Influence of Carburizing Chromization Process on Mechanical Properties of ASTM A36 Steel

Research on changes in microstructure and hardness properties of ASTM A36 steel caused by carburizing-chromization process has been conducted. Carburizing-chromization treatment process was conducted at various temperatures: 850 ℃, 900 ℃ and 950 ℃ and holding time: 6 hours, 9 hours and 12 hours. Carburizing media in a mixture of solid powder charcoal/BaCO3 and ferrochromium/alumina/NH4Cl, with heating carried out in an electric furnace. The obtained layers were investigated using X-ray and electron diffraction, optical and scanning electron microscopy, and hardness measurements were carried out with micro Vickers, and potentiodynamic measurements. The thickness of the carburizing layers ranged between 50 and 500 µm. In addition to the host c-phase, the layers were mostly composed of carbides (Fe7C3, Cr23C6, Cr7C3, and Fe3C) and traces of a¢-martensite. The average hardness value decreases smoothly from 680 HV at the surface of the sample to 200 HV in the center of the sample. Potentiodynamic tests revealed that the chromized samples have lower corrosion resistance compared to the untreated material. For the strong chromization regime, the corrosion rate increases fourfold compared to the untreated material, while the microhardness of the coating is threefold greater. These materials are suitable for use in environments requiring good corrosion resistance and wear properties.