• Corrosion Science and Technology
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• v.6 no.2
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• pp.56-61
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• 2007

Carbide dissolution during heating processes can change chemical composition of martensitic stainless steel in its austenitic phase. Although the austenitizing treatments were carried out at a homogeneous austenite region, the amount of carbon atom in the matrix differs. Increase in the amount of carbon contents in the matrix resulted in decreasing MS temperature, which consequently causes the volume fraction of the retained austenite to increase. This study reveals the effects of the austenitizing treatment on the properties of Fe - 0.3C - 14Cr - 3Mo martensitic stainless steel change with different austenitizing temperatures.

• Korean Journal of Materials Research
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• v.15 no.2
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• pp.115-120
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• 2005

The aim of this research is to develop the TRIP aided high strength low carbon steels using reverse transformation process. The $4\~8\%$ Mn steel sheets were reversely transformed by slow heating to intercritical temperature region and furnace cooling to room temperature. The stability of retained austenite depends on the enrichment of carbon and manganese by diffusion during the reverse transformation. The amount of retained austenite formed after reversely transformed at $625^{\circ}C$ for 6 hrs was about $50\;vol.\%$ in the $8\%Mn$ steel. The change in volume fraction of retained austenite with a holding temperature was consistent with the changes in elongation and the strength-ductility combination. The maximum strength-ductility combination of 40,000 $MPa{\cdot}\%$ was obtained when the $8\%Mn$ steel reversely transformed at $625^{\circ}C$ for 12 hrs. However, it's property was significantly decreased at higher holding temperature of $675^{\circ}C$ resulting from the decrease of ductility.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.2
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• pp.79-89
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• 2014

The effect of carbon on the microstructure and texture of low carbon steels was investigated in a series of 1.6 Mn-0.3Cr-0.2Mo-0.001B steels with carbon ranging from 0.021 to 0.048%. Intensity of {111} orientation increased with decreasing the carbon content, resulting in the increase in $r_m$ value. The highest $r_m$ value of 1.30 was obtained in 0.021%C steel annealed at $820{\sim}850^{\circ}C$ according to the typical galvannealing heat cycle. Martensite volume fraction was not substantially affected by the annealing temperature. It was found that the fine and uniformly distributed martensite particles which were present in amounts of about 5% volume fraction were desirable for the highest $r_m$ value. The other factor affecting the high $r_m$ value was the preferred epitaxial growth of retained ferrite with {111} orientation into austenite during cooling.

• Journal of Powder Materials
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• v.4 no.3
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• pp.222-229
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• 1997

A P/M high speed steel of ASP 30 grade was austenitized, gas quenched and tempered at various conditional. The mechanical properties such as hardness, bend strength and fracture toughness were evaluated after heat treatment. The microstructure and the type and volume fraction of carbides were analyzed by an optical microscope, image analyzer and XRD. The primary carbides after the heat treatment were MC and $M_6C$ type. The volume of the total carbide varied from 10 to 15% depending on the austenitizing and tempering temperature. The tempering temperature for maximum hardness was at around 52$0^{\circ}C$. But the maximum bend strength was obtained at about 55$0^{\circ}C$. The fracture toughness was largely affected by the presence of retained austenite after gas quenching and secondary hardening during tempering.

• Applied Microscopy
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• v.52
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• pp.5.1-5.10
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• 2022

The use of Pipelines for long-distance transportation of crude oil, natural gas and similar applications is increasing and has pivotal importance in recent times. High specific strength plays a crucial role in improving transport efficiency through increased pressure and improved laying efficiency through reduced diameter and weight of line pipes. TRIP-based high-strength and high-ductility alloys comprise a mixture of ferrite, bainite, and retained austenite that provide excellent mechanical properties such as dimensional stability, fatigue strength, and impact toughness. This study performs microstructure analysis using both Nital etching and LePera etching methods. At the time of Nital etching, it is difficult to distinctly observe second phase. However, using LePera etching conditions it is possible to distinctly measure the M/A phase and ferrite matrix. The fraction measurement was done using OM and SEM images which give similar results for the average volume fraction of the phases. Although it is possible to distinguish the M/A phase from the SEM image of the sample subjected to LePera etching. However, using Nital etching is nearly impossible. Nital etching is good at specific phase analysis than LePera etching when using SEM images.

