• Design & Manufacturing
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• v.16 no.1
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• pp.9-14
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• 2022

A lot of research is being done on metal materials to improve the lifespan of molded parts. As a result, excellent mold materials have been developed that withstand high hardness at high temperatures and frictional heat generated from high-speed cutting. In this study, the press mold life of powder high-speed tool steel and general high-speed tool steel was compared. Powdered high-speed steel is composed of alloying elements such as tungsten, maldividene, cobalt, chromium, and vanadium in steel, which improves wear resistance compared to high-hardness and high-speed tool steels. The mold parts of both steel types were manufactured in the same way from heat treatment to machining, and the powder high-speed tool steel was 66HRC and the high-speed tool steel was 61HRC. As a result of the experiment, it was observed that the number of punching of powder high-speed tool steel was improved by 40-50%, and powder high-speed tool steel had fewer impurities, uniform texture, and excellent surface structure. It has a microscopic structure.

• 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.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.6
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• pp.318-326
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• 2011

This study has been performed to investigate the effect of Al addition on High Temperature Gas Nitriding (HTGN) in 13%Cr-0.16%C stainless steel with different Al contents of 0.54%, 1.76% and 2.36%, respectively. HTGN treatment was carried out at $1100^{\circ}C$ for 1 hr, 5 hrs and 10 hrs. Nitrogen-permeated surface layers showed round type carbides of $Cr_{23}C_6$ and needle type nitrides of AlN in the matrix of martensite, representing 600~700 Hv. And the thickness of the surface layer increased with increasing Al content and HTGN treatment time. The inner region that was not permeated nitrogen showed chromium carbides in the mixed phase of martensite and ferrite for the 0.53% Al alloyed steel, however chromium carbides in the matrix of ferrite single phase were shown for the steels with the addition of 1.76%Al and 2.36%Al, representing the hardness of ~200 Hv. During nitrogen permeation from surface to the interior, substitutional elements of Cr, Al and Si moved toward the surface and interstitial element of carbon also moved from interior to the surface. This movement of alloying elements leads high concentration of these elements at the outmost surface, subsequently the lowest peak of substitutional elements were shown in the vicinity of near surface. After showing the lowest peak, the high concentration region of Al and C were formed due to the continuous movement of Al toward the surface. The long discontinuous precipitates of $Cr_{23}C_6$ and AlN were formed along the outmost surface owing to the high concentration of these alloying elements.

• Journal of Welding and Joining
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• v.28 no.4
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• pp.18-25
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• 2010

Super-duplex stainless steels (SDSS) have a good balance of mechanical property and corrosion resistance when they consist of approximately equal amount of austenite and ferrite. The SDSS needs to avoid the detrimental phases such as sigma(${\sigma}$), chi(${\chi}$), secondary austenite(${\gamma}2$), chromium carbide & nitride and to maintain the ratio of ferrite & austenite phase as well known. However, the effects of the subsequent weld thermal cycle were seldom experimentally studied on the micro-structural variation of weldment & pitting corrosion property. Therefore, the present study investigated the effect of the subsequent thermal cycle on the change of weld microstructure and pitting corrosion property at $40^{\circ}C$. The thermal history of root side was measured experimentally and the change of microstructure of weld root & the weight loss by pitting corrosion test were observed as a function of the thermal cycle of each weld layer. The ferrite contents of root weld were reduced with the subsequent weld thermal cycles. The pitting corrosion was occurred in the weld root region in case of the all pitted specimen & in the middle weld layer in some cases. And the weight loss by pitting corrosion was increased in proportional to the time exposed at high temperature of the root weld and also by the decrease of ferrite content. The subsequent weld thermal cycles destroy the phase balance of ferrite & austenite at the root weld. Conclusively, It is thought that as the more subsequent welds were added, the more the phase balance of ferrite & austenite was deviated from equality, therefore the pitting corrosion property was deteriorated by galvanic effect of the two phases and the increase of 2nd phases & grain boundary energy.

• Korean Journal of Materials Research
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• v.15 no.1
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• pp.19-24
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• 2005

For the good combination of high-temperature strength, toughness and creep property, $9-12\%$ chromium steels are often used for gas turbine compressors, steam turbine rotors, blade and casing. In this study, the correlation of microstructural evolution and mechanical properties was investigated fur the specimens heat-treated at 600, 650 and $700^{\circ}C$ for 1000, 3000 and 5000 hrs. The microstructure of as-received specimen was tempered martensite with a high dislocation density, small sub-grains and fine secondary phase such as $M_23C_6$. Aging for long-time at high temperature caused the growth of martensite lath and the decrease of dislocation density resulting in the decrease in strength. However, the evolution of secondary phases had influence on hardness, yield strength and impact property. In the group A specimen aged at $600^{\circ}C\;and\;650^{\circ}C$, Laves phase was observed. The Laves phase caused the increase of the hardness and the decrease of the impact property. In addition, the abrupt growth of secondary phases caused decrease of the impact property in both A and B group specimens.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1090-1096
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• 2010

