136 results on '"Un-Bong Baek"'
Search Results
52. Corrigendum to 'Hydrogen embrittlement susceptibility of X70 pipeline steel weld under a low partial hydrogen environment' [International Journal of Hydrogen Energy 45 (2020) 23739-23753]
- Author
-
Thanh Tuan Nguyen, Un Bong Baek, Naehyung Tak, Seung Hoon Nahm, and Jaeyeong Park
- Subjects
Materials science ,Hydrogen ,Renewable Energy, Sustainability and the Environment ,Pipeline (computing) ,Metallurgy ,Energy Engineering and Power Technology ,chemistry.chemical_element ,Welding ,Condensed Matter Physics ,law.invention ,Fuel Technology ,chemistry ,law ,Hydrogen fuel ,Hydrogen embrittlement - Published
- 2021
53. Analyses of permeation characteristics of hydrogen in nitrile butadiene rubber using gas chromatography
- Author
-
Jae Kap Jung, In Gyoo Kim, Ki Soo Chung, and Un Bong Baek
- Subjects
Materials science ,Nitrile ,Hydrogen ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,Carbon black ,Permeation ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermal diffusivity ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Natural rubber ,chemistry ,visual_art ,visual_art.visual_art_medium ,General Materials Science ,Gas chromatography ,Solubility ,0210 nano-technology - Abstract
Permeation of hydrogen gas (H2) into nitrile butadiene rubber (NBR), which is one of the strong candidates for sealing material in H2 energy infrastructures, was quantified using a gas chromatography (GC) and a self-developed diffusion-analysis program. NBR samples were charged with H2 in a high-pressure chamber for 24 h then decompressed into atmosphere, and the mass of H2 released from the sample was measured as a function of elapsed time after decompression. The developed program calculated the total charging amount C0 and diffusivity D, which were then used to calculate the H2 solubility S and permeability P for variation of pressure. The samples were polymerized with and without carbon black (CB) filler in cylindrical shapes with different diameters. It appeared that the filler contributes to increase S and decrease D. The uncertainty analysis against the evaluated data was carried out, too, in order that the method could be applicable as a standard test for the permeation properties of various polymer membranes.
- Published
- 2021
54. Evaluation of hydrogen related degradation of API X42 pipeline under hydrogen/natural gas mixture conditions using small punch test
- Author
-
Jong Seo Park, Thanh Tuan Nguyen, Seung Hoon Nahm, and Un Bong Baek
- Subjects
Materials science ,Hydrogen ,business.industry ,Applied Mathematics ,Mechanical Engineering ,chemistry.chemical_element ,Test method ,Condensed Matter Physics ,Stress (mechanics) ,Brittleness ,chemistry ,Natural gas ,Ferrite (iron) ,General Materials Science ,Composite material ,Pearlite ,business ,Embrittlement - Abstract
This study investigates the effect of a hydrogen/natural gas mixture on the mechanical properties of API X42 pipeline steel using small punch (SP) test. The hydrogen-assisted fracture behavior demonstrated a transition from ductile to brittle failure, similar to the temperature-assisted brittle fracture mode. The preferential sites for hydrogen-assisted crack initiation in the X42 pipeline steel were located at the ferrite/pearlite interface, where hydrogen diffusion is enhanced by localized stress/strain conditions. The feasibility of the hydrogen environment embrittlement susceptibility obtained in the SP test and the correlation to the conventional test method is also discussed.
- Published
- 2021
55. Nuclear Magnetic Resonance Study of O-ring Polymer Exposed to High-Pressure Hydrogen
- Author
-
Jae-Kap Jung, Kwon Sang Ryu, Chang Hoon Lee, Un Bong Baek, and Sang Koo Jeon
- Subjects
chemistry.chemical_classification ,Materials science ,0211 other engineering and technologies ,02 engineering and technology ,Polymer ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,Nuclear magnetic resonance ,chemistry ,law ,021105 building & construction ,High pressure hydrogen ,Electrical and Electronic Engineering ,O-ring ,0210 nano-technology - Published
- 2017
56. Notched-tensile properties under high-pressure gaseous hydrogen: Comparison of pipeline steel X70 and austenitic stainless type 304L, 316L steels
- Author
-
Seung-Wook Baek, Un Bong Baek, Eun Ju Song, and Seung Hoon Nahm
- Subjects
Austenite ,Materials science ,Renewable Energy, Sustainability and the Environment ,Pipeline (computing) ,05 social sciences ,Metallurgy ,Gaseous hydrogen ,Energy Engineering and Power Technology ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Fuel Technology ,High pressure ,0502 economics and business ,Ultimate tensile strength ,Fracture (geology) ,engineering ,050207 economics ,Austenitic stainless steel ,0210 nano-technology ,Hydrogen embrittlement - Abstract
The effect of high-pressure gaseous H2 on the fracture behavior of pipeline steel X70 and austenitic stainless steel type 304L and 316L was investigated by means of notched-tensile tests at 10 MPa H2 gas and various test speed. The notch tensile strength of pipeline X70 steel and austenitic stainless steels were degraded by gaseous H2, and the deterioration was accompanied by noticeable changes in fracture morphology. The loss of notch tensile strength of type 316L and X70 steels was comparable, but type 304L was more susceptible to hydrogen embrittlement than the others. In the X70 steel, hydrogen embrittlement increased as test speed decreased until the test speed reached 1.2 × 10−3 mm/s, but the effect of test speed was not significant in 304L and 316L steels.
- Published
- 2017
57. Hydrogen embrittlement of 3-D printing manufactured austenitic stainless steel part for hydrogen service
- Author
-
Seung-Wook Baek, Myungsik Jung, Seung Hoon Nahm, Un Bong Baek, Jung Hyun Kim, and Eun Ju Song
- Subjects
010302 applied physics ,Austenite ,Hydrogen infrastructure ,Materials science ,Hydrogen ,Mechanical Engineering ,Metallurgy ,Metals and Alloys ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Corrosion ,chemistry ,Mechanics of Materials ,Martensite ,Hydrogen fuel ,0103 physical sciences ,engineering ,General Materials Science ,Austenitic stainless steel ,0210 nano-technology ,Hydrogen embrittlement - Abstract
Metal additive manufacturing (AM) technology as the emerging future manufacturing technology can be applied to the hydrogen service including hydrogen energy utilized industry. Direct metal tooling (DMT), one of the 3-D printing technologies, was used to manufacture an austenitic stainless steel part, and its mechanical properties and hydrogen embrittlement (HE) behavior were studied using the small specimen test technique under 10-MPa pressurized hydrogen gas. This part showed high HE resistance with minimal strain-induced transformation of austenite to martensite. This result indicates that parts produced using DMT are suitable for use in facilities for hydrogen service and hydrogen infrastructure.
- Published
- 2017
58. Ductility and Fatigue Strength Loss of a Hydrogen-Charged 316L Austenitic Stainless Steel
- Author
-
Thanh Tuan Nguyen, Un Bong Baek, Kwon Sang Ryu, and Seung Hoon Nahm
- Subjects
Materials science ,Hydrogen ,chemistry.chemical_element ,engineering.material ,Fatigue limit ,chemistry ,Ultimate tensile strength ,engineering ,Low-cycle fatigue ,Austenitic stainless steel ,Elongation ,Deformation (engineering) ,Composite material ,Ductility - Abstract
The susceptibility of 316L-type austenite stainless steel to hydrogen was quantified by means of SSRT results and low-cycle fatigue life measurement. Both tests were conducted in the air condition after being charged with high-pressure hydrogen gas of 10 MPa and a temperature of 300°C for 120 hours. In addition, SSRT tests in gaseous hydrogen at a pressure of 10 MPa were also performed and compared to the tests conducted in hydrogen pre-charged and as-received conditions. The 0.2% yield strength and tensile strength did not show there to be a considerable difference between hydrogen pre-charging and the as-received conditions, whereas the gaseous hydrogen condition revealed a remarkable degradation in tensile properties, especially in terms of fracture elongation. In the case of fatigue life test, a considerable influence of hydrogen pre-charging in fatigue life properties was observed in the high strain amplitude regime whereas the measured values in the low strain deformation region are consistently comparable to that in the as-received condition. Fatigue limit was not affected by hydrogen pre-charging.