• Environmental Engineering Research
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• v.23 no.2
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• pp.195-204
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• 2018

A pilot scale study was conducted on a down-flow hanging sponge (DHS) reactor installed at a sewage treatment plant in Banda Aceh, Indonesia for treatment of desludging septic tank wastewater. Raw wastewater with an average biochemical oxygen demand (BOD) and total suspended solids of 139 mg/L and 191 mg/L, respectively, was pumped into the reactor. Two different hydraulic retention times (HRTs, 3 h and 4 h) were investigated, equivalent to organic loadings of 1.11 and $0.78kg\;BOD/m^3/d$, respectively. The average BOD concentration in the final effluent was 46 and 26 mg/L at HRTs of 3 and 4 h, respectively. The concentration of retained sludge along the reactor height was 10.2-18.7 g VSS/L-sponge, and the sludge activities were 0.24-0.32 and 0.04-0.40 mg/g VSS/h for heterotrophs and nitrification, respectively. Values of water hold-up volume, dispersion coefficient, and number of tank in-series found from tracer studies of clean sponge and biomass-loaded sponge confirmed that growth of retained sludge on the sponge module improved hydraulic performance of the reactor. Adoption of the DHS reactor by this Indonesian sewage treatment plant would enhance the role of the current desludging septic tank wastewater treatment system.

• Journal of Microbiology and Biotechnology
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• v.20 no.3
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• pp.513-517
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• 2010

A thermostable trehalose synthase (TtTSase) from Thermus thermophilus HJ6 was immobilized on chitosan activated with glutaraldehyde. The yield of immobilization was evaluated as 39.68%. The optimum pH of the immobilized enzyme was similar to that of the free enzyme. However, the optimal temperature ranges were shifted by about $4^{\circ}C$ owing to better thermal stability after immobilization. The half-life of heat inactivation for free and immobilized enzymes was 5.7 and 6.3 days at $70^{\circ}C$, respectively, thus showing a lager thermostability of the immobilized enzyme. When tested in batch reaction, the immobilized enzyme retained its relative activity of 53% after 30 reuses of reaction within 12 days, and still retained 82% of its initial activity even after 150 days at $4^{\circ}C$. A packed-bed bioreactor with immobilized enzyme showed a maximum yield of 56% trehalose from 100 mM maltose in a continuous recycling system (bed volume: 10 ml) under conditions of pH 7.0 and $70^{\circ}C$.

• The Journal of Engineering Geology
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• v.13 no.1
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• pp.51-65
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• 2003

A series of numerical simulations were carried out using STOMP( Subsurface Transport over Multiple Phase) simulator. The flow and distribution of LNAPL were analyzed in homogeneous fine and coarse sand. Vertical movement of LNAPL is faster in the coarser sand. But the total volume of LNAPL retained in the unsaturated zone is larger in the finer sand. A fine layer in the coarse sand domain is also simulated. The results showed that the retained LNAPL volume and shape are highly influenced by the Position of the fine layer. Flow and distributions of LNAPL were simulated when there were heterogeneous lenses in the sand domain. Water table fluctuation was also considered. In these cases, it was found that the heterogeneous lens was a barrier to LNAPL flow, and water table fluctuation stimulated the downward movement of retained LNAPL. The LNAPL flow and distribution observed in these numerical experiments show that in the subsurface environment, the behaviors of LNAPL highly depend on heterogeneities of unsaturated zone and the dynamic hydrogeologic condition such as water table fluctuation. These results can explain some of the complexity of LNAPL flow and distribution Patterns in LNAPL contaminated field sites.

• The Journal of Advanced Prosthodontics
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• v.3 no.2
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• pp.96-100
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• 2011

An 18-year-old male presented severe hypodontia due to hypohidrotic ectodermal dysplasia was treated with Le Fort I maxillary osteotomy with simultaneous sinus floor augmentation using the mixture of cortical autogenous bone graft harvested from iliac crest and organic Bio-Oss to position the maxilla in a right occlusal plane with respect to the mandible, and to construct adequate bone volume at posterior maxilla allowing proper implant placement. Due to the poor bone quality at other sites, ridge augmentation with onlay graft was done to construct adequate bone volume allowing proper implant placement, using tissue harvested from the iliac bone. Seven implants were placed in the maxilla and 7 implants were inserted in the mandible and screw-retained metal ceramic FPDs were fabricated. The two year follow up data showed that dental implants should be considered as a good treatment modality for patients with ectodermal dysplasia.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.2
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• pp.128-137
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• 1997

The formation processes of the retained austenite(${\gamma}_R$) in SHCP100 steel sheets were investigated in order to improve the transformation induced plasticity(TRIP) effect of ${\gamma}_R$. An excellent combination of elongation about 23% and high strength over 830 MPa was achieved by processing of intercritical annealing and isothermal holding. The mechanical properties of TRIP-aided dual phase steel was found to depend on the volume ratio of each phase and the volume fraction of ${\gamma}_R$. It was also noted that the proper mechanical stability of ${\gamma}_R$ improved the mechanical properties. In this work, the best balance of strength-ductility was obtained by holding the steel at $420^{\circ}C$ for 500sec. after annealing at $730^{\circ}C$ for 300 sec.