ZIG-ZAG GRAIN BOUNDARIES AND STRENGTH OF HEAT RESISTING ALLOYS.

Abstract

Zig-zag grain boundaries with coarse carbides can remarkably increase the rupture strength by increasing the critical hardness as a result of preventing the formation and the growth of cracks and cavities along grain boundaries. The combination of zig-zag grain boundaries and high hardness is quite beneficial to improve the rupture strength and for this purpose, two step cooling process, i. e. , direct furnace cooling to about 900 degree C after solution heating followed by rapid cooling, is very effective for both Fe base and Ni base superalloys. For Ni base superalloy containing low carbon, however, directly aging treatment to about 900 degree C is more useful than two step cooling process.