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Erratum to: Electrochemical Frequency Modulation: Solution Resistance and Double Layer Capacitance Considerations
Erratum to: CORROSION SCIENCE AND TECHNOLOGY, Vol. 20, No. 5(2021), pp.231~241
DOI: https://doi.org/10.14773/cst.2021.20.5.231

The objective of this study was to evaluate total current under steady-state conditions for a material undergoing corrosion using the electrochemical frequency modulation (EFM) technique, taking into account the presence of solution resistance and double layer capacitance. The analysis involving linearization of the Tafel curve allowed for the estimation of corrosion parameters. Results showed that the output signal was dependent on fundamental frequencies and their multiples. In addition, the output signal almost manifested itself at frequencies that were sums of fundamental frequencies of the applied sinusoidal signal. The harmonics calculated showed a significant shift from the principal frequency of input signals. The investigation involved the influence of corrosion current and anode-to-cathode Tafel slope ratio on faradaic and non-faradaic currents (including the average and RMS). The model presented showed both qualitative and quantitative improvements over the previously developed EFM technique that ignored the influence of solution resistance and the double layer capacitance while assuming the applied DC potential corresponded to the corrosion potential of the corroding material.
KEYWORDs : Modulation, Corrosion, EFM, Frequency
AUTHORs : Shashi Lalvani†, Sifat Ullah, and Lei Kerr

Page : 491 - 491 DOWNLOAD
Erratum to: 스테인리스 스틸의 표면 산화피막 성장과 내부식성 상관관계
Erratum to: CORROSION SCIENCE AND TECHNOLOGY, Vol. 20, No. 3(2021), pp.152~157
DOI: https://doi.org/10.14773/cst.2021.20.3.152

Stainless steel is a metal that does not generate rust. Due to its excellent workability, economic feasibility, and corrosion resistance, it is used in various industrial fields such as ships, piping, nuclear power, and machinery. However, stainless steel is vulnerable to corrosion in harsh environments. To solve this problem, its corrosion resistance could be improved by electrochemically forming an anodized film on its surface. In this study, 316L stainless steel was anodized at room temperature with ethylene glycol-based 0.1 M NH4F and 0.1M H2O electrolyte to adjust the thickness of the oxide film using different anodic oxidation voltages (30 V, 50 V, and 70 V) with time control. The anodic oxidation experiment was performed by increasing the time from 1 hour to 7 hours at 2-hour intervals. Corrosion resistance according to the thickness of the anodic oxide film was observed. Electrochemical corrosion behavior of oxide films was investigated through polarization experiments.
KEYWORDs : Stainless steel, Anodization, Oxide thickness, Nanostructure, Corrosion resistance
AUTHORs : 박영주 · 정찬영†

Page : 484 - 490 DOWNLOAD
인장 및 압축 등방 잔류응력 측정을 위한 누프 압입시험의 응력환산계수 결정
Instrumented indentation testing has been widely used for residual stress measurement. The Knoop indentation is mainly selected for determining anisotropic mechanical properties and non-equibiaxial residual stress. However, the measurement of equibiaxial stress state and compressive residual stress on a specimen surface using Knoop indentation is neither fully comprehended nor unavailable. In this study, we investigated stress conversion factors for measuring Knoop indentation on equibiaxial stress state through indentation depth using finite element analysis. Knoop indentation was conducted for specimens to determine tensile and compressive equibiaxial residual stress. Both were found to be increased proportionally according to indentation depth. The stress field beneath the indenter during each indentation test was also analyzed. Compressive residual stress suppressed the in-plane expansion of stress field during indentation. In contrast, stress fields beneath the indenter developed diagonally downward for tensile residual stress.
Furthermore, differences between trends of stress fields at long and short axes of Knoop indenter were observed due to difference in indenting angles and the projected area of plastic zone that was exposed to residual stress.
KEYWORDs : Equibiaxial stress, Residual stress, Knoop indentation, Stress conversion factor, FEM
AUTHORs : 정민재 · 김영천†

