Iranian Journal of Materials Science and Engineering
Year:2008 | Volume:5 | Issue:1|Papers Count:7

In the present investigation, the effects of thermo mechanical processing parameters and the steel chemical composition on the ultra fine ferrite formation characteristics were studied. This was programmed -relying on the capabilities of strain induced transformation (SIT) phenomenon and applying to different grades of Si-Mn TRIP (Transformation Induced Plasticity) steels. Accordingly, wedge shaped specimens were rolled at two different temperatures, above and below the austenite-to-ferr.ite transformation temperature (Ad). An ultra fine ferrite grain size, in the scale of some hundred nanometers, was obtained by rolling the specimens with lower Si content at a temperature below the related Ad temperature. The amount of reduction, which was resulted in the latter microstructure, was realized to be about 55%.

In chloride salt solutions, titanium alloys exhibit reasonably high pitting potentials as high as +10 V (vs. Ag/AgCl) at room temperatures. On the other hand, anodic pitting potentials are significantly lower in bromide solutions. In this study, pitting corrosion of commercially pure titanium in aqueous NaBr solution of 0.1 M concentration at room temperature was studied and the effect of an external magnetic field oriented both parallel and perpendicular to electrode surface was investigated. Cyclic potentiodynamic and potentiostatic polarization tests were carried out. Anodic breakdown potential of +1.45 V (vs. Ag/AgCl) obtained in the absence of magnetic field, decreasing to +1.11 V in the presence of a 0.05 T parallel magnetic field. The perpendicular magnetic field actually did not affect the breakdown potential. Applying of an external magnetic field, independent of its orientation, shifted the repassivation potential approximately 150 mV in the positive direction. SEM microscopy observations of sample surfaces indicated that applying of magnetic field results in some variations in the pit shapes and their sizes.

The application of inexpensive materials such as copper,zinc, lead, iron and steel slag in manufacturing of glass and glass-ceramic products in construction industry, lining materials as anti-corrosion and anti-abrasion coatings in metals and etc, has led to considerable progress in glass technology in recent years. The composition of slag glass-ceramics is mainly located in the SiO2Al2O3-CaO-MgO system, in which one of the most important problems is the lack of bulk crystallization. To resolve the above-mentioned problem, the crystallization behavior of various compositions containing different nucleating agents Cr2O3, Fe2O3 and nO2 in the single, double and triple forms were studied by differential thermal analysis (DTA).The precipitated crystalline phases was determined by the X-ray diffractometry and the micro-structural analysis was studies using the SEM micrographs. The three point bending strength, micro-hardness and the chemical resistance of the best composition were determined. According to the results, the resulted glass ceramic had a better specification than the stoneware floor tiles and the porcelain one, which are considered as the two important competitors for it.

In this paper solid state reduction of high carbon ferrochromium-chromite composite pellets in the temperature range of 900-1350°C was investigated. A two stage reduction mechanism is proposed. The first stage is likely to be controlled by the chemical reaction with activation energy of 127.2kJ/mol. In the second stage, solid state diffusion of carbon through the reaction product layer is suggested to be rate controlling. The activation energy of this stage was calculated to be 93.1Kj/mol. The reduction process was found to be favored by high temperatures as well as high vacuum. The results also show that pre-milling of initial mixture has a negative effect on the reduction degree.

Hard facing is one of the most useful and economical ways to increase the service life of components subjected to abrasive wear. Iron based hard facing alloys have long been considered as candidate coatings for wear-resistant applications in industry. In the present work two layer of Fe-34Cr-4.5C%wt hard facing alloy was deposited on ASTM A36 carbon steel plates by SMAW method The microstructure consists of large primary and eutectic M7C3 carbides, metastable austenite and small amount of secondary carbides. The microstructure was analyzed by optical and scanning electron microscopes. In the same condition of size, shape, distribution and volume fraction of carbides; the as-welded matrix changed to marten site, tempered marten site and ferrite by heat treatment processes. The wear resistance was measured by pin-on-disk method under loads of 5, 10 and 20N and for sliding distance of 1500m. The results showed that the as-welded sample with austenitic matrix has the most and the ferritic matrix specimen has the least wear resistance. The predominate mechanisms for mass losses were determined to be micro-cutting, microploughing.

Despite having a number of advantages, reinforced concrete can suffer rebar corrosion in high-chloride media, resulting in failure of reinforced concrete structures. In this research the corrosion inhibition capability of the mixture of calcium and ammonium nitrate of steel rebar corrosion was investigated in the simulated concrete pore solution. Cyclic polarization and Electrochemical Impedance Spectroscopy (EIS) techniques were applied on steel concrete pore solution containing 2 weight percent sodium chloride (NaCl). Results show that such mixtures had higher inhibition efficiency than calcium nitrate alone. The optimum concentration of the inhibitor mixture was determined to be 45 mgr/lit.

Thermodynamic computational packages MTDATA and Fact Sage have been used to carry out calculations on the variation with temperature of the phases precipitated on cooling in both oxidising and reducing conditions of a typical ladle slag composition, in the temperature range 1700 - 900°C. The current coverage of the databases associated with the computational packages is discussed in relation to their application to slag - refractory interaction and the validity of the results is compared with some relevant experimental data and phase equilibrium studies.