• Corrosion Science and Technology
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• 제17권2호
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• pp.81-89
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• 2018

In this study, the effect of Nb alloying element on the corrosion fatigue properties of high strength steel is investigated by conducting fatigue experiments under corrosive condition and hydrogen induced condition, potentiodynamic polarization test, tensile test and surface analyses. Nb element is added to enhance the mechanical property of medium carbon steel. This element forms MX-type phases such as carbides and nitrides which are playing an important role in the grain refinement. The grain refinement is one of the effective way to improve mechanical property because both tensile strength and toughness can be improved at the same time. However, MX-type phase precipitates can be a susceptible site to localized corrosion in corrosive environment due to the potential difference between matrix and precipitate. The obtained results showed that Nb-added steel improved corrosion fatigue property by grain refinement. However, it is degraded for hydrogen-induced fatigue property due to Nb, Ti-inclusions acting as a stronger trap.

• 한국주조공학회지
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• 제35권2호
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• pp.23-28
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• 2015

This work presents the effect of the cooling rate on the precipitation of super duplex stainless steel. Specimens of super duplex stainless steel with a specific composition were cooled at various cooling rates after being melted at $1550^{\circ}C$ in a directional solidification furnace. Ferrite (${\delta}$), Austenite (${\gamma}$), Sigma (${\sigma}$), and Chi (${\chi}$) phases were precipitated when the cooling rate was lower than 0.22 K/s. When the cooling rate was 0.22 K/s or faster, ${\sigma}$ and ${\chi}$ phases were not precipitated.

• Applied Microscopy
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• 제45권4호
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• pp.230-235
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• 2015

Crystallographic models are effective tools to interpret, calculate and even to predict the preferred crystallographic morphologies of precipitates in various precipitation systems. The present study gives an introduction on the recently developed secondary constrained coincident site lattice (II-CCSL) model. Using the II-CCSL model, the interface matching condition of the ${\beta}-Mg_{17}Al_{12}$ precipitates with ${\alpha}-Mg$ matrix in an aged AZ91 alloy has been analyzed to rationalize the morphologies of the precipitates. The results show that the characteristic crystallographic features of the observed ${\beta}-Mg_{17}Al_{12}$ precipitates, i.e., the habit plane of the ${\beta}-Mg_{17}Al_{12}$ lath with a Burgers orientation relationship (OR) and the growth direction of the ${\beta}-Mg_{17}Al_{12}$ with a Crawley OR exhibit a better lattice matching degree than their vicinal orientations. Moreover, the Crawley OR is preferred to the Burgers OR due to a better lattice match.

• 한국환경보건학회지
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• 제15권2호
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• pp.33-40
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• 1989

Dichromate reflux method for COD analysis is one of the useful and precise way to solve the organic content of the wastewater. But the standard procedure for COD is not entirely satisfactory for sample containing appreciable amounts of inhibiting substance, especially chloride ion. Under the conditions of the established test, a big disadvantage of the method is that dichromate oxidizes chloride quantitatively to chlorine. When it is necessary to use silver sulfate as a catalyst in the COD procedure, chloride must be removed before the addition of the catalyst. Silver sulfate and mecuric sulfate forms a precipitate of AgCl and HgCl$_{2}$ separately which is not completely oxidized during the test and, therefore, cannot be corrected for. So, we evaluate and compensate the amount of chloride oxidation in the absence of chemicals during the experimental procedure. Calculation of COD is made using the following reviced formula: real COD = tested COD - 0.2277Cl.

• Applied Microscopy
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• 제19권1호
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• pp.89-108
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• 1989

알루미늄-4%동 계에서의 ${\theta}$ 및 ${\theta}'$ 석출물과 석출물/기지 계면 전위를 투과전자현미경상으로 관찰하고 콘트라스트 실험 및 석출물 분석으로 석출물/기지 계면의 정합성과 여러 전위들의 Burgers 벡타를 규명하였다. 실험 결과, 변형장은 정벽면에 수직으로 되어 있고, 판상의 ${\theta}'$ 석출물은 {100}형 정벽면을 지니고 있었다. ${\theta}'$판 주위의 전위는 정벽면에 수직인 Burgers 벡타를 지닌 칼날전위였다. 그리고, 석출물과 기지 사이의 접합변형을 작게하기 위한 계면전위의 Burgers 벡타는 a<100>과 a/2<100>형이었다. 또한 Hornbogen의 예견과 일치하는 사실로, ${\theta}'$의 석출물의 끝부분에서 ${\theta}$상이 핵생성을 하는 사실을 발견하였다.

