Effect of Tib <sub>2</sub> Addition on Microstructure and Mechanical Properties of a Hypereutectic High Chromium Cast Iron

Abstract

Hypereutectic high chromium cast iron (HCCI) is featured with high abrasion resistance and hardness, making it one of the most widely used materials in mining, minerals and cementation industries. However, the alloy is also naturally brittle partially due to the coarse needle-shaped primary M7C3 carbides. The present work challenges one of the long-term issues associated with HCCIs to modify the primary carbide through addition of a newly discovered additive, TiB2. Addition of 300 ppm such particles led to significant decrease in the fraction of needle-shaped primary carbides by 35%, and reduction in average size of the carbide by 32% in length for the needle-shaped carbide and by 32% in diameter for the equiaxed carbide. As a result, the transverse rupture strength (TRS) of the alloy after heat treatment was increased by 37% together with no noticeable loss in wear or hardness. Although excess TiB2 addition up to 8000 ppm continued reducing the amount of needle-shaped carbide, the improvement in TRS was annulled by the embrittlement of TiB 2 . Detailed microstructural examination showed that upon addition, TiB 2 decomposed in the melt, leading to the formation of TiN particles with fresh surfaces, which acted as M7C3 carbide refiner through promotion of the heterogenous nucleation of the carbide.