• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.213-214
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• 2009

Recently the use of ferritic stainless steels for automotive exhaust system has been increased dramatically. A detailed knowledge of material behavior of ferritic stainless steel is important for successful manufacturing of exhaust systems. To achieve this goal, numerical study of square cup deep drawing for ferritic stainless steel sheet, type 409L was conducted with Yld2000-24. Uniaxial tensile test and hydraulic bulge test were performed to characterize plastic material behavior. Finite element simulation of square cup deep drawing was performed successfully.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03a
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• pp.149-152
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• 1999

The effect of initial orientation on the microstructure and texture evolution of two ferritic stainless steels was investigated. the columnar and equiaxed crystal specimens which were prepared from continuous casting slab were hot rolled annealed cold rolled and annealed respectively. The rolling and recrystallization textures at each process stage were examined by orientation distribution function (ODF) and electron back-scattered diffraction (EBSD); The observation showed that the orientation density of the $\alpha$-fibre of hot rolled band of columnar crystal specimen was more pronounced than that of the equaxed one at the center layer. Nevertheless the cold rolled textures of Type 430 steel have demonstrated a rather similar development . Compared to Type 430 steel the development of the $\alpha$-fibre in the center layer of Type 409L steel was much more pronounced. The relation between texture evolution and ridging behaviour has been discussed.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.5
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• pp.409-414
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• 2013

In this work, corrosion of 304 stainless steel was evaluated by using acoustic emission(AE) technique. AE measurement system was set for detecting acoustic signal during accelerated corrosion test of the specimen. AE signal started to be detected after the time of pitting corrosion initiation was evaluated by anodic polarization curve. Pitting corrosion damage was confirmed by optical microscopic observation of the surface morphology. AE cumulative counts and amplitude according to corrosion time could be divided into three stages. These trends were discussed in relation with changing pitting corrosion mechanism. Feasibilities of AE technique for evaluation of corrosion damage and mechanism were suggested.

• Transactions of Materials Processing
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• v.22 no.3
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• pp.133-142
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• 2013

Recently, electric vehicles and hybrid cars are being promoted as alternatives to reduce automobile emissions. Generally, thin sheet materials such as aluminum alloy AA300X and cold-rolled steel sheet such as JIS-G-3141 are used for the container for the lithium-ion secondary batteries. In this study, a multi-stage deep drawing process is used to produce a rectangular cup from thin stainless steel sheet material, SUS409L, with an initial blank thickness of 0.4mm for the battery container application. Numerical simulations of the first through the fifth stages for the multi-stage deep drawing with thin SUS409L sheet were conducted using LS-Dyna3D Implicit/Explicit. Special consideration was given to the deformation characteristics due to the normal anisotropy of the sheet material. The numerical simulations were conducted with both isotropic properties and the anisotropic properties of the initial blank material. An unexpected forming failure, barreling in the bottom region of the deep drawn rectangular cup, was observed. This failure mode can be avoided by additional ironing thickness control during the process.

• Journal of Welding and Joining
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• v.19 no.6
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• pp.608-613
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• 2001

In this study, the rotary bending fatigue test was carried out with two kinds of base metal, martensite stainless steel STR3 and austenite stainless steel STR35 and the dissimilar friction welded material with them. To compare the fatigue fifes according to the notch positions, the small circular defect was worked on the bonded line, 1.0mm and 0.5mm distance form the bonded line. The fatigue limits of the STR3 and STR35 base metal were 429.0MPa and 409.4MPa respectably. In comparison with fatigue life at the same notch positions, the STR35 specimens showed about 190% for base metal, 82% for 1.0mm distance notched specimens higher than that of the STR3. But the fatigue life of the 0.5mm distance notched STR35 specimen showed about 35% lower than that of the STR3 specimen. And the bonded line notched specimen was much lower fatigue life than the other specimens because of separation of the bonded line.

• Korean Journal of Metals and Materials
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• v.48 no.4
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• pp.297-304
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• 2010

The microstructure and hardness of $CO_2$ laser welds were investigated in the Ti-stabilized ferritic stainless steel 409L. The observed specimen was welded in a fully penetrated condition in which the power was 5 kW and the welding speed 5 m/min. The grain structure near the bond line of the laser welds was produced by epitaxial growth. The grain size was the largest in the fusion zone, and HAZ showed nearly the same grain size as that of the base metal. The HAZ microstructure consisted of subgrains and precipitates that were less than 100 nm in size and that were located along the subgrain boundaries. On the other hand, the hardness was the highest in the fusion zone due to the large amount of small precipitates present. These were composed of TiN, Ti(C,N) and $TiO_2$+Ti(C,N). The hardness decreased continuously from the fusion zone of the base metal. The HAZ hardness was slightly greater than that of the base metal due to the existence of subgrains and precipitates in the subgrain boundary.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.45-45
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• 2003

409L 페라이트강은 스테인레스강내 Ti을 첨가함으로써 내식성이 우수한 자동차 배기계 부품용으로 개발된 강이다. 그러나 Ti 첨가시 용존산소 및 질소와의 반응 생성물에 의해 용강의 주조성, 표면품질, 등축정율 저하등 조업 및 품질문제를 발생시킨다. 한편 용강의 응고시 생성되는 미세 질화물은 주편의 등축정율을 높혀, 주편의 가공성 및 최종제품의 품질을 향상시키는 것으로 알려져있다. 따라서 스테인레스 용강중 Ti의 반응 생성물 제어는 매우 중요하며, 이를 위해서는 고 Cr 함유 스테인레스 용강내 Ti의 열역학적 거동과 타 원소와의 상호작용계수를 측정하여야 한다.

