Deboronization Phenomena in Surface Layer of Steel with Carburizing Process

Abstract

As the loss of boron from surface layer of steel during austenitizing should diminish from its beneficial effect, the authors investigated the characteristics of B-treated steel in view of practical effectscaused in the deboronization with the carburizing.
First of all, the deboronization appeared with the decrease of the amount of effective B and the increase of the amount of ineffective B in the sense that itbecomes so remarkable while carburizing depth becomes deep, and the loss of effective B from carburizing surface brings about following changes on the hardness distribution of carburizing layer;
1. As boron available for the decrease of the amount of retained austenite is lost, the lowering of hardness occurs in the outer part of carburizing layer.
2. As the benefit of increasing hardenability by boron is lost, the practical hardening depth becomes remarkably thiner under the slow cooling condition, which is due to the large size of sample.
Of course it would be possible to diminish these failures with the increase of previously contained amount of boron, but it would be impossible to eliminate the disadvantage that the amount of ineffective B-compound increases on the surface layer.
To summarize, therefore, the characteristics of B-treated steel is in similar with higher alloy steel not containing boron which is used in small carburizing part with the thin hardening depth, to which unfavorable effect by the deboronization is ignored.