Page : 475 - 483 DOWNLOAD
불소 첨가/미첨가 인공타액 용액에서 연마 및 마스킹 조건이 적층제조 Ti-6Al-4V 합금의 동전위분극시험 결과에 미치는 영향
Additively manufactured titanium alloy is one of the promising materials in advanced medical industries. However, these additively manufactured alloys show corrosion properties different from those of conventional materials due to their unique microstructure. In this study, the effect of surface roughness and masking conditions on the results of the potentiodynamic polarization tests on additively manufactured or conventional Ti-6Al-4V alloys in artificial saliva solution with or without fluoride was investigated. The results showed that the corrosion potential was slightly lower with a flat cell with an O-ring than with masking tape. The corrosion rate was decreased with decreases in the surface roughness. Localized corrosion involving delamination of the surface layer occurred at 7 ~ 9 V (SSC) on the additively manufactured alloy in solution with or without fluoride when the samples were finished with 1000-grit SiC paper, whereas localized corrosion was not observed in the specimens finished with 1-μm alumina paste.
KEYWORDs : Ti-6Al-4V, Corrosion, Additive Manufacturing, Artificial Saliva, Fluoride ion
AUTHORs : 안경빈 · 장희진†

Page : 466 - 474 DOWNLOAD
해수 환경에서 듀플렉스 스테인리스강의 전기화학적 거동 및 캐비테이션 특성
A wet type scrubber for merchant vessel uses super austenitic stainless steels with pitting resistance equivalent number (PREN) of 40 or higher for operation in a harsh corrosive environment. However, it is expensive due to a high nickel content. Thus, electrochemical behavior and cavitation erosion characteristics of UNS S32750 as an alternative material were investigated. Microstructure analysis revealed fractions of ferritic and austenitic phases of 48% and 52%, respectively, confirming the existence of ferritic matrix and austenitic island. Potentiodynamic polarization test revealed damage at the interface of the two phases because of galvanic corrosion due to different chemical compositions of ferritic and austenitic phases.
After a cavitation test, a compressive residual stress was formed on the material surface due to impact pressure of cavity. Surface hardness was improved by water cavitation peening effect. Hardness value was the highest at 30 μm amplitude. Scanning electron microscopy revealed wave patterns due to plastic deformation caused by impact pressure of the cavity. The depth of surface damage increased with amplitude. Cavitation test revealed larger damage caused by erosion in the ferritic phase due to brittle fracture derived from different strain rate sensitivity index of FCC and BCC structures.
KEYWORDs : Duplex stainless steel, Cavitation, Erosion, Electrochemical corrosion, UNS S32750
AUTHORs : 허호성 · 김성종†

Page : 451 - 465 DOWNLOAD
고분자 전해질 연료전지 양극 작동 환경에서 실험 시간 및 작동 전압 변수에 따른 316L 스테인리스강의 전기화학적 특성과 손상 거동
In this investigation, electrochemical characteristics and damage behavior of 316L stainless steel polymer electrolyte membrane fuel cell(PEMFC) were analyzed by potentiodynamic and potentiostatic tests in cathode operating condition of PEMFC. As the result of potentiodynamic polarization test, range of passive region was larger than range of active region. In the result of potentiostatic test, damage depth and width, pit volume, and surface roughness were increased 1.57, 1.27, 2.48, and 1.34 times, respectively, at 1.2 V compared to 0.6 V at 24 hours. Also, as a result of linear regression analysis of damage depth and width graph, trend lines of damage depth and width according to applied potentials were 16.6 and 14.3 times larger, respectively. This demonstrated that applied potential had a greater effect on pitting damage depth of 316L stainless steel. The damage tendency values were 0.329 at 6 hours and 0.633 at 24 hours with
applied potentials, representing rapid growth in depth direction according to the test times and applied potentials. Scanning electron microscopy images revealed that surface of specimen exhibited clear pitting damage with test times and applied potentials, which was thought to be because a stable oxide film was formed by Cr and Mo.
KEYWORDs : PEMFC, Metallic bipolar plate, 316L Stainless steel, Electrochemical characteristics, Corrosion behavior
AUTHORs : 신동호 · 김성종†

Page : 435 - 450 DOWNLOAD
고분자 전해질 연료전지 금속분리판용 316L 스테인리스강의 양극작동조건에서 염화물 농도에 따른 부식 특성
The interest in eco-friendly energy is increasing, and polymer electrolyte membrane fuel cell (PEMFC) is attracting attention as alternative power sources. Research on metallic bipolar plates, a fuel cell component, is being actively conducted. However, since the operating conditions of PEMFC, in which sulfuric acid (H2SO4) and hydrofluoric acid (HF) are mixed, are strong acidity, the durability of the metallic bipolar plate is very important. In this research, the electrochemical characteristics and corrosion damage behavior of 316L stainless steel, a material for metallic bipolar plates, were analyzed through potentiostatic corrosion tests with test times and chloride concentrations. As the test times and chloride concentrations increased, the current density and corrosion damage increased. As a result of observation with scanning electron microscope(
SEM) and 3D microscope, both the depth and width of pitting corrosion increased with increases in test times and chloride concentrations. In particular, the pitting corrosion damage depth at test conditions of 6 hours and 1000 ppm chloride increased the most. The growth of the pitting corrosion damage was not directly proportional to time and increased significantly after a certain period.
KEYWORDs : PEMFC, Metallic bipolar plate, 316L Stainless steel, NaCl concentration, Electrochemical characteristics
AUTHORs : 신동호 · 김성종†

