• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.116-119
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• 1999

The effects of secondary phase morphology and carbon content on the plastic deformation of 0.2C-1.5Si-1.5mn TRIP(TRansformed Induced Plasticity) steel have been investigated at various annealing and bainitic transformation temperatures. The morphology of ferrite and secondary phases was controlled by the annealing temperature and the distribution of secondary phase was controlled by the bainitic transformation temperature. The secondary phase contributed to elongation and/or UTS depending on the ferrite morphology which determined deformation mode simple elongation or rotation of secondary phase along the tensile direction In case of the sample containing the granular type retained austenite the elongation was improved as carbon stabilized the austenite phase. If the film-shape retained austenite in acicular ferrite was dominant however UTS was enhanced as the transformed martensite was hardened by carbon.

• Corrosion Science and Technology
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• 제6권2호
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• pp.56-61
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• 2007

Carbide dissolution during heating processes can change chemical composition of martensitic stainless steel in its austenitic phase. Although the austenitizing treatments were carried out at a homogeneous austenite region, the amount of carbon atom in the matrix differs. Increase in the amount of carbon contents in the matrix resulted in decreasing MS temperature, which consequently causes the volume fraction of the retained austenite to increase. This study reveals the effects of the austenitizing treatment on the properties of Fe - 0.3C - 14Cr - 3Mo martensitic stainless steel change with different austenitizing temperatures.

• 열처리공학회지
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• 제7권2호
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• pp.88-95
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• 1994

In order to compare mechanical properties of ausformed martensite with those of marformed martemsite in Fe-30%Ni-0.1%C alloy and to investigate their strengthening mechanisms, ausformed martensite and marformed martensite were prepared by ausforming treatment and marforming treatment respectively. The microstructures were observed and the quantities of retained austenite, hardness, yield strength, ultimate tensile strength and elongation were examined. The strength of ausformed martensite was mainly increased because of the lattice defects inherited from austenite. The ductility of ausformed martensite was constant at the rate of 7-8% by ductile matrix formation of the retained austenite in spite of the increase in strength. The strength of marformed martensite was increased by the increment in dislocation density, the crossing of transformation twin with deformation twin and the mutual crossing of deformation twin. The ductility of mar formed martensite was slightly lower than that of ausformed martensite, but the strength of mar formed martensite was prominently higher.

• 열처리공학회지
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• 제21권3호
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• pp.137-143
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• 2008

Effect of quenching medium on the mechanical properties of ductil iron GCD 50 has been investigated using ADI treated specimens. The specimens have been austenitized at $900^{\circ}C$ for 2 hours, followed by controlled cooling to $800^{\circ}C$ under the cooling rate of $0.05^{\circ}C/sec$, then austempered at $380^{\circ}C$, $330^{\circ}C$, $280^{\circ}C$ and $230^{\circ}C$ for 1 hour. The specimens treated in the salt of 5% water were found to have higher tensile strength than that of the normal salt bath. Elongation and impact energy increased in proportion to the increase of retained austenite volume fraction. The increase of cooling rate of the salt by the addition of 5% water to the salt resulted in the increase of retained austenite volume fraction and the formation of fine bainitic ferrite.

• 대한기계학회논문집
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• 제12권3호
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• pp.489-496
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• 1988

본 연구에서는 오스템퍼링 처리된 구상흑연주철의 오스템퍼링 처리온도와 유 지시간을 변화시킨 후 대기중의 건조미끄름마찰실험을 하여 내마멸특성을 검토하는 것 을 목적으로 하였다.

• 열처리공학회지
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• 제12권2호
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• pp.108-116
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• 1999

Gray cast iron with a high damping capacity has been used for controlling the vibration and noise in various mechanical structures. Nevertheless, its usage has been often restricted due to its poor tensile strength. Therefore, it is necessary to improve tensile strength at the expense of a loss in damping capacity. This study is aimed at finding the best combination of tensile strength and damping capacity by varying austempering time and temperature range from $320^{\circ}C$ to $380^{\circ}C$ after austenization at $900^{\circ}C$ for 1hr. The effect of austempering condition on hardness and the volume fraction of retained austenite is investigated as well. The results obtained are summarized as follows : (1) With an increase in austempering temperature, both tensile strength and hardness decrease while damping capacity improves. (2) Austempering at $350^{\circ}C$, resulting in a mixture of upper and lower bainite with partially retained austenite, exhibits the optimum combination of tensile strength and damping capacity.

