فهرست مطالب

Iron and steel society of Iran - Volume:10 Issue: 2, Summer and Autumn 2013

International Journal of iron and steel society of Iran
Volume:10 Issue: 2, Summer and Autumn 2013

  • تاریخ انتشار: 1393/02/26
  • تعداد عناوین: 7
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  • A. Fattah-Alhosseini Pages 1-6
    This paper focused on the characterization of electrochemical behavior of a martensitic stainless steel in the acidic solutions. For this purpose, electrochemical parameters were derived from potentiodynamic polarization, Mott Schottky analysis and electrochemical impedance spectroscopy (EIS) techniques. The potentiodynamic polarization results showed that corrosion current density of AISI 420 stainless steel was decreased with the decrease in the concentration of solution. EIS studies also showed that as concentration was decreased, the measured value of polarization resistance was increased. This trend was due to the decrease in the corrosion current density, which corresponded to potentiodynamic polarization curves. Mott Schottky analysis revealed that passive films behaved as n-type and p-type semiconductors at potentials below and above the flat band potential, respectively. Also, Mott Schottky analysis indicated that the donor and acceptor densities were increased with solution concentration.
    Keywords: Martensitic stainless steel, Passive film, Mott–Schottky
  • G. Dini, H. Shekari Pages 7-10
    In this study, the effect of tensile test temperature (148 to 673 K) on the microstructural evolutions and the mechanical properties of high manganese twinning induced plasticity (TWIP) steel with the chemical composition of Fe- 31Mn-3Al-3Si (wt. %) was investigated. XRD, SEM and TEM were used to study the microstructural evolutions. Stacking fault energy (SFE) of the alloy was also calculated by a thermodynamic model. The results indicated that yield strength and tensile strength of steel were gradually decreased with increasing the temperature. However, total elongation reached a maximum value with increasing the temperature up to 248 K. Furthermore, microstructural investigations showed that in the temperature range of 473 to 673 K (SFE: 60-85mJ/ 2), deformation was mainly controlled by dislocation gild and there was no evidence suggesting that twins were formed during deformation. In the temperature range of 248 to 473 K (SFE: 35-60mJ/m2), both mechanisms contributed to reacing a maximum ductility. In the temperature range of 248 to 148 K (SFE: 20-35mJ/m2), twinning and dislocation glide were still the dominant deformation mechanisms, but the change in the formation kinetic of twins probably led to decrease in the total elongation.
    Keywords: TWIP steel, Deformation temperature, Stacking fault energy
  • M. Bagheri, M. Alizadeh Pages 11-17
    The main objective of this project was to investigate the behavior and the damaging effects of hot tear segregations in the continuously cast steel blooms on the final product quality. To achieve this aim, plant data from three different types of steels were used. Investigations using the scanning electron microscope (SEM) equipped with energy dispersive x-ray spectroscopy (EDS) probe and metallographic techniques showed that during the subsequent stages of the cast products, the hot tear segregations were transformed into spherical shapes, joined to each other and moved toward the surface. Also, it was observed that hot tear segregations affected the final product quality in two ways: (1) they could cause uneven surfaces in the final products, and (2) if they reached the surface in a line oriented pattern, they could make a surface crack. The hot tear segregations located near the surface could be crushed to the smaller ones during the rolling. This phenomenon made hot tear segregations less destructive.
    Keywords: Microanalysis, Steel, Continuous casting, Hot tear, Surface crack
  • Z. Samadi Shahreza, G. Dini, A. Taherizadeh Pages 18-22
    AISI 4340 steel is one of the super strong steels that can be selected for different applications. By designing the proper cycles of heat treatment, the optimum microstructure and properties of this steel can be achieved. In this study, different heat treatment cycles were introduced to achieve the optimum microstructure and improve the mechanical and magnetic properties of AISI 4340 steel. The results of tensile, impact, hardness, metallography and magnetic tests for various samples under different heat treatment cycles showed that parameters such as temperature and time of austenitizing and tempering were among the most important factors in achieving relatively a wide range of ultimate tensile strength (1467-933 MPa), impact energy (113-18 J), transport current density (1554-1347 mT), coercivity (1342-1240 A/M), diminished force (1165.6-947.5 mJ/kg) and microstructure (tempered martensite and bainite). This wide range of properties can lead to a large number of applications of this type of steel in various industries including manufacturing steel parts such as rotors.
    Keywords: AISI 4340 Steel, Heat treatment, Strength, Microstructure, mechanical properties, Magnetic properties
  • A. Shakiba, Kh. Edalati, J. Vahdati-Khaki, A. Zabet Pages 23-29
    Due to the abundance of the non-coking coal and limitations as well as the high costs of the natural gas, the present study examined the direct reduction of hematite (iron oxide) ore in the temperature range of 800-1000 °C by the non-coking coal volatiles. Approximately, 74.9% of the total amounts of volatiles and gases exit the coal up to 800°C. The onset temperature to exit volatiles from the non-coking coal was approximately 525°C. The SEM micrographs and XRD results indicated the non-uniform layered reduction of the hematite layer. As temperature was increased, the reduction of hematite ore was increased. At a constant temperature of 1000°C, the reduction rate of the hematite layer reached a maximum after 30 min and then it was decreased. Adding various amounts of calcium carbonate to the non-coking coal in optimal reduction conditions increased the reduction rate of the hematite ore. The optimal concentration of this catalyst was 5 wt% (relative to the coal).
    Keywords: Direct reduction, Iron ore, Non, coking coal, Calcium Carbonate
  • M. Heydarian Pages 30-35
    In this paper, an ultra low carbon High Strength Low Alloy Grade Steel was subjected to a two-step forging process and this was followed by different post cooling methods. The highest strength was obtained at a faster cooling rate due to the highly dislocated acicular ferrite structure with the fine precipitation of microalloying carbides and carbonitrides. At a slow cooling rate, the strength fell with an increase in ductility due to the larger volume fraction of the less dislocated polygonal ferrite structure. The strength remained almost unchanged with a further decrease in the middle cooling rate due to the formation of a predominantly polygonal ferrite microstructure. At the slower post cooling rates, a high impact toughness value was obtained at the ambient temperature and at -40°C testing temperature; this was due to the fine grained polygonal ferrite microstructure. At all post cooling methods, the change in the impact toughness value at the ambient temperature and at the temperature of 40°C was found to be negligible due to the ultra-low carbon content of the steel.
    Keywords: Thermo Mechanical Processing, Forging, mechanical properties, Microstructure
  • Z. Abed, H. Momeni Vesalian Pages 36-41
    The implementation of economic projects by targeting the subsidies can have a great effect on the cost competitiveness of the industries and their products. The global steel industry has been considered as a basic key industry in the industrialized countries. It is also among the industries that may be seriously affected by the enforcement of subsidies. This industry, requiring energy and high-tech, demands the capital. Accordingly, the energy input prices affect the cost of production and sales offers. The prime cost is one of the determinants of an industry''s competitiveness in the market. The study employed the law enforcement approach to the competitiveness of the industry during the 2007-2012 and combined data (panel data) to estimate the competitive capacity. The results showed that the effect of targeted energy subsidies on the competitiveness of this industry energy has fallen over time.
    Keywords: Subsidy, Energy carriers, Competitive, Panel data