• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 추계학술대회논문집
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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.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2006년도 춘계 학술대회 개요집
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• pp.140-142
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• 2006

The bend ductility of Type 410S ferritic stainless steel overlay weld on carbon steel was investigated. Overlay weld that was stabilized with Nb had large columnar ferrite grain and Nb precipitate on grain boundary. And that caused fracture when bend test without concern of PWHT condition. Proper bend ductility at as-welded condition was achieved by refining ferrite grain with addition of $0.04{\sim}0.09%$ Al and $0.2{\sim}0.5%$ Ti that make oxide, carbide and nitride at high temperature.

• 동력기계공학회지
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• 제4권1호
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• pp.74-80
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• 2000

This present study was investigated effect of Ni contents on the high temperature strength characteristic in 9Cr ferritic heat-resistant steel added 1.7%W in place of Mo in order to restraint laves phase formation. Precipitation amount of carbide, number of particle per unit area and particle size of carbide were decreased with increase of Ni content. In the steels, carbides of $M_{23}C_6$ type was mainly precipitated, but laves phases could not precipitated. Tensile and yield strength, creep strength and creep rupture time was decreased, but elongation were increased due to decreasing of particle number per unite area and carbide amount precipitated with increase of Ni content.

• Journal of Welding and Joining
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• 제20권5호
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• pp.63-71
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• 2002

One of the shortcoming of ferritic stainless steels is their limited toughness. The most important factor governing the toughness of ferritic stainless steels is hewn to be their interstitial contents. Due to the limited solubility of carbon and nitrogen in the ferrite matrix, it is difficult to avoid carbide and nitride precipitates. In the study, the role of nitrogen on the toughness of 260r-2Mo superferritic stainless steel welds has been investigated using alloys containing various nitrogen levels between 100 and 1640 ppm. Mechanical properties of weld metals have been evaluated by microhardness, Charpy impact test and notch tensile test. The alloys are mainly embrittled by the grain boundary and intragranular nitride precipitation. Grain boundary precipitates are considered to be more deleterious than intrauanular nitrides. Fracture mechanism have been elucidated through microscopic evaluation of notch tensile test

• 열처리공학회지
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• 제35권5호
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• pp.239-245
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• 2022

The purpose of this study is to evaluate the degree of microstructural change of materials using ultrasonic nonlinear parameters. For microstructure change, isothermal heat-treated ferritic 2.25Cr steel and low-cycle fatigue-damage copper alloy were prepared. The variation in ultrasonic nonlinearity was analyzed and evaluated through changes in hardness, ductile-brittle transition temperature, electron microscopy, and X-ray diffraction tests. Ultrasonic nonlinearity of 2.25Cr steel increased rapidly during the first 1,000 hours of deterioration and then gradually increased thereafter. The variation in non-linear parameters was shown to be coarsening of carbides and an increase in the volume fraction of stable M6C carbides during heat treatment. Due to the low-cycle fatigue deformation of oxygen-free copper, the dislocation that causes lattice deformation developed in the material, distorting the propagating ultrasonic waves, and causing an increase in the ultrasonic nonlinear parameters.

• 열처리공학회지
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• 제20권6호
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• pp.323-328
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• 2007

This study has been investigated the effect of high temperature gas nitriding (HTGN) heat treatment of STS 444 (18Cr-0.01Ni-0.01C-0.2Nb) ferritic stainless steel in an atmosphere of nitrogen gas at the temperature range between $1050^{\circ}C\;and\;1150^{\circ}C$. The surface layer was changed into martensite and austenite with the nitrides of NbCrN by HTGN treatment. Due to the precipitation of nitrides and matrensite formation, the hardness of the surface layer showed $400Hv{\sim}530Hv$. The nitrogen concentration of the surface layer appeared as 0.05%, 0.12% and 0.92%, respectively, at $1050^{\circ}C,\;1100^{\circ}C\;and\;1150^{\circ}C$. When the nitrogen is permeated from surface to interior, Nb and Cr, which have strong affinities with nitrogen, also move from interior to surface. Therefore it is considered that this counter-current of atoms promotes the formation of NbCrN at the surface layer.

