THE EFFECT OF GRAIN BOUNDARY CARBIDE CHARACTERISTICS ON THE IMPROVEMENT OF CREEP-FATIGUE PROPERTIES IN AISI 304 STAINLESS STEELS

摘要

The modification of carbide characteristics has been successfully made through grain boundary serration and its subsequent effect on the improvement of creep-fatigue life at 873K has been investigated, using AISI 304 stainless steels. It was found that the grain boundaries are considerably serrated when a specimen is furnace-cooled. The grain boundary serration leads to a change in the carbide characteristics as well as grain boundary configuration, i.e. the morphology of carbide from an acute triangular to a planar form and a lowered density. Additionally, an array of carbide particles is changed from a consistent to zigzag pattern, in terms of their preference to one grain between two neighboring grains to share the coherency. The improvement of creep-fatigue resistance is noticeably observed by the modification of carbides through grain boundary serration. This result is understood in light of that the modified carbides, whose interface energy is lower, have higher cavitation resistance, resulting in the retardation of cavity nucleation and growth to increase creep-fatigue life.