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

The total amount of carbides, eutectic carbides and primary carbides in alloy 2 are shown in the figure. The content of primary carbide fluctuates with the increase of pressure, but the content of eutectic carbide increases gradually. When the pressure is less than 100 MPa, the total amount of eutectic carbide increases obviously, which is about 1.25 times of that at normal pressure. When the pressure continues to increase, the content of eutectic carbide gradually slows down. When the pressure reaches 160MPa, the eutectic carbide content increases to about 1.5 times of the original. The increase of solidification pressure has a great contribution to the increase of eutectic carbide content, but it has no promoting effect or even inhibiting effect on primary carbide, which depends on the pressure value. The reason may be related to the state of primary carbides under different pressures. When the pressure increases the nucleation rate of primary phase, that is to say, the number of primary carbides increases, but when the size is small, the total content of primary carbides is less. On the contrary, when the nucleation rate remains unchanged, the primary carbide content increases with the increase of primary carbide size.

Primary carbide and eutectic carbide content in Alloy 2# under different pressure conditions

Generally speaking, the pressure first promotes the nucleation of primary phase, and then promotes the growth when the pressure reaches enough. 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. After analysis, no matter which composition of the alloy pressure will promote the growth of eutectic carbide. This is due to the fact that austenite nucleation is easier than carbide in the case of no pressure. In the process of austenite nucleation and continuous growth, carbide nucleates slowly between austenites, and the growth is limited by austenite grains. Under the pressure condition, the nucleation rate of carbide has been significantly improved. In addition, in the process of austenite growth, a large number of Cr atoms are discharged and enriched in the front of the solid-liquid interface, which affects the supply of Fe and C elements needed for austenite growth, and in the place of Cr enrichment, the conditions for carbide growth are provided. The nucleation and growth of carbides and austenite have changed into competition, which provides conditions for the increase of carbides.