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Carbon steels requires the corrosion resistance against sulfuric and hydrochloric acid dew-point corrosion at the low temperature section of FGD systems. The design of the corrosion-resistant steels was focused on a small number of conventional alloying elements such as Cu, Sb, W, Mo, Cr, Mn, Nb, Al, Co, P. The corrosion rate decreased in the following order: P > Blank > Cr, Co, Al, Nb, Mn, W, Mo ≫ Cu. The Cu-containing steel presents the lowest corrosion rates due to the accumulated Cu compound, Cu and Cu oxides, on the surface. The corrosion rate decreased in the following order: Cu-Cr, Cu-Mo > Cu > Cu-W > Cu-Sb. W, Mo and Cr is not effective with Cu content. Addition of Sb not only created a protective Sb oxides film on the steel surface, but also accelerated the reaction of copper deposition through the adsorbed complex salt, Cu-Sb species. (Received July 3, 2014)

keyword : alloys, rolling, corrosion, scanning electron microscopy，SEM, acid dew-point corrosion

A newly developed low-alloy corrosion-resistant steel shows superior properties to sulfuric and hydrochloric acid dew-point corrosion as well as excellent mechanical properties, weldability and machinability with attention to low cost and high efficiency. In addition, welding materials which can accommodate the corrosion-resistant properties and mechanical properties of newly developed low-alloy corrosion-resistant steel have also been developed. Generally, to assess corrosion performance of developed steels, specimens were evaluated by laboratory corrosion tests in a simulated field environment. However, a flue gas desulfurization (FGD) system included several environmental parameters such as change of corrosion environment depending on shutdown/ operation of power plants, location of steels in facilities and velocity of a moving fluid. Therefore, to verify the reliability of newly corrosion-resistant steel, plant qualification test is necessary. In an actual environment, new developed low-alloy corrosion-resistant steel was proved to have better corrosion resistance than the other steels (existing corrosion-resistant steels and ordinary carbon steel). (Received July 26, 2014)

keyword : alloys, rolling, corrosion, scanning electron microscopy，SEM, sulfuric and hydrochloric acid dew- point corrosion-resistant steels

Composite materials are artificially engineered materials composed of a matrix and filler with reinforcing agents embedded in the matrix to enhance various properties. These days, as the demand for lightweight and high performance composite materials is increasing, especially in the field of transportation, many efforts are focused on research activity in the area of carbon nanotube (CNT) composite materials. In this review paper, the first discovery of the CNT is considered and the various properties of CNTs, such as mechanical (stiffness, tensile strength, damping), electrical and thermal properties, are briefly explained. For the evaluation of the recent lightweight and high performance CNT composites research trends, papers published within the last 10 years are selected. The role of the strengthener CNTs (SWCNTs and MWCNTs) and several different polymers (epoxy resin, polypropylene and polystyrene) for the matrix materials are considered in the evaluation. It is found that many research activities for the modification of the CNT surface focus on the uniform distribution of the CNTs in the matrix. Research work for the improvement of the binding energy between CNTs and polymers is also emphasized to optimize the mechanical behaviors. (Received August 11, 2014)

keyword : functionally graded materials, FGM, extrusion, fracture, mechanical properties, scanning electron microscopy, SEM

We investigated effects of annealing conditions on the interface-correlated microstructural evolution and subsequent mechanical properties of a Ti/STS439 clad sheet. The evolution of the interface microstructure was first analyzed with optical microscopy, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. The generation and growth of a diffusive layer consisted of μm-scale β- Ti adjacent to the parent Ti, and the nm-scale intermetallic compounds Fe2Ti and FeTi adjacent to STS phases were indexed. The thicknesses of β-Ti, Fe2Ti, and FeTi increased with annealing time and temperature. Mechanical properties were evaluated by peel, microindentation and uniaxial tensile tests. Improvement of bonding strength between Ti and STS by feasible annealing below 650 ℃ seemed to be strongly related to the generation of considerable metallurgical bonding. (Received March 7, 2014)

keyword : composites, rolling, interfaces, scanning electron microscopy, SEM, mechanical properties

