Evaluation of creep deformation behaviour of different microstuctural zones of 316LN SS weld joint using impression creep testing technique

Abstract

Impression creep technique, which uses flat ended cylindrical indenter, is an attractive material non-invasive technique for evaluating creep properties as it enables probing small volume of material and requires short time for testing. The present investigation discusses the application of impression creep technique for characterising the creep behaviour of different microstructural regions in a high nitrogen grade of 316LN SS weld joint. Impression creep tests were carried out at 923 K on the weld metal, the base metal and the heat-affected zone in 316LN SS weld joint. The impression creep curves exhibited the first two characteristic stages of the creep processes, namely, a primary creep stage and a secondary creep stage. The rate at which the cylindrical flat punch penetrated into the test specimen was controlled by the time dependence of the movement of the material underneath the punch. The weld metal, the base metal and the heat affected zone exhibited distinct creep behaviour. The difference in creep behaviour of each zone was correlated with the difference in microstructure and morphology of the weld joint. A comparison was made between the data obtained from impression creep tests and from independent uniaxial creep tests on the weld metal and the base metal. A good correlation was established between impression creep and uniaxial creep results.