• 열처리공학회지
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• 제4권3호
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• pp.7-12
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• 1991

Effects of Mo content and aging conditions on the amount of retained austenite and mechanical properties of 18 Ni maraging steels were investigated. Maraging steels were fabricated with variation of Mo content. 3, 5, 7, 9% and heat treated by austenitizing at $840^{\circ}C$ for 1 hour and then aged at $480^{\circ}C$ for 0.5~100 hours. It was found that the amount of retained austenite after aolution treatment was negligible up to 5% Mo. 8 and 11 volume percents of retained austenite were obtained with 7 and 9% Mo respectively. The maximum hardness and yield strength without great loss of impact toughness were attained in the range of 4~8 hours of aging time at $480^{\circ}C$ with 5% Mo. It was concluded, as a result, that the optimum Mo content for the good combination of strength and toughness is to be 5% Mo.

• 열처리공학회지
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• 제11권1호
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• pp.46-53
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• 1998

The variation of the mechanical properties, microstructures and the formation of retained austenite with heat treatment conditions in austempered ductile cast iron has been investigated. In the case of austempered ductile cast iron below 25mm diameter, it has been found that a pearlite structure are not obtained under a super cooled condition at range of $0.05^{\circ}C/sec{\sim}10^{\circ}C/sec$, and the matrix is precipitated in graphite, bainite and retained austenite. After austempering treatment the retained austenite is increased with decreasing cooling rate. The elongation increases with decreasing super cooling rate, and the optimum result has been shown to be the elongation of 15.6% at super cooling rate of $0.05^{\circ}C/sec$. The optimum result has been shown to be the tensile strength-elongation balance of $1656kgf/mm^2.%$ and it is more than doubled to as the casting state and continuous cooling condition.

• 한국주조공학회지
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• 제12권6호
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• pp.450-457
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• 1992

The study aims to investigate the influence of alloying elements(V,Ti) and heat treatment on the mechanical properties in hypo-eutectic chromium cast iron. Before heat treatment, all of the specimen were fully annealed(950$^{\circ}C{\times}5Hr$) to homogenize their structures. The influence of heat treatment and alloying elements(V,Ti) on hardness, retained austenite volume, and charpy impact energy as well as tensile strength of the specimen was tested systematically. Retained austenite decreased with the increase of V and Ti, but incresed with the increase of number of cycles. The impact energy decreased, and hardness and tensile strength increased with the increase of alloying elements (V,Ti) and the decrease of the number of cycles. The hardness and tensile strength increased, but impact energy decreased with the increase of V and Ti elements and the temperature of destabillization heat treatment. After the destabillization heat treatment at the same temperature, the impact energy is increased, while hardness and tensile strength decreased as the increase of tempering temperature. Retained austenite increased with increase of destabilizatoin heat treatment temperature, while decrease with the increase of tempering temperature.

• 열처리공학회지
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• 제16권4호
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• pp.205-210
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• 2003

Various types of high strength steel sheets were usually used for improving the automobile safety and fuel efficiency by reducing the vehicle weight. The present study aimed to develop the TRIP (transformation induced plasticity) aided high-strength low carbon steel sheets by using a reverse transformation process. The 0.1C-4~8Mn steels were reverse-transformed by slow heating to intercritical temperature region and then furnace cooled to the room temperature. Granular type retained austenite was observed in 4Mn steel and lath type retained austenite was also observed in 6~8Mn steel. The results show that the 6Mn steel under reverse transformed at $625^{\circ}C$ for 6 hrs has maximum elongation up to 39%. The optimum strength-elongation combination was 3,888 ($kg/mm^2{\times}%$) when the 8Mn steel was reverse transformed at $625^{\circ}C$ for 12 h.