Effect of inoculation treatment on Microstructure of experimental gray cast iron

The composition of the experimental gray cast iron and the types of inoculants added. By comparing and analyzing the effects of four inoculants on the microstructure and mechanical properties of the experimental gray cast iron, the appropriate inoculants that can meet the production conditions are selected. The calculation shows that the carbon equivalent of this group of gray cast iron is about 3.90% and the Si / C ratio is 0.59. The modifier used in this group of experimental gray cast iron is jf-1 modifier, and the addition amount of modifier is 0.6wt.%, Different inoculants are used for inoculation treatment, and the addition amount of inoculant is 0.4wt.%, Among them, sample a adopts the most widely used 75 ferrosilicon inoculant, and samples B, C and D adopt silicon zirconium inoculant, silicon zirconium aluminum inoculant and silicon zirconium manganese inoculant respectively.

1. Effect of inoculation treatment on graphite structure of experimental gray cast iron

(a1),(a2)sample A—75Si-Fe inoculation treatment;
(b1),(b2)sample B—Zr-Si inoculation treatment;

Figure 1 shows the graphite microstructure of experimental gray cast iron. It can be seen from the figure that the morphological characteristics of graphite structure will be different after inoculating the experimental gray cast iron with different inoculants. In terms of size and uniformity of graphite: in sample a inoculated with 75 ferrosilicon inoculant, there are more large-size massive graphite and the uniformity of graphite structure is the worst, while in sample D inoculated with silicon zirconium manganese inoculant, there are few large-size graphite and the uniformity of graphite structure is the best; In terms of the bending degree and quantity of graphite: the graphite in samples a and B is sparsely distributed, and the graphite size is large and flat. Compared with samples a and B, the graphite in samples C and D is more curved, fine and densely distributed. It can be seen that different inoculants have different effects on the graphite structure, and Si Zr Mn inoculants are more conducive to obtain fine and curved graphite.

(c1),(c2)sample C—Zr-Si-Al inoculation treatment;
(d1),(d2)sample D—Zr-Si-Mn inoculation treatment.

2. Effect of inoculation treatment on matrix structure of experimental gray cast iron

(a1),(a2) sample A—75Si-Fe inoculation treatment ;
(b1),(b2) sample B—Zr-Si inoculation treatment;

Figure 2 shows the morphology of the matrix structure of experimental gray cast iron a, B, C and D under different magnification. It can be seen from the low magnification morphology that the matrix of the experimental gray cast iron is pearlite and the pearlite sheet spacing is relatively small; It can be seen from the high-power morphology diagram that there are certain differences in the lamellar spacing of pearlite structure of experimental gray cast iron matrix inoculated with different inoculants. The pearlite lamellar spacing of experimental gray cast iron sample C inoculated with silicon zirconium aluminum inoculant and experimental gray cast iron sample D inoculated with silicon zirconium manganese inoculant is relatively small, The pearlite flake spacing of the experimental gray cast iron sample a inoculated with 75 ferrosilicon is the largest. According to the pearlite flake spacing, the order of the four kinds of experimental gray cast iron is a → B → C → D. That is, when the alloy composition of gray cast iron sample is basically the same, silicon zirconium manganese inoculant has a good refining effect on matrix pearlite, which can significantly reduce the sheet spacing of pearlite, improve the hardness of matrix structure, and finally achieve the purpose of improving the strength of experimental gray cast iron.

(c1),(c2) sample C—Zr-Si-Al inoculation treatment;
(d1),(d2) sample D—Zr-Si-Mn inoculation treatment.

3. Effect of inoculation treatment on primary austenite structure of experimental gray cast iron

In order to understand the effect of different inoculants on the primary austenite structure of experimental gray cast iron, the experimental gray cast iron was tempered. The treatment process was as follows: heating the experimental gray cast iron to 860 ℃, holding for 30 minutes, furnace cooling to 600 ℃, air cooling to room temperature. The primary austenite structure will be formed first in the solidification process of gray cast iron, and the precipitation amount, size and morphology of primary austenite have a significant impact on the subsequent formation of eutectic clusters, the morphology, size and distribution of eutectic graphite and the formation of matrix pearlite structure. Therefore, the study of primary austenite is of great significance.

(a) sample A—75Si-Fe inoculation treatment ;
(b) sample B—Zr-Si inoculation treatment;
(c)sample C—Zr-Si-Al inoculation treatment;
(d)sample D—Zr-Si-Mn inoculation treatment.

Figure 3 shows the microstructure of primary austenite in experimental gray cast iron. It can be seen that the space network primary austenite is formed in the four kinds of experimental Gray Cast Iron Inoculated with different inoculants. The primary austenite network frame structure in sample a is relatively simple, and the primary austenite network frame structure in sample D is the most complex, with the most refined and developed secondary dendrites.

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