• Transactions of Materials Processing
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• v.18 no.1
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• pp.26-38
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• 2009

It was reported that the semi-solid forming process has many advantages over the conventional forming process, such as a long die life, good mechanical properties and energy savings. It is very important, however, to control liquid segregation to gain mechanical property improvement of materials. During forming process, rheology material has complex characteristics, thixotropic behavior. Also, difference of velocity between solid and liquid in the semi-solid state material makes a liquid segregation and specific stress variation. Therefore, it is difficult for a numerical simulation of the rheology process to be performed. General plastic or fluid dynamic analysis is not suitable for the behavior of rheology material. The behavior and stress of solid particle in the rheology material during forging process is affected by viscosity, temperature and solid fraction. In this study, compression experiments of aluminum alloy were performed under each other tool shape which is rectangle shape(square array), rectangle shape(hexagonal array), and free shape tool. In addition, the dynamics behavior compare with Okano equation to power law model which is viscosity equation.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.73-78
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• 2011

Weldability, especially HAZ cold cracking, weld metal solidification cracking, and HAZ liquation cracking susceptibilities, of ASTM A356 CA6NM martensitic stainless steel casting was investigated and compared with that of 9-12% Cr ferritic steel castings. Irrespective of the Cr and Ni content in the castings, the HAZ maximum hardness increased with an increase of carbon content. CA6NM steel, which has the lowest carbon content, had the lowest HAZ hardness and showed no cold cracking in y-slit cracking tests. CA6NM steel, meanwhile, showed the largest weld metal solidification cracking susceptibility in varestraint tests because of its higher amount of impurity elements, phosphorus, and sulfur. All castings investigated had good high temperature ductility in hot ductility tests and showed little difference in liquation cracking susceptibility.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.287-290
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• 2005

Once hot forgings for automotive parts such as wheel bearing flange to which cyclic asymmetric bending stress is continuously applied are produced, it is necessary to control their microstructure to obtain superior mechanical properties. It is however hard to control the microstructure uniformly because the strength is reduced as coarsening of ferrite grains. To investigate the microstructural alteration according to process variables during hot working, the variation of the ferrite grain size was studied by utilizing of the computer aided servo-hydraulic Gleeble tester which is hot deformation behavior reproduction equipment. In addition, the effect of the ferrite grain size of raw material on the austenite grain behavior of hot forgings was also examined. The rolling contact fatigue resistance of the induction hardened SAE 1055 steel was compared with the occasion of the same condition of SAE52100 bearing steel. As a result, it was confirmed that the ferrite grain sizes of the forgings depend on the heating temperature and cooling start temperature during hot forging and cooling processes. The induction hardened SAE1055 steel showed a superior rolling contact fatigue resistance to the induction hardened SAE52100 steel. The reason is that SAE1055 steel is freer from the material defect such as segregation than the comparative steel.

• Journal of Conservation Science
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• v.38 no.3
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• pp.217-233
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• 2022

The remains found in Geumcheok-ri, Gyeongju are located in close proximity to the Ancient Tombs in Geumcheok-ri, Gyeongju (Historic Site) which were built between the late 5th and early 6th centuries, and these tombs are known to belong to the powerful rulers of that area. Using metallurgical techniques, this study was conducted on the iron objects obtained from the excavated remains in Geumcheok-ri, Gyeongju which are presumed to have a close relation to the nearby ruins that played an important role in the growth of Silla. To identify differences in manufacturing techniques based on the purpose of the iron objects, eight objects were selected after classifying them by use and the microstructure and non-metallic inclusions were investigated. The analyses results confirmed that the manufacturing process involved forging iron with a high or low carbon content to produce a particular shape, and that the carburization process was applied to iron post forging a shape to increase its strength when necessary. The mechanical properties were improved by selectively applying the steelmaking method and the heat treatment technique considering the functions of the parts, and the low temperature reduction was applied to the smelting process. Furthermore, in comparison with the iron objects excavated from the remains located in the center of Gyeongju and its outskirts, it is confirmed that there is similarity in the smelting and manufacturing techniques between these objects.

• Journal of Conservation Science
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• v.30 no.4
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• pp.335-343
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• 2014

This study classified the result of non-metallic inclusion analysis and result of microstructure investigation on the ironware excavated in the Baekje region into Han River, Geum River, and Yeongsan River to estimate the iron making temperature and study the characteristics of regional and temporal characteristics of the heat treatment technology and steel making technology. Regardless of era, bloom iron and sponge iron are judged to be the major method for making as a directreduction process in all three regions. The result of the reinterpretation of the non-metallic inclusion by the oxide ternary constitutional diagram suggest that the temperature inside of the furnace is estimated to be between $1,100{\sim}1,300^{\circ}C$ while making the steel. The magnetic iron ores are the major raw material of steel ore and irons with high $TiO_2$ are estimated to use iron sands. Ironware with $CaO/SiO_2$ rate higher than 0.4% are considered to have artificially added the flux of calcareous materials. It was found that the iron making method is the solid caburizing-steel which caburizes low-carbon steels by the CO gas and $CO_2$ gas created when heating the forging furnace with charcoal. Also, the ironware manufacturers in the Baekje during 3rd century recognized the heat treatment technology as they performed carburizing process and quenching to intentionally increase the strength of necessary parts.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.6
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• pp.645-650
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• 2010

