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Iron and steel society of Iran - Volume:5 Issue: 1, Winter and Spring 2008

International Journal of iron and steel society of Iran
Volume:5 Issue: 1, Winter and Spring 2008

  • 50 صفحه،
  • تاریخ انتشار: 1387/11/01
  • تعداد عناوین: 7
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  • M.Safari, A.Saboonchi Pages 1-7
    A mathematical model of a continuous reheating furnace has been developed to identify the design and operating parameters that significantly affect furnace performance. In this study, the furnace is modeled 3 dimensionally and the Monte Carlo method is used to find the overall absorption factor. The overall absorption factor is then used to calculate the energy balance for furnace walls, the gas, and the moving slab. For this purpose, 1-D heat conduction in walls and 2-D heat transfer in the slab are assumed. Results include temperature distribution of gas, walls, and slab. The effects of emissivity of slab and furnace height on the efficiency of furnace are also analyzed. It is co ncluded that operating efficiency increases by increasing load emissivity and by decreasing furnace height.
  • H.Amini Mashhadi, A.R.Rastgoo, J.Vahdati Khaki Pages 8-14
    In this study, the isothermal reduction of iron oxid e pellets, made of Iranian Chadormalo, Gole-gohar, and Sangan iron ores, was investigated in the temperature range of 900-1100°C. Tab as, Pabdana, Babnizoo, Karmozd, and Shahrood do mestic coals were used as reductants. Parametric studies were performed and the effects of such factors as temperature, average particle size of iron o re and coal fines, pellet size, and BaCO3 additive on reduction process were investigated. It was found that bo th the rate of reduction in the early stages of the process and overall reduction increased for all the iron ores used with increasing temperature. Overall reduction, however, d ecreased when the size of Sangan iron ore pellet incraesed. It was laso observed that the rate of reduction decreased when the particle size of Sangan iron ore fines increased at the early stages of the process but increased thereafter d uring the process. The rate of reduction and the overall reduction in Sangan iron ore also increased considerably when BaCO3 was added to Tabas coal at 1100 °C. Finally, a kinetic study was performed for reduction of Sangan iron ore using Tabas co al to determine the activation energy of the reduction reaction. It was found that the activation energy decreased from 159 to 133 kJ/mol by increasing the BaCO3 content from 0% to 5%
  • R.Dehmolaei, M.Shamanian, A.Kermanpur Pages 15-21
    The microstructure of HP stainless steel in aged and aged + solution annealed conditions and solutionized alloy 800 was characterized by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) equipped by EDS. All phases present in the above condition were described. The effects of solution annealing heat treatment temperature on the microstructure, tensile, hardness, toughness, and ductility of aged HP stainless steel and its weldability to alloy 800 have been discussed. In addition, the effects of heat input, interpass temperature, and type of filler metal on weldability of two alloys were investigated. It was found that during solution annealing, the precipitates produced in the aging stage are decomposed and niobium carbide (Nb C) is formed. It was also observed that while tensile strength and hardness fell, ductility and to ughness were improved. Dissimilar welding between alloy 800 and aged HP stainless steel was not successful and cracks were observed in the HAZ of the aged HP stainless steel, while welding alloy 800 to HP stainless steel (aged + solution annealing at 1100-1200 C, low interpass temperature, and Inconel 8 2 or 617 filler metals) was successful.
  • H.Naffakh, M.Shamanian, F.Ashrafizadeh Pages 22-30
    The aim of this paper is to characterize welding of AISI 31 0 austenitic stainless steel to Inconel 657 for use in oil-refining ind ustries. The welds were produced using four typ es of filler materials; nickel-based allo ys designated as Inconel 82, A, 617, and 310 SS. The interfaces and heat-affected zo nes were characterized b y optical and scanning electron microscopy. Interfaces on the two sides of the joints showed unmixed and heat- affected zones, while a partially melted zone was observed in the interdendritic regions of the HAZ in Inconel 657. The microhardness profile fro m the base metal to the HAZ exhibited high hardness in the case of Inconel 657 as an indication of -Cr precipitation in the HAZ of all the filler materials investigated and as the occurrence of precipitation hardenin g. It was concluded that undesirable regions such as UZ, HAZ, and PMZ have the least average size for Inconel 82 and 310 SS weldments among the weld metals studied.
