• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.4
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• pp.154-160
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• 2000

Martensitic stainless steels containing 12%Cr are commonly used in quenched and tempered conditions. The quenching heat treatment involves annealing to obtain austenite and to dissolve the carbides , followed by cooling to transform the austenite into martensite and often to cause carbide predipitation. In this study, we used three different tempered specimens which were temperated at 30$0^{\circ}C$, 67$0^{\circ}C$ and 75$0^{\circ}C$ . The crack propagation and fracture toughness tests were performed on this three different specimens. The experimental results showed that the highest value of crack growth rate and the lowest value of fracture toughness were observed in the specimen which were temperated at $600^{\circ}C$, however, when the specimen were temperated at 75$0^{\circ}C$, the vale of crack growth rate was significantly decreased and the value of fracture toughness was significantly increased as compared to which were temperated at $600^{\circ}C$.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.364-369
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• 2003

Non-heat treated steels are attractive in the steel-wire industry since the spheroidization and quenching-tempering treatment are not involved during the processing. However, non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, three different steels such as dual phase steel, low-Si steel, and ultra low carbon bainitic steel were used to study their mechanical properties and the cold formability. The cold formability of three steels was investigated by estimating the deformation resistance and the forming limit. The deformation resistance was estimated by calculating the deformation energy, and the forming limit was evaluated by measuring the critical strain revealing crack initiation at the notch tip of the specimens. The results showed that deformation resistance was the lowest in the low-Si steel, and the forming limit strains of ultra low carbon bainitic steel and low-Si steel were higher than that of commercial SWRCH45F steel.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.1
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• pp.10-15
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• 2011

Recently, renewable energy sources such as wind turbine, solar cell are interested in preventing global warming which is caused by the consumption of fossil fuel. SCM440(H) and SNCM439 have been used in the major components of the wind turbine gear because of excellent mechanical properties. In the present study, the heat treated mechanical properties of SCM440(H) and SNCM439 with 150 mm diameter were compared with those with 25 mm diameter which is generally accepted material for structural application. Heat treated SCM440(H) showed better mechanical properties such as tensile strength, hardness and impact absorbed energy compared with those in SNCM439. Hardenss value between as-quenched and as-quenched followed by tempering showed big difference in SNCM439, however the difference in SCM440(H) was relatively small. Heat treated mechanical properties of the alloys with 25 mm diameter were more uniform value than those with 150 mm diameter.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.247-257
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• 1998

In order to evaluate the relation between prior structure and fatigue strength on a induction surface hardened medium carbon steel(SAE1050M) for automotive drive shafts, torsional fatigue test were conducted with various cases of different hardened depths and applied loads. Prior structures of the steel such as pearlite, fine pearlite and spheroidal pearlite were prepared by conventional nomalizing, tempering after quenching and spheroidized annealing, respectively. Maximum torsional fatigue strength can be obtained when the case depth is 18~25% diameter of the bar in each prior structure. The effect of case depth on the torsional fatigue strength was different depending on applied load to specimen, but the most good fatigue life was shown in the case of pearlitic structure when the case depth was 4.0~5.5mm(18~25% of bar diameter). Among three different prior structures, energy consumption, to obtain high strength or to get the same case depth, was the most saved in the case of pearlitic structure.

• Journal of Welding and Joining
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• v.2 no.2
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• pp.54-61
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• 1984

Construction of welding structure is greatly dependent upon welding heat cycle. Fracture toughness is decreased remarkablely due to coarse grained HAZ and inequal residual stress of three dimensions to originate in welding. Post weld heat treatment(PWHT) is carried out to increase the fracture toughness of HAZ and to remove the residual stress. There occur some problem such as toughness decrement and stress relief cracking(SRC) in the coarse grained HAZ subject to the effect of tempering treatment. Therefore, in this paper, the effect of heat inputs affecting cooling rate and PWHT under the no stress on fracture toughness were evaluated by crack opening displacement (COD), SEM and micro-hardness test. Experimental results are as follows; 1. Fracture toughness of weld HAZ is dependent upon weld heat cycle and it is decreased with increment of heat input, but the degree of improvement of fracture toughness after PWHT was linearly increased with heat input. 2. Hardness of the parent metal is not changed, but the softening of coarse grained HAZ is remarkable due to PWHT. 3. Fracture surface of as-weld show the perfect brittle fracture with the cleavage fracture, but after PWHT they appear the ductile fracture surface with dimple.

