The influence of sulfur content on the composition of molten iron on the design of preshrinking process

For many foundries whose production mode is from cupola to induction furnace, there is also a running in process for sulfur composition control. In fact, the effect of adding sulfur in coke in cupola is equivalent to a continuous process of increasing sulfur in molten iron, so it is necessary to add desulfurizer to avoid the decrease of casting performance of molten iron due to the high sulfur content.

However, for the induction furnace, there is no source of sulfur increase during the soldering process, and sulfur and other alloy elements are easy to form sulfide and form slag floating on the surface of molten iron. In addition, the long time when the molten iron is heated away from the temperature during the electric furnace soldering leads to a large amount of melting of the nucleation grains with sulfide as the matrix, which results in the poor nucleation ability of the molten iron graphite and the increase of white mouth defects. Therefore, the control of sulfur content in the electric furnace is very important.

WMH. Moore of the United States believes that sulfur plays an important role in the iron smelting process by increasing the graphite crystal core. Most of these nuclei are ferruginous sulfide and iron sulfide.

At the same time, with the increase of sulfur content, the number of eutectic in gray iron also changes, which are the metallographic pictures of eutectic in gray iron with sulfur content of 0.021% and 0.102% and without inoculation. It can be seen that the eutectic number of the gray cast iron with sulfur content of 0.102% is obviously more than that of the gray cast iron with sulfur content of 0.021%. Therefore, the increase of sulfur content can promote the increase of eutectic number of gray cast iron.

Effect of sulfur content on mechanical properties of gray cast iron. Use test block as brira test cuvette shown. It can be seen that sulfur content can significantly affect the mechanical properties of gray cast iron. When the sulfur content is from 0.02% to 0067%, the tensile strength of gray cast iron increases at least 641mpa, and the hardness Hb can also increase more than 25%. However, when the sulfur content continues to increase, the tensile strength and hardness will not change.

In conclusion, when the sulfur content is controlled between 0.06% and 0.08%, the graphite morphology and mechanical properties of gray cast iron are the best, while the tendency of white cast iron is the least. Although beyond this range, the number of eutectic clusters in the cast iron structure continues to increase, which can continue to improve some mechanical properties of gray iron, but at the same time improve the shrinkage tendency of the casting.

Although the proper sulfur can reduce the tendency of white mouth and improve the mechanical properties of castings, the sulfur has a negative effect on the ability of crack prevention of castings. The effective crystal range of Fe FES in molten iron is enlarged. Thus, the hot cracking tendency of gray iron is increased. Therefore, for the easily cracked parts, the content of s in the castings is minimized.

Therefore, based on the above reasons, in order to ensure that the castings have sufficient mechanical properties and have a small tendency of shrinkage, the sulfur content of the castings that are not easy to crack is generally controlled at about 0.06% to 0.08%. For castings that are easy to crack, the sulfur content shall be minimized.

Scroll to Top