• Journal of the Korean institute of surface engineering
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• v.37 no.4
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• pp.226-233
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• 2004

The residual stresses on the surfaces of low carbon 12Cr steels used as a nuclear steam turbine blade material have been studied by controlling the flame hardening surface treatments. The temperature cycles on the surfaces of 12Cr steel were controlled precisely as a function of both the surface temperature and cooling rate. The final residual stress state generated by flame hardening was dominated by two opposite competitive contributions; one is tensile stress due to phase transformation and the other is compressive stress due to thermal contraction on cooling. The optimum processing temperatures required for the desirable residual stress and hardness were in the range of $850^{\circ}C$ to $960^{\circ}C$ on the basis of the specification of GE power engineering. It was also observed that the high residual tensile stress generated by flame hardening induced the cracks on the surfaces, especially across the prior austenite grain boundaries, and the material failure virtually, which might limit practical use of the surface engineered parts by flame hardening.

• Journal of the Korean institute of surface engineering
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• v.39 no.2
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• pp.49-56
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• 2006

In this study, the movable flame hardening process of 12Cr steel for a uniform hardness and desirable residual stress have been investigated. For this, the temperature cycles have been controlled accurately as a function of the three processing variables, the flame intensity $I_f$, the scanning velocity $V_s$, and the initial flame holding time $t_h$, where the standard surface temperature $T_{s,\;max}$, was maintained at $960^{\circ}C$. The optimized conditions were $V_s=0.68mn/s\;and\;t_h=67sec$ for the $C_3H_8:O_2\;=\;5:20l/min,\;V_s=0.80mm/s$ and $t_h=56sec$ for the $C_3H_8:O_2=6:24l/min,\;V_s=1.01mm/s\;and\;t_h=48sec$ for the $C_3H_8:O_2=7:28l/min,\;and\;V_s=1.15mm/s$ and $t_h=39sec$ for the $C_3H_8:O_2$=8:32 l/min. The optimally flame-hardened surface exhibited uniform distributions of the hardness and residual compressive stress over the treated area with moderate levels of $470{\sim}490HV_{0.2}$in hardness and $-300{\sim}-450MPa$ in residual stress, which were acceptable on the basis of the acceptance criteria of Siemens AG-KWU and GE Power Generation Engineering.

• Journal of Korea Foundry Society
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• v.29 no.2
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• pp.70-77
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• 2009

The aim of this study was to develop a Mo and V free low alloy cast steel materials, enabling the significant cost- and time-savings in manufacturing and maintaining the insert of cold pressing die without impairment of the important properties. For this purpose, the effects of Si content on combinations of important properties such as hardness, hardenability, and weldability, and strength were systematically investigated. In order to evaluate the applicability as the insert of cold pressing die, the mechanical properties were measured after spheroidization annealing, quenching and tempering, and flame hardening heat treatments, respectively. After the Q/T and F.H. treatments, the developed 0.8${\sim}$1.6%Si containing Mo and V free low alloy cast steels showed excellent matrix strengthening effect, hardenability, and weldability, fulfilling the industrial criterion of the mechanical properties for automobile cold pressing die insert.

• Proceedings of the KWS Conference
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• 1996.05a
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• pp.26-27
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• 1996

• Proceedings of the Korean Nuclear Society Conference
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• 2002.05a
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• pp.263-263
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• 2002

• Composites Research
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• v.35 no.5
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• pp.309-316
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• 2022

The demand for cold-resistant cable material is increasing due to the rapid increase in the development of devices that operate in a low temperature environment. Cold tolerance of a thermoplastic polymer largely depends on the type and content of about 20 or more additives used to make the polymer. The phenomenon of polymer hardening at low temperature can be classified into hardening by simple temperature effect, embrittlement at the glass transition temperature, and hardening by crystallization of polymers that tend to crystallize. In this study, a thermoplastic polymer having a low glass transition temperature, a flame retardant, and an additive were mixed to evaluate the mechanical properties of a thermoplastic polymer composite material for electric wires. It has been confirmed that mechanical properties and processability are determined depending on the additives and compatibilizers added, and this study is considered to be useful as basic data for optimization to meet the performance requirements of wires developed for low-temperature use.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.2
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• pp.207-212
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• 2016

