The alloying treatment of cast iron can be traced back to the 1930s and 1940s. The alloying treatment has made a qualitative leap in the properties of cast iron. At the same time, some special purpose cast irons such as wear resistance, corrosion resistance and heat resistance have been born. The use of inoculation to produce cast iron was also produced during this period. In the late 1940s, cast iron with spherical graphite after inoculation replaced the usual flake graphite cast iron. We call this type of cast iron nodular cast iron.

The classification of spheroidization and despheroidization elements

Spheroidizing elements are generally divided into three groups according to their spheroidizing effect.

Despheroidizing elements: Sulfur and oxygen are common despheroidizing elements in cast iron. In addition, Ti, Al, B, As, Pb, Sn, Sb, Bi, Te, Se, etc. are common despheroidizing elements in molten iron . The attached table is classified according to its mechanism of action.

How to choose spheroidizing agent

Nodulizers and inoculants are the most important materials in the spheroidization process. In addition to stable quality, the following factors need to be considered when choosing a suitable nodulizer.

Sulfur content of raw iron liquid: If the sulfur content of the raw iron liquid is high, if the desulfurization treatment is not carried out, a high-magnesium, high-rare earth nodulizer is required, and the addition amount will be higher. The spheroidizing agent with low magnesium and rare earth can be used, and the added amount will be lower, and the cost of the spheroidizing agent with low magnesium and rare earth will be cheaper.

Different spheroidization methods

At present, the commonly used spheroidization methods are as follows: in-pack processing method (including straight-punching method, sandwich method and cover method), type inner spheroidization method, flow method, pure magnesium treatment process (including sub-packing method and core-packing method) Line method). The advantages and disadvantages of these spheroidization methods are briefly introduced as follows.

The attached picture compares various spheroidizing processes in terms of smoke, slag, and magnesium absorption rate..

Precautions for the production of ductile iron

Now briefly summarize the matters needing attention in the production of ductile iron.