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Iron and steel society of Iran - Volume:14 Issue: 2, Summer and Autumn 2017

International Journal of iron and steel society of Iran
Volume:14 Issue: 2, Summer and Autumn 2017

  • تاریخ انتشار: 1396/08/30
  • تعداد عناوین: 7
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  • H. Mostaan *, F. Nematzadeh Pages 1-8
    In the present work, a high power Nd:YAG laser has been employed to weld AISI 430 ferritic stainless steel thin sheets. Optical microscopy was used to study the microstructural evolutions during laser welding. Tensile test and microhardness measurement were employed in order to investigate the mechanical behaviors of welds. Also, vibrational sample magnetometry was used for characterizing magnetic properties. Texture evolution during laser welding of AISI 430 stainless steel was also studied and a correlation was made between texture evolution and magnetic properties of welded samples. The effects of welding cycle on the mechanical properties of the laser welds in terms of fracture strength and microhardness profile are discussed. It was found that the magnetic properties of welded samples experiences significant decrease due to the formation of large grains in the fusion zone which are oriented in an unfavorable direction. The results showed that the grain size of base metal increase from 17 μm up to 92 μm after laser welding. Also, base metal had a dominant -fiber, some α-fiber components and also rotated cube texture component. But after laser welding, the cube texture however has been diminished when α and -fiber completely disappears. These phenomena also led to decrease in fracture strength of welded samples.
    Keywords: Laser welding, Texture evolution, AISI 430, magnetic properties, mechanical properties
  • M. Ebrahimi, Iman Danaee *, H. Eskandari, S. Nikmanesh Pages 9-15
    In this study, the effect of molybdate on the electrochemical behavior and semi-conductive properties of duplex stainless steel 2205 passive film at NaCl solutions was investigated. Cyclic potentiodynamic polarization, impedance spectroscopy, mott-schottky plots and scanning electron microscopy (SEM) were used to study the passive behavior. Polarization curves showed that the corrosion current and passive current density of stainless steel decreased with increasing molybdate concentrations. Mott–Schottky analysis revealed that the passive films formed on duplex stainless steels behave as n-type and p-type semiconductors and the donor and acceptor densities reduced with increasing molybdate concentration. Electrochemical impedance spectroscopy (EIS) results showed that charge transfer and passive resistance increased in the presence of molybdate. In addition, double layer and film capacitance decreased with increasing molybdate concentration and passive film thickness increased. Scanning electron microscopy was used to study the steel surface and showed more uniform surface with lower damage in the presence of molybdate.
    Keywords: Duplex stainless steel 2205, Impedance, Mott–Schottky, Semiconductive property
  • M. R. Khanzadeh *, H. Bakhtiari, S. A. Akbarimusavi, A. Amadeh, G. Liaghat Pages 16-26
    An experimental test was carried out to explosively clad solution annealed Inconel 718 superalloy on quench-tempered AISI H13 hot tool steel. A wavy with vortices interface geometry was obtained from this experiment. A gradual change in the wavelength along the direction of welding was observed which was due to a change in the impact angle, following the plate contacts. In this paper, the experiment was simulated by the use of ABAQUS version 6.9 finite element software. The Williamsburg equations of state and Johnson- Cook constitutive equation were used to model the behavior of the explosive and plates, respectively. The numerical result showed that high localized plastic deformation was produced at the bond interface. Pressure magnitude was high enough to create deformation twins and slip lines in the vicinity of Inconel interface to accommodate the plastic deformation caused by shock wave velocity. SEM observation showed that the number of thin melt pockets produced in front of vortices at the interface of Inconel 718 was higher than that of AISI H13 steel. The reason was attributed to the difference between the thermal conductivity of welded alloys. The change of hardness was found to be more severe in superalloy than in steel.
