• Fire Science and Engineering
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• v.28 no.5
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• pp.52-57
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• 2014

When structural elements of steel framed structures are exposed to fire situations, the structural stability begins to decrease due to dislocation of substantial. The increase of the beam length causes an additional stress and deflection. These can be serious factors to cause a severe failure of structures. To improve the fire resistance of beams, prevention of the heat from a fire by coating with fire protection material is essential for beams. The FR 490 was developed to enhance fire resistance compared with SM 490 steel. However, the fire resistance of FR 490 H-beams has not been evaluated by analysis method since it was developed. In this paper, materials properties in high temperature and a heat transfer and thermal stress theory were used in the evaluation of the fire resistance of FR490 H-beams. The fire resistance of FR490 steel beams was compared with that of SM490 beams. The comparison verified that the structural stability of FR490 beams at high temperature was superior to that of SM490 beams.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.1 no.1
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• pp.71-78
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• 2002

Since the early 1980's the use of zinc-aluminum alloy-coated steel sheet(Galvalume) for vehicular corrosion protection has increased drastically. It is consisting of 55%Al-43.4% Zn-1.6%Si. Galvalume has a good corrosion resistance, heat reflectivity and shiny appearance, which has a dendritic structure of alloy layer. It has a good corrosion resistance due to dendritic structure. But, this also has a weak point against moisture during long period of transportation as sheeted and or coiled without any relation of chromating on the surface of steel sheet or not because of high humidity and temperature. Here, We studied the corrosion mechanism by the moisture.

• International Journal of High-Rise Buildings
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• v.7 no.4
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• pp.389-396
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• 2018

This paper presents a numerical investigation on the structural response of a multi-story building subjected to spreading multi-compartment fires. A recently proposed simple fire model has been used to simulate two spreading multi-compartment fire scenarios in a 10-story steel-framed office building. By assuming simple temperature rising and distribution profiles in the fire exposed structural components (steel beams, steel column and concrete slabs), finite element simulations using a three-dimensional structural model has been carried out to study the failure behavior of the whole structure in two multi-compartment fire conditions and also in a standard fire condition. The structure survived the standard fire but failed in the multi-compartment fire. Whilst more accurate fire models and heat transfer models are needed to better predict the behaviors of structures in realistic fires, the current study based on very simple models has demonstrated the importance and necessity of considering spreadingmulti-compartment fires in fire resistance design of multi-story buildings.

• Journal of Welding and Joining
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• v.25 no.4
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• pp.72-78
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• 2007

Aluminized steel sheet is a material with excellent heat resistance, thermal reflection and corrosion resistance. It has wide applications, owing to its low cost and excellent performance, in the petrochemical industry, electric power and other energy conversion systems, etc and has attracted the attention of many investigators. But the welding of aluminized steel sheet has a problem of decreasing tensile-shear strength, caused by mixed Al in the weld. This study investigated behavior of Al and its structural properties to resolve this problem. Several analysis equipment(SEM, EDX, EPMA) were used to investigate Al element in the weld. Also microhardness tester and TEM equipment were used to find the intermetallic compound. As a result of this study, Al-rich zones existed in the weld and Fe-Al intermetallic compounds were found in these zones. At the same time, the weldability of aluminized stainless steel sheet was investigated and compared with that of aluminized steel sheet. Although there is a difference between the base metal of the low carbon steel and stainless steel, it is interpreted that a behavior of Al element in the weld is similar.

• Corrosion Science and Technology
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• v.14 no.3
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• pp.120-126
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• 2015

The usage of bending products recently have increased since many industries such as automobile, aerospace, shipbuilding, and chemical plants need the application of pipings. Bending process is one of the inevitable steps to fabricate the facilities. Induction heat bending is composed of compressive bending process by local heating and cooling. This work focused on the effect of induction heat bending process on the properties of ASME SA312 Gr. TP304 stainless steel pipes. Tests were performed for base metal and bended area including extrados, intrados, crown up, and down parts. Microstructure was analyzed using an optical microscope and SEM. In order to determine intergranular corrosion resistance, Double Loop Electrochemical Potentiokinetic Reactivation (DL-EPR) test and ASTM A262 practice A and C tests were done. Every specimen revealed non-metallic inclusion free under the criteria of 1.5i of the standard and the induction heat bending process did not affect the non-metallic inclusion in the alloys. Also, all the bended specimens had finer grain size than ASTM grain size number 5 corresponding to the grain sizes of the base metal and thus the grain size of the pipe bended by induction heat bending process is acceptable. Hardness of transition start, bend, and transition end areas of ASME SA312 TP304 stainless steel was a little higher than that of base metal. Intergranular corrosion behavior was determined by ASTM A262 practice A and C and DL-EPR test, and respectively step structure, corrosion rate under 0.3 mm/y, and Degree of Sensitization (DOS) of 0.001~0.075% were obtained. That is, the induction heat bending process didn't affect the intergranular corrosion behavior of ASME SA312 TP304 stainless steel.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.1
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• pp.3-9
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• 2011

Plasma nitriding of stainless steels has been investigated over a range of temperature from 400 to $500^{\circ}C$ and time from 10 to 20 hours. Characterization of systematic materials was carried out in terms of mechanical properties and corrosion behaviors. The results showed that plasma nitriding conducted at low temperatures not only increased the surface hardness, but also improved the corrosion resistance of STS 316L, STS409L, and STS 420J2. It was found that plasma-nitriding treatment at $500^{\circ}C$ resulted in increasing the corrosion performance of STS 409L and STS 420J2, while STS 316L was observed with server and massive damage on surface due to the formation of CrN.

