Hanguang Fu

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

Abstract 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.

Effect of rare earth–aluminium additions on the microstructure of a semisolid low carbon Fe–B cast alloy

Abstract The present study investigates the effects of rare earth and aluminium on the microstructures of as cast and heat treated semisolid Fe–B cast alloys. The as cast microstructure of the semisolid modified Fe–B cast alloy consists of the eutectic boride, pearlite and ferrite. Moreover, compared to a net-like distribution of the coarse eutectic borides in the ordinary unmodified alloy, the eutectic boride structures in the semisolid modified alloy are greatly refined and less interconnected. After heat treatment, the phases in the semisolid modified Fe–B cast alloy consist of the boride and martensite. The additions of rare earth and aluminium help to promote the formation of the short rod shaped and round borides in the semisolid Fe–B cast alloy during heat treatment. Compared to the ordinary unmodified alloy, there is no significant change in the boride area fraction but an obvious decrease in average boride area in the semisolid modified alloy.

Effect of fluctuation, modification and surface chill on structure of 20%Cr hypereutectic white cast iron

Abstract The microstructural refinement of a cast hypereutectic Fe–20Cr–4C alloy using modification, surface chill and a novel fluctuation approach has been studied. Fluctuation involves the addition during pouring of powder or liquid metal to produce variations in temperature and/or composition in microareas of the liquid near the solidification front. The structures of the alloy were investigated using optical microscopy and image analysis. Increasing the degree of fluctuation (ferroalloy powder) resulted in finer primary and eutectic carbides. The combination of fluctuation with the addition of modifying agents (Fe–Si–Re alloy, aluminium and a laboratory intermediate alloy) and the application of surface chill, was found to increase the refinement of the carbides.

Investigation on high temperature compression behaviour of hydrogenated Ti6Al4V alloy

Abstract Isothermal compression of hydrogenated Ti6Al4V alloy was carried out on a Gleeble-1500D simulation tester at the strain rate 3×10−3 s−1 and high temperatures. Before the isothermal compression, a simplified thermohydrogen processing (THP) was used for Ti6Al4V. Attention was paid to the effect of THP on subsequent compression behaviour. The results show that hydrogen can effectively lower the flow stress and deformation temperature and enhance the strain rate sensitivity index (m value) for isothermal compression. The increasing amount of β phase and the ultrafine and equiaxial microstructure precipitated between the original α or β laths are the main reasons for the simplified THP to improve the formability of Ti6Al4V.