Abstract
An investigation was made of effect of cooling procedure after solution heating on the grain boundary reaction of austenitic heat resisting steels with high carbon and nitrogen contents, especially 21-4N steel. For cooling procedure after solution heating, water quenching, air cooling, furnace cooling and direct quenching were used.
It was found that the grain boundary reaction was considerably influenced by these cooling procedures. The grain boundary reaction occurred markedly during furnace cooling without the formation of general precipitates. The amount of grain boundary reaction occurring by ageing treatment decreased with increasing cooling rate from solution temperature, while the amount of general precipitation increased.
It was concluded from this results that general precipitation suppressed appreciably grain boundary reaction. This effect of cooling procedure was attributed to the fact that the dislocation density in specimens increased with increasing cooling rate, and that M23C6 precipitated preferentially on dislocations, and could not nucleate in the matrix homogeneously in 21-4N steel. Consequently it is implied that the grain boundary reaction predominates in specimens with low dislocation density, and general precipitation with high dislocation density.
