The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Minju Kang - One of the best experts on this subject based on the ideXlab platform.
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interpretation of Charpy impact energy characteristics by microstructural evolution of dynamically compressed specimens in three tempered martensitic steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: Jaeyeong Park, Minju KangAbstract:Abstract In this study, Charpy impact energy characteristics of three tempered martensitic steels were evaluated at room and low temperatures by instrumented Charpy impact tests, and were interpreted by fracture initiation and propagation mechanisms in relation with microstructural evolution of dynamically compressed specimens. As the tempering temperature increased, the volume fraction of total carbides increased, while carbides were spheroidized, and the overall Charpy absorbed energy increased at both 25 °C and −50 °C. At −50 °C, the fracture initiation energy largely increased in the tempering temperature range of 400–500 °C, while the propagation energy increased greatly (about 20 times) in the range of 500–600 °C. According to microstructural analyses of dynamically compressed specimens, adiabatic shear bands were formed in the 400 °C- and 500 °C-tempered steels, and worked as preferred fracture propagation paths to critically reduce the fracture propagation energy. In the 600 °C-tempered steel, the deformation energy due to the pendulum impact was effectively absorbed by the combination of fine spheroidized carbides and softened tempered martensitic matrix without forming adiabatic shear bands, thereby leading to the relatively homogeneous deformation in the pendulum-impacted region and the very large increase of fracture propagation energy.
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interpretation of cryogenic temperature Charpy impact toughness by microstructural evolution of dynamically compressed specimens in austenitic 0 4c 22 26 mn steels
Acta Materialia, 2015Co-Authors: Yumi Ha, Ki Hyuk Kwon, Minju KangAbstract:Abstract In this study, the Charpy impact toughness of three austenitic high-Mn steels was evaluated at room and cryogenic temperatures, and interpreted by deformation mechanisms in relation to the microstructural evolution of dynamically compressed specimens. Under dynamic compressive loading, nanocell structures composed of subgrains were formed by the reaction with twins and dislocations, and resulted in a high-strain-rate deformation mechanism that enhanced the strength, ductility and toughness within the stacking fault energy (SFE) range of the twinning-induced plasticity (TWIP) mechanism at room temperature. At cryogenic temperature, the formation of nanocell structures was activated with increasing Mn content, which showed the opposite trend to the room-temperature case. Since the cryogenic-temperature SFEs were lower by ∼30% than the room-temperature SFEs, a considerable amount of e-martensite was formed in the 0.4C–22Mn steel by the transformation-induced plasticity (TRIP) mechanism, while the TWIP mechanism was working, thereby leading to increased Charpy toughness compared to the 0.4C–24Mn and 0.4C–26Mn steels. The Charpy impact toughness results were discussed using a new schematic diagram of deformation mechanisms based on SFE, loading condition and test temperature.
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mechanisms of toughness improvement in Charpy impact and fracture toughness tests of non heat treating cold drawn steel bar
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Minju Kang, Hyeok Jae JungAbstract:Abstract In this study, toughness properties of a non-heat-treating cold-drawn bar were examined by Charpy impact test and fracture toughness test, and the toughness enhancement mechanisms were clarified in relation with microstructure. As the thickness of pearlite bands decreased after the cold drawing, the Charpy impact energy of the cold-drawn bar was higher than that of the as-rolled bar, which could be reasonably explained by the thin sheet toughening. On the other hand, thin pearlite bands negatively affected the fracture toughness because of the decreased spacing between crack or void initiation sites inside the fracture process zone in front of the pre-fatigued crack tip. The Charpy impact test data could also be correlated with the absorbed energy of the dynamic compressive test specimen whose orientation was matched with the hammer impact direction of the Charpy impact test, although the Charpy impact and dynamic compressive test specimens had a notched body and a smooth body, respectively.
Kyungshik Oh - One of the best experts on this subject based on the ideXlab platform.
