainless steel component has not been sensitized and thus weakened. In this study, induction infrared thermography (IIRT) was demonstrated to be an effective NDE tool for detecting sensitized steel in the heat-affected zone (HAZ) of welds in three types of stainless steel plate. The in situ IIRT scan results matched the conventional metallographic analysis of the HAZ in welds in samples of low-carbon 316L austenitic steel, high-carbon 440C martensitic steel, and high-carbon 301 austenitic steel.