32Crmov Çeliğinin Aşınma Direncini Arttırmak İçin Yeni Bir Isıl İşlem Metodunun Geliştirilmesi

Abstract

In the boriding process, steel materials are kept in the boron-rich media during a certain period of time at a given temperature in order to form very hard second phaseses such as FeB and Fe2B (1500HV-2000HV [1]) on the surface of the steel by penetrating the boron into the material [2–5]. In this thesis, both powder boronizing and paste boronizing are applied in the boriding process. Using the boron paste, the protective layer is formed during the heat treatment, and thus the material is protected against oxidation. On the other hand, in powder boronizing, the experiments are conducted in a controlled atmospheric environment to prevent oxidation and in this thesis, atmosphere control is performed by using the inert gas argon [6]. In both methods, after the heat treatment, the material is cooled rapidly by water quenching. This is due to the stabilization of the microstructure by rapid cooling. Different from the powder boronizing, the cooling process is also carried out in the cold part of the oven. Then, the material is cut in half to analyze the diffusion of boron to the surface. The material is first grinded using rough to fine SiC papers, and then the polishing process is performed with diamond suspension. The material is further etched with %2 nital solution in volume. Etching is a process for revealing the microstructure. The microstructures of etched materials are analyzed with optical microscope and Scanning Electron Microscope (SEM) is further utilized for observing the microstructures at higher magnification. To determine the phases formed on the surface, the materials are analyzed by X-Ray Diffraction (XRD) method. Carburizing experiments are conducted without the use of inert atmosphere. The reason is that for the carburizing reaction, the initial reaction is needed in carboncontaining power material and the resulting CO provides the diffusion of carbon atom into the material. Commercially available charcoal, is used as a carbon powder for the carburizing process, all the steps described above are applied in the same fashion.