Figure 1 and Figure 2 show the microstructure of gray cast iron corroded by 4% Vol. nitric acid alcohol under three-dimensional digital microscope and scanning electron microscope respectively. Figure 3 shows the area ratio of pearlite in the matrix and the average lamellar spacing.
In Figure 1, the bright white area is ferrite. It can be clearly seen that the matrix structure of all gray cast iron samples is ferrite + pearlite. It can be seen from Fig. 3 that the pearlite content generally decreases with the increase of molybdenum content. The proportion of pearlite in gray cast iron sample decreases from 95.01% of reference gray cast iron sample S1 (0.034% Mo) to about 89.85% of S4 (0.77% Mo).
From the pearlite lamellar spacing in Figure 2, the pearlite lamellar spacing decreases significantly with the increase of molybdenum content in gray cast iron samples. Figure 3 randomly counts the average pearlite layer spacing of 50 continuous fields of view with magnification of 3000 times. It can be seen that the average pearlite layer spacing decreases from 395 nm of reference gray cast iron sample S1 (0.034% Mo) to 229 nm of S4 (0.77% Mo).