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철도차량 적용을 위한 신개발강종 LDSS 3종의 점용접성 평가
임재용(Jae Yong Lim),정현승(Hyunseung Jung),김정국(Jeong Guk Kim),서승일(Sungil Seo),원성연(Sungyeun Won),최점용(Jeom Yong Choi) 한국철도학회 2014 한국철도학회 학술발표대회논문집 Vol.2014 No.5
스테인리스 철도차량 부재 적용을 목적으로 한 신개발강종인 Lean Duplex Stainless Steel (LDSS) 3종 점용접부의 강도평가를 수행하였다. 현재 스테인리스 전동차 부재의 연결이음부위는 KS R 9204 규격에서 규정한 바와 같이 STS301L 과 STS304 두 강종에 관하여만 언급하고 있으며 판 두께에 따른 허용 인장전단하중을 제시하고 있다. 이에 따라 본 연구에서는 LDSS 3종에 대한 점용접 시편을 제작하였으며, 너깃 지름과 허용 인장전단하중을 평가하였다. 시편 제작을 위해 우선적으로 점용접 조건을 탐색하였으며, 이를 바탕으로 제작된 시편을 이용하여 너깃 직경 측정과 인장-전단 시험을 수행하였다. 시험 결과 신개발 강종 3종의 점용접부는 0.4~4.5mm 판재 두께에 대해 KS B 0850에서 규정한 A급 품질의 요구조건을 모두 만족하였다. 결론적으로 우수한 내식성과 경제성을 내세운 LDSS 3종은 현재 철도차량 소재인 스테인리스 강을 대체할 수 있을 것으로 전망된다. In this study, the spot welding strengths of three Lean Duplex Stainless Steels (LDSSs) were evaluated for future railway applications. Currently, STS301L and STS304 have been noted for the parent materials of Korean urban transit vehicles in KS R 9204 regulations, in which their allowable tension-shear loads and nugget diameters are provided depending on their plate thickness and parent material. In this regard, spot welding specimens consisting of the three LDSSs were made after appropriate spot-welding conditions were determined, and their qualities such as nugget diameters and tension-shear strengths were evaluated. As a result, all the spot-welding plates ranging 0.4~4.5mm thicknesses satisfied the “A-class quality” specified in KS B 0850. In conclusion, the newly developed stainless steels, the three LDSSs, were expected to replace the conventional stainless steels, STS301L and STS304 for future railway applications.
린 듀플렉스 329LA강의 기계적 변형 거동에 관한 연구
윤병준 ( Byung Jun Yoon ),최점용 ( Jeom Yong Choi ),박경태 ( Kyung Tae Park ),이호성 ( Ho Seong Lee ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.9
The tensile response of Lean Duplex 329LA stainless steel was investigated over various strain rates. It was observed that the mechanical response, including in particular the total elongation of the tested alloy, was strongly affected by the strain rate. As the strain rate decreased from 10-1 s-1 to 10-4 s-1, the elongation increased. As the strain rate increased, the deformation mode in an austenite phase was dominated by dislocation glide, resulting in deterioration of the elongation. The substructure of the ferritic phase showed a dislocation cell structure, independent of the applied strain rate. The optimum mechanical properties of lean duplex stainless steel thus can be obtained by controlling the deformation mode in the austenitic phase.
정현승(Hyunseung Jung),임재용(Jae Yong Lim),김정국(Jeong-Guk Kim),서승일(Sungil Seo),원성연(Sungyeun Won),최점용(Jeom Yong Choi) 한국철도학회 2014 한국철도학회 학술발표대회논문집 Vol.2014 No.5
본 연구에서는 신규 개발 중인 린듀플렉스 스테인리스강(LDSS) 소재에 대한 철도차량 차체 적용 가능성을 검토하기 위해 실제 차체 생산라인의 제작방식으로 루프 블록시제품을 제작하였다. 루프 블록은 루프패널, 카라인, 퍼라인, 캔트레일 등의 4가지 부품으로 구성되어 있으며, 루프 부품 제작을 위해 굽힘가공, 롤포밍, 스트레치포밍 등의 가공기법이 적용되었고, 블록 조립을 위해 시임용접, 점용접 등의 저항용접기법이 적용되었다. 시제품 제작 결과, LDSS 소재는 기존 소재(STS304, STS301L)와 비교하여 동등이상의 가공성과 용접성을 가지고 있음을 확인하였다. In this study, a prototype of rolling stock roof block is constructed using LDSS(Lean Duplex Stainless Steel) to check the applicability of this new material to rolling stock structures. Roof block is composed of four components; roof panel, car line, pur line, cant rail. In the fabrication process of roof components, bending forming, roll forming and stretch forming are used. To assemble roof components, seam welding and spot welding is applied. As results, we can find that LDSS has equivalent fabricability and weldability compared to the conventional materials such as STS304 and STS301L.
