Alloying and modification of chromium white cast iron

The wide industrial application of chromium white cast iron attracts researchers to try different carbide forming elements to improve the alloy structure, such as W, V, Nb, Ti and B. By adding a carbide forming element different from cementite, the carbon content of the matrix is reduced, and the toughness and wear resistance of the material are improved.

Xiaohui Zhi alloyed hypereutectic high chromium cast iron containing 4.0 wt.% C and 20.0 wt.% Cr by adding NB. The mechanism of carbide modification is the same as that of V, Ti, Nb, re, B and other strong carbides, which can cause solid solution, segregation and precipitation in cast iron, and interact with carbon and nitrogen to produce a series of beneficial effects, such as grain refinement, precipitation strengthening, inclusion modification and so on.

E CORT é s Carrillo found that when the W content in high chromium cast iron was 4.0 wt%, the distribution of W in the matrix or M7C3 carbide made the alloy strengthen moderately in both phases and improved the overall hardness of the alloy. When the W content is more than 4.0 wt%, there are generally hard M2C and M6C carbides in the microstructure, which improves the overall hardness of the alloy. The wear behavior is consistent with the hardness value. With the increase of W content, the wear resistance is improved. However, when the W content reaches 10.3 wt%, the wear resistance of high chromium cast iron is not greatly improved, only 13% higher.

The addition of trace elements can form gap or replace solid solution through solid solution, change lattice constant and bonding properties, thus change the nucleation and growth mode, physical and chemical and mechanical properties of materials, and can change the morphology and distribution of carbides to a certain extent. However, due to the limited addition and the scarcity of some elements (such as Mo, V and W), this method is limited. For example, there are few reports about the effect of Nb on fracture toughness or its combination with high chromium white cast iron to obtain the best fracture toughness and wear resistance. The solubility of Ti in cast iron is very small, which leads to the limited addition of Ti. Even in low Ti melt, fine titanium carbide precipitates at higher temperature, which may affect subsequent solidification.