Influence of Nitrogen and Nitride-Forming Elements on Properties of Boron-Treated Steel

Abstract

Microalloying has received increased attention in recent years. The aims of the study were to identify and to examine the influence of nitrogen concentration in steel and small additions of nitride-forming elements on the hardenability of a boron-treated manganese-vanadium steel 40GF-VI. The study has shown that the increase in nitrogen concentration from 0.004% to 0.015% increases the hardenability of steel. It was found that a small amount of titanium (about 0.02%) in steel with low concentration of nitrogen (0.004%) is sufficient to bind it to nitrides, which makes it possible to save the most of boron in an active state (in a solid solution). A residual amount of titanium and aluminum in the range of 0.015-0.020% of each in steel with nitrogen concentration in the range of 0.010-0.015%, which is typical of an electric arc melting steel, is insufficient to bind all nitrogen. As a result, a part of nitrogen is spent on the formation of boron nitrides, which reduces the effect of boron on the hardenability of manganese-vanadium steel microalloyed with boron. Some methods of protecting boron in steel are briefly described. The study has established that grain refinement is observed with increasing nitrogen content in steel. Introduction of boron, in absence of titanium, does not change the size of the austenite grain in the entire range of the investigated temperatures. The optimum combination of strength, plastic and ductility characteristics in steel microalloyed with boron and additives of aluminum and titanium was obtained.