SM45C steel was welded by conventional CO2 arc and narrow gap welding (NGW). The fatigue strength of NGWed sample had a value about 90 MPa higher than that of the CO2 arc welded sample. The width of welding and heat affected zone in NGWed samples decreased about 40% compared to the conventional CO2 arc welded sample. The hardness value of the welding zone in the NGW sample was 33.3% higher than that of the CO2 arc welded sample. The microstructure change of the SM45C during NGW revealed that the matrix was transformed to the martensite phase. With the small width of welding and heat affected zone in the NGW, therefore, the specimen with NGW had a faster cooling rate after welding. We therefore concluded that the hardness was increased by hard martensite formation during cooling after NGW, and this increase in hardness resulted in better fatigue strength of SM45C steel compared to conventional CO2 arc welding. (Received March 13, 2014)

keyword : SM45C, welding, fatigue, hardness, narrow gap welding

Fe-(0.02-1.3)%Si-(0.2-0.8)%Mn alloys were oxidized between 1050 ℃ and 1200 ℃ for up to 1 h in air, and subsequently hot rolled. Thick, non-adherent, porous oxide scales formed due to the severe oxidizing conditions. Silicon was scattered as fine Si-rich oxides inside the oxide scale, formed a thin Fe2SiO4 layer at the scale-alloy interface, and formed Fe1.58SiO4 oxides in the subscale where small Fe-Si-Mn internal oxide precipitates coexisted. Unlike the iron oxides that fractured, disintegrated, and compressed during hot rolling, the thin Fe2SiO4 layer that formed during oxidation still existed even after hot rolling, which deteriorated the hot rolling performance. (Received March 5, 2013)

keyword : alloys, hot working, microstructure, oxidation, transmission electron microscopy, TEM, Si steel

In order to investigate the feasibility of use of DRI containing a large quantity of Al2O3 in BOF steelmaking process, the solubility of MgO in BOF slag system with the Al2O3 content was studied in the temperature range of 1550 to 1650 ℃. The saturation content of MgO in the BOF slag increases linearly with the increase of the Al2O3 content due to the complex ionization of Al2O3. The MgO solubility in the slag decreases with in increase of the slag basicity and FetO content, and increases with an increase in the temperature. The effect of MnO on the MgO solubility in the slag was negligible, and MnO had a dilution effect on the slag composition due to the increase in slag volume. An index of slag composition for MgO solubility was derived by a regression analysis. An empirical equation was derived for the saturation content of MgO in slag as a fuction of the slag composition index and the temperature. (Received January 13, 2014)

keyword : oxides, recycling, melting, X-ray diffraction, slag, MgO solubility

The equilibrium constant is an important parameter in solvent extraction equilibrium and can be used to represent the extractant capability. The paper describes the application of the equilibrium constant in calculating an extraction isotherm. The solvent extraction of Mn(II) from chloride solutions using a mixture of Cyanex 272 + Cyanex 301 and Cyanex 301+ TBP was studied. Extraction isotherms were obtained using both the mixtures and these isotherms were compared with the calculated isotherms. The calculated isotherms were obtained by utilizing the equilibrium constant for the synergistic mixture. A comparison was made between isotherms obtained experimentally and calculated. (Received February 21, 2013)

keyword : manganese, II, equilibrium constant, extraction isotherm, calculation

The present study aims at investigating the effects of eutectic Si and Secondary dendrite arm spacing (SDAS) on mechanical properties of Al-Si-Cu alloy. Heat treatment and controlling of solidification rate affect to microstructure of Al-Si-Cu alloy. Al-Si-Cu alloy was dissolved in an electric furnace. The alloy cast in STD61 mold which had been pre-heated to 95 ℃ and 200 ℃. Eutectic Si and SDAS were finer as cooling rate increased. Image analysis technique has been utilized to examine the microstructure. Micros- tructure observation results showed that T6 heat treatment has a strong influence eutectic Si particle morphology. The mechanical properties, such as tensile strength, yield strength, elongation, were improved by ASTM E8 standard. Tensile properties of the Al-Si-Cu alloys prepared by different cooling rates were the same as each other by T6 heat treatment. (Received December 19, 2013)

keyword : alloy, solidification, microstructure, image analysis, Si morphology

The effect of coating melting behavior on nugget growth during resistance spot welding of hot- stamped boron steels was evaluated. A comparative analysis of the dynamic resistance for bare hot stamped and Al-Si coated hot stamped boron steels was carried out. The dynamic resistance curve of Al-Si coated hot stamped boron steel was higher than bare hot stamped boron steel during the whole stages of weld time. Higher α-peak and β-peak for Al-Si coated hot stamped boron steel resulted in larger nugget size at higher than 4.0 kA weld current owing to non-linear layer structure of alloyed coating, which appears to restrict the current passage through the faying interface. In the case of Al-Si coated hot-stamped boron steel, most of the Al-Fe intermetallic coatings are expected to be pushed away while in the liquid state at the faying interface. The pressure build up during the early stage of weld pushes the liquid Al-Fe intermetallic coating towards the edge of the faying interface. The continuous liquid state of Al-Fe intermetallic through the faying interface ensures the large contact area for the current passage to enlarge the nugget diameter. (Received June 1, 2014)

keyword : metals, welding, melting, optical microscopy, hot stamped boron steel