Effects Of Composition And Heat Treatment On Microstructure And Properties Of Fe-C-B Alloy

In recent years, Fe-C-B alloy was thought as a new kind of structural materials. The present investigations were through the way to adding a certain amount of boron on the basis of chromium-cast steel. It was found in our studies that adding a certain amount of boron into Fe-C-B alloy could contribute to better properties. But the factors affecting the microstructure and properties need farther studies.In this paper, effects of the carbon content, the boron content and heat treatment methods on the microstructure and properties were mainly described. The amount of carbide and toughness of alloy mainly depend on the C content, and the type of boride, the amount of boride and the hardness of alloy mainly depend on the B content. The results indicate that a great amount of eutectic microstructure exist in common casting condition owing to adding boron element in the alloy. Though the carbon content is at range of medium or high carbon steels, the solidification structure has an essential difference from the medium-carbon steels. When the boron content is at the range from 0.59% to 4.13%, the solidification structure of this alloy is similar to white cast iron. The as-cast structure of Fe-C-B alloy consists of dendritic matrix and boride of boron carbide eutectic distributed in the dendritic matrix as a large and continuously net-like shape. The matrix structure is composed of pearlite, ferrite and a little martensite. As C content and B content increase, the amount of eutectic microstructure increases. Therefore, the hardness of alloy increases gradually but the toughness of alloy represents a falling trend with the increase of C content and B content. It should be noted that the effect of B content is more obvious than C content.In order to consider the effect of heat treatment on the microstructure and properties of Fe-C-B alloy, the samples were cooled in water, in furnace, in air and cooled in water then tempered respectively. The results of heat treatment methods for Fe-C-B alloy show that quenching,annealing and normalizing could change hardness obviously,but not evidently for toughness. the normalizing temperature at the range from 950℃to 1100℃has little influence on the morphology and the distribution of eutectic microstructure in casting Fe-C-B alloy. But part pearlite and ferrite can change into martensite. So both hardness and toughness of normalizing alloy are better than casting alloy. Another important law is that the morphology of continuously net-like distributed boron carbide can not be changed by normalizing temperature and cooling condition.Effects of heat treatment methods, C content and B content on the wear resistance of alloy are invested. Impact abrasive wearing tests show that when the impacting energy holds at 1J, the carbon content is fixed at about 0.40%, the wear resistance of normalized and quenched plus tempered Fe-C-B alloys increases with the increase of boron content. Yet, the wear resistance of Fe-C-1.46B alloy rises firstly then drops with the increase of C content. In all kinds of composition, the wear resistance of normalized Fe-1.34C-1.46B alloy reaches the maximum. During the process of impacting abrasive wearing, the modes of wear are main presented as cutting furrow, micro-cutting, fatigue flaking and brittle flaking.