An austenitic high manganess heat resisting alloy was newly designed. Effects of phosphorus addition and two step cooling process from solution temperature on the microstructure of the alloy were investigated in order to improve creep rupture properties.
A small addition of phosphorus resulted in the uniform dispersion of fine carbide precipitates in the matrix and the removal of the precipitate free zone along grain boundaries.
Two step heat treatment brought out the serration of grain boundary which was very effective in the prevention of the formation and the growth of cracks or cavities at the grain boundaries.
It was found that the grain size was closely related to the rupture life, i.e., the maximum rupture life was achieved at the optimum grain size.
As the result of combined effects of phosphorus addition and grain boundary strengthening by the serration, the rupture life was improved remarkably up to ten times at 600℃ and 26 kg/㎟.
