• Journal of the Korean Society of Safety
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• v.13 no.1
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• pp.13-18
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• 1998

It is well known in the fracture mechanics community that the fracture toughness of brittle materials, such as ceramics, can be improved improves significantly when fibers are added into the material. This is because in presence of fibers the cracks cannot propagate as freely as it can in absence of them. Fibers bridge the gap between two adjacent surfaces of the crack and reduce the crack tip opening displacement, thus make it harder to propagate. Several investigators have experimentally studied how the length, diameter and volume fraction of fibers affect the fracture toughness of chopped strand reinforced matrix composite materials. In this paper, matrix used ALS, Arizona Lunar Simulant, types of fiber used carbon steels and stainless steels. To analyze quantitatively fiber reinforced ALS composites, experimental and analytical methods was progressed. Load-displacement curve is used to experimental method, and FEM analysis program using ABAQUS is used analytical method.

• Journal of the Korean institute of surface engineering
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• v.22 no.1
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• pp.17-25
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• 1989

The structural Charactesties and adhesion of chemically vapor deposited TiN film on stain less steels have been investated as functions of deposition temperature, surface roughness of sub state, and types of substrates. The grain zine and the lattice parameter of TiN film decreased with decreasing roughness of substates. The(200) preferred orientation was developed dominatly and the lattlice parameter decreased as temperature intereased reardless of the surdless roughnessand type of the substrates used. The surface morphology of TiN film changed from bushed crystal to a plate and then to pyamidal dense crystals with an increase in the deposition temperature. The adhesion of TiN films increased with coating thinkness and decreased with surface roughness in general. The calculations using a Bejamin & Weaver's model have been compard. Maximum valuse of adhesion energy calculated using Laguier's model were W304=331Jm-2,w410=113Jm-2,andW430=107jm-2

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.116-117
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• 2006

Conventional high-speed steels, which are carbide decentralized materials, are used for sliding parts, but they lack sufficient hardness for some applications. Improvement of surface hardness is possible for high-Cr steels through nitriding. However, nitriding P/M parts is not advisable without sealing the porosity before treatment, as they will become brittle. However, it is difficult to seal the pores with steam treatment, because high-Cr steel has a passive film on the surface. Controlling nitriding by decreasing the amount of oxygen on the surface to be nitrided, and grinding to decrease the porosity of the surface, makes it possible to produce a material that has reasonable and sufficient hardness in the required areas.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.1
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• pp.31-37
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• 2019

This study investigates the effects of long-term artificial-aging on hardness variation in the dissimilar metal weldments for nuclear power plant facilities. These dissimilar welds are inevitably required to join the components in nozzle parts of pressurized vessels, such as austenitic stainless steels and ferritic steels. A artificial thermal aging was conducted in an electrical furnace to simulate material degradation at high temperatures. The test materials were held at the temperature of $600^{\circ}C$ for 10000 hours and interrupted at various levels of degraded specimens. The degradation of hardness is a well-known phenomenon resulting from long-term aging or high-temperature degradation of structural materials. In this study, the variation of hardness at each position was different, and complicated in relation to microstructures such as twins, grains, precipitates, phase transformations, and residual stresses in dissimilar weldments. We discussed the variation of hardness in terms of microstructural changes during long-term aging.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.139-149
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• 1995

Many pressure vessels for the power plants are fabricated from low alloy ferritic steels. The inner sides of the pressure vessels are commonly weld_cladded with austenitic stainless steels to minimize problems of corrosive attack. The submerged-arc welding(SAW) process is now used in preference to other processes because of the possibilities open to automation to reduce the overaII welding times. The most reliable way to avoid underclad cracks(UCC) which are often detected at the overlap of the clad beads is to use nonsusceptible steels such as SA508 class 3. At present domestically developed forging steel of SA508 cl.S is now being cladded with single layer by using 90mm wide strip, which transfers higher heat input into the base metal compared to the conventional two layers strip cladding which has been in wide use with 30-60 mm wide strip. But the current indices for the influence of heat input on crack susceptibility are not accurate enough to express the subtle difference in crack susceptibility of the steel. Therefore, the purpose of this present study is: l) To determine UCC susceptibility on domestic forging steel, SA508 cl.S cladded with single layer by using submerged arc 90mm strip and, 2) To optimize heat input range by which the crack susceptibility could be eliminated.

• Journal of the Korean institute of surface engineering
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• v.51 no.6
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• pp.354-359
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• 2018

NaCl-induced hot corrosion behavior of ASTM T22 (Fe-2.25Cr-1Mo), T91 (Fe-9Cr-1Mo), T92 (Fe-9Cr-1.8W-0.5Mo), 347HFG (Fe-18-Cr-11Ni), and 310H (Fe-25Cr-19Ni) steels was studied after spraying NaCl on the surface. During corrosion at $600-800^{\circ}C$ for 50-100 h, thick, non-adherent, fragile, somewhat porous oxide scales formed. All the alloys corroded fast with large weight gains owing to fast scaling and destruction of protective oxide scales. Corrosion rates increased progressively as the corrosion temperature and time increased. Corrosion resistance increased in the order of T22, T91, T92, 347HFG, and 310H, suggesting that the alloying elements of Cr, Ni, and W beneficially improved the corrosion resistance of steels. Basically, Fe oxidized to $Fe_2O_3$, and Cr oxidized to $Cr_2O_3$, some of which further reacted with FeO to form $FeCr_2O_4$ or with NiO to form $NiCr_2O_4$.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.1
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• pp.31-39
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• 1999

