carbon phosphorus and sulfur influence of ductile iron
The chemical composition of ductile iron mainly includes five elements, carbon, silicon, manganese, sulfur and phosphorus. For some castings with special requirements on structure and performance, it also includes a small amount of alloying elements. In order to ensure the spheroidization of graphite, ductile iron must also contain Traces of residual spheroidizing elements.
Today Anyang Huatuo Metallurgy share details description of carbon,phosphorus and sulfur in ductile iron and the influence of their content on performance:
1.Carbon: Carbon is the basic element of ductile iron, high carbon helps graphitization.Since the influence of graphite on mechanical properties has been reduced to a minimum after the graphite is spherical, the carbon content of ductile iron is generally high, between 3.5 and 3.9%, and the carbon equivalent is between 4.1 and 4.7%.When the casting wall is thin, the residual spheroidizing element is large or the inoculation is insufficient, take the upper limit; otherwise, take the lower limit.For ductile iron, selecting the carbon equivalent near the eutectic point can improve the fluidity of the molten iron, and the increase in the carbon equivalent will also improve the self-feeding ability of the molten iron due to the increased graphitization expansion during solidification of the cast iron. However, too high carbon content can cause graphite to float.
2.Sulfur: Sulfur is an anti-spheroidizing element. It has a strong affinity with spheroidizing elements such as magnesium and rare earth. The presence of sulfur will consume a large amount of spheroidizing elements in molten iron, forming sulfides of magnesium and rare earth, causing slag inclusion. , Casting defects such as pores. The content of sulfur in ductile iron is generally required to be less than 0.06%.For the gray cast iron, when the sulfur reach 0.06-0.1%, it can improve the cutting performance and inoculation of cast iron.
3.Phosphorus:Phosphorus is a harmful element. Its solubility in cast iron is extremely low, and when its content is less than 0.05%, it dissolves in the matrix and has little effect on mechanical properties. Phosphorus increases the ductile-brittle transition temperature of cast iron, and when the phosphorus content increases, the ductile-brittle transition temperature will increase.
In generally, the foundry factory need to keep suitable content of sulfur and phosphorus and carbon then promise to produce qualified ductile iron.