- Published
- 2019
59. Screening Technique of Hydrogen Embrittlement Sensitivity in Austenitic Stainless Steels Using In-Situ Small Punch Test Method
- Author
-
Seung-Hoon Nahm, Hyuckmin Kim, Un-Bong Baek, Kyung-Oh Bae, and Hyung-Seop Shin
- Subjects
Austenite ,In situ ,Materials science ,Hydrogen ,chemistry ,Metallurgy ,chemistry.chemical_element ,Test method ,Sensitivity (explosives) ,Hydrogen embrittlement - Abstract
In this study, a simple screening technique using an in-situ small-punch (SP) test and based on the hydrogen embrittlement (HE) sensitivity of austenitic stainless steels was developed for use in hydrogen energy facilities. To investigate the HE behaviors of metallic materials, the in-situ SP tests were carried out under high-pressure hydrogen gas environments. The reductions of thickness at the fractured parts of the specimen were measured. The relative reductions of thickness (RRT) were determined after conducting SP tests in both hydrogen and inert gas environments. Similar to the relative reduction of area (RRA) obtained using the slow strain-rate tensile test, RRT obtained using the in-situ SP test is a quantitative measure of the influence of the HE behaviors. The influence of punch velocity on HE sensitivity was examined. The HE behaviors of austenitic steels were evaluated qualitatively and quantitatively. The high-Mn steels were also evaluated because they are candidates for storage and transportation of hydrogen gas. A screening technique for determining the practical environmental conditions at the point of use could be established by confirming the effectiveness of the influencing factor, RRT, using this in-situ SP test method.
- Published
- 2019
60. Hydrogen Sensing Using Paper Sensors with Pencil Marks Decorated with Palladium
- Author
-
Un-Bong Baek, Nam Hee Lee, and Seung-Hoon Nahm
- Subjects
Materials science ,Hydrogen ,chemistry.chemical_element ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,lcsh:Chemical technology ,01 natural sciences ,Biochemistry ,paper-based sensor ,Article ,H2 sensing ,Analytical Chemistry ,law.invention ,law ,lcsh:TP1-1185 ,Electrical and Electronic Engineering ,chemiresistor ,Instrumentation ,Chemiresistor ,Detection limit ,Reproducibility ,business.industry ,Graphene ,021001 nanoscience & nanotechnology ,pencil marks ,palladium ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Pencil (optics) ,chemistry ,hydrogen ,Optoelectronics ,0210 nano-technology ,business ,Palladium - Abstract
Paper-based sensors fabricated using the pencil-on-paper method are expected to find wide usage in many fields owing to their low cost and high reproducibility. Here, hydrogen (H2) detection was realized by applying palladium (Pd) nanoparticles (NPs) to electronic circuits printed on paper using a metal mask and a pencil. We confirmed that multilayered graphene was produced by the pencil, and then characterized Pd NPs were added to the pencil marks. To evaluate the gas-sensing ability of the sensor, its sensitivities and reaction rates in the presence and absence of H2 were measured. In addition, sensing tests performed over a wide range of H2 concentrations confirmed that the sensor had a detection limit as low as 1 ppm. Furthermore, the sensor reacted within approximately 50 s at all H2 concentrations tested. The recovery time of the sensor was 32 s at 1 ppm and 78 s at 1000 ppm. Sensing tests were also performed using Pd NPs of different sizes to elucidate the relationship between the sensing rate and catalyst size. The experimental results confirmed the possibility of fabricating paper-based gas sensors with a superior sensing capability and response rate.
- Published
- 2019
61. Tensile and Fracture Behaviors of Austenitic High-Manganese Steels Subject to Different Hydrogen Embrittlement Test Methods
- Author
-
Sang-In Lee, Ji-Min Lee, Seung-Yong Lee, Han-Jin Kim, Jin-Yoo Suh, Jae-Hyeok Shim, Un-Bong Baek, Seung-Hoon Nahm, Joonho Lee, and Byoungchul Hwang
- Published
- 2019
62. Hydrogen Induced Crack and Phase Transformation in Hydrogen Pressured Tensile Test of 316L Stainless Steel
- Author
-
Young Suk Kim, Byung Hak Choe, Sung-Soo Kim, Sung Hoon Nam, Jong Hun Shim, Key-Yong Hong, Young Uk Kim, and Un Bong Baek
- Subjects
Materials science ,Hydrogen ,Metallurgy ,Metals and Alloys ,Iron alloys ,chemistry.chemical_element ,Planar slip ,Microstructure ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Transmission electron microscopy ,Modeling and Simulation ,Phase (matter) ,Deformation (engineering) ,Tensile testing - Published
- 2015
63. Failure Analysis of End Grain Attack and Pit Corrosion in 316L Stainless Steel Pipe
- Author
-
Sung Hoon Nam, Un Bong Baek, Eui Soo Kim, Jinhee Lee, Byung Hak Choe, and Jong Hun Shim
- Subjects
Materials science ,Modeling and Simulation ,Metallurgy ,Metals and Alloys ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Corrosion - Published
- 2015
64. Magnetic Shielding Effect on Halbach Cylinder used in Magnetic Refrigerators
- Author
-
Un Bong Baek, Seong-Cho Yu, Kwon-Sang Ryu, and Jong Suk Lee
- Subjects
Physics ,Magnetic energy ,Condensed matter physics ,Permeability (electromagnetism) ,Electromagnetic shielding ,Magnetic refrigeration ,Polar ,Curie temperature ,Magnetic pressure ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Magnetic field - Abstract
The system for producing magnetic field constitutes an important component of magnetic refrigerator. Many researchers have directed significant effort to increase the magnetic field intensity, because the magnetocaloric effect at the Curie temperature increases with the power of 2/3 of the magnetic field. In this study, we report the simulation of the magnetic field intensity at polar axis of a Halbach cylinder (HC) by i) changing the length and thickness of the HC, ii) having with or without gap of the HC, and iii) surrounding the HC with a soft magnet shell, acting as a shielding. We simulated the field distribution of a HC with a finite size. Furthermore, the detailed numerical results of the magnetic field distribution and its dependence on shielding are presented in this study.
