P91 steel and 316LN austenitic stainless steel are extensively used in the nuclear power plants, and their dissimilar combination of weld joint is inevitable.

In the present study, creep studies at 823K on the dissimilar metal weld joints (DMWJ) of P91 steel-Alloy800- 316LN SS (tri metallic joint-TMJ), P91 steel-316LN SS and P91BN steel-316LN SS have been carried out in the applied stress range of 320-180 MPa.

All the weld joints under creep exposure were ruptured prematurely as compared to the base metal. TMJ has exhibited higher creep life than the P91-316LN SS and P91BN-316LN SS joints at higher stress.

The differences in creep rupture life between the TMJ and P91 steel-316LN SS were higher at the higher stress level, however, rupture life of the both the joints were relatively comparable under lower applied stress.

P91BN-316LN SS joint has shown significantly higher creep rupture life than the TMJ and P91-316LN SS joint under longer creep exposure. The rupture location in the TMJ has shifted from P91 steel under higher stress level to the interface region which is P91 steel coarse grain heat affected zone (CGHAZ)-IN182 weld metal under lower applied stress.

The interface failure was accompanied extensively by lower ductility than the P91 steel region failure. Interface failure occurred early in the TMJ. Failure in the P91-316LN SS and P91BN-316LN SS joints were occurred in the P91 and P91BN steels region respectively over the investigated creep exposure.

The presence of boron in the P91BN steel and weld interface region resulted in increased microstructural stability causing delayed creep damage. The hardness, and microstructural investigations were carried out using optical and scanning electron microscope across the DMWJ to elucidate the causes for the premature failure of DMWJ.

This article is shared by T. Sakthivel and M. Vasudevan.