• Corrosion Science and Technology
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• v.2 no.3
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• pp.117-126
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• 2003

Due to excellent corrosion resistance and mechanical properties, austenitic stainless steel is widely used as the material for chemical plants. nuclear power plants, and food processing facilities. But, the zone affected by heat in the range of 400 to $800^{\circ}C$ during welding loses corrosion resistance and tensile strength since Cr-carbide precipitation like $Cr_{23}C_6$ forms at the grain boundary and thereby takes place the intergranular corrosion. In this study, AISI 304 stainless steel with the added Nb of 0.3 to 0.7 wt% was solutionized at $1050^{\circ}C$ and sensitized at $650^{\circ}C$. Specimen was welded by MIG. The phase and the microstructure of the specimens were examined by an optical microscope, a scanning electron microscope, and a x-ray diffractometer. The corrosion characteristics of specimens were tested by electrolytic etching and by double loop electrochemical potentiokinetic reactivation method(EPR) in the mixed solution of 0.5M $H_2SO_4$ + 0.01M KSCN. The melting zone had dendritic structure constituted of austenitic phase and $\delta$-ferrite phase. Cr carbide at the matrix did not appear, as Nb content increased. At the grain boundaries of the heat affected zone, the precipitates decreased and the twins appeared. The hardness increased, as Nb content increased. The hardness was highest in the order of the heat affected zone>melted zone>matrix. According to EPR curve, as the Nb content decreased, the reactivation current density(Ir) and the activation current density(la) were highest in the order of the melted zone

• Corrosion Science and Technology
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• v.9 no.5
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• pp.187-195
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• 2010

Hyper duplex stainless steels have been developed in Korea for the purpose of application to the seawater system of Korean nuclear power plants. This system supplies seawater to cooling water heat exchanger tubes, related pipes and chlorine injection system. In normal operation, seawater is supplied to heat exchanger through the exit of circulating water pump headers, and the heat exchanged sea water is extracted to the discharge pipes in circulating water system connected to the circulating water discharge lines. The high flow velocity of some part of seawater system in nuclear power plants accelerates damages of components. Therefore, high strength and high corrosion resistant steels need to be applied for this environment. Hyper duplex stainless steel (27Cr-7.0Ni-2.5Mo-3.2W-0.35N) has been newly developed in Korea and is being improved for applying to nuclear power plants. In this study, the physical & mechanical properties and corrosion resistance of newly developed materials are quantitatively evaluated in comparative to commercial stainless steels in other countries. The properties of weld & HAZ (heat affected zone) are analyzed and the best compositions are suggested. The optimum conditions in welding process are derived for ensuring the volume fraction of ferrite(${\alpha}$) and austenite(${\gamma}$) in HAZ and controlling weld cracks. For applying these materials to the seawater heat exchanger, CCT and CPT in weldments are measured. As a result of all experiments, it was found that the newly developed hyper duplex stainless steel WREMBA has higher corrosion resistance and mechanical properties than those of super austenitic stainless steels including welded area. It is expected to be a promising material for seawater systems of Korean nuclear power plants.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.4
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• pp.224-230
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• 2000

Garbon steel(SM35C) was gas nitrocarburized at $580^{\circ}C$ in $55%N_2-40%NH_3-5%CO_2$ mixed gas atmosphere, and then the steel was induction hardened at $850^{\circ}C$. The microstructure of gas nitrocarburized surface layer was observed by optical microscope and SEM. The phase analysis was carried out by X-ray diffraction method. The mechanical properties of gas nitrocarburized SM35C steel was evaluated by hardness, wear and fatigue test. The thickness of compound and diffusion layer were increased with increasing the gas nitrocarburizing time and the densest compound layer was obtained at 3 hours gas nitrocarburizing time. In case of 15sec induction hardening after gas nitrocarburizing, the surface hardness was decreased from 800Hv to 630Hv owing to the decomposition of compound layer, but wear resistance was increased because of increased hardness of diffusion layer. The fatigue strength of induction hardened steel after gas nitrocarburizing, $58kgf/mm^2$, was higher than $41.5kg/mm^2$ of gas nitrocarburized steel and $45kg/mm^2$ of induction hardened steel, respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.257-260
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• 2008

The heat resistance of steel materials tends to weaken due to its high heat transfer properties, which might result in deteriorated strength because of rapidly rising temperature on surface in a fire. Particularly in case of CFT column that bears tensile stress of the structure on its external steel members, a numerical analysis on deterioration of strength and variation of stress shall be first carried out to ensure the structure will have sufficient fire resistance. In the study, based on values obtained from the high temperature material property test of steel materials and concrete, the test to forecast the fire behavior of CFT column was conducted using a finite element analysis method (ABAQUS). An Analysis in a bid to predict the heat transfer and the behavior characteristics by varying the strength of the concrete filled to the range of 40MPA and 50MPA was carried out. As a result of analysis of CFT column on condition of 180-minute exposure under the standard fire condition, 123mm of strain appeared with 40MPA model, while 91mm contraction with 50MPA model.