Contribution to the Metallurgy of Cokeless Gas-fired Cupola and Coke Cupola

摘要

About 2/3 of the total amount of grey (lamellar) cast iron, spheroidal graphite cast iron and malleable cast iron in Germany are produced with the cupola furnace, 1/3 with the induction furnace. The main constituent of the charge is steel scrap followed by returns, pig iron, scrap iron and ferro-alloys. The increasing variety of the alloying and micro-alloying elements used with steel indicates the problem and the task, to transfer unwanted elements to the slag and to keep the desired ones within the melt. In order to meet these requirements, at first the basic relations of the metal-slag reactions must be known, in our case for melting in the cokeless natural gas-fired cupola furnace and in the coke cupola furnace. The metallic melting losses in a cokeless natural gas-fired test cupola furnace are very different: up to about 1 wt. % Fe, 1 to 10 wt. % C, 15 to 35 wt. % Si and 10 to 55 wt. % Mn. These melting losses contribute about 15 % to the total heat requirement of the furnace. The FeO content, the degree of the slag basicity and the temperature significantly influence the MnO and SiO_2 content of the slag and therefore the Mn and Si content of the base iron. These relations are also valid for the coke-fired' cupola furnace. FeO is reduced by Mn and MnO by Si. The MnO reduction by Si, the desulphurisation with CaO and the carbon pick-up increase with increasing slag basicity, similarly to the conditions in the blast furnace. Fundamental importance for all Fe-C-Si alloys has the crucible steel reaction: the SiO_2-reduction by carbon. Special interest is given to the interrelation between bath temperature and equilibrium temperature. Bath temperatures below the equilibrium temperature promote the melting loss of silicon. Bath temperatures above the equilibrium temperature increase the silicon content in the melt. Rising bath temperatures reduce the melting loss. Higher silicon contents increase the equilibrium temperature, higher carbon contents decrease it. In order to operate reasonably concerning metallurgy and costs, special interest should be given to the metal-slag reactions. The results of our investigations about oxidation and reduction processes in both cupola types are reported.