Application of Impression Creep Technique for Development of Creep Resistant Austenitic Stainless Steel

The present paper highlights the usefulness of impression creep technique as applicable to alloy development studies of a creep resistant austenitic stainless steel which has been used as structural material for Fast Breeder Reactors. The effect of nitrogen on creep deformation behavior of type 316LN stainless steel has been studied using impression creep testing technique. Impression creep tests have been carried out at 923 K on 316LN stainless steel containing 0.07, 0.11, 0.14, and 0.22 wt. % nitrogen, in the punching stress range of 472-760 MPa. The impression creep curves were characterized by a loading strain, a primary creep stage and a secondary creep stage similar to uniaxial creep curves. The tertiary stage observed in uniaxial creep curves was absent. The steady state impression velocity was found to increase with increasing punching stress. It was observed that impression velocity was sensitive to the variation in nitrogen content in the steel. Steady state impression velocity was found to decrease with increasing nitrogen content as was observed in conventional uniaxial creep tests. A good correlation between the impression creep test and the conventional creep test results was observed which demonstrates the applicability of impression creep testing technique for alloy development programme.