Formation of nonmetallic inclusions in the carburization of steel by high- and low-ash reagents

Resumo

The solution of high-ash carburizing agents (dry-quenching dust, coke breeze) and low-ash agents (MU-95) in molten steel is studied. Relatively stable C–O and C–O–Fe complexes are formed on solution. When high-ash carburizing agents are introduced in the melt, the liberation of volatiles leads to decrease in their particle size, increase in the open pore volume, and faster exchange of carbon and iron between the phases. Carbon from low-ash carburizing agents dissolves mainly through the outer surface of the particles. The oxygen present forms C_xO_y complexes with the remaining carbon, on account of strong C–O bonds. Consequently, the assimilation rate of the carburizing agents is reduced. The solution of the inclusions may be accelerated by introducing optimal quantities of rare-earth elements that reduce the carbon–oxygen complexes.