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Iron and steel society of Iran - Volume:9 Issue: 2, Summer and Autumn 2012

International Journal of iron and steel society of Iran
Volume:9 Issue: 2, Summer and Autumn 2012

  • 42 صفحه،
  • تاریخ انتشار: 1392/11/15
  • تعداد عناوین: 7
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  • A.Baibordi, M.H.Bina, K.Amini, A.Dehghan Page 1
    In this research, tribological characteristics of Ni-P electroless coating and double-layered Ni-P/Ni-B electroless coating were studied. For this purpose, Ni-P electroless coating with 25 μm thickness was initially applied to the surface of steel Ck45 samples; then, a double-layered Ni-P/Ni-B electroless coating, including inner layer of Ni-P with 15 μm thickness and outer layer of Ni-B with 10 μm thickness, was applied to the surface of similar samples and were heat treated at 400˚C for 1 h. Effect of heat treatment on morphology, structural variations and wear behavior of coating was investigated using different tests such SEM, XRD and pin on disk wear test at room temperature. Hardness of the obtained coatings was measured by a Vickers microhardness machine prior and after heat treatment of the samples. The results showed that the double-layer coating with the same thickness in each layer improved hardness and wear resistance compared to the single-layer coating. Heat treatment led also to the creation of nano crystalline structure; therefore, hardness and wear resistance of the coating increased due to change in structure from amorphous to crystalline structure and created rigid phases of Ni3P.
    Keywords: Double, layer electroless coating, Heat treatment, Nano crystalline structure, Hardness, Wear resistance
  • Gh.Zirehpour, R.Shoja Razavi, E.Moayerifar Page 5
    As the turbine industries need to manufacture turbine blades made of martensitic stainless steel AISI 420 with high toughness and wear resistance, local laser hardening has become more and more important. In this research, surface of the samples was initially hardened by high-power pulsed laser beam; then, optimum parameters of hardening were calculated and wear resistance of surface hardened samples were compared with the similar parameter in the surface raw samples. Scanning Electron Microscope (SEM) was used to determine microstructure and surface phases. Reciprocating wear test was also performed for surveying wear resistance of the samples. The results showed that laser surface treatment led to producing a martensitic-austenitic microstructure and dissolution and/or redistribution of carbides. Hardness of surface of hardened samples was obtained about 700 Hv after laser hardening. Wear mechanism was transformed from laminate to abrasive during the testing.
    Keywords: Martensitic stainless steel AISI 420, Laser surface hardening, Wear
  • S.Saeedipour, A.Kermanpur, A.Najafizadeh, M.Fadavi, M.Abbasi, Y.Mazaheri Page 9
    In this study, the effects of nitrogen addition on the production of ultrafine/nano grained AISI 201L stainlesssteel by advanced thermo-mechanical process were investigated. Cast samples were first homogenized at 1200 °C for 4 h, hot-rolled at 1100 °C and finally, solution-annealed at 1150 °C for 2.5 h. Unidirectional and cross multipass cold rolling at 25 °C was carried out to 90% reduction in thickness, followed by annealing at temperature and time range of 800–900 °C and 15–1800 s, respectively. The results showed that increasing nitrogen led to the decrease of delta ferrite content and austenite grain size after solution annealing. It was also found that decreasing nitrogen content and using cross rolling resulted in an increased volume fraction of the strain induced martensite (SIM) and reduced saturation strain of martensite formation during cold rolling. Also, the results from the reversion process revealed that with increasing nitrogen concentration, the formation of thermally induced martensite was suppressed.
    Keywords: Martensite thermomechanical processing, nitrogen, 201L stainless steel, Cold rolling, Reversion annealing
  • I.Hajiannia, M.Shamanian, M.Kasiri Page 14
    In the present study, the corrosion behavior of AISI 347 austenitic stainless steel to ASTM A335 low alloy For this purpose, two filler metals, ER309L and ERNiCr-3, were selected to be used during the gas tungsten arc welding process. To investigate the corrosion behavior of the joints after welding, the specimens were tested in 3.5% sodium chloride solution using Tafel and cyclic polarization tests. Also, the microstructures of base and weld metals were evaluated using optical microscopy. The microstructural evaluations showed that a two-phase structure consisting of dendritic and inter-dendritic regions with primary austenite solidification was observed in ERNiCr-3 filler metal and a primary skeleton-shaped ferrite in austenitic matrix was observed in 309L filler metal. The results of electrochemical tests also showed that 347 austenitic stainless steel base metal had more resistance to corrosion in comparison to A335 low alloy steel base metal, due to more amounts of chromium and nickel in its structure. Also, ERNiCr-3 filler metal displayed better resistanceto pitting corrosion.
    Keywords: Corrosion, Dissimilar Welding, Austenitic stainless steel, Low Alloy Steels, microstructure
  • M.Alizadeh Page 27
    In this research, the effects of oxygen injection during the induration process were studied in order to improve the quality specifications and increase the rate of production of the iron oxide pellets. Several experiments were carried out in palletizing pilot plant in different conditions of oxygen injection. The results suggested that if only the extra oxygen was injected into the furnace in a specific range of time and temperature, shortening of the time of heating process and increasing the rate of production in the induration machine could be achievable. Furthermore, the optimal condition for oxygen injection into the combustion gas was determined for the pellets containing the coke powder. The microstructures of a cross section of the pellets were investigated via scanning electron microscopy. The results showed that oxygen injection into the furnace provided the condition for the production of a uniform homogenous structure without cracks and microstructure defects in iron ore pellet.
    Keywords: Magnetite, Oxygen injection, Iron ore pellet, Coke powder
  • M.Akbarzadeh, A.Shafyei, H.R.Salimijazi Page 32
    In this study, physical vapor deposition (PVD) Ti-Cr-N coatings were deposited at two different temperatures100 and 400ºC on hardened and tempered tool steel substrates. The influence of the applied deposition temperature on the physical and mechanical properties of coatings such as roughness, thickness, phase composition, hardness and Young’s modulus were evaluated. Phase compositions were studied by X-ray diffraction method. Mechanical properties were determined by Nano indentation. The results showed different behavior s in the mechanical properties by changing the deposition temperature. (Ti, Cr)N and TiN coatings consisted of only one solid solution cubic phase, while CrN coatings exhibited hexagonal Cr2N and cubic CrN phases. Mechanical behavior of the (Ti, Cr)N coatings was related to the Ti content and their hardness reduced by decreasing the Ti content. (Ti, Cr)N coatings deposited at high temperature exhibited better mechanical properties compared to the coating deposited at low temperatures.
    Keywords: physical vapor deposition, characterization, microstructure, mechanical property, Ti, Cr, N coating