    Keywords: Explosive cladding, Plastic deformation, Deformation twin, Vortices
  • M. N. Yoozbashi *, T. Hajiloo, E. Akbarzadeh, S. Yazdani Pages 27-32
    Terms of service of the steels with retained austenite in the microstructure, is severely depended on the stability of austenite during the course of deformation. The present work aims to evaluate the mechanical stability of austenite in nanostructured, carbide free bainitic steels during tensile testing and cold rolling process. To achieve the microstructure with retained austenite, the steel with chemical composition of (in wt.%) 0.76C-1.95Si-1.4Mn-0.12Ni-0.24Mo-0.69Al isothermally transformed at temperatures of 200, 250 and 300°C for 6, 16 and 72 hours, respectively, after austenitizing at 950°C for 30 min. Austenite stability was evaluated by means of microhardness testing, x-ray diffraction pattern analysis and color metallography. Further study was carried out by comparing the incremental work hardening exponent obtained from the stress-strain curve. According to the results, austenite transforms into martensite in a progressive manner; blocky austenite at the early, but filmy austenite at the later stage of deformation. Samples transformed at the 300 °C have a good capability of retained austenite to martensite transformation. This is as a result of the higher mechanical stability of the austenite in this microstructure.
    Keywords: Mechanical stability, Retained Austenite, Tensile testing, Cold rolling, Nano bainite
  • S. Abbasi *, M. Esmailian, S. Ahangarani Pages 33-37
    In this research the role of alloying elements on the microstructure and mechanical properties of an as cast and hot rolled high strength low alloy (HSLA) steel was studied. Different compositions with different amount of copper in the presence of nickel, hot rolled and quenched in oil. Tensile test, hardness test, scanning electron microscope (SEM) and optical microscope (OM) were used to evaluate different properties of each sample. The results showed that, all the samples revealed a ferrite-perlite structure in as cast structure, however finer structure with higher hardness was seen in the samples with higher amount of copper. Furthermore, in hot rolled samples, it was seen that addition of nickel and copper resulted in grain refinement. A remarkable drop was seen in elongation due to copper precipitation. Fractography also revealed that, increasing copper amount led to variation of fracture mechanism from ductile to shear ductile fracture.
    Keywords: HSLA steel, Composition, Mechanical properties, Microstructure
  • A. Meysami *, H.I. Rahimzadeh, R. Amini Najafabadi, T. Dallali Isfahani Pages 38-42
    Steel pipes with circular cross-sections are usually used in cooling panels of electric arc furnaces. In the present study pipes with square cross-sections under equivalent conditions were used to obtain more information on the possibility of increasing the heat transfer and cooling efficiency. The results showed increased efficiency of the square pipe compared to the circular cross-section pipes. This increase led to an increase in the cooling power and life expectancy under similar conditions. The fluid flow field and heat transfer were obtained using simulation. A comparison of the heat transfer and the energy of the circular and square cross-sections showed that the square cross-sections had a higher rate of heat transfer and work efficiency.
    Keywords: Pipe, Arc furnace, Radiator, computational fluid dynamics
  • E. Karamian, R. Emadi *, A. Monshi, H. Emadi Pages 43-48
    This study describes the role of in situ nano SiC whiskers on the strength and density of alumina silicate–SiC-carbon refractory compounds. The prepared specimens were composed of 65 wt. % chamotte as alumina silicate compound, 15 wt. % SiC-containing material regenerates and 10 wt. % fine coke and 10 wt. % liquid resole as binder. Different values of additives (such as silicon and ferrosilicon metal) were added to a batch of 100 g of mixture. Cold crushing strength (CCS) and bulk density(BD) were measured after tempering at 200 ºC for 2h and firing at 1100 ºC and 1400 ºC for 2h. At low temperature of 200 ºC, the resit structure was formed in resole and by in-creasing the cross linking, the CCS values were approximately achieved 65 MPa. But at high temperature of 1400 ºC, in situ β-SiC whiskers of nano sized diameter were formed, and the CCS values improved by almost four times in the samples containing 6 wt. % ferrosilicon metal. The cross linking was destroyed at 1100 ºC and in situ β-SiC whisker was not fully formed
    Keywords: Alumina silicate, Chamotte, SiC, Carbon, Silicon, Resole