Structure Property CoRelationship during Creep of Dissimilar Weld Joint of 316LN Modified 9Cr1Mo Steels using Conventional and Miniaturized Sample Testing

Abstract

Ferritic-martensitic P91 steel and austenitic 316LN stainless steel (SS) dissimilar weld newlinejoints are extensively used in nuclear fast breeder reactors. The dissimilar welds so newlineformed are present at the junction of the heat exchanger units. Such weld joints newlineexperience severe temperature conditions and undergo creep deformation. Creep newlinecavitation phenomenon resulting at high temperatures, has been found to lead to Type-IV newlinecracking. Hence, it is important to study creep behavior of such weld joints to study the newlinedamage mechanism. newlineMicrostructural studies were carried out in the as-welded and post weld heat treatment newline(PWHT) condition. Various microstructural characterisation techniques such as optical newlinemicroscopy (OM), Scanning electron microscopy (SEM), Field Emission Gun-Scanning newlineelectron microscopy (FEG-SEM) and electron backscatter diffraction microscopy (EBSD) newlinewere employed. Microstructures showed the presence of prior austenitic grains with newlinemartensitic laths in P91 steel. The most widely M23C6 precipitates were observed which newlinecoarsened during the heat treatment conditions. EBSD characterization helped in newlineanalysing the strain accumulation inside the grains due to post weld heat treatment and newlinecreep exposure. newlineAutomated ball indentation (ABI) test was performed to evaluate the tensile properties newlineacross all weld regions. The tensile properties were measured at each condition of aswelded, newlinePWHT, and creep tested. A decrease in strength gradient from as-welded to newlinePWHT to creep tested was observed. Hardness values measured showed results matching newlinewith the ABI test results. This helped in understanding the weakest region, of the newlineweldment. newlineA static stress distribution along P91 steel HAZ was simulated using ABAQUS software newlineto study the creep behaviour at high temperature. Small punch creep testing, a newlineminiaturised specimen test, was used to estimate minimum creep rate and related newlineparameters for each region of P91 steel HAZ required for FE simulation. newlineCreep testing was carried out on dissimilar weld joint to evaluate its creep l