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effects of oxides on tensile and Charpy impact properties and fracture toughness in heat affected zones of oxide containing api x80 linepipe steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: Hyokyung Sung, Sang Yong Shin, Seok Su Sohn, Kyungshik OhAbstract:This study is concerned with effects of complex oxides on acicular ferrite (AF) formation, tensile and Charpy impact properties, and fracture toughness in heat affected zones (HAZs) of oxide-containing API X80 linepipe steels. Three steels were fabricated by adding Mg and O2 to form oxides, and various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs. The no. of oxides increased with increasing amount of Mg and O2, while the volume fraction of AF present in the steel HAZs increased with increasing the no. of oxides. The strengths of the HAZ specimens were generally higher than those of the base metals because of the formation of hard microstructures of bainitic ferrite and granular bainite. When the total Charpy absorbed energy was divided into the fracture initiation and propagation energies, the fracture initiation energy was maintained constant at about 75 J at room temperature, irrespective of volume fraction of AF. The fracture propagation energy rapidly increased from 75 to 150 J and saturated when the volume fraction of AF exceeded 30 pct. At 253 K (−20 °C), the total absorbed energy increased with increasing volume fraction of AF, as the cleavage fracture was changed to the ductile fracture when the volume fraction of AF exceeded 45 pct. Thus, 45 vol pct of AF at least was needed to improve the Charpy impact energy, which could be achieved by forming a no. of oxides. The fracture toughness increased with increasing the no. of oxides because of the increased volume fraction of AF formed around oxides. The fracture toughness did not show a visible correlation with the Charpy absorbed energy at room temperature, because toughness properties obtained from these two toughness testing methods had different significations in view of fracture mechanics.
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effects of acicular ferrite on Charpy impact properties in heat affected zones of oxide containing api x80 linepipe steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: Hyokyung Sung, Sang Yong Shin, Kyungshik OhAbstract:Abstract This study was concerned with effects of acicular ferrite on Charpy impact properties in heat affected zones (HAZs) of two API X80 linepipe steels containing oxides. In the one steel, Mg and O 2 were additionally added to form a larger amount of oxides than the other steel, which was a conventional X80 steel containing a considerable amount of Al and Ti. Various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs of 35 kJ cm −1 and 60 kJ cm −1 . Oxides present in the API X80 linepipe steels were complex oxides whose average size was 1–2 μm, and the number of oxides increased with increasing amount of Mg and O 2 . The volume fraction of acicular ferrite present in the steel HAZs increased with increasing number of oxides, and decreased with increasing heat input. When the volume fraction of acicular in the HAZ was higher than 20%, Charpy impact energy at −20 °C was higher than 100 J as the ductile fracture mode was dominant. Particularly in the steel HAZs having a larger amount of oxides, Charpy impact properties were excellent because oxides worked as nucleation sites of acicular ferrite during welding. Charpy impact properties of the HAZs could be well correlated with the volume fraction of acicular ferrite and number of oxides under different heat input conditions.
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Charpy impact properties of heat affected zones of api x80 linepipe steels containing complex oxides
Korean Journal of Metals and Materials, 2010Co-Authors: Hyokyung Sung, Sang Yong Shin, Kyungshik OhAbstract:This study assessed the Charpy impact properties of the heat-affected zones (HAZs) of API X80 linepipe steels containing complex oxides. Three types of steel were fabricated by adding Mg and O2 to form complex oxides and their microstructures and Charpy impact properties were investigated. The number of complex oxides increased with the amount of excess Mg and O2 that was included in the steels. Simulated HAZs containing a number of oxides showed a high volume fraction of acicular ferrite (AF) because the oxides acted as nucleation sites for AF, thereby leading to an improvement in the Charpy impact properties. According to a correlation study between the heat input, the volume fraction of the AF, and the Charpy impact properties, ductile fractures occurred predominantly when the fraction of the AF was 20% or higher; moreover, the Charpy absorbed energy was excellent at more than 100 J. These findings suggest that the improvement of the Charpy impact properties of the HAZs was associated with the active nucleation of AF in the oxidecontaining steel HAZs. (Received March 17, 2010)
Sang Yong Shin - One of the best experts on this subject based on the ideXlab platform.
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effects of oxides on tensile and Charpy impact properties and fracture toughness in heat affected zones of oxide containing api x80 linepipe steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: Hyokyung Sung, Sang Yong Shin, Seok Su Sohn, Kyungshik OhAbstract:This study is concerned with effects of complex oxides on acicular ferrite (AF) formation, tensile and Charpy impact properties, and fracture toughness in heat affected zones (HAZs) of oxide-containing API X80 linepipe steels. Three steels were fabricated by adding Mg and O2 to form oxides, and various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs. The no. of oxides increased with increasing amount of Mg and O2, while the volume fraction of AF present in the steel HAZs increased with increasing the no. of oxides. The strengths of the HAZ specimens were generally higher than those of the base metals because of the formation of hard microstructures of bainitic ferrite and granular bainite. When the total Charpy absorbed energy was divided into the fracture initiation and propagation energies, the fracture initiation energy was maintained constant at about 75 J at room temperature, irrespective of volume fraction of AF. The fracture propagation energy rapidly increased from 75 to 150 J and saturated when the volume fraction of AF exceeded 30 pct. At 253 K (−20 °C), the total absorbed energy increased with increasing volume fraction of AF, as the cleavage fracture was changed to the ductile fracture when the volume fraction of AF exceeded 45 pct. Thus, 45 vol pct of AF at least was needed to improve the Charpy impact energy, which could be achieved by forming a no. of oxides. The fracture toughness increased with increasing the no. of oxides because of the increased volume fraction of AF formed around oxides. The fracture toughness did not show a visible correlation with the Charpy absorbed energy at room temperature, because toughness properties obtained from these two toughness testing methods had different significations in view of fracture mechanics.
