발간논문

Home > KJMM 논문 > 발간논문

Wear of blades, buckets, plates and chisel occurred in operation of construction machinery, agricultural equipments, earthmoving equipments and offshore structures cause earlier failure of the components, resulting in the increased energy consumption, cost of maintenance and replacement. To solve the problems, advanced materials with higher resistance to abrasive wear have been attempted to make through alloy design and hot deformation followed by air cooling. 0.25C-1.4Mn-1.0Cr-0.7Ni-0.2Mo-0.08V-0.02Cu steels produced by hot forging were cooled in air to form bainite, showing higher resistance to wear than any other steels with different chemical composition in the sliding wear tests under the applied load of 74N. Higher strain hardening during sliding wear of 0.25C-1.4Mn-1.0Cr-0.7Ni-0.2Mo-0.08V-0.02Cu steels to cause microploughing wear mode seems to be one of the main reasons for showing higher resistance to wear than any other steels in this study.

keyword : Alloys design, Bainite, Wear, Strain hardening, Hot forging, Air cooling microploughing wear mode, Higher resistance to wear

The plasma spray technique has been known as one of the surface modification methods to improve the mechanical properties or the functional characteristics of materials. This paper has aimed to investigate the effects of spray conditions, such as spray distance and arc power level, on the sliding wear properties of plasma sprayed Al_2O_3-40%TiO_2 coating layer. The sliding wear test using pin-on-disc type machine, has been conducted at several sliding speeds for the Al_2O_3-40%TiO_2 coating layer. The sliding wear test using pin-on-disc type machine, has been conducted at several sliding speeds for the Al_2O_3-40%TiO_2 layer coated on mild steel under different sprayed conditions. It is observed that the wear resistance of the plasma sprayed Al_2O_3-40%TiO_2 coating layer is changed with the spray distance and the arc power level. The wear resistance could be improved by decreasing the spray distance and by increasing the arc power level.

keyword : Plasma spray, Al2O3-40%TiO2, Sliding wear characteristics, Spray distance, Arc power level, Residual stress

Alloying element, Nitrogen is known to improve the resistance to pitting corrosing of stainless steels increasing the local pH within the active sites and enhancing repassivation of pits. However chloride ion is believed to promote the localized dissolution, due to the absorption of chloride ions on the passive film. Alloying element Nitrogen and chloride ion may also have influence on the electronic properties of passive films, causing the change of the resistance to the localized corrosion. The electronic properties of passive films formed on austenitic stainless steels, such as 316L and 316LN with different Nitrogen content were investigated in neutral 0.1N Na_2So_4 and 0.N NaCl solutions. In-situ capacitance measurements were performed to obtain the information on the donor concentration and the thickness of space charge region within the passive film. Besides, potentiostatic polarization tests were carried out, to investigate the metastable pitting susceptibility. Results showed that alloying element Nitrogen increased the thickness of space charge layer while chloride ions increased the donor density and the metastable pitting susceptibility. Analyses of AES and AFM indicated that Nitrogen led to the increase in Cr peak within the film and the smoothness on the surface of film. The relationship between semiconducting properties of the passive film and the metastable pitting susceptibility was examined.

keyword : 316L, 316LN, Mott-Schottky plot, AES, Metastable pitting susceptibility

Effects of stabilizing elements such as titanium and niobium, and aluminium on toughness and corrosion of ferritic stainless steels were studied as a series of basic studies for optimizing the concentrations of minor alloying elements. Aluminum reduced the concentration of total oxygen and the size of oxides to improve toughness. Niobium, one of stabilizing elements used in this study improved toughness as well as corrosion resistance. It is due to the fact that niobium retards the formation of chromium-carbonnitride known as a site for crack initiation and as resulting in chromium depleted zone. Unexpectedly, titanium, the other of stabilizing elements did not improve toughness as effective as niobium. The cause in a angular shaped TiN formed at the temperature around the solidus line of the alloy. It was proved by inclusion analysis, measurements of DBTT, and the calculation on phase equilibrium. In addition, the reducement of pitting corrosion resistance by titamium seems to be contradictory to the previous known fact that titanium removes sulfur in steels and improves corrosion resistance. The discrepancy was solved by observation of the angular TiN on the surface causing micro cracks to provide a site for pitting.

keyword : Surface defects, TiN, Pitting corrosion, Crevice corrosion, Dual stabilization

