Effects of peak temperature of weld thermal cycle on the microstructure and mechanical properties in the IRHAZ of nuclear RPV steel weld

摘要

The microstructure and mechanical properties inthe intercritically-reheated heat-affected zone (IRHAZ) of an SA508 Cl.3 Mn-Mo-Ni reactor pressure vessel (RPV) steel have beeninvestigated systematically using the welding thermal cyclesimulated specimens. The double thermal cycles with varying peaktemperatures(Tp1, TP2) in the range 700~800℃ were applied tosimulate the various IRHAZs using a Gleeble 1500 thermalsimulator. The effect of post-weld heat treatment (PWHT) wasalso studied. The microstructures of the IRHAZs were mainlycomposed of bainite, martensite and tempered bainite. But thespecimens subjected to Tp1= TP2 = 750℃ (before PWHT) andsubjected to Tp1 = TP2 = 700℃ (after PWHT) showed lowesttoughness. The microstructural factors affecting toughness werediscussed with reference to the fraction of high carbon martensitefor the specimen before PWHT, and to the coarsened carbide andsoftened matrix for the specimen after PWHT.