In this research, the problem of combustion and its system in Hyundai Heavy Industries and Sachuan Unison will be analyzed in order to provide some methods of thermal efficiency improvement and help to make a positive influence on fuel savings and their productivity. In forging industries, in order to improve the material properties of the industrial heating elements which are being used, depending on different operation conditions of system equipment and combustion systems, fuel consumption and material properties can get a profound influence. Thus, analyzing about combustion system characteristics of 100 tons heating furnace and heat treatment furnace which are in operation in Hyundai Heavy Industry will be done. In usual, air-fuel ratio is proper for capacity of burner installed in each heating device, otherwise burner gets an automatic turn down ratio. It has a profound influence on heating performance and precision of temperature because it is the fixed characteristics of every industrial furnace. Even if there are some methods to improve the heating performance of a furnace installed with a large capacity burner, it is very difficult to obtain the precision of temperature in maintenance interval. Based on this, performance of burner can be drove to best by improving combustion system. Proper Combustion characteristic for each heating interval was analyzed in heating furnace in Hyundai Heavy Industry. A project plan for improving fuel savings and increasing precision of temperature was presented in this research.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.9
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• pp.100-106
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• 2020

This study analyzes the residual stress of AISI 1536V for an engine shaft of the shipbuilding industry and AISI A387 for a reactor shell of the chemical refining industry by the hole drilling method with a strain gauge rosette, which transforms fine mechanical changes into electrical signals. Tensile residual stress is generated in the forging and heat treatment process because specimens are affected by thermal stress and metal transformation stress. In the heat treatment process, the residual stress of AISI A387 is almost 170% the yield strength at 402 MPa. Since during the machining process, variable physical loads are applied to the material, compressive residual stress is generated. Under the same condition, the mechanical properties greatly affect the residual stress during the machining process. After the stress-relieving heat treatment process, the residual stress of AISI A387 is reduced below the yield strength at 182 MPa. Therefore, it is necessary to control the temperature, avoid rapid heat change, and select machining conditions depending on the mechanical properties of materials during manufacturing processes. In addition, to sufficiently reduce the residual stress, it is necessary to study the optimum condition of the stress-relieving heat treatment process for each material.

• Journal of Conservation Science
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• v.31 no.4
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• pp.489-497
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• 2015

Iron sickle is tool used in various ways and have various form. It has agricultural feature as well as is used in weapon. Previous studies have been focused on features of farming tools. In this study, metallurgical analysis of iron sickles are introduced because examples of analysis for iron sickles is rare. Two sickles form Yeongi Jangjae-ri are investigated and compared to one sickle of Yeongi Songwon-ri. Three sickles have forging molding process and heat treatment process. No.1 sickle of Jangjae-ri have martensite of quenching. No.2 sickle of Jangjae-ri was undergone high temperature as compared with others. This show manufacturing technology of sickles from Jangjae-ri in over the Songwon-ri's.

• 보존과학연구
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• s.21
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• pp.177-206
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• 2000

In the study of iron artifacts, microstructure investigation is an indispensable step to find out the manufacturing method and skill. The iron weapons that we have excavated and investigated at the ruins of Gohyun Castle site, Hadong-gun, Kyungnam Province are traced to the era of Choson Dynasty. By sampling specimens of some artifacts, we have made microstructure investigation and component analysis of them. For microstructure investigation we used metallographic microscopes, and for component analysis we used the methods of C/S analysis and Inductively coupled plasma emission spectrometry (ICP) analysis which is designed to verify components and contenets of a very small amount elememt. Microstructure of the artifacts is mainly divided into three parts. Inner part is Widmanstatten, a typical overheated structure, upon which we can see another part with fine grains and with extremely small quantities of carbon. And on the surface, there is a carbonized part. When the shape is formed through forging process at a high temperature the carbon content of the surface is getting down and the grains come to be finer. Next, carbonizing process is to be done for hardening the surface, which is followed by cooling process. Cooling rates seem to be different from artifacts to artifacts. All artifacts have clearly distinguishable grain boundaries in their unique structure. Since this kind of structure is rarely found, it seems to offer a clue to find out the manufacturing method. The outcome of component analysis is almost the same with that of microstructure investigation. As is demonstrated by C/S analysis, carbon content is 0.39-1.24% and sulfur is contained 0.0005-0.010%.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.5
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• pp.239-249
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• 2015

Various amount of NbC carbide was intentionally formed in a matrix-type cold-work tool steel by controlled amount of Nb and C addition. And the effect of NbC addition on the mechanical properties was investigated. Four alloys with different Nb and C contents were cast by vacuum induction melting, then hot forging and spheroidizing annealing were conducted. The machinability of the annealed specimens was examined with 3 different cutting tools. And tensile tests at room temperature were conducted. After quenching and tempering, hardness and impact toughness were measured, while wear resistance was evaluated by disk-on-plate type wear test. The increasing amount of NbC addition resulted in degraded machinability with increased strength, whereas the absence of NbC also led to poor machinability due to high toughness. After quenching and tempering, the additional NbC improved wear resistance with increasing hardness, whereas it deteriorated impact toughness. Therefore, it could be found that a moderate addition of NbC was desirable for the balanced combination of mechanical properties.