Melting process of large nodular cast iron roll

1. Selection of raw materials

High quality raw materials are required for the production of as Cast High Toughness Nodular Cast iron. Generally, high-purity pig iron with low manganese, low phosphorus and low sulfur shall be selected. In particular, the content of impurity elements such as Ti, V, Cr, Pb, Sn, as and B shall be seriously controlled. The sum of mass fractions of trace elements shall not be greater than 0.06%

Carbon scrap with stable composition shall be used, and the scrap used shall be sampled for spectral analysis, inspection and control ω (Mn)≤0.30%, ω (Ti)<0.030%.

2. Spheroidizing treatment

It is generally believed that in the production of thick and large section ductile iron castings, compared with light rare earth, heavy rare earth has stronger anti spheroidizing recession effect. Therefore, yttrium based heavy rare earth spheroidizing agent is advocated in thick and large section ductile iron. However, there are different opinions. It is considered that the anti spheroidization decline effect of heavy rare earth is not stronger than that of light rare earth below 1300 ℃. Considering that the wall thickness of the roll body is not too large, an empirical method is adopted to mix heavy rare earth and light rare earth in a certain proportion, and the mass fraction is controlled at 1.3% ~ 1.4%.

Spheroidization was carried out by impulse method. The discharging temperature of molten iron shall be controlled at 1430 ℃ ~ 1450 ℃ to prevent serious burning loss of spheroidizing agent. In the process of operation, prevent the molten iron from reacting in advance. After the spheroidizing agent is put into the dam type molten iron ladle, the surface is covered with silicon steel sheet.

3. Inoculation treatment

Inoculation treatment is the key to liquid iron treatment of nodular cast iron. The inoculant adopts 75#, high calcium barium inoculant and three times inoculation method. The mass fraction of inoculant added for bottom inoculation is 0.2% ~ 0.3%, the mass fraction of inoculant added for flow inoculation is 0.4% ~ 0.5%, the mass fraction of inoculant added for instantaneous inoculation is 0.1% ~ 0.2%, and the mass fraction of total inoculant is controlled at 0.8% ~ 1.0%. Control the pouring temperature at 1350 ℃ ~ 1360 ℃.