Method for improving purity degree of nodular cast iron smelting molten iron

The invention relates to a method for improving the purity degree of nodular cast iron smelting molten iron. The method comprises the steps that firstly, proportion determining is conducted, and the waste steel and pig iron smelting raw material proportion is determined; secondly, component detection is conducted, and chemical components of to-be-smelted waste steel are determined; thirdly, parameter calculation is conducted, and the temperature of an overheated zone and the iron discharging temperature are determined according to the chemical components of the smelted waste steel and the smelting raw material proportion; fourthly, sample trial smelting is conducted, and detection samples are manufactured according to the temperature of the overheated zone and the iron discharging temperature; fifthly, different heating rates are adopted, and crystalline phase analysis of the multiple detection samples obtained in the fourth step is repeatedly conducted; sixthly, according to the crystalline phase analysis of