PSI - Issue 71

Ganesh Nigudage et al. / Procedia Structural Integrity 71 (2025) 218–225

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Fig. 7. Fracture surface of –(a), (b) as-fabricated condition; (c), (d) 1200h aged; (e), (f) 1800h aged .

3.6. Carbide distribution The volume fraction, size, morphology and distribution of precipitates have a strong effect on the mechanical properties of low alloy steels. The change in size distribution of carbides with thermal ageing was evaluated using high resolution SEM micrographs. The samples were etched using 2% Nital solution and then observed under SEM. Fig. 8 shows the SEM micrographs of carbides in RPV steel in as-fabricated, 1200h and 1800h thermal aged specimens. Carbides were seen along grain/packet boundaries and in the matrix. The average carbide size for as-fabricated specimen was 253 nm and for thermal aged specimen was 270 nm. Fig.9 shows the plot indicating change in number density of carbides with thermal ageing time. The density and size of the carbides did not change significantly during thermal ageing.