논문 : 머플러용 스테인리스강의 내식성에 미치는 열적 산화의 영향

김동우 ( Dong Woo Kim ),김희산 ( Hee San Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 대한금속·재료학회지 Vol.46 No.10

Reduction of NOx in emission gas, improvement of engine efficiency, and extension of warranty period has made demands for developing materials more corrosively resistant to the inner-muffler environments or predicting the lifetime of materials used in muffler more precisely. The corrosion inside muffler has been explained with condensate corrosion mainly though thermal oxidation experiences prior to condensate corrosion. Hence, the aim of this study is to describe how the thermal oxidation affects the corrosion of stainless steel exposed to the inner-muffler environments. Auger electron spectroscopy and electrochemical tests were employed to analyze oxide scale and to evaluate corrosion resistance, respectively. Thermal oxidation has different role of condensate corrosion depending on the temperature: inhibiting condensate corrosion below 380℃ and enhancing condensate corrosion above 380℃. The low temperature oxidation causes to form compact oxide layer functioning a barrier for penetrating condensate into a matrix. Although though thermal oxidation caused chromium-depleted layer between oxide layer and matrix, the enhancement of the condensate corrosion in high temperature oxidation resulted from corrosion-induced crevice formed by oxide scale rather than corrosion in chromium-depleted layer. It was proved by aids of anodic polarization tests and measurements of pitting corrosion potentials. By the study, the role of high temperature oxidation layer affecting the condensate corrosion of stainless steels used as muffler materials was well understood.

Magnetic NDE for Sensitization of Inconel 600 Alloy

Hiroaki Kikuchi,Takaki Sumimoto,Yasuhiro Kamada,Satoru Kobayashi 한국자기학회 2013 Journal of Magnetics Vol.18 No.3

Inconel 600 alloy, Ni base alloy, is widely used for steam generator tubings where sensitization occurs at grain boundaries and sensitization will induce tubing failures. This alloy has usually paramagnetic property, however, it transforms into ferromagnetic property along grain boundaries when sensitization occurs: this means NDE using magnetism for sensitization is possible. Therefore, in this study, Inconel 600 alloys were heat treated at 873 K from 0 to 400 hours so as to generate sensitization and their magnetic properties were investigated in detail. The saturation and the residual magnetization increase with increasing heat treatment time and take a maximum. On the other hand, the coercive force decreases with the increase in time of heat treatment. We confirmed that characteristics at only grain boundaries change into ferromagnetic phase by a MFM observation. As a trial for industrial application, heat treated Inconel 600 alloy was scanned by a magnetic field sensor, and the variations in magnetization were obtained nondestructively. The results indicate a feasibility of magnetic NDE for sensitization of Inconel 600 alloy.

스테인리스강 입계부식

김홍표 ( Hong Pyo Kim ),김동진 ( Dong Jin Kim ) 한국부식방식학회 2018 Corrosion Science and Technology Vol.17 No.4

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.

GTAW에 의한 스테인리스강 용접부위의 부식특성에 관한 전기화학적 평가

문경만(Kyung-Man Moon),이규환(Kyu-Hwan Lee),김진경(Jin-Gyeong Kim) 한국마린엔지니어링학회 2010 한국마린엔지니어링학회지 Vol.34 No.4

STS304와 22APU 스테인리스강에 가스 텅스텐 아크용접을 하였다. 이 경우 두 강의 용접부의 부식특성을 전기화학적 방법으로 검토하였다. STS304 용접금속의 경도(Hv-250)는 22APU 강 (Hv-217) 보다 상대적으로 높은 값을 보였다. 22APU의 용접금속과 STS 304의 열영향부의 부식전류밀도는 다른 용접부위와 비교하여 각각 높은 값이 관찰 되었으며, 이것은 예민화 온도 영역에 있는 STS304의 열영향부와 22APU의 용접금속에 형성된 크롬탄화물로 크롬결핍이 더욱 활성태의 양극으로 쉽게 부식된 것에 기인하는 것으로 사료된다. 그리고 이들 두 강의 용접금속과 열영향부는 크롬결핍상태에 있는 입자 사이 경계의 선택부식으로 입계부식을 나타내었다. 결과적으로 다른 용접방법의 적용이나 적절한 용접봉 사용은 두 강의 용접부에 대한 내식성을 개선하기 위해서 필요한 것으로 사료된다. GTAW was carried out to the austenitic 304(STS 304) and 22 APU stainless steels. In this case, difference of the corrosion characteristics of welded zone with STS 304 and 22APU mentioned above was investigated with electrochemical methods. Vickers hardness of weld metal in case of STS 304 (Hv-250) showed a relatively higher value than this of 22 APU(Hv-217). The corrosion current densities of weld metal of 22APU and heat affected zone of STS 304 were observed at the highest value compared to those of other welding zone respectively. This is probably because chromium depletion field due to chromium carbide formed to weld metal of 22APU and to heat affected zone of STS 304 can preferentially easily be corroded with more active anode than other fields. Consequently it is thought that application of the other welding methods like as laser welding or using of the optimum filler metals is necessary to improve the corrosion resistance of welding parts of these steels.

