1. Main quality problems of rolls

Produced φ 800 mm × 1880 mm high chromium cast iron roll (as shown in the figure), the core material is nodular cast iron, which is melted in the medium frequency furnace. The main quality problems of molten iron are:

(1) the bottom wave attenuation of X-ray flaw detection is ≤ 10% due to the shrinkage defect in the roll at a distance of 600~800 mm from the upper roll diameter section;

(2) Tensile strength of lower roll diameter ≤ 400 MPa;

(3) Poor spheroidization of roll diameter section.

2. Influencing factors

(1) When smelting nodular cast iron, the adverse effects of the interference elements Pb, Sb, as, B, etc. contained in the furnace charge can not be ignored. In order to ensure the quality of the roll, the measures of finishing are taken.

(2) The temperature of molten iron not only directly affects the mechanical properties, casting properties and processing properties of ductile iron, but also affects the chemical composition and purity of molten iron. When the temperature of molten iron exceeds the equilibrium temperature, the reaction sio2+2c=si+2co proceeds to the right, resulting in carbon reduction and silicon increase in molten iron, causing changes in roll performance; The corrosion of furnace lining intensifies, and the content of inclusions in molten iron increases, resulting in the tensile strength not meeting the requirements.

(3) The casting and riser system failed to achieve sequential solidification, resulting in the shrinkage and looseness of the upper part of the nodular cast iron roll.