Effect of solidification pressure on eutectic content and size of chromium white cast iron

Because the primary phase in the solidification structure of alloy 1 is austenite, the eutectic austenite in the divorced eutectic will first grow up on the primary austenite, which makes it difficult to distinguish the eutectic structure from the solidification structure. Therefore, the effect of pressure on the content of eutectic structure is further discussed by choosing the solidification structure of eutectic alloy.

According to the statistics of the content of primary phase and eutectic structure of alloy 2 under different pressures, as shown in Figure 1, the content of primary phase and eutectic structure fluctuate with the increase of pressure, instead of increasing the melting temperature of the alloy under pressure as deduced by the formula, so as to expand the volume proportion of eutectic structure. Compared with the nucleation rate of primary phase under different pressures, when the content of primary phase is less, it is usually in the case of increasing nucleation rate of primary phase. Compared with the size of primary phase, it can be seen that with the increase of pressure, when the nucleation rate of primary phase is similar, the size of primary phase increases obviously, which indicates that pressure has a promoting effect on the growth of primary phase. Generally speaking, the pressure first promotes the nucleation of primary phase, and then promotes the growth when the pressure reaches enough. When the pressure is less than nucleation, the growth rate of crystal is also very important. Therefore, for the primary phase, the increase of pressure will make it repeat between nucleation growth nucleation. When the nucleation rate increases, the eutectic structure increases, and when the nucleation rate decreases, the eutectic structure decreases.

During the solidification process of Cr white cast iron at atmospheric pressure, the order of eutectic cluster diameter of the alloy with the same Cr content is hypereutectic alloy > eutectic alloy > hypoeutectic alloy.

The influence of cooling rate on eutectic temperature range and eutectic cluster diameter is as follows:

Where:

EW — eutectic diameter;

Δ Te — eutectic solidification temperature range;

A — normal number determined by the composition of high chromium cast iron;

Re — eutectic solidification rate (cm / min).

According to the formula, the range of crystallization temperature and the diameter of eutectic cluster increase with the increase of pressure. As shown in Fig. 2, the eutectic point of alloy 1 #, 2 #, will shift to the left, and the eutectic temperature will increase. The increase of eutectic temperature leads to the increase of eutectic area and the content of eutectic structure.

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