• Corrosion Science and Technology
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• v.10 no.2
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• pp.60-64
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• 2011

Lean duplex stainless steels have been developed in Korea for the purpose of being used in the seawater systems of industry. There are also many important seawater systems in nuclear power plants. These systems supply seawater to cooling water condenser tubes, heat exchanger tubes, related pipes and chlorine injection systems. The flow velocity of some part of seawater systems in nuclear power plants is high and damages of components from corrosion are severe. The considered lean duplex stainless steels are STS329LD (20.3Cr-2.2Ni-1.4Mo) and STS329J3L (22.4Cr-5.7Ni-3Mo) and PRENs of them are 29.4 and 37.3 respectively. Physical, mechanical and micro-structural properties of them are evaluated, and electrochemical corrosion resistance is measured quantitatively in NaCl solution. Critical Pitting Temperatures (CPT)s are measured on these alloys and pit depths are evaluated using laser microscope. Long period field tests on these alloys are now being performed, and some results are going to be presented in the following study.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.583-584
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• 2006

This work presents mechanical properties and corrosion resistance of duplex stainless steels obtained through powder metallurgy starting from austenitic, martensitic powders by controlled addition of alloying elements in the right quantity to obtain the chemical composition of the structure similar to biphasic one. In the mixes preparations the Schaffler's diagram was taken into consideration. Prepared mixes of powders have been sintered in a vacuum furnace with argon backfilling. After sintering rapid cooling was applied using nitrogen. Corrosion properties have been studied through electrochemical methods in 1M NaCl.

• Steel and Composite Structures
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• v.42 no.1
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• pp.91-106
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• 2022

Concrete-filled square stainless steel tubes (CFSSST), which possess relatively large flexural stiffness, high corrosion resistance and require simple joint configurations and low maintenance cost, have a great potential in constructional applications. Despite that the use of stainless steel may result in high initial cost compared to their conventional carbon steel counterparts, the whole-life cost of CFSSST is however considered to be lower, which offers a competitive choice in engineering practice. In this paper, a comprehensive experimental and numerical program on 24 CFSSST stub column specimens, including 3 austenitic and 3 duplex stainless steel square hollow section (SHS) stub columns and 9 austenitic and 9 duplex CFSSST stub columns, has been carried out. Finite element (FE) models were developed to be used in parametric analysis to investigate the influence of the tube thickness and concrete strength on the ultimate capacities more accurately. Comparisons of the experimental and numerical results with the predictions made by design guides ACI 318, ANSI/AISC 360, Eurocode 4 and GB 50936 have been performed. It was found that these design methods generally give conservative predictions to the ultimate capacities of CFSSST stub columns. Improved calculation methods, developed based on the Continuous Strength Method, have been proposed to provide more accurate estimations of the ultimate resistances of CFSSST stub columns. The suitability of these proposals has been validated by comparison with the test results, where a good agreement between the predictions and the test results have been achieved.

• Corrosion Science and Technology
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• v.13 no.2
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• pp.70-80
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• 2014

Duplex stainless steels with nearly equal fraction of the ferrite(${\alpha}$) phase and austenite(${\gamma}$) phase have been increasingly used for various applications such as power plants, desalination facilities due to their high resistance to corrosion, good weldability, and excellent mechanical properties. Hyper duplex stainless steel (HDSS) is defined as the future duplex stainless steel with a pitting resistance equivalent (PRE=wt.%Cr+3.3(wt.%Mo+0.5wt.%W)+30wt.%N) of above 50. However, when HDSS is welded with gas tungsten arc (GTA), incorporation of nitrogen in the Ar shielding gas are very important because the volume fraction of ${\alpha}$-phase and ${\gamma}$-phase is changed and harmful secondary phases can be formed in the welded zone. In other words, the balance of corrosion resistance between two phases and reduction of $Cr_2N$ are the key points of this study. The primary results of this study are as follows. The addition of $N_2$ to the Ar shielding gas provides phase balance under weld-cooling conditions and increases the transformation temperature of the ${\alpha}$-phase to ${\gamma}$-phase, increasing the fraction of ${\gamma}$-phase as well as decreasing the precipitation of $Cr_2N$. In the anodic polarization test, the addition of nitrogen gas in the Ar shielding gas improved values of the electrochemical parameters, compared to the Pure Ar. Also, in the erosion-corrosion test, the HDSS welded with shielding gas containing $N_2$ decreased the weight loss, compared to HDSS welded with the Ar pure gas. This result showed the resistance of erosion-corrosion was increased due to increasing the fraction of ${\gamma}$-phase and the stability of passive film according to the addition $N_2$ gas to the Ar shielding gas. As a result, the addition of nitrogen gas to the shielding gas improved the resistance of erosion-corrosion.

