• Corrosion Science and Technology
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• 제18권3호
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• pp.73-77
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• 2019

Hot-dip aluminized coating has been widely used to protect steel substrate against corrosion. In this study, the corrosion behavior of hot-dip aluminized type 409L (11% Cr) stainless steel (SS) was investigated using macro- and micro-scale polarization tests. An Al-Fe-Si alloy layer that was formed due to inter-diffusion of alloying elements between Al coating and SS substrate was observed between Al coating and 409L SS substrate. In both macro- and micro-scale polarization tests, the corrosion potential ($E_{corr}$) of the 409L SS substrate was much nobler than that of the Al coating and alloy layer. $E_{corr}$ of the alloy layer was between that of Al coating and 409L SS substrate. This indicates that the alloy layer can act as a buffer between the more active Al coating and the nobler SS substrate for pit growth in aluminized SS. The presence of the alloy layer appears to be helpful in hindering pitting corrosion of aluminized SS.

• 열처리공학회지
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• 제23권2호
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• pp.90-95
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• 2010

The effects of grain size on the corrosion resistance of 429EM ferritic stainless steels for automobile exhaust system were investigated. Using specimens held at maximum service temperature of $950^{\circ}C$ for 10~70 hours, electrochemical polarization tests were conducted. While corrosion current density, $I_{corr}$, was influenced little by grain size, pitting potential, $E_p$, was increased with an increase of grain size. Sensitizaton at grain boundary occurred when the specimen were held at $950^{\circ}C$ for above 50 hours because of the dissolution of precipitates and grain coarsening.

• 한국표면공학회지
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• 제31권2호
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• pp.73-80
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• 1998

The aim of this study is to develop sintered stainless steels (SSS) with good mechanical strength, wear resistance, and corrosion resistance by nitrogen ion implantation on the Culated SSS surface. Stainless steel compacts containg Cu (2-10 wt%) were prepared by electroless Cu-pating method which results in the increased3 homogenization in alloying powder. Nitrogen ion implantation was carried out by using N2 gas as the ion source. Nitrogen ions were embedded by an acceleratol of 130keV with doese $3.0\times10^{17}\;ions/\textrm{cm}^2$ on the SSS at $25^{\circ}C$ in$2\times10^{-6}$ torr vacuum. The nitrogen ion implanted SSS obtained from anodic ploarization curves revealed higher corrosion potential than that of nitrogen ion unimplante one. And nitrogen ion implanted 316LSSS had good resistance to pitting corrosion due to the synergistic effect of Mo and N, and the inhibition of $NH_4\;^+$<\TEX>, against $CI^-$<\TEX>.

• 한국표면공학회지
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• 제51권1호
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• pp.54-61
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• 2018

Plasma Nitriding treatment was performed on STS 204Cu stainless steel samples at a temperature of $400^{\circ}C$ for 15 hours with varying $N_2$ content as 10%, 15% and 25%. Regardless of the content of $N_2$, S-Phase which is a hardened layer of Nitrogen (N) supersaturated phase, was formed in the surface of plasma treated samples. When $N_2$ content was 25%, the thickness of the hardened layer reached up to about $7{\mu}m$ and the surface hardness reached a value of $560Hv_{0.05}$, which is about 2.5 times higher than that of untreated sample (as received $220Hv_{0.05}$). From potentiodynamic polarization test, it was observed that compared to as received sample, the corrosion potential and the corrosion current density of the plasma treated samples were decreased regardless of the $N_2$ content, but the corrosion resistance was not increased much due to the precipitation of $Cr_2N$. On the other hand, pitting potential of the samples treated with 10% and 15% $N_2$ was higher than that of as received sample, however, the samples treated with 25% exhibited a lower pitting potential. Therefore, 10% $N_2$ content was selected as optimum plasma nitriding condition and to further increase both the thickness and surface hardness and the corrosion resistance of the hardened layer, different $CH_4$ content such as 1%, 3% and 5% was introduced into the plasma nitriding atmosphere. With 1% $CH_4$, the thickness of the hardened layer reached up to about $11{\mu}m$ and the surface hardness was measured as about $620Hv_{0.05}$, which is about 2.8 times that of as received sample. And the corrosion resistance of the plasma treated sample by using 1% $CH_4$ was improved significantly due to much higher pitting potential, and lower corrosion current density. When the $CH_4$ content was more than 1%, the thickness and surface hardness of the hardened layer decreased slightly and the corrosion resistance also decreased.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.97-97
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• 2017

This study investigated the corrosion protection by electrodeposited copper layer on AZ31 Mg alloy with and without additional silver layer by immersion test, salt spray test, OCP transient and potentiodynamic polarization experiment. The single electrodeposited Cu layer on AZ31 Mg alloy showed a nodular structure with many imperfections of crevices between the nodules, which resulted in the fast initiation of pitting corrosion within first few hours of immersion. Double-layer coating of Cu and outer Ag layer slightly increased the initiation time for pitting corrosion. Triple-layer coatings of Cu/Ag/Cu exhibited the most efficient corrosion protection of AZ31 Mg alloy, compared to the single- and double-layer coatings. Surface morphology of the outer Cu layer in the triple-layer was changed from the nodular structure to fine particle structure with no crevices due to the presence of an additional Ag layer. Thus, the improved corrosion resistance of AZ31 Mg alloy by electrodeposited Cu/Ag or Cu/Ag/Cu layers is readily ascribed to the decreased number of imperfections in the electrodeposited layers due to the additional silver layer. It is concluded that the additional silver layer provides many nucleation sites for the second Cu plating, resulting in the formation of finer and denser structure than the first Cu electrodeposit.

