Study of the Effects of Stress-State and Strain-Rate

Study of the Effects of Stress-State and Strain-Rate on Constitutive Response of Polymer Gels via Experiments and Continuum Mechanics Modeling

In coming decade, the need of low pollutants (CO, CO2) and higher operating efficiency necessitate the application of creep strength enhanced martensitic (CSEM) steels in power plants and in fast breeder reactors. The dissimilar joining of the CSEM steels to austenitic steel is required in practical conditions based on end application requirements. The dissimilar joining of the CSEM steels with austenitic steel leads to number of problem including the formation of brittle intermetallic compound, formation of soft transaction heat affected zone along martensitic steel, delta ferrite formation in fusion zone, diffusion related problem and residual stresses which necessitates thorough study and qualification of welds. The selection of the filler metal is another important issue in dissimilar welds joint. The matching filler with martensitic plate mainly leads to the formation of the unwanted delta ferrite in weld fusion zone, heterogeneity across the welds joint and also needed the buttering layer of the filler across the stainless-steel side before the filler deposition (1,2). The heterogeneity across the dissimilar welded joint leads to premature Type IV cracking in soft inter-critical heat affected zone (ICHAZ) and rupture life of the welded joint was measured less as compared to the base joint (3). The SS grade filler leads the premature failure of the welded joint due to undesirable carbon and chromium diffusion and carbon and chromium depleted and enriched region along the dissimilar weld interface and unwanted sigma phase formation (4). Martensitic steels show the lower thermal expansion coefficient as compared to austenitic steel that results in generation of thermal stresses and premature failure of the dissimilar welded joint during the creep exposure.

To overcome the difference in thermal expansion coefficient and thermal conductivity of both the steels, buttering layer was also suggested in the previous research (5). However, to overcome the weldability issue and withstand such high temperature, nickel based super alloys fillers are being preferred. Parker and Stratford (4) reported that high temperature nickel based super alloy as a filler metal is quite helpful in retarding the local migration of C along the interface thus also stops the formation of localized C depleted and enriched region.