NOTCH TOUGHNESS AND RETAINED AUSTENITE IN SYNTHETIC HAZ OF 9% Ni STEEL.

There was a fairly good correlation between the amount of retained austenite and toughness. However, when grains were coarsened by the primary thermal cycle, toughness was no longer improved unless the secondary thermal cycle was above 800 degree C. This secondary thermal cycle resulted in grain refinement and the formation of an enriched zone of alloying elements where stable austenite precipitated in a third thermal cycle, mainly, at prior austenite grain boundaries.