한국부식방식학회

HOME > >

Page : 193 - 201 DOWNLOAD
자동차 강재의 수소취성 연구에 대한 고찰
In order to suppress CO2 emission and protect passengers in case of vehicle collision, continuous efforts are being made to increase the application ratio and tensile strength of advanced high strength steels used in the manufacturing of automotive body. Simultaneously, hydrogen embrittlement which was not a concern in the past has currently become a major issue due to microstructure that is sensitive
to hydrogen uptake. The sensitivity increases with residual stress and hydrogen uptake content. Many automotive OEM companies and mill makers are setting specifications to control hydrogen embrittlement. The factors which lead to hydrogen embrittlement are material sensitivity, residual stress, and hydrogen concentration; researches are in progress to develop countermeasures. To reduce material sensitivity, mill makers add high energy trap elements or microstructure refinement elements. Automotive OEM companies design the car parts not to concentrate local stress. And they manage the levels to not to exceed critical hydrogen concentration. In this article, we have reviewed hydrogen embrittlement evaluation methods and corresponding solutions that are being studied in automobile manufacturing
industries and mill makers.
KEYWORDs : Automotives, CO2 emission, Advanced high strength steel, Hydrogen embrittlement
AUTHORs : 양 원 석,†·서 지 원·안 승 호

Page : 183 - 192 DOWNLOAD
스테인리스강 입계부식
Stainless steel can be classified into three categories depending on the microstructure as austenitic stainless steel, ferritic stainless steel and martensitic stainless steel. Generally, stainless steel is extremely resistant to corrosion as the name implies. However, under specific environments, susceptibility to localized corrosion such as pitting, intergranular corrosion and stress corrosion cracking increases. This paper reviewed the state of arts on intergranular corrosion mechanisms, countermeasures on intergranular corrosion and intergranular corrosion test methods. Intergranular corrosion is mostly related with chromium depletion at the grain boundary and sometimes with segregation of electroactive elements in solution
annealed stainless steel. Countermeasures on intergranular corrosion include avoiding chromium depletion by heat treatment and the addition of alloying elements. Sensitization evaluation of stainless steel was performed either through acid immersion test or electrochemical test. The methods were standardized in (Japanese Industrial Standards) . Even though are useful in evaluating the degree of sensitization for industrial purpose but do not provide detailed information about sensitization mechanism, cause and chromium profile.
KEYWORDs : Intergranular corrosion, Sensitization, Stainless steel, Chromium depletion, Grain boundary
AUTHORs : 김 홍 표†·김 동 진

Page : 176 - 182 DOWNLOAD
잔류 염소가 포함된 해수에서의 Cu-Ni 합금의 부식 거동 연구
Corrosion of the Cu alloy with 10wt% Ni in stagnant seawater with residual free chlorine was investigated. Despite that fact that Cu alloys are widely used for seawater applications due to their stubborn resistance to chloride attack, not much is known as to how the residual free chlorine in seawater affects corrosion of Cu and its alloys. In this work, immersion tests were conducted in the presence of different levels of chlorine for 90-10 Cu-Ni samples, one of the most frequently used Cu alloys for seawater application, mostly in shipbuilding. The results revealed no evidence for accelerated corrosion of the Cu-Ni alloy even in the presence of 5 ppm residual chlorine in seawater, signifying that the Cu-Ni alloy can be more tolerant to residual chlorine that has been commonly cited by the shipbuilding industry. However, comparison of polarization behavior of the alloy samples in the presence of different electrolytes with different concentrations of residual chlorine suggests that higher concentration of chlorine could increase the corrosion rate of the Cu-Ni alloy. Furthermore, it is suggested that microorganisms in the seawater could increase the corrosion rate of the Cu-Ni alloy by encouraging exfoliation of the corrosion product
off the metal surface.
KEYWORDs : MIC, Chlorination, Cu alloy, Residual chlorine, Seawater corrosion
AUTHORs : 정 근 수†·윤 병 영·임 채 선

