The use of CaO-CaF2 as an effective desulfurizer

Ductile iron or Modular iron as it is commonly known is very sensitive to sulfur levels which require effective process control. The control of the base sulfur is a key parameter if the proper ductile structure is to be produced in the casting. Sulfur control can be accomplished by various methods using different types of chemical materials. One of the methods of desulfurization used in the early production of ductile iron was the use of excess Magnesium which reacted with the sulfur and also produced the required microstructure in the casting. This is a very costly method of producing ductile iron because of the high cost Magnesium alloy. Manufacturers started experimenting with different processes using different materials to accomplish the task of producing low sulfur base iron at a lower cost. The use of Calcium Carbide was utilized to desulfurize base iron to desired sulfur levels. This material is a very effective desulfurizer, however when in contact with water, acetylene gas will form which creates a potential safety hazard. A large Automotive manufacturer started experimenting with Calcium Oxide(CaO) blended with Calcium Fluoride(CaF2)) for the purpose of desulfurization. The results produced low sulfur base iron, while reducing the potential safety problems associated with the use of CaC2 (Calcium Carbide). The use of CaO-CaF2 provides a low cost process for the desulfurization of base iron. This paper will explain the key process control factors that have to be implemented in order to use this material.