  • M.Paghandeh, A.Monshi, R.Emadi Pages 31-35
    A basic alumina-spinel low cement castable (LCC) composed of sintered bauxite, reactive alumina, calcined alumina, calcined magnesia, microsilica, and high alumina refractory cement was prepared (castable A) to which 5% sodium hexa-meta phosphate was later added (castab le B) to prepare samples for heat treatment at 110 C, 900 C, and 1400 C. Bulk Density (BD), Apparent Porosity (AP), and Cold Crushing Strength (CCS) were measured and XRD and SEM studies were performed. It was shown that after heat treating at 110 C, CCS of castable B increased by more than 3 times while its AP value was less than half that of castable A. The main difference between the two samples was found to lie in the presence of Mg2P2O7 and AlPO4. 2H2 O which are responsible for increases in CCS. At the temperature range of 800-1000 C where the hydraulic bond reverses to the dehydrated condition and castable A becomes weak with high porosity, castable B showed a CCS value of mo re than 4 times. Needles of magnesium phosphate were found to be responsible for reinforcing the microstructure of castable B at 900 C. After firing at 1400 C, castable B showed extraordinary CCS values of up 100 MPa (about 1000 Kg/Cm2), 5 times stronger, and AP% of below 1/5 times that of castable A. The phases present after firing were alumina, Al2 O3, spinel, MgAl2O4, calcium phosphate, Ca3 (PO4)2 and Enstatite, and MgSiO3. Magnesium phosphate melted at 1300-1 400 C and aided the formation of ceramic b ond s. The Ca coming from calcium aluminate cement reacted with phosphate and developed refractory calcium phosphate.
  • M.H.Joulazadeh Pages 36-40
    EAF plants normally consume coal and coke as reactants, alloying elements, or fuel. The price of these materials varies from € 0.20-0.35/kg. This is while nearly 10 million pieces of tires are annually discarded in Iran. The present study shows that scrap tires can be used as a substitute for coal and coke in EAF plants. Thirteen grades of steel including low, medium, and high carbon steels as well as low and high alloys were produced during 73 heats in a 6t EAF. Coke consumption reduced from 18.00 to 0.00 kg/ton f steel produced and power consumption decreased from 448 to 388 kWh/t. Stack gas analysis and easurements were performed to find that the gaseous pollutants released such as O, NOx, and SO2 were are less than the permitted standard limits. More than 00 heats have so far been carried out using waste ires in Esfahan Steel Co. ESCo) where experiments were conducted in this tudy. Industrial tests were eplicated in Iran Alloy Steel Company (IASCo) where 20 heats were made in a 0t EAF, which resulted n coke consumption to reduced from 15 to 0 kg/ts and power consumption to reduce by 10%. Similar esults were obtained in the EAF Unit of Malayer Alloy Steel Company operating a 25-ton heat capacity AF. The results of this study show that the process is reliable, economical, and eco riendly leading to a roduction cost reduction of 5 €/t.
  • M.Meratian, A.Hadjari Pages 41-46
    A full scale physical model of a thin slab caster with a four-hole design submerged entry nozzle (SEN) was constructed. On the basis of the dimensionless Reynolds and Froude similitude criteria, the fluid flow in a full- scale model is similar to that of the actual system and, hence, the data obtained from the water model can be applied to the actual system. In order to determine the optimum o perational parameters, experiments were carried out under different casting conditions. The results showed that the four-hole nozzle design leads to a special flow pattern. It was also shown that increased casting speed and gas injection both resulted in surface turbulence. In order to avoid surface turbulence and the related casting problems, it is recommended that SEN depths o f 30 and 40 cm be used for casting speeds of 3.5 and 4.5 m/min, respectively.