- Published
- 2014
65. Effect of highly pressurized hydrogen gas charging on the hydrogen embrittlement of API X70 steel
- Author
-
Seung-Hoon Nahm, Sang-Pill Lee, In-Soo Son, Young-Rae Cho, Jin-Kyung Lee, Hyun-Ju Bang, Chi-Eun Sung, Dong-Su Bae, and Un-Bong Baek
- Subjects
Materials science ,Hydrogen ,business.industry ,Metallurgy ,Metals and Alloys ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Acicular ferrite ,030218 nuclear medicine & medical imaging ,03 medical and health sciences ,0302 clinical medicine ,chemistry ,Mechanics of Materials ,Natural gas ,Ferrite (iron) ,Ultimate tensile strength ,Materials Chemistry ,0210 nano-technology ,business ,Embrittlement ,Hydrogen embrittlement ,Tensile testing - Abstract
During the use of API X70 steel as a pipeline structural material for the transportation of natural gas, hydrogen embrittlement can occur due to the hydrogen contained in natural gas. The aim of this study is to investigate the effects of the hydrogen content under high-pressure hydrogen gas conditions on the hydrogen embrittlement of air-cooled API X70 steel. The air-cooled API X70 steel was manufactured by hot rolling and was then air-cooled to room temperature. Tensile test specimens were held for 0 h, 1000 h, and 2000 h within a pressure vessel filled with 100% hydrogen gas at a gas pressure of 10 MPa, with the tensile tests then performed at room temperature. The microstructure of the API X70 steel consists of coarse polygonal ferrite, coarse pearlite, and fine acicular ferrite. The yield and tensile strength increased and elongation decreased considerably after a holding time of 2000 h compared to those of 0 h and 1000 h within the pressure vessel. The morphology of the fracture surface changed from ductile to brittle upon hydrogen gas charging. Secondary cracks were observed in both of the hydrogen-gas-charged specimens. No external cracks were formed on the surface of the tensile-tested specimen with a 0 h holding time; however, many external cracks were observed on the specimen surface subjected to hydrogen gas charging.
- Published
- 2014
66. Evaluation on hydrogen embrittlement of material using nondestructive test
- Author
-
Sang-Pill Lee, Insu Son, Dong-Su Bae, Joon-Hyun Lee, Jin-Kyung Lee, Seung-Hoon Nahm, and Un-Bong Baek
- Subjects
Materials science ,Hydrogen ,business.industry ,Mechanical Engineering ,Ultrasonic testing ,chemistry.chemical_element ,Structural engineering ,engineering.material ,Industrial and Manufacturing Engineering ,Cracking ,chemistry ,Acoustic emission ,Ultimate tensile strength ,engineering ,Ultrasonic sensor ,Electrical and Electronic Engineering ,Composite material ,Austenitic stainless steel ,business ,Hydrogen embrittlement - Abstract
The objective of this research is to study the effect of various hydrogen charging quantities in austenitic stainless steel using nondestructive technique. The hydrogen charging equipment was designed to make charging the steel, and the specimens were charged for 2, 4, 10 and 24 hours in the equipment. An acoustic emission (AE) technique, nondestructive test, was used to evaluate the dynamic behavior of the hydrogen charged austenitic stainless steel specimen. The tensile load was applied the charged specimen with the attached AE sensor, and elastic waves caused plastic deformation and cracking in the specimen by external tensile loading were caught at the AE sensor and analyzed by the AE parameters such as count, energy, duration time, event and amplitude. In addition, ultrasonic wave was also used to evaluate the degree of hydrogen charging. The velocity and the attenuation ratio of the ultrasonic wave on the specimen with different hydrogen charging conditions were measured. The velocity was not changed but the attenuation ratio was linearly increased with the hydrogen charging time. The relationship between the results of nondestructive test including AE test and ultrasonic test and fractographic analysis by using SEM was discussed.
- Published
- 2014
67. Stress-dependent hardening-to-softening transition of hydrogen effects in nanoindentation of a linepipe steel
- Author
-
Dong Hyun Lee, Moo-Young Seok, Jung A. Lee, Un Bong Baek, Jae-il Jang, and Seung Hoon Nahm
- Subjects
Materials science ,Stress effects ,Hydrogen ,Renewable Energy, Sustainability and the Environment ,Metallurgy ,Energy Engineering and Power Technology ,chemistry.chemical_element ,Nanoindentation ,Condensed Matter Physics ,Fuel Technology ,chemistry ,Indentation ,Electromagnetic shielding ,Hardening (metallurgy) ,Rate dependency ,Softening - Abstract
We explored the influences of hydrogen on small-scale strength of a linepipe steel through nanoindentation experiments with four pyramidal indenters. Interestingly, a transition from hydrogen-induced hardening to softening was observed as indenter sharpness increases. The transition was analyzed based on the enhancement in hydrogen's elastic shielding effects for a sharper indenter, which could be indirectly evidenced by the stress effects on indentation pile-up, dislocation density, and rate dependency of hardness.
- Published
- 2014
68. Development of High Concentration References for Measuring Hydrogen Ingress into Steels
- Author
-
Hae Moo Lee, Yun-Hee Lee, Ki-Bok Kim, Yong-Il Kim, and Un-Bong Baek
- Subjects
High concentration ,chemistry.chemical_compound ,Materials science ,chemistry ,Hydrogen ,Mechanics of Materials ,Mechanical Engineering ,Metallurgy ,Materials Chemistry ,Metals and Alloys ,Titanium hydride ,chemistry.chemical_element - Published
- 2014
69. Influence of Punch Velocity on Gas Hydrogen Embrittlement Behaviors in SA372 Steel
- Author
-
Un-Bong Baek, Seung-Hoon Nahm, Hae-Moo Lee, Jong-Seo Park, Kyung-Oh Bae, and Hyung-Seop Shin
- Subjects
Materials science ,Atmospheric pressure ,Hydrogen ,chemistry ,Hydrogen pressure ,Mechanical Engineering ,Metallurgy ,chemistry.chemical_element ,Fractography ,Test method ,Energy source ,Hydrogen embrittlement - Abstract
When using hydrogen gas as an ecofriendly energy sources, it is necessary to conduct a safety assessment and ensure thereliability of the hydrogen pressure vessel against hydrogen embrittlement expected in the steel materials. In this study, by applying the in-situ SP test method, the gas hydrogen embrittlement behaviors in SA372 steel, which is commonly used as a pressurized hydrogen gas storage container, were evaluated. To investigate the hydrogen embrittlement behavior, SP tests at different punch velocities were conducted for specimens with differently fabricated surfaces at atmospheric pressure and under high-pressure hydrogen gas conditions. As a result, the SA372 steel showed significant hydrogen embrittlement under pressurized hydrogen gas conditions. The effect of punch velocity on the hydrogen embrittlement appeared clearly; the lower punch velocity case indicated significant hydrogen embrittlement resulting in lower SP energy. The fractographic morphologies observed after SP test also revealed the hydrogen embrittlement behavior corresponding to the punch velocity adopted. Under this pressurized gas hydrogen test condition, the influence of specimen surface condition on the extent of hydrogen embrittlement could not be determined clearly.
- Published
- 2013
70. Effect of the Electro-Chemical Hydrogen Charging Time on Hydrogen Embrittlement of X70 Steel Using for Gas Pipeline
- Author
-
Seung-Hoon Nahm, Un-Bong Baek, Chi-Eun Sung, Sang-Pill Lee, Hyeon-Jee Jeon, Jin-Kyung Lee, Seok-Cheol Lee, Dong-Su Bae, and In-Soo Son
- Subjects
Materials science ,Hydrogen ,chemistry ,Modeling and Simulation ,Metallurgy ,Metals and Alloys ,chemistry.chemical_element ,Gas pipeline ,Compressed hydrogen ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Hydrogen embrittlement - Published
- 2013
71. Microstructure evolution in nanoporous gold thin films made from sputter-deposited precursors
- Author
-
Hae Moo Lee, Un Bong Baek, Na-Ri Kang, Eun-Ji Gwak, Seung Hoon Nahm, and Ju-Young Kim
- Subjects
Surface diffusion ,Materials science ,Nanoporous ,Mechanical Engineering ,Metals and Alloys ,Oxide ,Nanotechnology ,Condensed Matter Physics ,Microstructure ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Sputtering ,Nitric acid ,General Materials Science ,Thin film ,Dissolution - Abstract
We fabricate almost crack-free 1.5 μm thick nanoporous gold thin films using free-corrosion dealloying and transfer processes from sputter-deposited precursors. By controlling the temperature and the concentration of the nitric acid solution during free-corrosion dealloying, we obtain ligament sizes in nanoporous gold between 22 and 155 nm. We investigate the effects of dissolution rate of Ag atoms, surface diffusivity of Au atoms and formation of Ag oxide on nanoporosity evolution.
