Effect of solidification pressure on carbide of cast chromium white cast iron

In addition to the fine grain strengthening effect under pressure, the effect of pressure on carbide morphology is also worth studying. The hardness of carbides varies with different types of carbides. Previous studies mainly focused on the composition of the alloy, that is, Cr / C. Through the previous discussion, it can be concluded that the pressure has a decisive effect on the diffusion of alloy elements. In this case, there must be the distribution of alloy elements between carbide and matrix. It is of great significance to study the mechanical properties of the alloy under pressure solidification to study whether the redistribution of alloying elements will affect the morphology and type of carbides and further determine the strengthening effect of carbides as reinforcement phase.

(1) Increasing the solidification pressure can increase the carbide content in the solidification structure of chromium white cast iron. The volume ratio of carbides in hypoeutectic alloy 1 under 160 MPa pressure is 2 times of that under normal pressure solidification, and the volume ratio of carbides in hypoeutectic alloy 2 increases about 1.5 times; The content of primary carbide fluctuates with the increase of pressure, but the volume of eutectic carbide increases gradually. When the pressure reaches 160MPa, the content of eutectic carbide increases to about 1.5 times of the original.

(2) For hypoeutectic alloy 1, with the increase of pressure, the diameter of eutectic cluster increases, and the hypoeutectic alloy transforms from divorced eutectic to regular eutectic; For eutectic alloy 2, the solidification structure changes from eutectic to hypereutectic, and polygonal primary carbides appear with the increase of pressure; The eutectic structure is obviously refined and the eutectic spacing is obviously reduced; With the increase of pressure, the primary carbides fluctuate between nucleation and growth, and the eutectic phase further refines and transforms to equiaxed or polygonal.

(3) Increasing the solidification pressure can change the growth mode of eutectic carbide from facet to non facet. This is because the solidification pressure reduces the Jackson factor of eutectic carbide and increases the roughness of solid-liquid interface.

(4) The effect of pressure on the transformation of carbide type is related to the phase stability of different carbides, and pressure can promote the formation of stable M7C3 carbides. With the increase of solidification pressure, the amount of m3c type carbides in alloy 1 decreases and M7C3 type carbides increase. The results show that the content of M23C6 carbide in alloy 2 decreases and the content of M7C3 carbide increases. The stability of eutectic carbides in chromium white cast iron during cooling was studied by first principles method. It is concluded that pressure promotes the precipitation of carbides with high stability.