신규 스테인리스강의 철도차량 적용을 위한 KS 규격 개정 방안
김정국(Jeongguk Kim),정현승(Hyunseung Jung),임재용(Jae Yong Lim),서승일(Sungil Seo),원성연(Sungyeun Won),최점용(Jeom Yong Choi) 한국철도학회 2014 한국철도학회 학술발표대회논문집 Vol.2014 No.5
철도차량의 차체 소재로는 주로 STS 304 또는 STS 301L 등의 스테인리스 강이 이용되고 있다. 본 연구에서는 신규 개발된 스테인리스 강의 철도차량 차체 적용을 위한 방안을 검토하였다. 신규 소재가 철도 차량의 차체에 적용되기 위해서는 소재의 기술적 적용성 검토와 기술적 검증이 필요하고, 이와 함께 실질적 적용을 위해서는 규격에 대한 개정 검토도 필요하다. 본 논문에서는 철도차량 차체제작 관련 KS 규격에서 요구하고 있는 요건들에 대한 검토를 수행하였다. 구체적으로 철도 차량용 스테인리스 강재의 아크 용접과 점용접 설계 방안과 허용응력, 점용접 이음의 허용전단 인장 하중 조건 등에 대한 검토와 함께 설계 세목에 대한 검토를 진행하였으며, 개별 항목에 대한 요구조건 등에 대해 소개하고자 한다. The stainless steels such as STS 304 or STS 301L, have been used for the carbody materials in railway rolling stocks. The lean duplex stainless steels (LDSS) are newly developed materials, and provide cost effective and better strength as compared to the traditional stainless steels. In this investigation, the employment of new LDSS to carbody materials in railway rolling stocks was studied. In order to employ LDSS to railway carbody, several different types of technical review were carried out. The technical review includes arc and spot welding conditions, allowable stress, tensile strength condition between spot welding panels, etc. Moreover, revised KS guideline with technical review will be introduced and provided.
오스테나이트계 스테인레스강의 열간가공성에 미치는 Cu 의 영향
최점용,진원 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.1
The effect of Cu on the hot workability of austenitic stainless steel has been investigated by performing tensile tests and examination by scanning electron microscopy and Auger electron spectroscopy. Reduction of area decreased linearly with increasing Cu contents at deformation temperature above 1100℃. But, at the deformation temperature below 1100℃, the effect of Cu on reduction of area changed drastically at about 3.2% Cu. At lower Cu contents, reduction of area decreased in the same manner with that observed above 1100℃. However, as Cu contents exceeded about 3.2%, reduction of area rapidly decreased with increasing Cu contents. Fracture mode changed from ductile rupture to intergranular decohesion as Cu contents increased in the ductility trough. The occurrence of embrittlement would be attributed to the segregation of Cu and S at austenite grain boundary.
신선가공시 오스테나이트계 스테인리스강의 미세조직 변화 및 가공경화 거동
최점용,진원 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.3
The strain induced α′-martensite formation and the strain hardening behavior of metastable austenitic stainless steel during cold drawing have been investigated. The strain induced α′-martensite nucleates mainly at the intersection of the mechanical twins rather than ε-martensite. It could be explained by the increase of stacking fault energy which arises from the heat generated during high speed drawing and, for AISI 304/Cu, the additional effect of Cu additions. The strain hardening behavior of austenitic stainless steel is strongly related to the microstructural evolution accompanied by strain induced α′-martensite. The work hardening rates of cold-drawn 304 increased with increasing interstitial element(C,N) contents which affect the strength of the strain induced α′-martensite.
질소 첨가 13%Cr 마르텐사이트 스테인리스강의 상변태 및 석출 거동
李胤龍,崔点鎔 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.3
The substitution of carbon by nitrogen was employed to prevent center segregation of carbides during continuous casting of 13%Cr martensitic stainless steel. Characteristics of phase transformation and precipitation behavior have been studied. The substitution of carbon by nitrogen in 13%Cr steel increases its solidus, Ac_1, and Ms temperatures. The nose temperature of TTT diagram of high carbon steel was 675-700℃ while the one of high nitrogen steel was about 725℃. Maximum hardness can be obtained by austenitizing treatment at 1050-1100℃ for the high carbon steel and 1000℃ for the nitrogen added steel. The secondary hardening was maximized by tempering at 500℃. It is due to the precipitation of fine carbide and M_2N nitride. The hardness was drastically decreased as tempered at 550℃ by precipitation of M_23C_6 carbide at prior austenite grain boundaries.
손인진,최종술,문인기,최점용,손영일 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.10
In order to establish bainitic transformation mechanism of steel, low carbon-Ni-Cr-Mo steel was used as at. experimental alloy. Transformation-time curve in upper bainite of the steel showed S-shaped curve indicating diffusional transformation of nucleation and growth, while transformation time curve in lower bainite showed C-shaped curve often appearing in isothermal martensitic transformation. Furthermore, the bainitic trans formation rate showed negative dependence on temperature and the degree of the negative dependence was greater in the lower bainite than in the upper bainite. It was concluded by these results that the lower bainite was produced by shear transformation and that the upper bainite was formed by shear and diffusional transformations. A new mechanism to explain how the lower bainite is formed martensitically at temperatures above Ms temperature has been proposed on the basis of carbon concentration fluctuation model. The width of ferrite lath in the lower bainite was decreased and the bainte finishing time was shorter with increasing deformation degree of metastable austenite in bainitic bay. These experimental results well supported the proposed bainite transformation mechanism.