- Published
- 2013
72. Hydrogen-induced toughness drop in weld coarse-grained heat-affected zones of linepipe steel
- Author
-
Jae-il Jang, Jung A. Lee, Seung Hoon Nahm, Moo-Young Seok, Yun-Hee Lee, Un Bong Baek, and Dong Hyun Lee
- Subjects
Heat-affected zone ,Toughness ,Materials science ,Hydrogen ,Mechanical Engineering ,Drop (liquid) ,Metallurgy ,chemistry.chemical_element ,Welding ,Condensed Matter Physics ,Microstructure ,law.invention ,Brittleness ,chemistry ,Mechanics of Materials ,law ,General Materials Science ,Composite material ,Hydrogen embrittlement - Abstract
In this study, hydrogen effects on the impact toughness of simulated coarse-grained heat-affected zones (CGHAZs) in a linepipe steel were investigated in search of the possible “local brittle zone phenomenon” in hydrogen pipeline welds. After hydrogen charging, the inter-critically reheated and unaltered CGHAZ exhibited very low impact energies as well as occurrence of splitting. This hydrogen-induced toughness drop is discussed in terms of combined effects of brittle microstructures and hydrogen trapping.
- Published
- 2013
73. Change in Ultrasonic Characteristics with Isothermal Heat Treatment of 2.25Cr-1Mo Steel
- Author
-
Young-Hyun Nam, Seung-Hoon Nahm, Jong-Seo Park, and Un-Bong Baek
- Subjects
Toughness ,Materials science ,Mechanical Engineering ,Attenuation ,technology, industry, and agriculture ,Charpy impact test ,Ultrasonic sensor ,Composite material ,Indentation hardness ,Pressure vessel ,Longitudinal wave ,Isothermal process - Abstract
The ultrasonic characteristics of 2.25Cr-1Mo steel were investigated in relation to the isothermal heat treatment temperature and time. Charpy impact tests and hardness tests were conducted on individual specimens with three different heat treatment conditions. A pulse-echo method with longitudinal waves was used to measure the attenuation and velocity of ultrasonic waves. The FATT (fracture appearance transition temperature) increased with an increase in the isothermal heat treatment time, which implies that the toughness decreased. As the isothermal heat treatment time and temperature increased, the longitudinal wave velocity and ultrasonic attenuation coefficient were raised.
- Published
- 2013
74. Variation of Hydrogen Residue on Metallic Samples by Thermal Soaking in an Inert Gas Environment
- Author
-
Jong-Seo Park, Yun-Hee Lee, Un-Bong Baek, and Seung-Hoon Nahm
- Subjects
Hydrogen ,Thermal desorption spectroscopy ,technology, industry, and agriculture ,Analytical chemistry ,chemistry.chemical_element ,Atmospheric temperature range ,Microstructure ,Metal ,chemistry.chemical_compound ,chemistry ,visual_art ,visual_art.visual_art_medium ,Acetone ,Sample preparation ,Inert gas - Abstract
Hydrogen penetration into a metal leads to damages and mechanical degradations and its content measurement is of importance. For a precise measurement, a sample preparation procedure must be optimized through a series of studies on sample washing and drying. In this study, two-step washing with organic solvents and thermal soaking in inert gas were tried with a rod-shaped, API X65 steel sample. The samples were machined from a steel plate and then washed in acetone and etyl-alcohol for 5 minute each and dried with compressed air. After then, the samples were thermally soaked in a home-made nitrogen gas chamber during 10 minute at different heat gun temperatures from 100 to and corresponding temperature range in the soaking chamber was from 77 to according to the temperature calibration. Hydrogen residue in the samples was measured with a hot extraction system after each soaking step; hydrogen residue of wppm after the thermal soaking at decayed with increase of the soaking temperature. By adopting the heat transfer model, decay behavior of the hydrogen residue was fitted into an exponential decay function of the soaking temperature. Saturated value or lower bound of the hydrogen residue was 0.36 wppm and chamber temperature required to lower the hydrogen residue about 95% of the lower bound was . Furthermore, a thermal desorption spectroscopy was done for the fully soaked samples at . Weak hydrogen peak was observed for whole temperature range and it means that hydrogen-related contaminants of the sample surface are steadily removed by heating. In addition, a broad peak found around means that parts of the hydrogen residue are irreversibly trapped in the steel microstructure.
- Published
- 2013
75. Nondestructive evaluation for remanent life of aged 12Cr ferrite heat resisting steel by reversible permeability
- Author
-
Un-Bong Baek, Kwon-Sang Ryu, Chung-Seok Kim, and Jong Suk Lee
- Subjects
Materials science ,Electromagnetic coil ,business.industry ,Harmonics ,Ferrite (iron) ,Nondestructive testing ,Ultimate tensile strength ,Vickers hardness test ,Composite material ,Condensed Matter Physics ,business ,Electronic, Optical and Magnetic Materials ,Voltage - Abstract
We present a magnetic and nondestructive method to evaluate the remanent life of advanced ferritic steel using the value of reversible permeability. The method to measure reversible permeability is based on the theory that the value of reversible permeability is the same differential of the hysteresis loop. The measurement principle is based on the foundation of harmonics voltage induced in a sensing coil using a lock-in amplifier tuned to the frequency of the exciting one. Results obtained for reversible permeability, Vickers hardness, and tensile strength on the aged samples show that the peak interval of reversible permeability, Vickers hardness and tensile strength decrease as aging time increases. We could estimate the remanent life of advanced ferritic steel by using the relationship between the peak interval of reversible permeability and the Larson–Miller parameter, non-destructively.
- Published
- 2013
76. Metal-supported SOFC with an aerosol deposited in-situ LSM and 8YSZ composite cathode
- Author
-
Seung-Wook Baek, Harald Schlegl, Dae Soo Park, Jihoon Jeong, Jung Hyun Kim, Un Bong Baek, and Abul Kalam Azad
- Subjects
Materials science ,020209 energy ,Oxide ,02 engineering and technology ,Electrolyte ,engineering.material ,Electrochemistry ,law.invention ,Metal ,chemistry.chemical_compound ,Coating ,law ,0202 electrical engineering, electronic engineering, information engineering ,Materials Chemistry ,Cubic zirconia ,Composite material ,Power density ,Process Chemistry and Technology ,021001 nanoscience & nanotechnology ,Cathode ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,visual_art ,Ceramics and Composites ,engineering ,visual_art.visual_art_medium ,0210 nano-technology - Abstract
This study reports the micro-structural and electrochemical properties of metal-supported solid oxide fuel cells (MS-SOFCs) with an La0.8Sr0.2MnO3−d (LSM)/8 mol% yttria-stabilized zirconia (8YSZ) composite cathode, fabricated at room temperature using the aerosol deposition process (ADP). The composite cathode fabricated with the ADP technique shows uniform distribution of components and pores and the interface between the cathode and the electrolyte displays excellent joining properties. The area specific resistance (ASR) of the ADP-LSM/8YSZ sample is approximately 1.50 Ω cm2 at 800 °C, so this sample shows a significantly lower ASR value than the values usually reported for samples fabricated by the in-situ treatment method for MS-SOFCs. The power density of the cells with the ADP-LSM/8YSZ cathode coated on MS-SOFCs shows a maximum value of 0.38 mW cm−2 at 800 °C and stable performance in the severe thermal durability test. Therefore, these research results can broaden the opportunities for adoption of the ADP coating processes to fabricate cathode materials in MS-SOFCs.
