Effect of solidification pressure on eutectic morphology of near eutectic chromium white cast iron

The metallographic structure shown in the figure is the metallographic structure photo of near eutectic alloy 2. It can be seen from figure (a) that the solidification structure of the alloy under normal pressure has two forms with very large size difference, among which the larger one is white lath structure with less quantity. The large lath is surrounded by black-and-white eutectic structure. According to the enlarged picture of (a ‘), the small white structure is short rod-shaped with sharp ends and uneven distribution in the middle of the black structure.

Representative optical micrographs of eutectic structure of Alloy 2# under different pressures: (a) 2-1-T; (b) 2-2-T; (c) 2-3-T;

As shown in figure (b), in the solidified structure after pressure of 70MPa, the huge lath disappears under normal pressure and becomes a number of smaller polygons. Although the difference between the size and the surrounding structure is small, the shape is obviously different and can be distinguished. In the enlarged picture (B ‘), it can be found that the white structure is obviously refined compared with the solidified structure under normal pressure, but the shapes are different and very complex, including short rod, curved panel strip, equiaxed, polygonal, etc., and even the primary phase and eutectic phase can not be distinguished.

When the pressure further increases, as shown in figure (c), a larger primary phase appears, but its shape becomes polygonal, and the size becomes larger than 70MPa. The size of eutectic structure is basically the same as that of 70MPa, but in the region near the primary phase, the white structure presents curved surface strip, while in the position far away from the primary phase, the equiaxed and polygonal structure appears.

Representative optical micrographs of eutectic structure of Alloy 2# under different pressures: (d) 2-4-T; (e) 2-5-T

When the pressure increases to 130 MPa, as shown in figure (d), the solidification structure is basically similar to that of 100 MPa, and the primary phase is also polygonal, and the number and size are basically the same. However, in the enlarged figure (d ‘), it can be seen that the curved panel strip close to the primary phase becomes shorter, and has equiaxed appearance, and the gap between its size and the structure far away from the primary phase decreases.

When the pressure reaches 160MPa, as shown in figure (E), the number of polygonal blocks becomes more, but the size becomes smaller than before. Other structures present cellular or equiaxed grains, and are not affected by the growth of multilateral blocks, and the distribution is more uniform.

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