Which element is considered harmful to molten ferrous metal in greater quantities?

The presence of sulfur in molten ferrous metal is considered harmful because it can lead to the formation of brittle iron sulfide compounds. This inherently compromises the mechanical properties of the final cast product, often resulting in reduced ductility and increased brittleness. When sulfur exceeds acceptable levels in cast iron or steel, it can make the material prone to cracking and failure under stress, significantly affecting the structural integrity and performance of components made from these metals.

Silicon, aluminum, and oxides can influence the properties of molten ferrous metals, but in controlled amounts, they can serve beneficial roles. Silicon is often used as a deoxidizer and can help improve castability, while aluminum can impart desirable qualities such as strength and corrosion resistance. Oxides, although typically undesirable, can sometimes be managed in lesser quantities without overwhelmingly detrimental effects on the material properties. In contrast, excessive sulfur is unequivocally detrimental, emphasizing why it's viewed as particularly harmful in greater quantities in molten ferrous metals.