Abstract: Based on our experimental results and those reported in the literature, a number of factors which cause the brittleness of the boride layer on steel are analyzed and diseased. Furthermore, some methods to alleviate the brittleness of boride layer are proposed as follows. Introducing such elements as nitrogen, some transition or rare earth metals can effectively decrease the intrinsic brittleness of the boride layer. This can be attributed to the following reasons. The structure of the boride layer is mainly composed of Fe2B phase, along with a small amount of dispersed second phase particles. The grain boundary structure of the boride layer is improved. The structure of the boride layer becomes not only fine but also compact. The microstructure of the core matrix and the transition layer of a co-penetrated steel part can be improved by selecting the type of steels. Also, the growth texture of the boride phase can be alleviated. Thus, the apparent brittleness of the co-penetrated boride layer can be decreased. The apparent brittleness of the boride layer can be controlled by the purification of the technical materials used, too. The apparent brittleness can be lessened by optimization of the polybasic boronizing parameters and the parameters of the post-heat treatment. In addition, the measuring methods for boride layer brittleness are reviewed. Several practical useful measuring methods are recommended in order to evaluate correctly the apparent brittleness of the boride layer.

Key words: Boride layer, Brittleness, Control, Polybasic boronizing