- Published
- 2016
77. Material Degradation of 2Cr and 12Cr Tube Steels for High Temperature and Long-Time Exposure
- Author
-
남승훈 ( Sung Hoon Nam ), 최병학 ( Byung Hak Choe ), 이길재 ( Gil Jae Lee ), and 백운봉 ( Un Bong Baek )
- Subjects
Chemistry ,Material Degradation ,Nuclear chemistry - Abstract
보일러 튜브용 크롬강의 열화기구에 대해 고찰하였다. 크롬강의 열화는 경도 및 응력-파단 수명의 변화를 동반하는데, 이는 주로 탄화물 분해 거동에 의존한다. 그런데 2Cr강인 T22의 열화는 이러한 탄화물 거동에 따르지만 12Cr강인 X20의 열화는 마르텐사이트 래쓰 성장거동에 따르기도 한다. T22와 X20의 열화에 의한 경도값과 응력-파단수명 변화현상을 미세조직적인 측면에서 고찰하였다.
- Published
- 2012
78. Nondestructive Evaluation for Remanent Life of 1Cr-0.5Mo Steel by Reversible Permeability
- Author
-
Kwon-Sang Ryu, Un Bong Baek, Yun-Hee Lee, and Jong Seo Park
- Subjects
Materials science ,business.industry ,Amplifier ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Rockwell scale ,Permeability (electromagnetism) ,Electromagnetic coil ,Nondestructive testing ,Harmonics ,Measuring principle ,Electrical and Electronic Engineering ,Composite material ,business ,Voltage - Abstract
Peak interval for reversible permeability is presented for nondestructively evaluating the remanent life of 1Cr-0.5Mo steel. The method to measure the peak interval of reversible permeability is based on the value of reversible permeability is the same as the differential value of the hysteresis loop. The measurement principle is based on the first harmonics voltage induced in a sensing coil using a lock-in amplifier tuned to a frequency of the exciting voltage. Results obtained for the peak interval of reversible permeability and Rockwell hardness on the aged samples decrease as aging time and the Larson-Miller parameter increase. We could estimate the remanent life of 1Cr-0.5Mo steel by using the relationship between the peak interval of reversible permeability and the Larson-Miller parameter, nondestructively.
- Published
- 2012
79. Effect of He-pre-injection on dislocation loop formation and irradiation-induced segregation of Fe–12%Cr–15%Mn austenitic steel
- Author
-
Un-Bong Baek, Sang-Pill Lee, Seung-Hoon Nahm, Dong-Su Bae, Heishichiro Takahashi, and Jin-Kyung Lee
- Subjects
Austenite ,Materials science ,Radiation material science ,Mechanical Engineering ,Analytical chemistry ,Electron ,Ion ,Nuclear Energy and Engineering ,General Materials Science ,Grain boundary ,Irradiation ,Dislocation ,High voltage electron microscopy ,Civil and Structural Engineering - Abstract
The effect of He-injection on irradiation-induced segregation of aging treated Fe–12%Cr–15%Mn austenitic steels, which are candidate materials as the reduced radio-activation of structure material for nuclear and/or fusion reactors was investigated by using the 1250 kV high voltage electron microscope (HVEM) connected with an ion accelerator. The Fe–Mn–Cr steel has been irradiated at 573 K by three irradiation modes of single electron-beam irradiation, electron-beam irradiation after He-injection and electron/He+-ion dual-beam irradiation in a HVEM. Irradiation-induced segregation analyses were carried out by an energy dispersive X-ray analyzer (EDX) in a 200 kV FE-TEM with beam diameter of about 0.5 nm. Dislocation loops with strain contrast were formed during irradiation and the loop numbers density increased rapidly with irradiation dose for He-pre-injected specimens. Voids were not observed after irradiations with three irradiation modes up to 5.4 dpa at 573 K. Irradiation-induced segregations of Cr and Mn near grain boundary were observed in each irradiation condition, but the amounts of Mn segregation decreased in the cases of electron/He+-ion dual-beam irradiation compared with single electron-beam and electron-beam irradiation after He-injection conditions.
- Published
- 2012
80. EVALUATION OF IMPACT PROPERTIES TO FORGED 3CR STEEL BY BARKHAUSEN NOISE
- Author
-
Seok Cheol Lee, Un Bong Baek, Young Hyun Nam, and Seung Hoon Nahm
- Subjects
symbols.namesake ,Materials science ,Transition temperature ,Metallurgy ,Fracture (geology) ,symbols ,Charpy impact test ,Impact test ,Barkhausen effect ,Voltage - Abstract
This paper reports that the Barkhausen noise method can be used to accurately characterize forged reactor vessels. The Charpy V-notch impact tests were conducted on the respective specimens with three different types of heat history. Various test results including fracture appearance transition temperature (FATT) were obtained. The Barkhausen noise voltage changed with heat treatment temperature (870~1000°C) and conditions (Tempered, PWHT). The fracture appearance transition temperature can be predicted using the Barkhausen noise voltage.
- Published
- 2012
81. UNSM Surface Technology for Manufacturing and Remanufacturing Torsion Bars for Crawler Vehicles
- Author
-
Un-Bong Baek, Young-Sik Pyoun, Chang-Min Suh, and In Ho Cho
- Subjects
Materials science ,business.industry ,Residual stress ,Stress relaxation ,Torsion (mechanics) ,Peening ,Ultrasonic sensor ,Structural engineering ,business ,Shot peening ,Durability ,Torsion spring - Abstract
The Ultrasonic Nanocrystal Surface Modification (UNSM) technology improves the fatigue life of a torsion bar by inducing compressive residual stress on the surface layer. The UNSM is applied to replace the presetting method and shot peening technology. The torsion bar must be changed periodically because of a lack of durability and a phenomenon related to the stress relaxation. The torsion fatigue test specimens were made of DIN17221 material, and the results showed that the fatigue life was 5 times more than under durability test conditions. A comparison test between the commercial vehicles' presetting method and shot peened torsion bar and the UNSM torsion bar showed that the UNSM could replace the presetting method and shot peening.
- Published
- 2011
82. Development of Evaluation Technique for Hydrogen Embrittlement Behavior of Metallic Materials Using in-situ SP Testing under Pressurized Hydrogen Gas Conditions
- Author
-
Un-Bong Baek, Hyung-Seop Shin, Ki-Hyun Kim, and Seung-Hoon Nahm
- Subjects
Materials science ,Hydrogen ,Explosive material ,business.industry ,Mechanical Engineering ,Metallurgy ,Fossil fuel ,chemistry.chemical_element ,chemistry ,Hydrogen fuel ,Metallic materials ,Current (fluid) ,business ,Helium ,Hydrogen embrittlement - Abstract
Recently, alternative and novel energy resources have been developed for use in the future because of the current environmental problems and exhaustion of fossil energy resources. Hydrogen energy has many merits, such as its environmental friendliness, easy storage, and easy production, but it also has disadvantages, in that it is highly combustible and explosive. In this study, a test procedure using a simple SP test under highly pressurized hydrogen gas conditions was established. In order to evaluate its applicability, SP tests were carried out using a stainless steel (SUS316L) sample under atmospheric, pressurized helium, and pressurized hydrogen gas conditions. The results under the pressurized hydrogen gas condition showed fissuring and produced a reduction of the elongation in the plastic instability region due to hydrogen embrittlement, showing the effectiveness of the current in-situ SP test.
