Low cycle fatigue properties of modified 9Cr-1Mo ferritic martensitic steel weld joints in sodium environment

Abstract

Mod.9Cr-1Mo ferritic-martensitic steel is the material chosen for the steam generator of the Prototype Fast Breeder Reactor being built at Kalpakkam, India. The use of sodium as a heat transfer medium for Liquid Metal Fast Breeder Reactors (LMFBRs) necessitates a comprehensive understanding of the effects of dynamic sodium on the Low Cycle Fatigue (LCF) behaviour of structural components. Moreover welds being the weak links in any structure, it is necessary to evaluate the LCF behaviour of joints in sodium environment, more so in Mod.9Cr-1Mo steel because of the well established Type -IV cracking in this material. With this aim in view, a programme has been initiated to evaluate the LCF properties of weld joints of this steel in dynamic sodium environment. A facility has been developed in-house for mechanical property evaluation in dynamic sodium. LCF tests conducted in flowing sodium environment at 823 and 873 K showed a similar trend in cyclic stress response in air and sodium environments exhibiting a continuous cyclic softening behaviour. The fatigue lives are significantly improved in sodium environment when compared to the data obtained under identical testing conditions in air environment. The lack of oxidation in sodium environment is considered to be responsible for the delayed crack initiation and consequent increase in fatigue life. Comparison with RCC-MR code shows that the design curve based on air tests is conservative.

High Temperature, Low Cycle Fatigue Characterisation of P91 Weld and Heat Affected Zone Material

“…Sandhya et al [19] evaluated the HTLCF behaviour of modified 9Cr-1Mo weld joints, tested in air and dynamic sodium environment. The sodium environment resulted in increased fatigue life.…”

Cyclic plasticity of welded P91 material for simple and complex power plant connections

“…A number of authors have presented experimental results on the creep (including Type IV cracking), CF, low cycle fatigue (LCF) and TMF behaviour of P91 welded materials and simple welded joints [21][22][23][24][25][26][27][28]. Some work had been carried out by Fournier and co-workers [29], which emphasizes that creep-fatigue type loading will be caused by the repeated startstop intermittent operation cycle.…”

High Temperature, Low Cycle Fatigue Characterization of P91 Weld and Heat Affected Zone Material

“…It was also reported that the base material and the weld joint exhibited similar fatigue lives at 550 o C; however, at 600 o C lower lives were observed for the weld joints. Sandhya et al [19] evaluated the HTLCF behaviour of modified 9Cr-1Mo weld joints, tested in air and dynamic sodium environment. The sodium environment resulted in increased fatigue life.…”