Page : 426 - 434 DOWNLOAD
소둔 및 용접후열처리가 슈퍼 오스테나이트계 스테인리스강의 부식거동에 미치는 영향
The effect of two different annealing temperatures on the level of the second phase precipitated in the microstructure
and the corrosion behaviors of super austenitic stainless steel were examined. The sample annealed
at a higher temperature had a significantly lower fraction of the sigma phase enriched with Cr and Mo elements,
showing more stable passivity behavior during the potentiodynamic polarization measurement. However,
after the welding process with Inconel-type welding material, severe corrosion damage along the
interface between the base metal and the weld metal was observed regardless of the annealing temperature.
This was closely associated with the precipitation of the fine sigma phase with a high Mo concentration in the
unmixed zone (UMZ) during the welding process, leading to the local depletion of Mo concentrations around
the sigma phase. On the other hand, the fraction of the newly precipitated fine sigma phase in the UMZ was
greatly reduced by post-weld heat treatment (PWHT), and the corrosion resistance was greatly improved.
Based on the results, it is proposed that the alloy composition of welding materials and PWHT conditions
should be further optimized to ensure the superior corrosion resistance of welded super austenitic stainless
steel.
KEYWORDs : Super austenitic stainless steel, GTAW, Sigma phase, Alloy 625, PWHT
AUTHORs : 윤덕빈 · 박진성 · 조동민 · 홍승갑 · 김성진†

Page : 412 - 425 DOWNLOAD
슈퍼오스테나이트 스테인리스강의 순환동전위 분극특성에 미치는 해수온도의 영향과 손상 거동에 관한 미시적 분석
Because austenitic stainless steel causes localized corrosion such as pitting and crevice corrosion in environments containing chlorine, corrosion resistance is improved by surface treatment or changes of the alloy element content. Accordingly, research using cyclic potentiodynamic polarization experiment to evaluate the properties of the passivation film of super austenitic stainless steel that improved corrosion resistance is being actively conducted. In this investigation, the electrochemical properties of austenitic stainless steel and super austenitic stainless steel were compared and analyzed through cyclic potentiodynamic polarization
experiment with varying temperatures. Repassivation properties were not observed in austenitic stainless steels at all temperature conditions, but super austenitic stainless steels exhibited repassivation behaviors at all temperatures. This is expressed as α values using a relational formula comparing the localized corrosion rate and general corrosion rate. As the α values of UNS S31603 decreased with temperature, the tendency of general corrosion was expected to be higher, and the α value of UNS N08367 increased with increasing temperatures, so it is considered that the tendency of localized corrosion was dominant.
KEYWORDs : UNS S31603, UNS N08367, Sea water, Temperature, Cyclic potentiodynamic polarization
AUTHORs : 황현규 · 김성종†

Page : 403 - 411 DOWNLOAD
배관의 부식 상태 진단에 사용되는 ER 부식센서의 가속부식환경에서의 신뢰성 평가
In this study, the reliability of a commercial ER-type corrosion sensor was evaluated under an accelerated corrosion environment to verify its suitability for application in monitoring of ship’s seawater piping system. A closed-loop pump piping testbed was designed and constructed to compare the wall thickness reduction of the pipe and the response from the sensor. The sensor was attached inside the pipe near the outlet of the pump that was exposed to a 3.5% NaCl solution with or without copper accelerated acetic acid (CASS). The results demonstrated that the presence of CASS significantly increased the corrosivity of the solution as well as the thickness reduction of the pipe, as expected. On the other hand, the corrosion products formed by the solution with CASS were thicker compared with those without CASS. The sensor response to temperature variation was found to be a clear linear relationship for the solution without CASS
but there was a non-linear relationship where CASS was present.
KEYWORDs : CASS Solution, Corrosion Monitoring, Temperature, ER Sensor, Linear Fitting
AUTHORs : 황현규 · 신동호 · 김헌희 · 이정형†

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