- Published
- 2011
83. A CORRELATION BETWEEN THE AGING PARAMETER AND ELECTRICAL RESISTIVITY FOR THE DEGRADED 9 <font>CR</font> STEEL
- Author
-
Yun-Hee Lee, Un Bong Baek, Ho Jun Na, Seung Hoon Nahm, and Young Hyun Nam
- Subjects
Materials science ,Creep ,Electrical resistivity and conductivity ,Ultimate tensile strength ,Statistical and Nonlinear Physics ,Composite material ,Condensed Matter Physics ,Material properties ,Isothermal process - Abstract
It is advantageous to use a non-destructive evaluation (NDE) method to assess the mechanical properties of materials since conventional methods are time-consuming and usually require sampling from the material or component. In this study, an electrical resistivity method was attempted for the estimation of the creep damage of degraded 9 Cr steel. The specimens with six different kinds of aging periods were prepared by an isothermal heat treatment at 690 °C. The electrical resistivity was determined by a standard DC four-point probe method at 24±0.5 °C. The home-made probe station and Burster 2304 were utilized for the resistance measurement. A correlation between the measured electrical resistivity and the tensile properties was studied. The electrical resistivity showed a declining tendency with the increase of aging time because the electrical resistivity is strongly dependent on the microstructural changes. A correlation between the electrical resistivity and aging parameter was established, which allows one to estimate the material degradation of 9 Cr steel.
- Published
- 2010
84. A STUDY ON THE ALTERNATIVE TECHNOLOGY USING UNSM INSTEAD OF THE PRESETTING METHOD FOR TORSION BAR
- Author
-
Chong-Ho Chi, Chang Sik Kim, Un-Bong Baek, Min-Ho Kim, Young-Sik Pyoun, and Chang-Min Suh
- Subjects
Materials science ,Residual stress ,Stress relaxation ,Peening ,Statistical and Nonlinear Physics ,Ultrasonic sensor ,Composite material ,Condensed Matter Physics ,Shot peening ,Durability ,Torsion spring ,Shock (mechanics) - Abstract
The torsion bar must be changed periodically due to its lack of durability and a phenomenon related to stress relaxation. Therefore technical development regarding the torsion bar's durability is urgently needed. In order to improve the fatigue life and durability of the dynamic components, new surface treatment technology such as ultrasonic shot peening, deep rolling, laser shock peening, etc. are developing widely. In this study, Ultrasonic Nanocrystal Surface Modification (UNSM) technology is applied as an advanced one to replace the presetting method (PM). UNSM and PM technology also induced the compressive residual stress on the surface layer of the torsion bar, which is the main improvement factor of fatigue life. DIN17221 material as a new MIL specification of torsion bar and SCM440 (as an alternative one to a old MIL-DTL-62567C) were processed with the UNSM technology to obtain the basic data and compare it between two, and then torsion fatigue tests of two materials were carried out to obtain the characteristics of torsion fatigue in this study.
- Published
- 2010
85. Analysis of Residual Stress through a Recovery Factor of Remnant Indents Formed on Artificially Stressed Metallic Glass Surfaces
- Author
-
Seung-Hoon Nahm, Ha-Young Yu, Yun-Hee Lee, and Un-Bong Baek
- Subjects
Amorphous metal ,Materials science ,Residual stress ,Modeling and Simulation ,Metals and Alloys ,Composite material ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2010
86. Aging estimation of reactor pressure vessel in the field using magnetic properties
- Author
-
Un Bong Baek, Kwon Sang Ryu, Seung Hoon Nahm, and Amkee Kim
- Subjects
Materials science ,Field (physics) ,business.industry ,Nondestructive measurement ,General Chemical Engineering ,Nuclear engineering ,Energy Engineering and Power Technology ,Steel structures ,Structural engineering ,Management Science and Operations Research ,Coercivity ,equipment and supplies ,Industrial and Manufacturing Engineering ,Control and Systems Engineering ,Safety, Risk, Reliability and Quality ,business ,human activities ,Reactor pressure vessel ,Food Science - Abstract
Many researchers have been interested in the nondestructive measurement methods for estimating components damage in order to assure the safe service of steel structures. It is recognized that the evaluating techniques based on magnetic measurement can offer a great potential because of high susceptibility to the change of several metallurgical factors. Magnetic property such as coercive force was measured. The coercive force at room temperature monotonously increased with the increase of frequency. The correlation between the magnetic properties of used material and that of un-used material was studied. The coercive force gradient at room temperature increased with the increase of aging. Hence the estimating method using magnetic properties allows one to evaluate the extent of material aging for reactor pressure vessel.
- Published
- 2009
87. Multiaxial deformation characteristic of a Zr-based bulk metallic glass: Variations of the plastic constraint factor underneath a spherical indenter
- Author
-
Ju-Young Kim, Yun-Hee Lee, Un-Bong Baek, and Seung-Hoon Nahm
- Subjects
Materials science ,Amorphous metal ,Mechanical Engineering ,Stress–strain curve ,Flow stress ,Condensed Matter Physics ,Finite element method ,Amorphous solid ,Stress (mechanics) ,Mechanics of Materials ,Indentation ,General Materials Science ,Composite material ,Deformation (engineering) - Abstract
Multiaxial deformation of Zr55Al10Ni5Cu30 metallic glass was investigated by instrumented indentation tests with a spherical indenter. Contrary to the elastic–rigid-plastic behavior of bulk metallic glasses (BMGs), indentation pressure showed a significant increase with increasing indentation strain, and it was ascribed to a rapid transition of the plastic constraint factor (PCF). However, it was impossible to measure the PCF values from the indentation pressures in the Zr-based BMG because information on uniaxial flow stress was insufficient due to the limited flow strain of 2.2%. Here we developed a PCF assessment method using a relative residual depth hf/hmax, which was experimentally confirmed by adopting it to spherical indentations of a steel sample having well-known flow properties. Flow properties of the BMG were calculated using the new PCF assessment method, and the effects of the materials pileup and low strain indentations on PCF and flow properties were discussed.
- Published
- 2007
88. Stress characterization of surface damages on soda-lime glass using a nanocontact deformation method
- Author
-
Un-Bong Baek, Seung-Hoon Nahm, Yun-Hee Lee, and Ju-Young Kim
- Subjects
Materials science ,Deformation (mechanics) ,Mechanical Engineering ,Fracture mechanics ,Stress (mechanics) ,Mechanics of Materials ,Residual stress ,Indentation ,Solid mechanics ,Forensic engineering ,Cylinder stress ,General Materials Science ,Composite material ,Radial stress - Abstract
A nanocontact deformation method was used to measure the local and graded residual stresses around contact damages. By analyzing influences of the residual stress on nanocontact deformation itself instead of measuring the secondary crack emanated from it, 0.65 μm spatial resolution, which was superior to the highest level 1.8 μm attained by previous indentation fracture mechanics tests with an acute cube-corner indenter, was obtained with a general Berkovich indenter. However, a stress model combined with the nanocontact deformation provided only average stress variation around the contact damages. Thus, a resolution of two principal components from the residual stress in a biaxial state has been attempted in this study. By introducing radial microcracks around artificial microVickers damages, a crack-normal circumferential stress component disappeared and a series of nanoindentations close to the microcrack line yielded a variation of the radial stress component. By comparing this result with the average stress variation mentioned above, the crack-opening circumferential stress was measured and showed a good consistency with the previous study in soda-lime glass. In addition, distinctive features of present method were compared with previous indentation fracture mechanics method.