This pitting corrosion study of welded joints of austenitic stainless steels (AISI 304L and 316L) has addressed the differentiating solidification mode using three newly introduced filler wires with a flux-cored arc welding process (FCAW). The delta ferrite (${\delta}$-ferrite) content in the welded metals increased with an increasing equivalent weight ratio of chromium/nickel ($Cr_{eq}/Ni_{eq}$). Ductility dip cracking (DDC) was observed in the welded metal containing ferrite with none of AISI 304L and 0.1% of AISI 316L. The potentiodynamic anodic polarization results revealed that the $Cr_{eq}/Ni_{eq}$ ratio in a 3.5% NaCl solution didn't much affect the pitting potential ($E_{pit}$). The AISI 316L welded metals with ${\ddot{a}}$-ferrite content of over 10% had a superior $E_{pit}$ value. Though the AISI 316L welded metal with 0.1% ferrite had larger molybdenum contents than AISI 304L specimens, it showed a similar $E_{pit}$ value because the concentration of chloride ions and the corrosion product induced severe damage near the DDC.

• Journal of Korea Foundry Society
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• v.41 no.6
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• pp.543-549
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• 2021

Aluminum cast iron has excellent oxidation resistance and good resistance to sulfide and corrosion. Compared to Ti and Ni alloys, it is expected to be a substitute material for structural materials and stainless steels because it is relatively inexpensive to use Fe, which is a non-strategic element. This results in a weight reduction effect of about 30% as compared to the use of stainless steel. With regard to aluminum as an alloying material, it is an element that has been widely used for the alloying of cast iron in recent years. Practical use has been delayed owing to the resulting lack of ductility at room temperature and the sharp decrease in the strength above 600℃ of this alloy, however. The cause of the weak room temperature ductility is known to be environmental embrittlement by hydrogen, and the addition of various alloying elements has been attempted in order to mitigate these shortcomings. Although alloying elements such as vanadium, chromium, and manganese are mainly used to increase the hardness and wear resistance of gray cast iron, the price of finished products containing these elements and the problems associated with alloys with this material impose many limitations.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.1018-1024
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• 1999

The effects of operating temperature and stress on degradation of components in high temperature steam generator were investigated. Several 2.25CrlMo tubes which had operated over 20 years and an unused 9CrlMoVNb tube were tested. For the former samples, the amount of $\textrm{M}_{6}\textrm{C}$ carbide and its size are increased with the aging or operating time. The precipitation behavior of carbides ($\textrm{M}_{2}\textrm{O}$, $\textrm{M}_{6}\textrm{C}$) is changed with the operating temperature of the tubes. However, unused 9CrlMoVNb samples show a different carbide precipitation process due to high chromium, vanadium, and niobium contents. The amount of Cr-rich $\textrm{M}_{23}\textrm{C}_{6}$ carbide is significantly increased with aging time, but that of $\textrm{M}_{6}\textrm{C}$ type carbide is rarely changed with aging time at elevated temperatures.

• The korean journal of orthodontics
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• v.28 no.2 s.67
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• pp.329-341
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• 1998

Sterilization has received much attention in orthodontic practices over the past several years. The present study was undertaken to investigate the effects of sterilization on the physical properties of orthodontic pliers-AEZ, Unitek, and Dentronix ligature cutters. This study was designed to examine the tips of ligature cutters before and after 200 and 400 sterilization cycles using the Bowmar RHT-1000, the Dentronix DDS-5000, and the Eschmann SES-2000. The tip surface and the fracture surface were observed with a scanning electron microscope. The microstructure was observed with an optical microscope. The hardness test was carried out with the mic개-Vickers hardness tester and the Rockwell C Scale hardness tester. The chemical composition was analyzed by energy dispersive X-ray spectrometer. The results of this study were as follows : 1. The number and the size of corrosion products on the tip surface and the proportion of cleavage planes in fractured specimen increased, but the hardness of the tip decreased in proportion to sterilization cycles. From these observations, it was considered that mechanical properities decreased in proportion to sterilization cycles. 2. The number and the size of chromium carbides increased in proportion to sterilization cycles. Coarse microstructure decreased mechanical properities. 3. The AEZ and Unitek ligature cutters were Fe-Cr stainless steels, but the Dentronix ligature cutter was Co-Cr alloy. There were many differences among manufactures, but the chemical composition was .not changed after sterilization cycles. 4. The tip edge of ligature cutter used in a clinic revealed microcracks with the SEM observation. Clinical experience confirmed that ligature cutters were gradually degraded by sterilization.