• Journal of the korean Society of Automotive Engineers
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• v.13 no.6
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• pp.39-47
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• 1991

본 연구논문의 내용은 현재 국내 자동차 업계에서 자동차 배기부품으로 전량 수입되고 있는 STS 409L 스테인레스강을 국산화하기 위한 개발연구에 대한 내용으로서 배기관용 스테인레스강 409L의 제조기술과 관련된 국내외 기술개발 동향과 포항제철 스테인레스 제조설비에 맞는 적정합금성분계와 조업조건을 도출하기 위하여 실험적으로 시험조사하여 품질 제특성을 평가한 연구결과이다. 주요 내용으로서 합금원소가 열연 및 냉연 소둔조업조건에 미치는 영향을 조사하기 위하여, C, N과 Ti 또는 Ti+Nb 원소 첨가를 변화시킨 409L 계열강에 있어서 소둔조업조건에 따른 재결정과 상변태 거동을 조사하엿으며, TIG용접에 의한 용접부의 기계적 특성과 가공성 그리고 고온부식 및 응축수 부식 시험을 통한 내식성 등의 품질 특성 평가를 조사 서술하였다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.203-204
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• 2002

The wear behaviour of steam generator (SG) tubes (Inconel 600 and 690) against support materials (405 and 409 ferritic stainless steels) has been experimentally studied in room temperature water using reciprocating wear apparatus with tube-an-plate configuration. The results showed that the wear rate of Inconel 690 was lower than that of lnconel 600 with increasing normal loads and sliding amplitudes. Also, plastic deformation layers appear below the surface of both SG tubes, which have a specific thickness and are small compared with their grain size. This means that wear rate of SG tubes in water condition is closely related to the formation and fracture of plastic deformation layers.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.42-42
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• 2009

마찰교반접합 (Friction Stir Welding)은 1991년 영국 TWI에서 개발된 접합 법으로서 회전하는 툴이 재료내부에 삽입되면 툴과 재료사이에서 발생하는 마찰열에 의하여 온도가 상승하게 되어 재료는 연화되고, 이러한 재료 내부에서 회전하는 툴이 이동하게 되면 재료 내부는 기계적 교반에 의해 소성변형이 일어남과 동시에 접합이 이루어진다. 마찰교반접합은 동적 재결정에 의한 접합부의 미세한 결정립 형성으로 인하여 기계적 특성이 향상되며 보호 가스가 필요 없어 친환경적임과 동시에 용융 용접 법에 비해 접합 시 에너지 소모가 적으며 또한 접합 후 접합부에서의 변형이 상대적으로 적다는 장점이 있다. 이러한 장점을 가진 마찰교반접합은 알루미늄 합금, 마그네슘 합금 그리고 동 합금과 같은 저 융점 비철재료에 많은 연구와 적용 사례들이 있어왔다. 하지만 최근에는 일반 탄소강, 연강, 오스테나이트계 스테인리스강, 니켈 합금, 티타늄 합금과 같은 고융점 재료에도 연구 및 적용이 진행되고 있는 추세이다. 페라이트계 스테인리스강은 가격이 비싼 Ni을 함유하지 않아 오스테나이트계 스테인리스강에 비하여 강재의 가격은 낮으면서도 고온특성 및 내식성이 우수하여 건축용, 자동차 배기계용으로 널리 사용되고 있다. 하지만 이런 장점을 가진 페라이트계 스테인리스강을 기존의 용융 용접 법으로 접합 시 용접부 및 열영향부에서의 결정립의 조대화로 인한 인성 및 연성이 저하되며, 특히 예민화된 열영향부 입계 내에 Cr 탄화물이 석출되어 입계주변에 Cr 결핍 층을 형성되어 입계부식이 발생되는 문제점이 발생된다. 본 연구에서는 마찰교반접합을 이용하여 두께 3mm의 409 스테인리스강에 대해 맞대기 접합을 실시하였다. 접합 변수를 툴의 재료 (WC-12wt%Co, $Si_3N_4$)로 하여 접합을 실시하였고 접합 후 외관상태 점검, 광학 현미경과 주사 전자 현미경을 통하여 미세조직을 관찰하였으며 황산-황산동 부식 시험을 실시하여 접합부의 부식 특성을 평가하였다.