- Published
- 2007
89. A Study on Fatigue Properties of Sc and Zr Added Al Alloy
- Author
-
Tae Won Park, In Hyun Chung, Seung Hoon Nahm, Jong Seo Park, and Un Bong Baek
- Subjects
Zirconium ,Materials science ,Mechanical Engineering ,Alloy ,Metallurgy ,chemistry.chemical_element ,engineering.material ,Microstructure ,Fatigue limit ,Specific strength ,chemistry ,Mechanics of Materials ,visual_art ,Ultimate tensile strength ,engineering ,Aluminium alloy ,visual_art.visual_art_medium ,General Materials Science ,Scandium - Abstract
Al alloy is used extensively in several fields because specific strength is good and workability is superior. It is known that If Sc is added to Al alloy, strength is increased and re-crystallization temperature rises because microstructure becomes fine. The high cycle fatigue properties of four kinds of Al-Mg-Si alloys without and with only scandium of 0.20 % or with both scandium(Sc) of 0.20 % and zirconium(Zr) of 0.12% were investigated. The fatigue strength was determined at R = -1.0 under constant amplitude loading conditions in air. The alloy with scandium of 0.20 % showed a little higher fatigue strength values. The alloy with 0.20 % Sc and 0.12 % Zr showed highest tensile yield strength and highest fatigue strength. The fine grained Al 6061+0.20Sc+0.12Zr alloy exhibited a higher resistance against fatigue crack nucleation in comparison to the coarse grained Al 6061 alloy. The results can be explained mainly with the micro-structural differences among four alloys. This results are due to the presence of coherent Al3 (Sc, Zr) precipitates and a very fine sub-grain structure.
- Published
- 2007
90. On the measurement of pile-up corrected hardness based on the early Hertzian loading analysis
- Author
-
Seung-Hoon Nahm, Un-Bong Baek, Yong-Il Kim, and Yun-Hee Lee
- Subjects
Microscope ,Materials science ,Mechanical Engineering ,Boundary (topology) ,Modulus ,chemistry.chemical_element ,Nanoindentation ,Tungsten ,Condensed Matter Physics ,law.invention ,Crystallography ,chemistry ,Mechanics of Materials ,law ,General Materials Science ,Composite material ,Contact area ,Pile ,Elastic modulus - Abstract
Nanoindentation has been used to gain insight into the elastic/plastic contact responses of material at very small scales. The Oliver and Pharr's analysis (W.C. Oliver and G.M. Pharr, J. Mater. Res. 7 (1992) 1564) on the nanoindentation curve, however, can be meaningless when plastically deformed material piles around the indented points. This study suggests a measuring methodology of the real contact area enlarged by the material pile-up and its corresponding mechanical properties; the pile-up corrected contact area can be calculated inversely from the reduced modulus formulation with input information of the independently determined Young's modulus based on the Hertzian loading analysis. This contact correction relaxed overestimates in the elastic modulus and hardness interpreted from the nanoindentation curve and yielded actual mechanical properties comparable to the literature values of a (100) tungsten monocrystal. In addition, theoretically estimated upheaval amount of the contact boundary in this study was nearly consistent with the average pile-up height measured from an atomic-force microscope.
- Published
- 2007
91. Hydrogen Embrittlement for X-70 Pipeline Steel in High Pressure Hydrogen Gas
- Author
-
Un Bong Baek, Seung-Wook Baek, Seung Hoon Nahm, and Hae Moon Lee
- Subjects
Pipeline transport ,Materials science ,Fracture toughness ,Hydrogen ,chemistry ,Metallurgy ,Ultimate tensile strength ,Fracture (geology) ,chemistry.chemical_element ,Paris' law ,Environmental stress fracture ,Hydrogen embrittlement - Abstract
The tensile properties of API 5L X70 pipeline steels have been measured in a high-pressure (10 MPa) hydrogen gas environment. Significant decreases in elongation at failure and reduction of area were observed when testing in hydrogen as compared with air, and those changes were accompanied by noticeable changes in fracture morphology. The present paper exposes the changes in mechanical properties of a grade API 5L X70 steel through numerous mechanical tests, i.e. tensile tests, notch tensile tests, fracture toughness and fatigue crack growth measurements, performed either in atmosphere or in 10 MPa pressure of hydrogen gas.Copyright © 2015 by ASME
- Published
- 2015
92. Experimental Study on the Physical and Mechanical Properties of a Copper Alloy for Liquid Rocket Combustion Chamber Application
- Author
-
Chul-Sung Ryu, Hwan-Seok Choi, and Un-Bong Baek
- Subjects
Materials science ,Thermal conductivity ,Creep ,Mechanical Engineering ,Ultimate tensile strength ,Metallurgy ,technology, industry, and agriculture ,Stress relaxation ,Combustion chamber ,Composite material ,Strain rate ,Strain hardening exponent ,Thermal expansion - Abstract
Mechanical and physical properties of a copper alloy for a liquid rocket engine(LRE) combustion chamber liner application were tested at various temperatures. All test specimens were heat treated with the condition they might experience during actual fabrication process of the LRE combustion chamber. Physical properties measured include thermal conductivity, specific heat and thermal expansion data. Uniaxial tension tests were preformed to get mechanical properties at several temperatures ranging from room temperature to 600. The result demonstrated that yield stress and ultimate tensile stress of the copper alloy decreases considerably and strain hardening increases as the result of the heat treatment. Since the LRE combustion chamber operates at higher temperature over 400, the copper alloy can exhibit time-dependent behavior. Strain rate, creep and stress relaxation tests were performed to check the time-dependent behavior of the copper alloy. Strain rate tests revealed that strain rate effect is negligible up to 400 while stress-strain curve is changed at 500 as the strain rate is changed. Creep tests were conducted at 250 and 500 and the secondary creep rate was found to be very small at both temperatures implying that creep effect is negligible for the combustion chamber liner because its operating time is quite short.
- Published
- 2006
93. CHARACTERIZATION OF TRIS (8-HYDROXYQUINOLINE) ALUMINUM (<font>Alq</font>3) FILM USING SPECTROSCOPIC ELLIPSOMETRY
- Author
-
Won Chegal, Un Bong Baek, Seung Hoon Nahm, Hyun Mo Cho, Hye Yong Chu, Jeong-Ik Lee, Hyun Jong Kim, and Yong Jai Cho
- Subjects
Materials science ,Silicon ,Band gap ,business.industry ,Extrapolation ,Analytical chemistry ,chemistry.chemical_element ,Statistical and Nonlinear Physics ,Photon energy ,Condensed Matter Physics ,Spectral line ,Optics ,chemistry ,Aluminium ,Ellipsometry ,business ,Refractive index - Abstract
We have applied spectroscopic ellipsometry to obtain the optical constants, i.e., refractive indices (n) and extinction coefficients (k) of a thin tris (8-hydroxyquinoline) aluminum ( Alq 3) film evaporated on the top of 300-nm-thick SiO 2 layer on a silicon substrate. Using a spectroscopic ellipsometer we collected the ellipsometric data of Ψ and Δ at 3 incident angles of 65°, 70° and 75° and 226 energies of 1.5 eV to 6.0 eV. For the organic sample, we adopted a simple two-film model consisting of ambient/organic film/ SiO 2 film/silicon substrate. Using the multiple oscillators of Tauc-Lorentz (TL) dispersion function and the two-film model, we obtained the thickness of the Alq 3 film. By data inversion technique, the spectra of n and k for the Alq 3 film are calculated from measured Ψ and Δ at each photon energy when the film thickness is fixed to a value obtained by the TL dispersion fitting. The extrapolation of optical function near band gap yields the band gap of 2.64 eV for Alq 3 film.
