a.shafyei

In the petrochemical industry and in the cracking process, during the reactions that lead to the production of such products as ethylene and propylene, unfavorable reactions are also formed, which cause the formation of coke in the furnace coils. Appropriate coating of the steel can increase the resistance to hot corrosion and high temperature oxidation, largely prevent coke deposition and result in longer life of the reactors. In this research, in order to increase the anti-coking ratio and improve the resistance to oxidation and carburization of HP-micro alloyed steel, aluminide diffusion coatings were investigated. First, the chemical composition of the substrate was determined by optical spectroscopy and, then, the aluminizing process was employed to create a diffusion coating. The coating operation was carried out at 1000 degrees C and a holding time of 5 hours. The results of the X-ray diffraction test on the aluminized sample indicated the presence of NiAl phase on the surface. In order to evaluate the resistance to coke deposition, the coking test was performed to determine the anti-coking ratio. The results showed that the aluminized specimens significantly prevented the formation of filamentary coke due to the presence of the protective oxide layer, while in the untreated steel, the initial filaments formed by the reaction of hydrocarbon and the active elements of the substrate in large amounts over the surface.

Nowadays, roller plates are used in the steel industry and pellet making unit in order to classify iron ore pellets. Roller plates or screen rolls are a type of screening device, which are used to determine size, granulation, and transfer of materials. In this research, the corrosion behavior of these rolls was evaluated in two different water environments including fresh water (drinking) and return water (C60). First, the spark spectrometry test was performed to measure the chemical composition, and then the electrochemical corrosion tests were performed on steel parts A+, A, B at a temperature of 25 °C. The open circuit potential test was performed to measure the open circuit potential and study the general behavior of the components. Then electrochemical impedance spectroscopy test was performed to evaluate corrosion resistance and surface conditions, potential dynamic polarization test to determine corrosion rate and, pitting test to evaluate pitting corrosion conditions. The results of these tests showed that the A+ part had the highest corrosion resistance and the A part had the highest corrosion rate in both environments due to the presence of a larger amount of molybdenum element in the structure of A+ part compared to A. Also, the results showed that the corrosion of all parts in fresh water was less than the corrosion in C60 water. The main reason for this difference was related to less aggressive ions such as chlorine in fresh water compared to C60 water. In addition to uniform corrosion and pitting corrosion, galvanic corrosion between phases in the microstructure was also determined as one of the main causes of alloy corrosion. According to the metallographic images of the parts and the hardness measurement results, the microstructure of all three parts was martensitic, which was observed in parts A, B, and delta ferrite phase in the martensitic field.

Intensified environmental regulations have posed numerous challenges in the disposal of industrial wastes. The steel industry is one of the biggest production industries, with a considerable amount of daily wastes. Production of glass-ceramic from the steel industry waters is one of the proper solutions for this problem. In this study, the application utilization of different wastes (such as blast-furnace slag, converter slag, and dust) as the raw material for glass-ceramic production was evaluated. After mixing the precursors, the mixture was melted at 1450℃. The obtained melt was cooled down at 10°C/min cooling rate in metallic molds, and the glass was derived. Ceramic phases were grown by application of isothermal heat treatment periods up-to 6 h, at 750, 800, 850, and 900℃. The mean length of the ceramic phases was measured after each heat treatment period by scanning electron microscopy. It was shown that crystal growth followed a parabolic kinetic model. The activation energy of crystallization was also determined as 129 kJ/mol in the temperature range of 750-900°C.

In the present study, CrN, TiN and (Ti, Cr)N coatings were deposited on D6 tool steel substrates. Physical and mechanical properties of coatings such as microstructure, thickness, phase composition, and hardness were evaluated. Phase compositions were studies by X-ray diffraction method. Mechanical properties were determined by nano-indentation technique. The friction and wear behaviour of the coatings were investigated using ball-on-disc tests under normal loads of 5, 7 and 9 N at sliding distance of 500 m, at room temperature. Scanning electron microscope equipped with energy dispersive spectroscopy, optical microscope, and 2D/3D profilometry were utilized to investigate the microstructures and wear mechanisms. Wear test results clarified that the wear resistance of (Ti, Cr)N and TiN coatings was better than that of CrN coating. The wear resistance of the (Ti, Cr)N coatings was related to the Ti content in the coatings and reduced by decreasing the Ti content. The dominant wear mechanisms were characterized to be abrasive and tribochemical wear.