The welding of nuclear grade P91 and P92 steel plate of thickness 5.2 mm were performed using the autogenous tungsten

inert gas (TIG) welding process. The welded joint of P91 and P92 steel plate were subjected to the varying post weld heat-treatment

(PWHT) including the post weld heat treatment (PWHT) and re-austenitizing based tempering (PWNT). A comparative study was

performed related to the microstructure evolution in fusion zone (FZ) of both the welded joint using the scanning electron microscope

and optical microscope in a different condition of heat treatment. The hardness test of the FZ for both joints was also conducted in

a different condition of heat treatment. P92 steel welded joint have observed the higher tendency of the δ ferrite formation that led

to the great variation in hardness of the P92 FZ. The homogeneous microstructure (absence of δ ferrite) and acceptable hardness

was observed after the PWNT treatment for both the welded joint.

In present work, two nuclear grade steel (P91, P92) are joined using the arc welding process. The welded joints were subjected to the heat treatment in order to restore the mechanical properties and overcome the heterogeneity across the joints. The weldments were studied for microstructure evolution and mechanical behavior under different condition of heat treatment. The variation in mechanical behavior obtained for the welded joints were tried to relate the microstructural evolution. After the normalizing based heat treatment, homogeneity with negligible δ ferrite across the welded joints was observed.

P92 steel is a modern martensitic heat-resistant steel currently used for seamless products for pressure equipment operating in supercritical operating parameters. The paper presents the results of a study on the strength properties and structure of a P92 steel welded joint used for pressure components of power units. The paper presents an assessment of the suitability for further operation of both the parent material and a circumferential similar welded joint of finished products in the form of P92 steel pipes after annealing for 3000 hours at 600 and 650°C. Annealing at 650°C results in faster increase in the size of the precipitates and their coagulation along grain boundaries of former austenite and martensite laths. The changes in mechanical properties were compared in relation to the state of the structure of the parent material and the material of the welded joint. Quantitative analysis of M₂₃C₆ precipitates was also carried out.