There are two different types of white cast iron. They are called this way due to the fact that a white surface appears when a fracture occurs. Within their microstructure no graphite can be found in comparison to grey cast iron where carbon resides in the form of carbides. They can be used in conditions where resistance to extreme abrasion is required.

Depending on their chemical structure we can find two principal groups of white cast iron:

Ni Hard (ASTM A 532 Class I) with nickel contents within the range of 3.3 – 7% and chrome with the range of 1.4 – 11%. The relation Ni/Cr must be kept within the ratio 3:1 in order to avoid the formation of pearlite, developing a martensitic structure whenever the cooling speeds are adequate.

Hi Chrome (ASTM A 532 Class II) with Ni contents upto 2.5% and Cr within the range of 11-30%, when the Cr is found above the 10% level of hardness and the carbide forms appearing allow a mayor resistance to wear and impact , compared to those that are developed with less Cr content.

The operation conditions may significantly impact the performance of the white cast iron but in general terms the materials that form part of the High Chrome group showcase a better performance in conditions of abrasion and impact (compared to those that fall under the Ni Hard group).  

The difference in performance is mainly due to the structure that is generated when you control several factors such as chemical composition, filtering temperature including time and thermal treatment cycle duration.