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effects of acicular ferrite on Charpy impact properties in heat affected zones of oxide containing api x80 linepipe steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: Hyokyung Sung, Sang Yong Shin, Kyungshik OhAbstract:Abstract This study was concerned with effects of acicular ferrite on Charpy impact properties in heat affected zones (HAZs) of two API X80 linepipe steels containing oxides. In the one steel, Mg and O 2 were additionally added to form a larger amount of oxides than the other steel, which was a conventional X80 steel containing a considerable amount of Al and Ti. Various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs of 35 kJ cm −1 and 60 kJ cm −1 . Oxides present in the API X80 linepipe steels were complex oxides whose average size was 1–2 μm, and the number of oxides increased with increasing amount of Mg and O 2 . The volume fraction of acicular ferrite present in the steel HAZs increased with increasing number of oxides, and decreased with increasing heat input. When the volume fraction of acicular in the HAZ was higher than 20%, Charpy impact energy at −20 °C was higher than 100 J as the ductile fracture mode was dominant. Particularly in the steel HAZs having a larger amount of oxides, Charpy impact properties were excellent because oxides worked as nucleation sites of acicular ferrite during welding. Charpy impact properties of the HAZs could be well correlated with the volume fraction of acicular ferrite and number of oxides under different heat input conditions.
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Charpy impact properties of heat affected zones of api x80 linepipe steels containing complex oxides
Korean Journal of Metals and Materials, 2010Co-Authors: Hyokyung Sung, Sang Yong Shin, Kyungshik OhAbstract:This study assessed the Charpy impact properties of the heat-affected zones (HAZs) of API X80 linepipe steels containing complex oxides. Three types of steel were fabricated by adding Mg and O2 to form complex oxides and their microstructures and Charpy impact properties were investigated. The number of complex oxides increased with the amount of excess Mg and O2 that was included in the steels. Simulated HAZs containing a number of oxides showed a high volume fraction of acicular ferrite (AF) because the oxides acted as nucleation sites for AF, thereby leading to an improvement in the Charpy impact properties. According to a correlation study between the heat input, the volume fraction of the AF, and the Charpy impact properties, ductile fractures occurred predominantly when the fraction of the AF was 20% or higher; moreover, the Charpy absorbed energy was excellent at more than 100 J. These findings suggest that the improvement of the Charpy impact properties of the HAZs was associated with the active nucleation of AF in the oxidecontaining steel HAZs. (Received March 17, 2010)
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correlation of microstructure and Charpy impact properties in api x70 and x80 line pipe steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007Co-Authors: Sang Yong Shin, Byoungchul HwangAbstract:This study aims at correlating microstructure and Charpy impact properties in high-toughness API X70 and X80 line-pipe steels. Three kinds of steels were fabricated by varying alloying elements and hot rolling conditions, and their microstructures and Charpy impact properties were investigated. In addition, their effective grain sizes were characterized by the electron back-scatter diffraction (EBSD) analysis. The Charpy impact test results indicated that the steels rolled in the single phase region had the higher upper shelf energy (USE) than the steel rolled in the two phase region because their microstructures were composed of acicular ferrites. In the X80 steel rolled in the single phase region, the decreased energy transition temperature (ETT) could be explained by the decrease in the overall effective grain size due to the presence of acicular ferrite having smaller effective grain size. Thus, it had excellent mechanical properties in yield and tensile strengths, absorbed energy, and transition temperature, except in ductility.
Hyokyung Sung - One of the best experts on this subject based on the ideXlab platform.