• 한국강구조학회 논문집
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• 제25권6호
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• pp.659-669
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• 2013

본 연구는 페라이트계 스테인리스강 일면전단 볼트접합부의 구조거동에 관한 기존실험연구를 바탕으로 유한요소해석법을 이용하여 접합부의 최대내력과 면외변형에 대해 조사하는 것을 목적으로 한다. 유한요소해석결과와 실험결과의 비교를 통해 접합부의 구조거동을 예측하는데 있어 해석의 타당성을 검증하였다. 면외변형에 의해 유발되는 접합부의 연단거리 조건을 조사하고 최대내력저하정도를 정량적으로 평가하였다. 또한, 변수해석을 통해 얻어진 해석결과의 최대내력과 현행기준식인 AISC, KBC2009, AIJ 및 AISI에 의해 예측된 내력과 비교하여 그 적용성을 검토하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제39권5호
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• pp.527-535
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• 2015

As a new technical approach, a hydraulic and magnetic clamp device was attempted to realize a magnetic clamp crane system that uses 8 simultaneously actuating individual hydraulic cylinders. Through this approach, a Sr type of ferritic permanent magnet ($SrO{\cdot}6Fe_2O_3$), not the previously employed electro-magnet, was utilized for the purpose of lifting and transporting the heavy weighted and oversized curved steel plates used for manufacturing the ships. This study is aimed at manufacturing and developing the hydraulic magnetic clamp prototype, which is composed of three main parts - the base frame, cylinder joint, and magnet joint - in order to safely transport such curved steel plates. Furthermore, this research was pursued to conduct a performance evaluation as to the prototype manufacture and acquire the planned quantity value and the development purpose items. The most significant item for a performance evaluation was estimated for the magnetic adhesive force (G) and in this process, a ferritic permanent magnet (Sr type) with 3700~4000 G of residual induction (Br) and 2640/2770 Oe of coercive force (Hc) was utilized. In addition, other relevant items such as hoist tension (kN), transportation time (sec), and the applied load (Kgf) exerted on the hydraulic cylinders were also evaluated in order to acquire the optimum quantity value. As a result of the evaluation, the relevant device turned out to be suitable for safely transporting the curved steel plates.

• 열처리공학회지
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• 제13권1호
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• pp.27-34
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• 2000

This present study were investigated effect of Ni contents on the microstructure and strength characteristic in 9Cr ferritic heat-resistant steel added 1.7%W in place of Mo in order to restrain laves phase formation. The result obtained from this study are as follow. Volume fraction, number of particles per unite area and particle size of carbide decreased with increase of Ni contents. Other side, carbides of $M_{23}C_6$ type was mainly precipitated in this steel, but laves phases could not precipitated in spite of increasing of aging time. With increase of tempering temperature, hardness was increased, and maximum value was showed around 873k by secondary hardening due to precipitation of $W_2C$ type carbide and then, was decreased. Tensile and yield strength due to decrease precipitation amount of carbide and number of particles per unite area was decreased, but elongation and impact value was increased. In case of aged specimen after tempering than tempered specimen, strength was higher and elongation was lower due to increasing of precipitated amount of carbide and number of particles per unite area.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.300-305
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• 2003

Reduced activation ferritic (JLF-1) steel is leading candidates for blanket/first-wall structures of the D-T fusion reactor. In fusion application, structural materials will suffer effects of repeated changes of temperature. Therefore, the data base of tensile strength and fracture toughness at operated temperature $400^{\circ}C$ are very important. Fracture toughness ($J_{IC}$) and tensile tests were carried out at room temperature and elevated temperature ($400^{\circ}C$). Fracture toughness tests were performed with two type size to investigate the relationship between the constraint effect of a size and the fracture toughness resistance curve. As the results, the tensile strength and the fracture toughness values of the JLF-1 steel are slightly decreased with increasing temperature. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. The fracture toughness values of JLF-1 steel at room temperature and at $400^{\circ}C$ shows an excellent fracture toughness ($J_{IC}$) of about $530kJ/m^2\;and\;340kJ/m^2$, respectively.