Page : 166 - 175 DOWNLOAD
적층가공된 티타늄 합금의 전기화학적 특성에 미치는 불산의 영향
In this study, the electrochemical properties of CP-Ti (commercially pure titanium) and Ti-64 (Ti-6Al-4V) were evaluated and the effect of hydrofluoric acid on corrosion resistance and electrochemical properties was elucidated. Additive manufactured materials were made by DMT (Directed Metal Tooling) method.
Samples were heat-treated for 1 hour at 760 oC and then air cooled. Surface morphologies were studied by optical microscope and SEM. Electrochemical properties were evaluated by anodic polarization method and AC-impedance measurement. The oxide film formed on the surface was analyzed using an XPS. The addition of HF led to an increase in the passive current density and critical current
density and decreased the polarization resistance regardless of the alloys employed. Based on the composition of the oxide film, the compositional difference observed by the addition of HF was little, regardless of the nature of alloys. The Warburg impedance obtained by AC-impedance measurement indicates the dissolution of the constituents of CP-Ti and Ti-64 through a porous oxide film.
KEYWORDs : Additive manufacture (3D printing), CP-Ti, Ti-6Al-4V, Hydrofluoric acid, Electrochemical properties
AUTHORs : 김기태･조현우･장현영･김영식†

Page : 154 - 165 DOWNLOAD
Effects of Sulfuric Acid Concentration and Alloying Elements on the Corrosion Resistance of Cu-bearing low Alloy Steels
During the process of sulfur dioxide removal, flue gas desulfurization equipment provides a serious internal corrosion environment in creating sulfuric acid dew point corrosion. Therefore, the utilities must use the excellent corrosion resistance of steel desulfurization facilities in the atmosphere. Until now, the trend in developing anti-sulfuric acid steels was essentially the addition of Cu, in order to improve the corrosion resistance. The experimental alloy used in this study is Fe-0.03C-1.0Mn–0.3Si-0.15Ni-0.31Cu alloys to which Ru, Zn and Ta were added. In order to investigate the effect of H2SO4 concentration and the alloying elements, chemical and electrochemical corrosion tests were performed. In a low concentration of H2SO4 solution, the major factor affecting the corrosion rate of low alloy steels was the exchange current density for H+/H2 reaction, while in a high concentration of H2SO4 solution, the major factors were the thin and dense passive film and resulting passivation behavior. The alloying elements reducing the exchange current density in low concentration of H2SO4, and the alloying elements decreasing the passive current density in high concentration of H2SO4, together play an important role in determining the corrosion rate of Cu-bearing low alloy steels in a wide range of H2SO4 solution.
KEYWORDs : Cu-bearing low alloy steel, Sulfuric acid, Exchange current density, Passivation
AUTHORs : Ki Tae Kim and Young Sik Kim†

Page : 147 - 153 DOWNLOAD
Corrosion of Copper in Anoxic Ground Water in the Presence of SRB
Copper is used in various applications in environments favoring and enabling formation of biofilms by naturally occurring microbes. Copper is also the chosen corrosion barrier for nuclear waste in Finland. The copper canisters should have lifetimes of 100,000 years. Copper is commonly considered to be resistant to corrosion in oxygen-free water. This is an important argument for using copper as a corrosion protection in the planned canisters for spent nuclear-fuel encapsulation. However, microbial biofilm formation on metal surfaces can increase corrosion in various conditions and provide conditions where corrosion would not otherwise occur. Microbes can alter pH and redox potential, excrete corrosion-inducing metabolites, directly or indirectly reduce or oxidize the corrosion products, and form biofilms that create corrosive microenvironments. Microbial metabolites are known to initiate, facilitate, or accelerate general or localized corrosion, galvanic corrosion, and intergranular corrosion, as well as enable stress-corrosion cracking. Sulfate-reducing bacteria (SRB) are present in the repository environment. Sulfide is known to be a corrosive agent for copper. Here we show results from corrosion of copper in anoxic simulated ground water in the presence of SRB enriched from the planned disposal site.
KEYWORDs : Copper, Repository, Sulfate reducing bacteria, Anoxic ground water, Corrosion
AUTHORs : L. Carpén†, P. Rajala, and M. Bomberg

<
1
>