In the present study, oxidation behavior of 304 and 316 stainless steels was investigated. After solution treatment, specimens were polished up to $1{\mu}m$ $Al_2O_3$ grade and then subjected to oxidation treatment in dry air. The range of temperature was used for oxidation treatment at $300^{\circ}C{\sim}500^{\circ}C$ and TEM was used for analyzing the components and structure of oxide film. Also, these results were compared with the results of ESCA and TG. According to the results of TEM analysis, it was found that Cr oxide film was formed on top of the surface after room temperature oxidation but amorphous Fe oxide was formed on top of the surface and polycrystalline $(Cr,Fe)_2O_3$ was formed below the amorphous Fe oxide layer after $500^{\circ}C$ oxidation treatment. The oxidized specimens at $500^{\circ}C$ showed that 316 stainless steel resists more strongly to grain and grain boundary oxidation than 304 stainless steel. These results suggested that Mo component resolved in 316 stainless steel matrix suppressed the formation of Cr carbide which may results in local Cr deplete area.

• Corrosion Science and Technology
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• v.15 no.6
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• pp.281-289
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• 2016

The effect of nitrogen on the electrochemical corrosion and nanomechanical behaviors of martensitic stainless steel was examined using potentiodynamic polarization and nanoindentation test methods. The results indicate that partial replacement of carbon with nitrogen effectively improved the passivation and pitting corrosion resistance of conventional high-carbon and high- chromium martensitic steels. Post-test observation of the samples after a potentiodynamic test revealed a severe pitting attacks in conventional martensitic steel compared with nitrogen- containing martensitic stainless steel. This was shown to be due to (i) microstructural refinement results in retaining a high-chromium content in the matrix, and (ii) the presence of reversed austenite formed during the tempering process. Since nitrogen addition also resulted in the formation of a $Cr_2N$ phase as a process of secondary hardening, the hardness of the nitrogen- containing steel is slightly higher than the conventional martensitic stainless steel under tempered conditions, even though the carbon content is lowered. The added nitrogen also improved the wear resistance of the steel as the critical load (Lc2) is less, along with a lower scratch friction coefficient (SFC) when compared to conventional martensitic stainless steel such as AISI 440C.

• Journal of Welding and Joining
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• v.1 no.2
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• pp.45-52
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• 1983

Many pressure vessels for the hot H$\sub$2//H$\sub$2/S service are made of 2+1/4Cr-1Mo steel with austenitic stainless steel overlay to combat agressive corrosion due to hydrogen sulfide. Hydrogen dissolves in to materials during operation, and sometimes gives rise to unfore-seeable damages. Appropriate precautions must, therefore, be taken to avoid the hydrogen induced damages in the design, fabrication and operation stage of such reactor vessels. Recently, hydrogeninduced cracking (or Disbonding) was found at the interface between base metal and stainless weld overlay of a desulfurizing reactor. Since the stainless steel overlay weld metal is subjected to thermal and internal-pressure loads in reactor operation, it is desirable for the overlay weld metal to have high strength and ductility from the stand point of structural safety. In section III of ASME Boiler and Pressure Vessel Code, Post-Weld Heat Treatment(PWHT) of more than one hour per inch at over 1100.deg. F(593.deg. C) is required for the weld joints of low alloy pressure vessel steels. This heat treatment to relieve stresses in the welded joint during construction of the pressure vessel is considered to cause sensitization of the overlay weld metal. The present study was carried out to make clear the diffusion of carbon migration by PWHT in dissimilar metal welded joint. The main conclusion reached from this study are as follows: 1) The theoretical analysis for diffusion of carbon in stainless steel overlay weld metal does not agree with Fick's 2nd law but the general law of molecular diffusion phenomenon by thermodynamic chemical potential. 2) In the stainless steel overlay welded joint, the PWHT at 720.deg. C for 10 hours causes a diffusion of carbon atoms from ferritic steel into austenitic steel according to the theoretical analysis for carbon migration and its experiment. 3) In case of PWHT at 720.deg. C for 10 hours, the micro-hardness of stainless steel weld metal in bonded zone increase very highly in the carburized layer with remarkable hardening than that of weld metal.

• Analytical Science and Technology
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• v.17 no.5
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• pp.416-422
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• 2004

Time-resolved laser induced breakdown spectroscopy (TRELIBS) has been developed and applied to the qualitative analysis of the component materials of nuclear power plant. The alloy samples used in this work were carbon steels (A106 Gr. B; A336 P11; A335 P22), stainless steels (type 304; type 316) and inconel alloys (Inconel 600; Inconel 690; Inconel 800). Carbon steels can be individually distinguished by the intensity ratio of chromium to iron and molybdenum to iron emission lines observed at the wavelength raging from 485 to 575 nm. Type 316 stainless steel can be easily differentiated from type 304 by identification of the molybdenum emission lines at an emission wavelength ranging from 485 to 575 nm: type 304 does not give any molybdenum emission lines, but type 316 does. The inconel alloys can be individually distinguished by the intensity ratio of Cr/Fe and Ni/Fe emission lines at the wavelength raging from 420 to 510 nm. TRELIBS has been proved to be a powerful analytical technique for direct analysis of alloys due to its non-destructivity and simplicity.