High-frequency induction hardening (HFIH) is used in many industries and has a number of advantages, including reliability and repeatability. It is a non-contact method of providing energy-efficient heat in the minimum amount of time without using a flame. Recently, HFIH has been actively studied using the finite-element method (FEM), however, these studies only focused on the accuracy of the analysis. In this paper, we analyzed HFIH by using a variable frequency based on the conditions of the same shape and input power then comparing the analysis results to experimental results. The analysis and experimental results indicate that the hardening depths are approximately the same using the optimal frequency of 3kHz.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.5
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• pp.393-400
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• 2016

High frequency induction heating (HFIH) is used in many industries and has a number of advantages, including reliability and repeatability. It is a non-contact method of providing energy-efficient heat in the minimum amount of time without using a flame. Recently, HFIH has been actively studied using the finite element method (FEM), however, these studies only focused on the accuracy of the analysis. In this paper, we can measure joule heat distributions by the electromagnetic analysis for HFIH and the temperature distribution from the heat transfer analysis by applying joule heat for a sprocket. The sprocket is heated over $850^{\circ}C$ due to joule heat and then cooled to under $200^{\circ}C$ by using cooling $20^{\circ}C$ water. These processes were used to calculate the FEM and then compared to our experimental results. The calculated outcome may be used to predict hardening depth in HFIH.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.78-84
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• 2012

Mold may experience deterioration of molding quality as the abrasion of mold occurring due to friction between mold and molded product works as allowance in the course of press process. Therefore, to improve the wear-resistance of mold, methods like nitriding, carburizing, flame and induction surface hardening treatment etc have been applied. However, as such methods are accompanied by problems like shape limitation or product deformation etc, laser surface treatment technology is under review as surface treatment method that can solve such problems. Therefore, in this study, mold material cast iron was surface-treated by using high power diode laser. In previous report 1 and report 2, the heat treatment characteristics were compared by the differences of die materials and shapes, then this paper observed microstructure by using optical microscope and scanning electronic microscope to analyze the structural difference of hardened zone, interface area and base metal after heat treatment. And the structural condition was grasped through EDS. As a result of microstructure, hardened zone showed formation of acicular martensite.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.330-337
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• 2021

3D printing is not only at the fundamental study and small-scale level, but has recently been producing buildings that can be inhabited by people. Buildings require a lot of cost and labor to work on the form work, but if 3D printing is applied to the building, the construction industry is received attention from technologies using 3D printing as it can reduce the construction period and cost. 3D printing technology for buildings can be divided into structural and non-structural materials, of which 3D printing is applied to non-structural materials. Because 3D printing needs to be additive manufacturing, control such as curing speed and workability is needed. Since cement mortar has a large shrinkage due to evaporation of water, cement polymer dispersion is used to improve the hardening speed, workability, and adhesion strength. The addition of polymer dispersion to cement mortar improves the tensile strength and brittleness between the cement hydrate and the polymer film. Cement mortar using polymer materials can be additive manufacturing but it has limited height that can be additive manufacturing due to its high density. When light-weight materials are mixed with polymer cement mortar, the density of polymer cement mortar is lowered and the height of additive manufacturing, so it is essential to use light-weight materials. However, the use of EVA redispersible polymer powder and light-weight materials, additional damage such as cracks in cement mortar can occur at high temperatures such as fires. This study produced a test specimen incorporating light-weight materials and EVA redispersible polymer powder to produce exterior building materials using 3D printing, and examined flame resistance performance through water absorption rate, length change rate, and cone calorimeter test and non-flammable test. From the test result, the test specimen using silica sand and light-weight aggregate showed good flame resistance performance, and if the EVA redispersible polymer powder is applied below 5%, it shows good flame resistance performance.