• Journal of Ocean Engineering and Technology
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• v.26 no.6
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• pp.27-32
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• 2012

The effects of reheating during welding on the microstructure and impact toughness of weld metal in 25% Cr super duplex stainless steels were investigated. Using different heat inputs, weld metals with different reheated regions were obtained. This showed that, depending on the reheating temperature, the microstructure in the reheated region was quite different from that of the as-deposited microstructure. When reheated into the ${\gamma}+{\alpha}$ temperature range, fine intragranular austenite was formed in the as-deposited columnar structure. However, when reheated above the ${\alpha}$ solvus temperature range, most of the columnar structure disappeared and fine equiaxed austenite and ferrite were formed. Because of the larger amount of fine austenite in the reheated region, a higher impact toughness was obtained in the weld metal with a higher amount of reheated region.

• Steel and Composite Structures
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• v.33 no.1
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• pp.37-66
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• 2019

In cold-formed steel structures, such as trusses, wall frames and portal frames, the use of back-to-back built-up cold-formed stainless-steel lipped channels as compression members are becoming increasingly popular. The advantages of using stainless-steel as structural members are corrosion resistance and durability, compared with carbon steel. The AISI/ASCE Standard, SEI/ASCE-8-02 and AS/NZS do not include the design of stainless-steel built-up channels and very few experimental tests or finite element analyses have been reported in the literature for such back-to back cold-formed stainless-steel channels. Current guidance by the American Iron and Steel Institute (AISI) and the Australian and New Zealand (gAS/NZS) standards for built-up carbon steel sections only describe a modified slenderness approach, to consider the spacing of the intermediate fasteners. Thus, this paper presents a numerical investigation on the behavior of back-to-back cold-formed stainless-steel built-up lipped channels. Three different grades of stainless steel i.e., duplex EN1.4462, ferritic EN1.4003 and austenitic EN1.4404 have been considered. Effect of screw spacing on the axial strength of such built-up channels was investigated. As expected, most of the short and intermediate columns failed by either local-global or local-distortional buckling interactions, whereas the long columns, failed by global buckling. All three grades of stainless-steel stub columns failed by local buckling. A comprehensive parametric study was then carried out covering a wide range of slenderness and different cross-sectional geometries to assess the performance of the current design guidelines by AISI and AS/NZS. In total, 647 finite element models were analyzed. From the results of the parametric study, it was found that the AISI & AS/NZS are conservative by around 10 to 20% for cold-formed stainless-steel built-up lipped channels failed through overall buckling, irrespective of the stainless-steel grades. However, the AISI and AS/NZS can be un-conservative by around 6% for all three grades of stainless-steel built-up channels, which failed by local buckling.

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.250-252
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• 2003

• Proceedings of the KWS Conference
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• 1996.10a
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• pp.49-50
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• 1996

• Journal of Welding and Joining
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• v.33 no.5
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• pp.20-25
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• 2015

Clad steel has good corrosion resistance and mechanical properties arising from the hot rolling of dissimilar metals, such as carbon steel and stainless steel. However both good corrosion resistance from the cladding plate material(stainless steel) and mechanical properties from the base plate material (carbon steel) are difficult to obtain because the different steels display opposite behaviors during the cladding process. In order to make clad steel for application in the hulls of ships, proper materials selection and heat-treatment conditions are necessary. In this study, mechanical properties of base plate materials with different chemical composition were evaluated according to heat condition of cladding plate material.

• Composites Research
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• v.37 no.2
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• pp.94-100
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• 2024

In order to evade the premature failure of super duplex stainless steels (SDSSs) in some harsh environments, the increase of their mechanical properties is a promising approach. In this study, based on the laser powder bed fusion (LPBF) technique, SDSS matrix composites without post heat treatment were fabricated by using the powder mixture of SDSSs, super austenitic stainless steels (SASSs) and micron-sized TiC particles. Many in-situ TiC_xN_y nanoparticles were found to be formed by using micron-sized TiC particles in as-built composites, and both fine ferrite and austenite grains were generated. The as-built composites exhibited an excellent combination of high ultimate tensile strength (UTS) (~1066 MPa) and good uniform elongation (UE) (~15.6%), showing a better mechanical property compared with other reported LPBF-fabricated SDSSs, which was mainly attributed to the fine grain, Orowan and dislocation strengthening mechanisms. In particular, the successful fabrication of SDSS matrix composites can set the stage for producing high-performance metallic parts via LPBF technique.