Corrosion Characteristics of Welding Zones by Laser and TIG Welding of 304 Stainless Steel

( Kyung Man Moon ),( Myung Hoon Lee ) 한국부식방식학회 2010 Corrosion Science and Technology Vol.9 No.6

Two types of welding methods were performed on austenitic 304 stainless steel: laser welding and TIG welding. The differences of the corrosion characteristics of the welded zones from the two welding methods were investigated with electrochemical methods, such as measurement of the corrosion potential, polarization curves, cyclic voltammogram, etc. The vickers hardness of all laser-welded zones (WM:Weld Metal, HAZ:Heat Affected Zone, BM:Base Metal) was relatively higher while their corrosion current densities exhibited a comparatively lower value than those which were TIG welded. In particular, the corrosion current density of the TIG-welded HAZ had the highest value among all other welding zones, which suggests that chromium depletion due to the formation of chromium carbide occurs in the HAZ, which is in the sensitization temperature range, thus it can easily be corroded with an active anode. Intergrenular corrosion was also observed at the TIG-welded HAZ and WM zones. Consequently, we can see that corrosion resistance of all austenitic 304 stainless steel welding zones can be improved via the use of laser welding.

Laser 용접한 스테인리스강의 용접부위의 부식특성에 관한 평가

문경만(Kyung-Man Moon),원종필(Jong-Pil Won),박동현(Dong-Hyun Park),김윤해(Yun-Hae Kim),이명훈(Myung-Hoon Lee),김진경(Jin-Gyeong Kim) 한국해양공학회 2012 韓國海洋工學會誌 Vol.26 No.4

Laser welding was carried out on austenitic 304 (STS 304) and 2 APU stainless steels. In this case, the differences between the corrosion caracteristics of th welding zones of the two stainless steels were investigated using electrochemical methods. The Vickers hardness values of the weld metal (WM) zones in both cases, the STS 304 and 22 APU stainless steels, showed relatively higher values than those of other welding zones. The corrosion current densities of the heat affected zone (HAZ) of the 22 APU and the base metal (BM) zone of the STS 304 exhibited the highest values compared to the other welding zones. It is generally accepted that whe STS 304 stainless steel is welded using a general welding method, intergranular corrosion is often observed at the grain boundary because of its chromium depletion area. However, when laser welding was performed on both the STS 304 and 22 APU stainless steels, no intergranular corrosion was observed at any of the welding zones. Consequently, it is considered that the intergranular corrosion of stainless steel can be controlled with the application of laser welding.

Selective Catalytic Reduction (SCR) 환경에서 18% 크롬 스테인리스강의 부식 거동

김희산 ( Heesan Kim ) 한국부식방식학회 2023 Corrosion Science and Technology Vol.22 No.3

Effects of high-temperature environment and low-temperature environment on corrosion behaviours of 18Cr stainless steels (type 304L, type 441) in simulated selective catalytic reduction (SCR) environments were studied using weight loss test in each environment and rust analysis. With time to exposure to the hightemperature environment, type 441 was more resistant to corrosion than type 304L due to both higher diffusivity of Cr and lower thermal expansion coefficient in α-iron. The former provides a stable protective Cr₂O₃ layer. The latter leaded to low residual stress between scale and steel, reducing the spallation of the scale. With time to exposure to the low-temperature environment, on the other hand, type 304L was more resistant to corrosion than type 441. The lower resistance of type 441 was caused by Cr-depleted zone with less than 11% formed during the pre-exposure to a high-temperature environment, unlike type 304L. It was confirmed by results from the crevice corrosion test of sensitised 11Cr steel. Hence, to achieve higher corrosion resistance in simulated SCR environments, ferritic stainless steels having lower thermal expansion coefficient and higher diffusivity of Cr but containing more than 18% Cr are recommended.

스테인리스강의 GTAW 용접부위 부식특성에 관한 전기화학적 평가

문경만(Kyung-Man Moon),이규환(Kyu-Hwan Lee),김진경(Jin-Gyeong Kim) 한국마린엔지니어링학회 2010 한국마린엔지니어링학회 학술대회 논문집 Vol.2010 No.4

GTAW carried out to austenitic 304 stainless steel and 22 APU. In this case difference of corrosion characteristics of welded zone with two welding base metals mentioned above was investigated with electrochemical methods such as measurement of corrosion potential, polarization curves and cyclic voltammogram etc.. The corrosion current density in weld metal of 22SPU and heat affected zone of STS304 in those of other welding zone were observed with highest value. We can see that corrosion resistance of weld metal of 22APU stainless steel can apparently be improved by using of the other high density welding methods.

오스테나이트계 중탄소 및 저탄소 스테인리스강의 입계부식 거동 분석

김영식,원석연,김규빈,유영란,최승헌 한국부식방식학회 2022 Corrosion Science and Technology Vol.21 No.3

Austenitic stainless steel has been widely used because of its good corrosion resistance and mechanical properties. However, intergranular corrosion can occur if the alloy is welded or aged. The objective of this study was to determine intergranular corrosion behaviors of austenitic medium carbon (0.05 wt%) and low carbon (0.02 wt%) stainless steel aged at several conditions. Alloys were evaluated according to ASTM A262 Practice A, ISO 12732 DL-EPR (double loop-electrochemical potentiokinetic reactivation) test, and ASTM A262 Practice C. The degree of sensitization and intergranular corrosion rate were obtained. The relationship between the degree of sensitization and the intergranular corrosion rate showed a very large fluctuation. Such behavior might be related to whether two-dimension tests or three-dimension tests were performed. On the other hand, regardless of carbon content of alloys, when the intergranular corrosion rate increased, the degree of sensitization also increased. However, the DL-EPR test showed a higher sensitivity than the Huey test for differentiating the intergranular corrosion property at a low intergranular corrosion rate, while the Huey test had a higher sensitivity than the DL-EPR test for distinguishing the intergranular corrosion property at a high intergranular corrosion rate.

GTAW에 의한 스테인리스강 용접부위의 부식특성에 관한 전기화학적 평가

문경만(Kyung-Man Moon),이규환(Kyu-Hwan Lee),김진경(Jin-Gyeong Kim) 한국마린엔지니어링학회 2010 한국마린엔지니어링학회지 Vol.34 No.5