Notch Toughness and Retained Austenite in Synthetic HAZ of 9% Ni Steel

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The effect of retained austenite on notch toughness in heat-affected zone (HAZ) of 9% nickel steel welds has been discussed in author's previous paper. In this paper, the above correlation and factors affecting the formation of retained austenite during welding process are investigated in more detail by using the simulation technique of weld HAZ. The obtained result indicates a noticeable effect of a peak temperature, in particular near 620℃ which is closer to A_<cc1> temperature (about 630℃), of secondary thermal cycle, after primary thermal cycle 850 to 1350℃, on the amount of retained austenite, but a lesser effect of other factors, such as heating and cooling rates, etc. on it. On the other hand, since the formation of globular austenite occurred rapidly and abundantly during heating process in welding, as compared with the ordinary heat treatment, there was a variation in the amount of the retained austenite in very short time if the peak temperature of tempering cycle was held. It was found that there was a fairly good correlation between the amount of retained austenite and toughness. When the grains, however, were remarkably coarsend by the primary thermal cycle similarly to that near weld bond, the toughness was no longer improved regardless of the amount of retained austenite, unless the secondary thermal cycle was above 800℃. This secondary thermal cycle resulted in the grain refinement and the formation of an enriched zone of alloying elements, where the stable austenite precipitated in 3rd thermal cycle, mainly, at prior austenite grain boundaries.
社団法人溶接学会の論文
1982-04-01

Notch Toughness and Retained Austenite in Synthetic HAZ of 9% Ni Steel

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