Method for producing spheroidal graphite cast iron

Abstract

A method for producing high-purity spheroidal graphite cast iron. The method comprises at least the steps of pretreating the melt in a closed converter and adding an inocculant when casting it into the mold. The solubility of the substances formed during the pretreatment and during the addition of the inocculant an be adjusted. The nucleation in the melt and the solidification in the mold can be brought into conformity by coordinating the pretreatment and the addition of inocculant.

1 . A process for producing nodular cast iron, at least comprising the process steps of pretreatment with pure magnesium in a converter and an addition of inoculant during casting into the mold, characterized in that the solubility of the substances formed in the pretreatment and in the addition of inoculant is adjustable.  
     
     
         2 . The process for producing nodular cast iron as claimed in  claim 1 , characterized in that the pretreatment is carried out using a mixture or a compound of pure metallic magnesium with one or more metals from groups IIa and IIIa of the periodic system and with sulfur.  
     
     
         3 . The process for producing nodular cast iron as claimed in  claim 1  or  2 , characterized in that the quantity of an inoculant based on FeSi or CaSi which is added during casting into the mold is significantly lower, preferably four times lower, than the amount of the compounds or mixtures which form oxysulfides which is added in the pretreatment with magnesium.  
     
     
         4 . The process for producing nodular cast iron as claimed in one of  claims 1  to  3 , characterized in that the pretreatment is carried out using a mixture or a compound of pure metallic magnesium with sulfur and with Ca, Ba, La or rare earths, the mixture or compound forming oxysulfides by reacting with the molten metal.  
     
     
         5 . The process for producing nodular cast iron as claimed in one of  claims 1  to  4 , characterized in that during the subsequent addition of inoculant, the inoculant based on FeSi or CaSi contains Mg, Ca, Ba, Au, Ge, Bi, La or rare earths.  
     
     
         6 . The process for producing nodular cast iron as claimed in one of  claims 1  to  5 , characterized in that the oxysulfides formed have a grain size of 0.001 to 0.03 mm.  
     
     
         7 . The process for producing nodular cast iron as claimed in one of  claims 1  to  6 , characterized in that the oxysulfides formed have a relative density of 4000 to 6000 kg/m 3 .  
     
     
         8 . The process for producing nodular cast iron as claimed in one of  claims 1  to  7 , characterized in that the oxysulfides formed have a melting point of 1250 to 1550° C.  
     
     
         9 . The process for producing nodular cast iron as claimed in one of  claims 1  to  8 , characterized in that the specific number of nuclei of the oxysulfides formed is between 60 and 1200 mm −2 .  
     
     
         10 . The process for producing nodular cast iron as claimed in one of  claims 1  to  9 , characterized in that the compounds or mixtures used for the pretreatment are introduced into the molten material in the converter separately from the pure magnesium, joined or alloyed to the magnesium or embedded in the magnesium as a wire, as granules or in the form of a sandwich.  
     
     
         11 . The process for producing nodular cast iron as claimed in one of  claims 1  to  10 , characterized in that the amount and type of inoculants introduced during casting into the mold are matched to the amount and type of the compounds or mixtures with magnesium and sulfur forming oxysulfides which are introduced during the pretreatment in the converter.  
     
     
         12 . The process for producing nodular cast iron as claimed in one of  claims 1  to  11 , characterized in that the amount and type of the compounds or mixtures introduced during the pretreatment in the converter are selected in such a manner that there is no need to add inoculant during casting into the mold.