In solid cast iron, almost all silicon is solid soluble in austenite and ferrite, and does not enter carbide. Silicon atoms and iron atoms can be combined into siliceous ferrite with strong covalent bond, which not only promotes the formation of ferrite, but also enhances the ferrite.

In order to understand the ability of silicon to strengthen ferrite, in 1950s, foreign researchers added different amount of silicon into steel with carbon content of 0.1% and no other alloy elements, so as to compare the influence of silicon on mechanical properties. The results are shown in Table 1. In Table 1, the properties of carbon steel with all pearlite and without other alloy elements are also listed for comparison.

As for gray iron, because of the effect of flake graphite cutting matrix, the strength of cast iron is not high, and the elongation is not required generally; Besides, except for the low grade gray iron with little demand, the matrix structure is generally required to be pearlite. In order to obtain pearlite matrix, the silicon content in cast iron should not be too high. Therefore, the casting colleagues seldom notice the solid solution strengthening effect of silicon. Although the strength of gray iron is mainly controlled by controlling the shape and quantity of graphite and reducing the size of eutectic group, the effect of strengthening matrix structure is not negligible.