• Journal of the Korean Society for Heat Treatment
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• v.6 no.3
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• pp.144-151
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• 1993

For the purpose of studying the influence of stress relieving on microstructures and mechanical properties of weld metal, manual arc welding, onepole and twopole submerged arc welding were accomplished on $60kg/mm^2$ quenched and tempered high strength steel. After stress relieving, a lot of carbides were precipitated, developed and subsequently coarsened at the grain boundaries and within matrix due tn multiple tempering effect in manual arc welding, resulting in deterioated toughness. Meanwhile pearlite and cementite films were spheroidized and shortened in submerged arc welding, resulting in improved considerable toughness. It was observed that main effect of stress relieving was to reduce solut supersaturation by nucleation and growth of carbide precipitates, and stress relieving led to some reduction in the yield and tensile strenath but did not significantly affect elongation.

• Journal of Ocean Engineering and Technology
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• v.25 no.6
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• pp.97-104
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• 2011

Modified C95600 bronze contains Fe component of 0.7 weight percentage besides Cu-7Al-2.5Si composition. The shape of centrifugal cast is a circular pipe with thick wall. Specimens machined from the centrifugal cast were quenched in oil after isothermal holding at a given heat treatment temperature in the range of $700{\sim}900^{\circ}C$. Mechanical properties and structural morphology are depended on the quenching heat treatment temperature regardless of isothermal holding time. Tensile strength or Brinell hardness is increased with increasing heat treatment temperature. The microstructure caused by quenching contains mixing phases of ${\alpha}+{\beta}'+FeSi+{\kappa}$ which martensite of ${\beta}'$ phase has been transformed from ${\beta}$ phase. Effect of isothermal holding temperature on mechanical properties in case of quenching heat treatment attributes to the change of volume fraction of ${\beta}'$ on the structural morphology. Mechanical characteristics of specimen, initially quenched from $850^{\circ}C$, and then tempered at $500^{\circ}C$, does not show an obvious softening indication, because disappearance of ${\beta}'$ during tempering process can be compensated by precipitation of brittle phase ${\gamma}$.

• Korean Journal of Materials Research
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• v.33 no.12
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• pp.558-564
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• 2023

In this study, we designed and manufactured a large angular contact ball bearing (LACBB) with low deformation using JIS-SUJ2 steel and analyzed changes in its structural characteristics and chemical composition upon heat treatment. The bearing was produced by hot forging and heat treatment including a quenching and tempering (Q/T) process, and its properties were analyzed using 4 mm thick specimens. A difference in the size distribution of the carbide in the outer and inner parts of the bearing was observed and it was confirmed that large and non-uniform carbide was distributed in the inner part of the bearing. After heat treatment, the hardness value of the outer part increased from 13.4 HRC to 61 HRC and the inner part increased from 8.0 HRC to 59.7 HRC. As a result of X-ray diffraction (XRD) measurements, the volume fraction of the retained austenite contained in the outer part was calculated to be 3.5~4.8 % and the inner part was calculated to be 3.6~5.0 %. The surface chemical composition and the content of chemical bonds were quantified through X-ray photoelectron spectroscopy (XPS), and a decrease in C=C bonds and an increase in Fe-C bonds were confirmed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.252-261
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• 2017

This study examined the effect of heat treatment on the microstructure and mechanical properties of J55 line pipe steel. The experiments were carried out at under the following various conditions: austenization temperature($880^{\circ}C$, $910^{\circ}C$, $940^{\circ}C$), cooling methods(water quenching, oil quenching) and tempering temperature(none, $550^{\circ}C$, $650^{\circ}C$). The phase diagram and CCT curve were simulated based on the chemical composition of J55 steel to predict the microstructures. In the results, A1, A3 temperature decreased. As the austenization temperature increased, existing austenite grains grew exponentially which seriously degraded their mechanical properties. Various microstructures, including martensite, bainite, ferrite, and pearlite, developed in accordance with the heat treatments and were closely correlated with hardness, tensile strength and toughness. Martensite was formed after water quenching, but bainite and ferrite appeared after oil quenching. FeC precipitation formed and coarsened during tempering, which improved their toughness.

• Journal of computational fluids engineering
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• v.17 no.4
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• pp.16-23
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• 2012

Current display manufacturing processes apply thermal treatment of glass backplanes widely for hydrogen degassing, crystallization of thin-films, tempering, forming, and precompaction. Estimation of the characteristics of transient heating stages and thermal non-uniformities on a single glass substrate or in a stack of glasses are extremely helpful to understand non-homogeneity of mechanical and electronic features of nano/micro structures of end products. Based on simple heat transfer models and using an electric muffle furnace, temperature variations in a glass stack were predicted and measured for glass backplanes of $1.5{\times}1.85m^2$ in size and 0.7 mm in thickness. Except for the period of putting glass backplanes into the furnace, thermal radiation was the major heating mechanism for the treatment and theoretical predictions agreed well to the experimental temperatures on the backplanes. Using the theoretical model, thermal fields for a glass stack of glass-size, $2.2{\times}2.5m^2$, and of the number of sheets, 1 to 12, were calculated for practical design and manufacturing of the muffle furnace for large-scale displays, e.g. up to $8^{th}$ generation.