Addition of fly ash has beneficial effects on some mechanical properties of concrete, as well as the corrosion process induced by the chloride ion. The aim of this study was to investigate the effect of fly ash on the steel corrosion in concrete with various water-to-binder ratios. The corrosion process of steel bars embedded in concrete without fly ash and with 20% fly ash was tested under complete immersion, in 3.5 wt.% NaCl solution. Monitoring of open-circuit potential and linear polarization method and electrochemical impedance spectroscopy(EIS) were used to follow the corrosion process. Also, ASTM C1202 test method was used to estimate the concrete`s resistivity of chloride penetration in concrete. The results obtained from electrochemical tests show that the use of fly ash has led to the improvement of corrosion resistance. Partial cement replacement by fly ash caused significant pore refinement, reduced permeability to chloride ions, and increased corrosion resistance.

keyword : Corrosion, Concrete, Fly ash, Immersion test, EIS

The AA5083/AA1050/SS41 plates were manufactured by an explosive welding method using an AA1050 aluminum alloy interlayer plate, and the effects of the interlayer thickness on the interface morphology and the shear deformation behavior were studied. The interfacial zone, FeAl_3, was generated due to the kinetic energy loss from collision at AA1050/SS41 interface, and contained some internal cracks after explosive welding. The crack propagation behavior in shear deformation varied according to the thickness and morphology of the interfacial zone, which depended on the thickness of AA1050 interlayer.

keyword : Explosive welding, AA5083/AA1050/SS41, Interlayer, Interfacial zone

The influence of weld defect on the continuous low cycle fatigue property for Type 316LN stainless steel base metal and weldment was investigated with a strain rate of 4×10_3/sec in air atmosphere. Low cycle fatigue test were conducted at temperature of 823K and 873K. Total strain amplitude was controlled to be 0.4-0.6%. The 308L stainless steel was used as the welding rod. The welding was done by the GtAW process with the welding direction perpendicular to the rolling direction of the base metal. The microstructures of the base metal and weldment are Υ phase and Υ/δ duplex-ferrite, respectively. The fatigue lives of the base metal had twice higher than those of weldment having no visible defect. From the tensile result, the uniform elongation of the base metal had twice higher than that of the weldment. For the base metal and HAZ, the fatigue lives at the same condition were reliable. But some results of the fatigue lives in the weldment had the lowest fatigue life at the same condition. From the observation of the fracture surface after fatigue tests, there were porosities and welding defects. For weldments having the many porosities and welding defects, the fatigue lives decreased 50% and 60-70%, respectively. From the observation of the microstructure near the internal crack, the internal weld defects was existed at the interface among the dendrites grown along the different direction.

keyword : Type 316LN, Low-cycle fatigue, Weldment, Weld defect, Porosity, HAZ

The solubility of nickel in molten CaO-Fe_tO-SiO_2-MgO slag system at 1723K was measured to understand the dissolution mechanism of nickel into the slag. The dependence of solubility of nickel on oxygen partial pressure and slag basicity indicated that the nickel was dissolved as an oxide ionic species NiO^2-_2 by following reaction: ［Ni(s)+｛1/2O_2(g)+O_2-(slag)｝=NiO^2-_2］ The distribution ratio of nickel increased with the increase of (X_CaO+X_MgO)/(X_SiO_2) at a fixed Fe_tO content. However, in CaO-SiO_2-Fe_tO-MgO_satd slag system , Fe_tO is considered to work as a relatively acidic component such as FeO_2￣at composition higher than about X_FgtO=0.25. MgO is revealed to be weaker basic oxide than CaO in CaO-SiO_2-Fe_tO-MgO_satd slag system.

keyword : Nickel, Dissolution behavior, Distribution ratio, Basicity, FetO, Recovery

To simulate the sulfuric acid leaching solutions of zinc calcine, synthetic solutions with the composition of ZnSO_4-Fe_2(SO_4)_3-Na_2SO_4-H_2SO_4-NaOH-H_2O were prepared and solution pH was measured at the temperature of 25, 50 and 75℃. The effect of temperature on the ionic equilibria of these solutions was analyzed by considering chemical equilibria, mass balance and charge balance equations. Activity coefficients of solutes and activity of water were calculated by using Pitzer equation. The mole fractions of iron containing species were greatly affected by solution temperature and the concentration of Fe_2(SO_4)_3. In the experimental ranges of ionic strength of solution up to 9m, the pH values calculated in this study were in good agreement with those measured.

keyword : Zinc calcine, Leaching, Sulfuric acid, Ionic equilibria, Pitzer, Temperature

keyword :