발간논문

Home > KJMM 논문 > 발간논문

The objective of this study was to examine the wear-corrosion behavior of 18Mn(V, Mo) steel, which had a minor amount of Cr addition (< 3 wt%), in an artificial seawater environment, and compare it to conventional carbon steel. A variety of electrochemical experiments, including linear polarization resistance, impedance spectroscopy, and galvanostatic polarization, were conducted, along with weight loss measurements after immersion and wear-corrosion testing. These tests aimed to determine the static corrosion and wear-corrosion mechanisms of 18Mn(V, Mo) steel with respect to Cr addition. The results of this study indicated that the addition of Cr to 18Mn(V, Mo) steel refined the V₄C₃ particles in the microstructure, which led to an increase in surface hardness. Moreover, the 18Mn(V, Mo) steel with Cr addition exhibited the lowest corrosion and corrosion-wear losses, compared to 18Mn(V, Mo) steel without Cr and conventional carbon steel. This beneficial effect was primarily attributed to the formation of a thin Crenriched corrosion scale that adhered to the underlying steel. This corrosion scale served as a protective barrier against the penetration of corrosive species and as a lubricant for mechanical wear. The 18Mn(V, Mo) steel with Cr addition has potential application in various industrial fields, particularly in marine and offshore environments, owing to its low corrosion-induced wear loss rate in a brine environment. (Received 12 April, 2023; Accepted 22 May, 2023)

keyword : 18Mn steel, Cr, corrosion, wear, seawater

Conventional non-skid coatings for marine construction contain polymeric materials. These materials are generally susceptible to high temperature environments because of their low thermal conductivity and thermal resistance. A metal-based non-skid coating has great potential for high temperature applications, yet, there has only been limited research. In this study, twin wire arc spray (TWAS) was used to fabricate Al and Al-3%Ti coatings on a high strength low alloyed (HSLA) steel substrate. The purpose of this study is to confirm the feasibility of TWAS Al-based coating for non-skid areas on marine construction. The static coefficient friction of TWAS Al-based coatings exhibited excellent and uniform values compared with a conventional epoxy-based non-skid coating. The specific heat and thermal conductivity of TWAS Al-based coating was measured and compared with that of the substrate. The thermal property values of the TWAS Al-based coating were reported for the first time in this study. The TWAS Al-based coating had A continuous interface with the substrate and the general microstructural features of a thermal-sprayed metal coating. After exposure to 500℃ for 24 hours, the an Fe-Al intermetallic compound and oxide were formed inside of the coating and coating-substrate interface. The adhesion strength indicated that the TWAS Al-based coating sustained its strength after the isothermal exposure test. The Vickers hardness of the TWAS Al-3%Ti coating was higher than that of the Al coating. The solid solution hardening of Ti atoms in the as-deposited coating and the precipitation hardening of the TiAl3 compound in the heat-treated coating contributed to the improvement of in Vickers hardness. Thus, the TWAS Al-3%Ti coating is proven to be a promising nonskid coating for high temperature applications. (Received 14 April, 2023; Accepted 16 June, 2023)

keyword : twin wire arc spray (TWAS), non-skid coating, microstructure, high temperature exposure, mechanical property

A cold roll-bonding (CRB) process is applied to study the effects of stacking number on the microstructure and mechanical properties of roll-bonded and age-treated Al sheets. Commercial AA1050 and AA6061 sheets with a thickness of 2 mm were stacked alternately on each other to two and four layers, and roll-bonded by multi-pass cold rolling. The roll-bonded Al sheets were then subjected to natural aging (T4) and artificial aging (T6) treatments. The as roll-bonded Al sheets showed a typical deformation structure, where the grains are elongated in the rolling direction regardless of the stacking number. However, after the T4 and T6 aging treatments, the Al sheets had a recrystallization structure consisting of coarse grains in both the AA5052 and AA6061 regions with different grain sizes in each. In addition, the sheets showed an inhomogeneous hardness distribution in the thickness direction, with higher hardness in AA6061 than in AA1050 after the T4 and T6 age treatments. The tensile strength of the T6-treated specimen was higher than that of the T4-treated one for both the 2 and 4-layer CRBs. In addition, both the tensile strength and elongation of the specimens processed by the 4-layer stack CRB were higher than those of the 2-layer stack CRB for all experimental conditions. (Received 4 May, 2023; Accepted 16 June, 2023)

keyword : aluminum alloys, cold roll-bonding, aging treatment, mechanical properties, microstructure

