Eutectic growth mechanism of chromium white cast iron under pressure

Through the characterization and analysis of the morphology of the above hypoeutectic alloy 1 # eutectic structure, the eutectic morphology under pressure can be summarized as the basic process as shown in the figure, which presents the state of eutectic structure under atmospheric pressure. Austenite and carbide do not interfere with each other and grow along a certain direction, thus forming divorced eutectic.

Schematic illustration of process of Fe-Cr-C white cast iron solidified under pressures

With the increase of pressure, the edge of eutectic phase changes from flat to wavy except for the decrease of eutectic spacing. With the increase of pressure, the straight lath transforms into dendritic protrusion. In addition, the eutectic phase of eutectic chromium white cast iron changes from long lath to curved short bar instead of dendrite, and then forms equiaxed phase directly. At atmospheric pressure, the nucleation of carbide is more difficult than that of austenite, but the growth rate of carbide is higher than that of austenite.

Under the pressure condition, not only the austenite nucleation becomes more, but also the carbide nucleation is greatly improved, which directly leads to the decrease of eutectic spacing. The enrichment of Cr element in the front of austenite can not be further diffused under pressure, which prevents the entry of Fe atoms needed for austenite growth and inhibits the growth of austenite. In the front of the solid-liquid interface of the carbide, the same situation also appears. The carbide that has been nucleated can not get more CR atoms to grow rapidly. At the same time, the conditions of carbide nucleation and growth are achieved in the CR rich region, and the conditions of austenite nucleation and growth are also achieved in the Fe rich region. When this happens repeatedly, the competitive growth of austenite and carbide in eutectic structure is formed.