• Corrosion Science and Technology
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• 제5권5호
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• pp.181-188
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• 2006

In this study, the characteristics of the experimentally produced high N-high Cr bearing stainless steels are discussed as a part of applications of materials for FGD (Fuel Gas Desulfurization) system of thermal power plants or for power plants using seawater as coolant. Corrosion resistance of developed alloys is especially investigated in detail. Corrosion characteristics of vacuum melted cast are shown to be superior to that of air melted one. From the viewpoint of CPT, It is estimated that the differences of corrosion resistance are $21.8^{\circ}C{\sim}24.6^{\circ}C$ at PRE 40 and $8^{\circ}C{\sim}12.4^{\circ}C$ at PRE 50, and the gaps becomes bigger as the PRE values are lower. In the evaluation of corrosion resistance in alloy A2501, Z3101, and A3301 according to Cr concentration, alloy A3301 shows a deviation from the general tendency in chloride solutions. It has relatively high PRE value as 48.6, but it has relatively poor pitting resistance. It is, however, difficult to observe a specific phase except ferrite in microstructure analysis and neither detects special phase such as sigma phase.

• Corrosion Science and Technology
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• 제10권5호
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• pp.167-174
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• 2011

Due to commercialization of nuclear power, most countries have taken interest in decontamination process of nuclear power plant and tried to develop a optimum process. Because open literature of the decontamination process are rare, it is hard to obtain skills on decontamination of foreign country and it is necessarily to develop proper chemical decontamination process system in Korea. In this study, applicable possibility in chemical decontamination for reactor coolant pump (RCP) was investigated for the various stainless steels. The stainless steel (STS) 304 showed the best electrochemical properties for corrosion resistance and the lowest weight loss ratio in chemical decontamination process with immersion type than other materials. However, the pitting corrosion was generated in both STS 415 and STS 431 with the increasing numbers of cycle. The intergranular corrosion in STS 431 was sporadically observed. The sizes of their pitting corrosion also increased with increasing cycle numbers.

• Corrosion Science and Technology
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• 제13권3호
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• pp.87-94
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• 2014

Recently, the application of bending products has been increased since the industries such as automobile, aerospace, ships, and plants greatly need the usage of pipes. For facility fabrication, bending process is one of key technologies for pipings. Induction heat bending process is composed of bending deformation by repeated local heat and cooling. Because of local heating and compressive strain, detrimental phases may be precipitated and microstructural change can be induced. This work focused on the effect of induction heat bending process on the properties of ASME SA312 TP316 stainless steel. Evaluation was done on the base metal and the bended areas before and after heat treatment. Microstructure analysis, intergranular corrosion test including Huey test, double loop electropotentiokinetic reactivation test, oxalic acid etch test, and anodic polarization test were performed. On the base of microstructural analysis, grain boundaries in bended extrados area were zagged by bending process, but there were no precipitates in grain and grain boundary and the intergranular corrosion rate was similar to that of base metal. However, pitting potentials of bended area were lower than that of the base metal and zagged boundaries was one of the pitting initiation sites. By re-annealing treatment, grain boundary was recovered and pitting potential was similar to that of the base metal.

• Corrosion Science and Technology
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• 제15권6호
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• pp.281-289
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• 2016

The effect of nitrogen on the electrochemical corrosion and nanomechanical behaviors of martensitic stainless steel was examined using potentiodynamic polarization and nanoindentation test methods. The results indicate that partial replacement of carbon with nitrogen effectively improved the passivation and pitting corrosion resistance of conventional high-carbon and high- chromium martensitic steels. Post-test observation of the samples after a potentiodynamic test revealed a severe pitting attacks in conventional martensitic steel compared with nitrogen- containing martensitic stainless steel. This was shown to be due to (i) microstructural refinement results in retaining a high-chromium content in the matrix, and (ii) the presence of reversed austenite formed during the tempering process. Since nitrogen addition also resulted in the formation of a $Cr_2N$ phase as a process of secondary hardening, the hardness of the nitrogen- containing steel is slightly higher than the conventional martensitic stainless steel under tempered conditions, even though the carbon content is lowered. The added nitrogen also improved the wear resistance of the steel as the critical load (Lc2) is less, along with a lower scratch friction coefficient (SFC) when compared to conventional martensitic stainless steel such as AISI 440C.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.143.1-143.1
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• 2005