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effects of oxides on tensile and Charpy impact properties and fracture toughness in heat affected zones of oxide containing api x80 linepipe steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: Hyokyung Sung, Sang Yong Shin, Seok Su Sohn, Kyungshik OhAbstract:This study is concerned with effects of complex oxides on acicular ferrite (AF) formation, tensile and Charpy impact properties, and fracture toughness in heat affected zones (HAZs) of oxide-containing API X80 linepipe steels. Three steels were fabricated by adding Mg and O2 to form oxides, and various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs. The no. of oxides increased with increasing amount of Mg and O2, while the volume fraction of AF present in the steel HAZs increased with increasing the no. of oxides. The strengths of the HAZ specimens were generally higher than those of the base metals because of the formation of hard microstructures of bainitic ferrite and granular bainite. When the total Charpy absorbed energy was divided into the fracture initiation and propagation energies, the fracture initiation energy was maintained constant at about 75 J at room temperature, irrespective of volume fraction of AF. The fracture propagation energy rapidly increased from 75 to 150 J and saturated when the volume fraction of AF exceeded 30 pct. At 253 K (−20 °C), the total absorbed energy increased with increasing volume fraction of AF, as the cleavage fracture was changed to the ductile fracture when the volume fraction of AF exceeded 45 pct. Thus, 45 vol pct of AF at least was needed to improve the Charpy impact energy, which could be achieved by forming a no. of oxides. The fracture toughness increased with increasing the no. of oxides because of the increased volume fraction of AF formed around oxides. The fracture toughness did not show a visible correlation with the Charpy absorbed energy at room temperature, because toughness properties obtained from these two toughness testing methods had different significations in view of fracture mechanics.
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effects of acicular ferrite on Charpy impact properties in heat affected zones of oxide containing api x80 linepipe steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: Hyokyung Sung, Sang Yong Shin, Kyungshik OhAbstract:Abstract This study was concerned with effects of acicular ferrite on Charpy impact properties in heat affected zones (HAZs) of two API X80 linepipe steels containing oxides. In the one steel, Mg and O 2 were additionally added to form a larger amount of oxides than the other steel, which was a conventional X80 steel containing a considerable amount of Al and Ti. Various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs of 35 kJ cm −1 and 60 kJ cm −1 . Oxides present in the API X80 linepipe steels were complex oxides whose average size was 1–2 μm, and the number of oxides increased with increasing amount of Mg and O 2 . The volume fraction of acicular ferrite present in the steel HAZs increased with increasing number of oxides, and decreased with increasing heat input. When the volume fraction of acicular in the HAZ was higher than 20%, Charpy impact energy at −20 °C was higher than 100 J as the ductile fracture mode was dominant. Particularly in the steel HAZs having a larger amount of oxides, Charpy impact properties were excellent because oxides worked as nucleation sites of acicular ferrite during welding. Charpy impact properties of the HAZs could be well correlated with the volume fraction of acicular ferrite and number of oxides under different heat input conditions.
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Charpy impact properties of heat affected zones of api x80 linepipe steels containing complex oxides
Korean Journal of Metals and Materials, 2010Co-Authors: Hyokyung Sung, Sang Yong Shin, Kyungshik OhAbstract:This study assessed the Charpy impact properties of the heat-affected zones (HAZs) of API X80 linepipe steels containing complex oxides. Three types of steel were fabricated by adding Mg and O2 to form complex oxides and their microstructures and Charpy impact properties were investigated. The number of complex oxides increased with the amount of excess Mg and O2 that was included in the steels. Simulated HAZs containing a number of oxides showed a high volume fraction of acicular ferrite (AF) because the oxides acted as nucleation sites for AF, thereby leading to an improvement in the Charpy impact properties. According to a correlation study between the heat input, the volume fraction of the AF, and the Charpy impact properties, ductile fractures occurred predominantly when the fraction of the AF was 20% or higher; moreover, the Charpy absorbed energy was excellent at more than 100 J. These findings suggest that the improvement of the Charpy impact properties of the HAZs was associated with the active nucleation of AF in the oxidecontaining steel HAZs. (Received March 17, 2010)
H K D H Bhadeshia - One of the best experts on this subject based on the ideXlab platform.
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role of delamination and crystallography on anisotropy of Charpy toughness in api x80 steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: H K D H BhadeshiaAbstract:Abstract The orientation dependence of Charpy toughness has been investigated in API-X80 linepipe steel. The occurrence of delamination and preferential alignment of {1 0 0} cleavage planes are found to contribute to the observed anisotropy in Charpy properties. Delamination is also related to the presence of banding in the hot-rolled alloy, and the additional plasticity it entails during the process of fracture leads to an effective increase in toughness. As a consequence, the toughness is worst when the Charpy specimen is machined at 45° to the rolling direction because the extent of delamination at that orientation is minimal. The rolling and transformation textures also lead to a greater propensity of {1 0 0} ferrite planes parallel to the fracture surface for the 45° orientation, leading to a further decrease in toughness. Some revealing results are also reported for unconventional Charpy test orientations in which the notch is prepared parallel to the plate.