• 한국자동차공학회논문집
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• 제8권4호
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• pp.141-148
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• 2000

As the steel plates used for automobile safety the TRIP-assisted multiphase steels are being introduced to automobile industry with respect to their remarkable mechanical properties for the combination of high strength and large elongation. This multiphase structure is generated by two stage heat treatment (intercritical annealing & isothermal treatment) The metastable retained austenite can be transformed to martensite when plastically deformed which results in TRIP effect. Actually the microstructure of TRIP-assisted steels consist of a fine dispersite. There present discussion deals with bainite reaction kinetics of austenite in the process o f two stage heat treatment. In relation to bainite transformation the characteristics of bainite reaction is found to be influenced by the bainite tempering temperature and also by the relative rate in which carbides precipitate within residual austenite.

• 한국미생물·생명공학회지
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• 제24권3호
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• pp.364-370
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• 1996

Sediments collected from the Jungnang-cheon and its tributaries were used to enumerate anaerobic bacteria by most probable number (MPN) methods. A simple method was developed to detect ferrous ion in the culture fluid in order to count the number of iron ion reducers, and sulfate-reducing bacteria (SRB) and methanogens were detected by the presence of FeS precipitate in the culture or methane in the head space, respectively. The numbers of iron reducer was in the range of 10$^{7}$ - 10$^{8}$ /g in the sediment of the stream containing higher organic content than the tributaries. The sediments of tributaries were analyzed to contain iron reducers less than 10$^{7}$ cells/g. With one exception the numbers of SRB and methanogens were less than 10$^{3}$ cells/g in the sediment. From these results it is concluded that organics in the sediment support the growth of iron reducers, which out-compete SRB and methanogens.

• 한국해양공학회지
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• 제15권3호
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• pp.58-62
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• 2001

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high n austenitic steels. After measuring the internal stress in minimum creep rate state under applied stress of 236MPa at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band widths and values of internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

• 한국세라믹학회지
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• 제29권12호
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• pp.963-969
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• 1992

This paper describes the feasibility for a direct production of zinc oxalate powders from zinc-loaded D2EHPA solutions combining the purification and the precipitation in one operation unit. This process has the potential as an alternative to conventional method for the synthesis of zinc oxide precursor particles from the hydrometal-lurgical processes. Zinc was extracted into D2EHPA in kerosene and then zinc-loaded D2EHPA solution was emulsified with oxalic acid-HCl solution to precipitate zinc oxalate powder, which was readily calcined to zinc oxide. The precipitation kinetics and yield were sensitive to experimental conditions. The morphology, size and size distribution of the zinc oxalate powders varied with zinc/oxalate ion riatio, temperature, and the presence of SPAN 60, which affected nucleation, growth, and the emulsion characteristics.

• 한국세라믹학회지
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• 제24권3호
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• pp.215-222
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• 1987

${\alpha}$-Ferric Hydrous Oxide and ${\alpha}$-Ferric Oxide were obtained as following processes that Ferric Nitrate solution was adjusted to pH 6-8 with Ammonium Hydroxide, refluxed the Iron precipitate for 1 hr. at 80$^{\circ}C$, washed it with water and Methanol (95%), dried it to obtain ${\alpha}$-Ferric Hydrous Oxide at 60$^{\circ}C$, and then heated in atmosphere to prepare ${\alpha}$-Ferric Oxide for 1 hr. at 450$^{\circ}C$. Mica particles cleaned with ultrasonicator (45KHz) in water were mixed with Ferric Nitrate solution and treated it to adsorb ${\alpha}$-Ferric Oxide on the surface of mica particles by using the abovementioned processes, but the heated temperature was at 500$^{\circ}C$. The maximum wavelength of reflected light on the surface of mica-${\alpha}$-Ferric Oxide (50%) was appeared at 546nm but -Ferric Oxide free mica only was at 436 nm. The maximum wavelength was shifted to longer when the weight ratios of ${\alpha}$-Ferric Oxide to mica was changed from 1% to 50%.