Effects of RE-Al additions and austenitising time on structural variations of medium carbon Fe-B cast alloy

The aim of the present study is to investigate the effects of rare earth and aluminium on the structural variations of medium carbon Fe-B cast alloy under the same austenitising temperature and different austenitising times. It is observed that the as cast microstructure of Fe-B cast alloy consists of the eutectic boride, pearlite, martensite and ferrite. Moreover, the as cast eutectic boride structures are greatly refined, and a blocky, less interconnected boride network is obtained when rare earth and Al are added. After different austenitising times, in each case, the phases in modified Fe-B cast alloy consist of the boride and martensite. The addition of RE in Fe-B cast alloy accelerates the diffusion process of B and Fe atoms during austenitising. Based on this favourable condition, the numbers of the fractured boride networks and isolated granular borides increase with increase in austenitising time. The boride volume fraction, Vickers hardness of martensite matrix and boride, and Rockwell hardness of Fe-B cast alloy modified by rare earth and aluminium have no significant change at different austenitising times. However, the average diameter of boride decreases and the impact toughness increases with increasing austenitising time.