In this study, the influence of heat input and post-seam annealing (PSA) temperature on the microstructure and impact toughness of electric resistance welded (ERWed) API X70 steel pipe was investigated. The ERW seam welds of pipes were fabricated with low, moderate, and high heat inputs, and followed by the PSA process at 950 ℃. Regardless of heat input, the API X70 steel pipe exhibited good weldability, resulting in similar microstructure factors, i.e., metal flow angle (~70°), bondline width (~22 μm), and ferrite grain size (~4.4 μm). Although (Mn, Si)-rich oxide penetrators which are known to impair impact toughness were observed at the bondline, the area fraction was estimated to be as low as 0.011% in all the ERW seam welds. The impact toughness was not affected by these penetrators because of their minimal fraction, leading to ductile fracture at -20 ℃. However, different PSA temperatures (870, 950, and 1040 ℃) resulted in the different grain sizes of the seam welds. The ERW seam weld annealed at 1040 ℃ (PSA1040) exhibited the largest ferrite grain size near the bondline, whilst the smallest grain size was found in the ERW weld annealed at 870 ℃ (PSA870). In spite of having the smallest grain size, PSA870 exhibited the lowest impact toughness value, showing brittle fracture at -20 ℃. It was observed that the difference in residual stresses was not macroscopically detectable by the hole drilling method. The kernel average misorientation (KAM) maps indicated that the highest level of residual stress was observed near the bondline of PSA870, as evidenced by a high density of dislocations. This study provides instructive results, indicating that the impact toughness of ERW seam welds are significantly more affected by residual stresses than by the grain refinement effect. (Received 19 April, 2023; Accepted 26 June, 2023)

keyword : electric resistance welding, post seam annealing, microstructure, impact toughness, residual stress

A Fe-based filler material with the composition of Fe-20Ni-5Co-2.5Mn-0.2C was used for welding 9% Ni steel, and the effect of post-weld heat treatment on the microstructure and mechanical properties of the welded joints was investigated. Post-weld heat treatment of the welded joint was performed in the temperature range of 200 to 600 ℃. After the experimental selection, the microstructure changes of the weld metal and base metal were investigated in detail at heat treatment temperatures of 350 and 600 ℃. Grain morphology, size, and the location of precipitated cementite were studied using SEM and EBSD phase maps. The mechanical properties of the weld joint were characterized by tensile properties and micro-hardness. Based on the experimental results, this study provides key insights into the applicability of post-weld heat treatment to weld joints of 9% Ni steel prepared using Fe-based filler material to improve the mechanical properties, toughness and ductility of the weld joints. (Received 20 April, 2023; Accepted 2 June, 2023)

keyword : Fe-based filler material, 9% Ni steel, welding metallurgy, post-weld heat treatment

With the increasing numbers of electric vehicles and the prevalence of high heat generating devices, recent studies have attempted to address the limitations of conventional solder materials, including their low durability at temperatures exceeding 200 ℃, insufficient mechanical properties in a joint, and low thermal conductivity. Transient liquid-phase (TLP) partial bonding using solders or Sn, and sinter bonding using Ag particles, are alternative bonding methods which involve a modification or change of the material. Advanced alternatives can significantly reduce bonding time or material cost. Various additional studies have investigated various core-cell particles that can be used to form an all-metallic bondline. This review summarizes reports of bonding studies using different core-cell particles. The particles were not only applied as a form of paste but also preform. In the TLP bonding using X(Cu, Ag, Ni)@Sn particles, the degree of voids generated in the formed bondline was dependent on the type of intermetallic compound formed. The preforms consisting of X@Sn particles provided relatively uniform microstructure and void distribution, compared to the pastes containing identical X@Sn particles, resulting in better long-term mechanical reliability. The addition of Zn@Sn particles contributed to the more practical control of microstructure and mechanical properties in the joint formed by pure Sn and Sn-58Bi solder alloys. Cu@Ag particles can be considered a promising low-cost material for compression-assisted sinter bonding, replacing pure Ag particles. The application of core-cell particles is expected to improve the processes used for forming metallic bondlines. (Received 1 November, 2022; Accepted 17 May, 2023)

keyword : metallic bondline, core-shell particle, bonding property, transient liquid-phase bonding, sinter bonding

