GRAIN BOUNDARY SEGREGATION OF IMPURITY AND ALLOYING ELEMENTS IN LOW CARBON STEELS.

In relation to temper brittleness of low carbon steels, the segregation of impurities such as phosphorus and nitrogen and some alloying elements to grain boundary was investigated by Auger electron spectroscopy. Two types of segregation behavior at the embrittlement temperature were observed. One is influenced by austenitizing conditions; the other one shows little effect. Nitrogen belongs to the former and phosphorus to the latter. Nitrogen is harmful when quenched-in from high austenite temperatures, since it segregates to the prior austenite grain boundaries at the temperature of temper-embrittlement. This behavior can be correlated with the increase in ductile-brittle transition temperature of Charpy impact tests.