Formation Of Iron Oxide Layer Research Articles

The Influence of Austenisation Temperature and Holding Time on Mechanical Properties, Scale Thickness, and Microstructure in Alloy Steel

The application of steel products have been widely used and various research have been developed to find a good and appropriate quality of steel and can be produced in the country without have to be imported, for example alloy steels. One of the alloy steels that have been constantly developed is Ni-Cr-Mo alloy steel with additional nickel, chromium and molybdenum which can increase hardness, tensile strength, ductility and toughness. The effect during the production process is at the heating process that causes the formation of iron oxide layer (scale) and the loss of steel weight. Therefore, the selection of heat treatment methods and techniques are required to increase the mechanical properties of steel, such as hardness, tensile strength, and toughness, with the scale is about <5% of steel weight. In this research, the heat treatment was carried out at austenisation temperature of 800°, 850°, 900°C and at holding time of 20, 40, 60 minutes, then followed by a rapid cooling (quenching) to improve the mechanical properties of hardness. This research also tested the mechanical properties of steel that consist of hardness test and impact test, and metallographic observation that consist of micro structure observation and scale thickness observation. The micro structure from heat treatment process is martensite, it is due to a rapid cooling (quenching) that rapidly change the austenite phase into martensite. The data showed the highest hardness is 588.35 HVN at 850°C of temperature and 60 minutes of holding time, 8.5 Joules of impact energy, and 91.5 μm of scale thickness. While the lowest hardness is 539.34 HVN at 800°C of temperature, 5 Joules of impact energy, and 47.81 μm of scale thickness.

Impedance spectra of anodic dissolution of iron in distillery vinasse

Electrocoagulation technique has a great application potential to treat distillery vinasse, a liquid effluent generated from alcohol distilleries. The anodic dissolution of carbon steel in this effluent in the potential range of -750mV to -100mV was investigated by potentiodynamic polarization; likewise, the electrochemical impedance spectroscopy spectra were registered over anodic potentials of -560mV, -500mV and -400mV (overpotentials of 20mV, 80mV and 180mV) corresponding to the active dissolution region in order to propose a mechanism for describing the behavior of the carbon steel electrodissolution. Were explored the effects of the flow regime (Reynolds number of 5,500 and 11,500) and the temperature (60°C and 80°C) over the behavior of the spectra. At low current densities the impedance behavior can be satisfactorily described by the combination of the catalytic and non-catalytic mechanism of iron dissolution. It was also found that the dissolution must be carry out at current densities closely to 1mAcm−2 to prevent the possible formation of iron oxide layers on the anode. The anodic dissolution was favored by increasing the flow regime and temperature as well.

Experimental Simulation of Iron Oxide Formation on Low Alloy Steel Evaporator Tubes for Power Plant in the Presence of Iron Ions

Presented are the formation of iron oxide layers on evaporator tubes in an actual fossil power plant operated under all volatile treatment (AVT) condition and an experimental simulation of iron oxide formation in the presence of ferrous and ferric ions. After actual operations for 12781 and 36326 hr in the power plant, two iron oxide layers of magnetite on the evaporator tubes were found: a continuous inner layer and a porous outer layer. The experimental simulation (i.e., artificial corrosion in the presence of ferrous and ferric ions at 100 ppm level for 100 hr) reveals that ferrous ions turn the continuous inner oxide layer on tube metal to cracks and pores, while ferric ions facilitate the production of porous outer oxide layer consisting of large crystallites. Based on a comparison of the oxide layers produced in the experimental simulation with those observed on the actually used tubes, we propose possible routes for oxid layer formation schematically. In addition, the limits of the proposed corrosion routes are discussed in detail.

In situ observations of early oxide formation in steel under hot‐rolling conditions

A technique was developed to study in situ the early stages of the reaction between iron and air. Using a high-temperature microscope, we observed at temperatures between 1000 degrees C and 1050 degrees C and within the first 30 s of reaction, the formation of iron-oxide layers on the surface of low-carbon steel. We observed the nucleation and growth of a first layer of iron oxide and the consecutive formation in sequence, of higher iron oxides sweeping over the surface of the former oxide. The grain boundaries of the steel substrate remain visible for quite some time following exposure to an oxidizing atmosphere indicating that diffusion through steel grain boundaries may have a determining influence on the formation of oxides. These findings emphasize the importance of conducting further studies to better understand the kinetics and mechanisms by which iron-oxide layers form in the early stages of oxidation.