- Published
- 2006
94. A Study on Material Degradation in Carbon Steel for Pressure Vessel at 179°C
- Author
-
Hyuck Mo Lee, Jong Seo Park, Un Bong Baek, and Seung Hoon Nahm
- Subjects
Materials science ,Carbon steel ,Mechanical Engineering ,Transition temperature ,Metallurgy ,Charpy impact test ,engineering.material ,Pressure vessel ,Brittleness ,Mechanics of Materials ,engineering ,Degradation (geology) ,General Materials Science ,Composite material ,Material properties ,Tensile testing - Abstract
In spite of frequent defect in industrial boilers, life assessment or diagnostic method for them has not been studied. In this research, SB410 carbon steel used in industrial boilers is simulated with artificial aging heat treatment. To do qualitative life assessment, differences in micro-structures and hardness of SB410 by the degradation time are studied. In addition, variation in material properties by aging was observed with the tensile test at room temperature and 179 °C and changes in ductile to brittle transition temperature was observed with the charpy impact test performed at several test temperature.
- Published
- 2006
95. The Application of Nondestructive Methods for Degradation Evaluation of Modified 9Cr-1Mo Steel
- Author
-
Jong Seo Park, Sang In Han, Song Chun Choi, Seung Hoon Nahm, and Un Bong Baek
- Subjects
Measurement method ,Materials science ,business.industry ,Mechanical Engineering ,Isothermal process ,Creep ,Mechanics of Materials ,Ultrasonic velocity ,Material Degradation ,Nondestructive testing ,Ultimate tensile strength ,Degradation (geology) ,General Materials Science ,Composite material ,business - Abstract
The nondestructive evaluation technique for the material degradation is necessary because of the limitation of conventional destructive methods. In this study, an ultrasonic velocity measurement method was attempted for the estimation of the creep damage of degraded modified 9Cr-1Mo steel. The specimens with seven different kinds of aging periods were prepared by an isothermal heat treatment at 690 . The ultrasonic velocity was measured by an immersion method. The correlation between the measured ultrasonic velocity and tensile properties were studied. The ultrasonic velocity has an declining tendency with the increase of heat treatment time. A correlation between the ultrasonic velocity and aging parameter were established, which allows one to estimate the material degradation of modified 9Cr-1Mo steel.
- Published
- 2006
96. Degradation Evaluation of 2.25Cr-1Mo Steel Using Nondestructive Method
- Author
-
Jeong Min Kim, Bong Young Ahn, Un Bong Baek, Jong Seo Park, and Seung Hoon Nahm
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Ultrasonic testing ,Isothermal process ,Creep ,Mechanics of Materials ,Electrical resistivity and conductivity ,Indentation ,Material Degradation ,Nondestructive testing ,Forensic engineering ,Degradation (geology) ,General Materials Science ,Composite material ,business - Abstract
Several nondestructive evaluation methods were attempted for the estimation of the creep damage of degraded 2.25Cr-1Mo steel. The specimens of three different aging periods were prepared by an isothermal heat treatment at 430°C, 482°C, and 515°C. The effect of probe configuration on the electrical resistivity was studied. Single configuration method and dual-configuration method were utilized for measuring electrical resistivity. The electrical resistivity was determined by a standard DC four-point probe method at 24±0.5°C. Indentation test, magnetic characteristics test and ultrasonic test were carried out to investigate the correlation between the major characteristics and aging parameter. Unlike the electrical resistivity characteristics, ultrasonic attenuation coefficient and indentation characteristics did not show a relation to Larson-Miller parameter. However, a correlation between the electrical resistivity and aging parameter was identified, which allows one to estimate the extent of material degradation.
- Published
- 2005
97. A Study on Fatigue Properties of Sc Added Al 2519 Alloy
- Author
-
Jong Seo Park, Yong Yun Lee, Young Hwa Ma, In Hyun Chung, Seung Hoon Nahm, and Un Bong Baek
- Subjects
Materials science ,Mechanical Engineering ,Lower yield ,Metallurgy ,Alloy ,chemistry.chemical_element ,Fatigue testing ,engineering.material ,Fatigue limit ,Stress (mechanics) ,Fatigue crack nucleation ,chemistry ,Mechanics of Materials ,Ultimate tensile strength ,engineering ,General Materials Science ,Scandium - Abstract
The high cycle fatigue properties of two kinds of wrought Al 2519 alloys without and with scandium of 0.10% were investigated. The fatigue strength was determined at R = 0.1 under constant amplitude loading conditions in air. The alloy with scandium of 0.10% showed a little lower tensile yield strength and higher fatigue strength values. The fine grained Al-0.10Sc alloy exhibited a higher resistance against fatigue crack nucleation despite the lower yield stress in comparison to the coarse grained Al 2519 alloy. The results can be explained mainly with the microstructural differences between both alloys. This results are due to the presence of coherent Al3 (Sc, Zr) precipitates and a very fine subgrain structure.
- Published
- 2005
98. Evaluation of Creep Fatigue Crack Growth Behavior of 9Cr Steel Employing Creep Reversal Parameter
- Author
-
Young-Wha Ma, Un-Bong Baek, and Kee-Bong Yoon
- Subjects
Ideal (set theory) ,Materials science ,Creep ,business.industry ,Condensed Matter::Superconductivity ,Mechanical Engineering ,Structural engineering ,Mechanics ,Creep fatigue ,business ,Physics::Geophysics - Abstract
Creep-fatigue crack growth models have been proposed employing as a crack tip parameter characterizing the time-dependent crack growth. The basic assumptions made in these previous models were ideal creep reversal conditions such as no creep reversal and complete creep reversal condition. Due to this assumption, the applicability of the models was limited since they did not consider partial creep reversal condition which is usually observed in many engineering metals at high temperature. In this paper the creep reversal parameter, Temperature;, which was defined by Grover, is critically evaluated to quantity the extent of partial creep reversal at the crack tip. This approach does not rely on any simplifying assumptions regarding the extent of the amount of creep reversal during the unloading part of a trapezoidal fatigue cycles. It is shown that the value calculated for 9Cr steel agrees well with the experimentally measured one. It is argued that the extent of improvement is not significant when the result is compared with that of the conventional model which has an assumption of full creep reversal behavior.
- Published
- 2002
99. Mechanical Properties of X70 Steel in Gaseous Hydrogen
- Author
-
Hae-Moo Lee, Yun-Hee Lee, Seung-Hoon Nahm, and Un-Bong Baek
- Subjects
Materials science ,Metallurgy ,Gaseous hydrogen ,Hydrogen embrittlement - Published
- 2014
100. On-Line Temperature Monitoring Practice for Damaged Part of High Temperature Reformer Tubes
- Author
-
Dong Young Kim, Un Bong Baek, Woan Kyu Lee, and Kee Bong Yoon
- Subjects
Pigtail ,Engineering ,geography ,geography.geographical_feature_category ,business.industry ,Mechanical engineering ,Atmospheric temperature range ,Inlet ,Line (electrical engineering) ,law.invention ,Reliability (semiconductor) ,Creep ,law ,Tube (fluid conveyance) ,business ,Pyrometer - Abstract
One of major damage mechanisms of the reformer tube used in chemical plants is high temperature creep at the inner surface of the tube at critical height. The metal temperature can go up to 900°C-1,050°C. Hence there has been efforts to monitor the metal temperature at mid-height location of the tube for safe operation of the reformer and for extending its useful life. However, reliable sensors at such a high temperature range were very few. In this study, a method is proposed for monitoring the tube metal temperature at the inner surface of the tube from the temperature data measured with existing sensors installed at the inlet pigtail and the outlet collector, which are outside of the furnace heating box. The proposed method does not need installation of the temperature sensors directly at the inner surface of the tube, which is almost impossible from engineering viewpoint. The predicted temperature values are compared with those measured with a pyrometer and the accuracy and reliability of the proposed method is discussed.
- Published
- 2001
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.