Effect of chemical composition (C, Si content) of molten iron on graphite morphology

Silicon, on the other hand, promotes the graphitization process, which together affects the growth and distribution of graphite.If the carbon equivalent (CE=C 0.3Si) is too low, the graphitization process is hindered, and cementite and white mouth structure are easy to form, resulting in hard and brittle castings that are difficult to process. If the carbon equivalent is too high, the graphite will be coarse and unevenly distributed, significantly reducing the strength and toughness of the casting. 

When the carbon equivalent is less than 4.0%, castings are prone to white mouth defects, especially in thin-walled areas, where rapid cooling exacerbates the problem of insufficient graphitization.On the contrary, if the carbon equivalent exceeds 4.3%, thick-walled castings are prone to the phenomenon of "graphite floating", and coarse flake graphite aggregation appears in the upper layer, which destroys the uniformity of the matrix structure.In actual production, the carbon equivalent of thin-walled castings (<10mm) should="" be="" controlled="" at="" and="" those="" of="" thick-walled="" castings="">30mm) should be kept at 4.0%~4.1%, while ensuring that the Si/C ratio is between 0.4~0.55.