Relation between Hardenability and Segregation to Austenite Grain Boundaries of Boron Atom on Direct Quenching Process

Abstract

The effect of boron (B) on hardenability is explained by the decrease of boundary energy due to the segregation of B atoms to austenite grain boundaries. In this paper, the effect of niobium (Nb) on hardenability of B treated direct quenching steel is studied with varing the condition of B segregation to austenite boundaries. And it is clarified that the effect of B on hardenability is fully obtained even at unrecrystallized state of austenite, and that the maximum hardenability in direct quenching process can be attained at about 10 ppm soluble B which is about three times as the optimum ones of conventional reheat quenching process. It is concluded that the addition of 0.015% Nb rather give rise to the hardenability of B even in unrecrystallized state of austenite in direct quenching process because Nb hinders boundary migration of austenite and enables soluble B to segregate to the grain boundaries and deformation bands.