Wet chemical analysis techniques for four elements (M = As, Pb, Sb, and Sn) in Ag - M binary alloys were investigated with emphasis on the choice of solvent acid and the characteristic wavelength used in the ICP-AES (Inductively-Coupled Plasma Atomic Emission Spectrometer) analysis. The elements are representative tramp elements in ferrous scrap. The activity of these elements needs to be increased to remove them efficiently during the molten scrap refining process. The activity of these elements in the molten scrap (molten iron alloy) is usually measured by a chemical equilibration technique with molten Ag. Therefore, performing an accurate and reliable chemical analysis of these elements in the molten iron alloy and the molten Ag alloy is important. Preliminary tests using conventional acids (hydrochloric acid, nitric acid) resulted in unreliable results. In the present study, the proper choice of acids as solvents was investigated for each element M in the Ag-M alloys. Several synthesized Ag-M alloys of known compositions were analyzed using two ICP-AES systems independently, for cross-checking. As and Pb in Ag alloys could be successfully dissolved in the nitric acid-based solution. On the other hand, Sb and Sn in Ag alloys did not dissolve in the nitric acid-based solution completely, leaving some precipitates. It was found that the addition of hydrofluoric acid could resolve this problem. In addition to this, the effect of the mass of the Ag-M alloy and wavelength selection during ICP-AES analysis on the accuracy and the reproducibility were investigated. An optimized procedure for the wet chemical analysis of these elements in Ag-M alloys is reported. (Received 8 March, 2023; Accepted 19 June, 2023)

keyword : Ag-M (M= As. Pb. Sb. and Sn), tramp element, wet chemical analysis, ICP-AES

Azurite is an inorganic pigment commonly used in traditional painting arts and even today. This pigment has two types: natural azurite and synthetic artificial azurite, called blue verditer or blue bice. Because they have the same structure and similar appearance they are difficult to distinguish. The purpose of this study is to compare these two types pigments, focusing on material properties and accelerated weathering behavior. Natural azurite consist of copper carbonate and mineral compounds like quartz, kaolinite. On the other hand, artificial azurites are synthesized using azurite and calcite. As a result of thermal analysis, unlike natural azurite, the calcite in artificial azurite resulted in weight loss at three temperatures, at approximately 350 ℃, 650 ℃, and 840 ℃. According to the microscope analysis results, natural azurites have clearly blue angular particles with sharp edges, produced by crushing. Artificial azurite showed spherules and aggregates with tiny rounded or fibrous particles. After accelerated weathering tests, the natural azurites had no change in color, particle shape or original components, but the artificial azurites noticeably changed color and shape. The color changes of artificial azurites occurred due to the growth of calcite crystallite, a slight new product formation, and change in particle shape. Even though natural azurites are more expensive pigments, they provide superior color durability and particle shape stability compared to artificial azurites. (Received 17 May, 2023; Accepted 13 June, 2023)

keyword : azurite, pigment, blue verditer, blue bice, accelerated weathering

Titanium alloys are used in many fields including military, aerospace, and biomedical because of their excellent specific strength, corrosion resistance, and biocompatibility. Recently, much research has been focused on addressing the disadvantages of conventional manufacturing methods, including reducing material and energy waste when manufacturing titanium alloy parts by additive manufacturing methods. However, due to rapid cooling, during the additive manufacturing process the material develops acicular and lamellar microstructures, and despite high strength, those features are detrimental to ductility and toughness, as compared with conventionally manufactured alloys. As a result, numerous studies have sought to obtain an equiaxed microstructure through heat treatment. However, the developed heat treatment processes are quite complex, and involve several heat treatment cycles, making such processes economically unfavorable. To overcome these limitations we suggest a different approach to obtaining an equiaxed structure in 3D-printed titanium alloy, by controlling the oxygen level. The present study analyzed the globularization behavior of Direct Energy Deposited (DED) Ti-6Al-4V alloy as a function of oxygen content and a simple heat treatment. The microstructure was globularized through oxygen level control and furnace cooling to compensate the disadvantages in the mechanical properties of additive manufactured alloys. (Received 14 December, 2022; Accepted 12 June, 2023)

keyword : Additive manufacturing, Ti-6Al-4V, Oxygen level, Microstructure, Mechanical properties