Take the metallographic sample from the high chromium cast iron layer and carbon steel layer of the bimetal lining plate and place it under the optical microscope to obtain the following metallographic diagram. Figure 1A shows the as cast structure of high complex cast iron, which belongs to typical hypoeutectic structure. The matrix structure is austenite, on which eutectic carbide (Fe, Cr) 7C3 is distributed; Fig. 1b shows the as cast structure of carbon steel, which belongs to typical hypoeutectoid steel structure and consists of ferrite and pearlite.
The matrix, carbide and carbon steel layer of high chromium cast iron layer were analyzed by X-ray energy dispersion spectroscopy with scanning electron microscope. The elements contained in each layer are shown in the figure below. The specific contents of corresponding components are shown in the table below. The composition proportions of each element are described in detail in the table with wt% by weight and at% by atom.
Through energy spectrum analysis of the phase in Fig. 2a, it can be clearly observed that the phase is mainly composed of Cr, Fe and C, of which the content of Cr is the highest. The first column in the table quantitatively expresses the constituent elements of the phase. The data show and describe the iron complex carbides, and the characteristics are consistent.
Through energy spectrum analysis of the phase in Fig. 2B, it can be clearly observed that the phase is mainly composed of Fe, Cr and C, of which the content of Fe is the highest. The second column of the table quantitatively expresses the constituent elements of the phase. Since a large number of Cr, C and Fe form carbides during solidification and precipitate from austenite, the content of Cr in the phase is greatly reduced, Data show that austenite matrix structure of the high chromium cast iron is consistent with the that described above.
Through energy spectrum analysis of the phase in Figure 2c, it can be clearly observed that the phase is mainly composed of a large amount of Fe and a small amount of C. The third column in the table quantitatively expresses the constituent elements of the phase. The data show that the hypoeutectoid structure characteristics of carbon steel are consistent with those described.
| Element | Fig.2a(wt.%) | Fig.2a(at.%) | Fig.2b(wt.%) | Fig.2b(at.%) | Fig.2c(wt.%) | Fig.2c(at.%) |
| C | 10.20 | 33.50 | 8.96 | 31.02 | 7.54 | 26.37 |
| O | — | — | — | — | 2.07 | 5.42 |
| Si | — | — | 0.46 | 0.68 | 0.27 | 0.40 |
| Cr | 57.60 | 43.70 | 15.32 | 12.25 | 0.70 | 0.57 |
| Mn | — | — | — | — | 1.32 | 1.01 |
| Fe | 31.44 | 22.21 | 75.26 | 56.05 | 88.09 | 66.22 |
To sum up, the as cast structure of high chromium cast iron is bainite, martensite and retained austenite, of which the latter two items are more, because casting is equivalent to austenitizing at the solidus temperature, and the carbon and chromium content in the matrix is higher than that of normal heat-treated austenite. Although the cooling is slow in the EPC dry sand mold, the matrix structure of as cast high chromium cast iron is mainly austenite because the high carbon and high chromium make the iron have good extraction permeability, the pearlite transformation is restrained, and the martensite transformation temperature is low.