Influence of manganese on the impact transition temperature of as-rolled plain carbon–manganese steels

Abstract

The influence of manganese on the 50% fibre Charpy impact transition temperature of as-rolled low-silicon and silicon-killed steels has been examined. The steels were found to have similar grain-boundary carbide thicknesses so that the changes in the transition temperature could be related almost entirely to changes occurring in the ferrite. Whereas manganese had only a small influence on the transition temperature of silicon-killed steels, a very significant improvement occurred with low-silicon steels, a rise of 1% manganese causing an approximate 40°C lowering of the impact transition temperature after correcting to constant grain size and pearlite volume fraction. The decrease in transition temperature is believed to be due predominantly to the prevention of grain-boundary segregation of nitrogen by manganese, as is shown by the accompanying fall in k_y value and the lack of any increase in the hardness of ferrite grains close to their grain boundaries.