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10 results on '"Hyo Ju Bae"'

1. Effect of heat treatment conditions on the plastic deformation behavior of the Inconel 706 alloy

Author

Hyogeon Kim, Hojun Oh, Hyo Ju Bae, Hyokyung Sung, Firooz Taleghani, Eun Yoo Yoon, Jae Bok Seol, Sangshik Kim, and Jung Gi Kim

Subjects
Inconel alloy, Mechanical property, Microstructure, Plastic deformation, Mining engineering. Metallurgy, TN1-997
Abstract

Although the Inconel 706 alloy has been developed to reduce the manufacturing cost for mass production, the effect of post-heat treatment on the deformation mechanisms of this alloy system has not been well investigated yet. In this study, the effect of heat treatment conditions on the plastic deformation behavior of the Inconel 706 alloy was analyzed. The size of the coherent γ'/γ'' co-precipitates in the sample subjected to 3-step aging (3STEP) is larger than that in the sample subjected to 2-step aging (2STEP). However, the yield strength of 3STEP is lower than that of 2STEP due to the precipitate-free zone near its η phase which reduces the volume fraction of the γ'/γ'' co-precipitates. The coarsened η phase in 3STEP also acts as a crack initiation site, inducing intergranular fracture. Meanwhile, serrated flows were observed in the tensile stress-strain curve of 2STEP tested at a high temperature condition, which resulted in ductility degradation. The present result indicates that the different heat treatment conditions for the Inconel 706 alloy affect the morphology of the precipitate in the matrix, which can be attributed to their deformation behaviors.

Published
2022
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2. Quantitative analysis of retained austenite in Nb added Fe-based alloy

Author

Kwang Kyu Ko, Jin Ho Jang, Saurabh Tiwari, Hyo Ju Bae, Hyo Kyung Sung, Jung Gi Kim, and Jae Bok Seol

Subjects
Retained austenite, LePera etching, Nital etching, Optical microscopy, Microscopy, QH201-278.5
Abstract

Abstract 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.

Published
2022
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6. Development of 1.2 GPa Ferrite-based Lightweight Steels via Low-temperature Tempering

Author

Hyokyung Sung, Kwang Kyu Ko, Hyo Ju Bae, Jae Bok Seol, Jung Gi Kim, Jae Seok Jeong, and Hyoung Seok Park

Subjects
Materials science, Ferrite (iron), Modeling and Simulation, Metallurgy, Metals and Alloys, Tempering, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials
Abstract

Previously reported low-Mn ferritic-based lightweight steels are potential candidates for industrial applications, however, they typically exhibit lower strength, with < 1 GPa and lower strength-ductility balance, than medium- and high-Mn austenitic lightweight steels. Herein, we introduce a low-temperature tempering-induced partitioning (LTP) treatment that avoids the strength-ductility dilemma of low-Mn ferriticbased steels. When the LTP process was performed at 330 oC for 665 s, the strength of typical ferritic base Fe-2.8Mn5.7Al0.3C (wt%) steel with heterogeneously sized metastable austenite grains embedded in a ferrite matrix, exceeded 1.1 GPa. Notably, the increased strength-ductility balance of the LTP-processed ferritic steel was comparable to that of the high-Mn based austenitic lightweight steel series. Using microscale to nearatomic scale characterization we found that the simultaneous improvement in strength and total elongation could be attributed to size-dependent dislocation movement, and controlled deformation-induced martensitic transformation.

Published
2021

9. Near atomic-scale comparison of passive film on a 17 wt% Cr-added 18 wt% Mn steel with those on typical austenitic stainless steels

Author

Muhammad Ishtiaq, Jung Gi Kim, Hyokyung Sung, Jong Chan Han, Kwang Kyu Ko, Eun Tae Kim, Jae Bok Seol, and Hyo Ju Bae

Subjects
Austenite, chemistry.chemical_classification, Materials science, Base (chemistry), Mechanical Engineering, Metals and Alloys, Atom probe, Condensed Matter Physics, Atomic units, Corrosion, law.invention, Cracking, chemistry, Mechanics of Materials, law, Scanning transmission electron microscopy, General Materials Science, Composite material, Wurtzite crystal structure
Abstract

The passive films on typical stainless steels (SS) and on a newly developed high-Cr (17 wt%)-added 18 wt%-Mn steel (HCr-HMnS) were compared by Cs-corrected scanning transmission electron microscopy and atom probe tomography. Although the passive films of all samples having similar Cr contents had the same thickness, unprecedented hexagonal wurtzite MnO inside the passive film of HCr-HMnS specimen was susceptible to corrosion cracking; this was not observed in the SS samples. This MnO caused crack formation during potentiodynamic polarization test, suggesting that reducing the harmful MnO by adding Mo and Ni facilitates the development of high-Mn base SS materials . Furthermore, higher MoO2 composition of the passive films on 316 type austenitic SS than 304 type series might would result in primarily the improved pitting resistance.

Published
2021

10. Quality Characteristics of Kimchi with Added Stevioside-containing Sweetener

Author

Hyo Ju Bae and Ju Youn Lee

Subjects
integumentary system, biology, Chemistry, biology.organism_classification, Acid production, Lactic acid, chemistry.chemical_compound, nervous system, Odor, Food science, Stevioside, Quality characteristics, Sugar, tissues, Bacteria
Abstract

The effects of stevioside-containing sweetener (SCS) on kimchi quality were evaluated by investigating acid production, growth of lactic acid bacteria, sensory properties, and several volatile odor component (VOC)s of SCS-added kimchi. The concentrations of SCS added to kimchi instead of 1% white sugar were 0.165, 0.33, 0.66, and 1.32% (w/w). The pH of kimchi with higher amounts of added SCS generally increased, and the acidity of kimchi with higher amounts of added SCS generally decreased. Addition of higher amounts of SCS generally inhibited the growth of lactic acid bacteria in kimchi. Scores of overall acceptability for 0.33 or 0.66% SCS-added kimchi were significantly higher than those for other samples (p

Published
2013

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