• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.126-129
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• 2005

Microstructures and tensile properties of low carbon steels, 5083 Al alloy and Ti-6Al-4V alloy fabricated by equal channel angular pressing (ECAP) were examined in order to understand their deformation response associated with a formation of an ultrafine grained (UFG) structure. Room temperature tensile properties of UFG low carbon ferrite/pearlite steels and UFG ferrite/martensite dual phase steel were compared for exploring a feasibility enhancing the strain hardening capability of UFG materials. In addition, low temperature and high strain rate superplasticity of the two grades of the UFG 5083 Al alloy, and Ti-6Al-4V alloy were presented. From the analysis of a series of experiments, it was found that UFG materials exhibited the enhanced mechanical properties compared to coarse grained counterparts.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.456-459
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• 2005

Continuous cooling transformation behaviors were studied fur low carbon HSLA steels containing three different level $(1\~3\;wt\%)$ of Ni addition. Thermo-mechanical processing (TMP) simulations to construct continuous cooling (CCT) diagram were conducted by using Gleeble system. As cooling rate increased, pearlite, granular bainite, acicular ferrite, bainitic ferrite and lath martensite were transformed from deformed austenite. Fully bainitic microstructure were developed at all cooling rate condition in high Ni containing steel due to hardenability increasing effects of Ni. Ni also influenced the transformation kinetics. At the slowest cooling rate of $0.3^{\circ}C/s$, transformation delayed with decreasing Ni contents because of the diffusion of substitutional alloy elements. However, cooling rate slightly increased to $1^{\circ}C/s$, transformation kinetics accelerated with decreasing Ni contents because nucleation of bainite was sluggish due to hardening of residual austenite.

• 열처리공학회지
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• 제13권4호
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• pp.253-258
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• 2000

The present study aimed to develop the TRIP(transformation induced plasticity) aided high strength low carbon steel sheets using reverse transformation process. The cold-rolled 0.14C-6.5Mn steel was reverse-transformed by slow heating to intercritical temperature region and air cooling to room temperature. An excellant combination of tensile strength and elongation of $98.3kgf/mm^2$ and 44.4% appears. This combination comes from TRIP phenomena of retained austenite during deformation. The stability of retained austenite Is very Important for the good ductility and it depends on diffusion of carbon and manganese during reverse transformation. The air cooling after holding at intercritical temperature retards the formation of pearlite and provides the carbon enrichment in retained austenite, resulting the increase of elongation in cold-roiled TRIP steel.

• 한국주조공학회지
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• 제9권4호
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• pp.327-335
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• 1989

The matrix structure and the morphology of CV graphite are affected by the addition of many kinds of elements, which are contained in the CV graphite cast iron, additives, fading time and cooling rate. The effects of cooling rate on the matrix structure, the shape of CV graphite, mechanical properties and propagation of ultrasonic wave in hypoeutectic CV graphite cast iron were studied. When the diameters of the samples are 50mm, 35mm and 20mm 1. CV graphite number showed average 17.9% increase and CV graphite length showed 10.3% decrease with decreasing diameter of the samples. 2. The amount of graphite and ferrite showed average 11.2, 4.1 % decrease and the amount of pearlite showed average 15.7% increase. 3. Hardness and tensile strength showed average 3.5%, 11.3% increase and impact strength showed average 1.5% decrease. 4. Ultrasonic wave velocity showed average 1.1% increase.

• 한국주조공학회지
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• 제9권4호
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• pp.336-344
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• 1989

The matrix structure and the morphology of CV graphite are affected by the addition of many kinds of elements, which are contained in the CV graphite cast iron, additives, fading time and cooling rate. The effects of cooling rate on the matrix structure, the shape of CV graphite, mechanical properties and propagation of ultrasonic wave in eutectic CV graphite cast iron were studied. When the diameters of the samples are 50mm, 35mm and 20mm 1. CV graphite number showed average 13.8% increase and CV graphite length showed 12.3% decrease with decreasing diameter of the samples. 2. The amount of graphite and ferrite showed average 10.6, 4.3% decrease and the amount of pearlite showed average 23.4% increase. 3. Hardness and tensile strength showed average 3.2%, 9.5% increase and impact strength showed average 1.3% decrease. 4. Ultrasonic wave velocity showed average 1.1% increase.

• 한국주조공학회지
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• 제13권6호
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• pp.555-562
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• 1993

A study was investgated the relationship between fracture characteristics and microstructure changes according to Cu addition and heat treatment methods on the ductile cast iron. According to increment of Cu addition pearlite volume fraction was increased due to the deffect of anti-ferritizing of Cu. At the case of austempering heat treatment, fracture toughness of Cu contained specimen was decreased. The reason for the results seems to be responsible for decrement of plastic zone size at the crack tip. It was observed that the excellent fracture toughness can be obtained at the condition of normalizing and the specimen was not contained Cu. Under the such conditions, fractographs is composed of dimple pattern and fracture toughness 71.6MPa $\sqrt{m}$, tensile strength determined as the value of 961.6MPa, respectively.

• Corrosion Science and Technology
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• 제5권1호
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• pp.23-26
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• 2006

Recent development of ultrafine grained (UFG) low carbon steels by using equal channel angular pressing (ECAP) and their room temperature tensile properties are reviewed, focusing on the strategies overcoming their inherent mechanical drawbacks. In addition to ferrite grain refinement, when proper post heat treatments are imposed, carbon atom dissolution from pearlitic cementite during ECAP can be utilized for microstructural modification such as uniform distribution of nano-sized cementite particles or microalloying element carbides inside UFG ferrite grains and fabrication of UFG ferrite/martensite dual phase steel. The utilization of nano-sized particles is effective on improving thermal stability of UFG low carbon ferrite/pearlite steel but less effective on improving its tensile properties. By contrast, UFG ferrite/martensite dual phase steel exhibits an excellent combination of ultrahigh strength, large uniform elongation and extensive strain hardenability.

• 한국기계연구소 소보
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• 통권16호
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• pp.29-39
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• 1986

Several heat treatment were applied to on HSLA steel of type StE47 (German standard) to produce five ferrite microstructures of different strength and at least two different grain sizes respectively. Whereas the ferrite microstructure had a strong influence on yield strength the effect of grain size was negligible. The different strength levels could be explained by regarding the arrangement of dislocations and vanadium carbide particles, and their mutual interaction. Specimens tranformed at $600^{\circ}C$ showed the highest strength levels. In this case precipitation has occured after the $\gamma$- $\alpha$ transformation. Very small VC particles are arranged mostly along dislocation lines. Increasing both, grain size and pearlite volume fraction leads to a remarkable shift of transition temperature which was further enhanced by increasing ferrite strength.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.120-123
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• 2007

The effects of annealing condition on the occurrence of the delamination in cold drawn hyper-eutectoid steel wires, were investigated. Annealing treatment was performed on cold drawn steel wires for temperature range of $425^{\circ}C\sim500^{\circ}C$ with the variation of annealing time from 30sec to 15min. The increase of annealing temperature and time would cause the decrease of tensile strength and the increase of ductility. However, the occurrence of the delamination, representing torsional ductility, showed the different way from the variation of ductility.

• Journal of Welding and Joining
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• 제18권5호
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• pp.55-62
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• 2000

A metallurgical model for the phase transformation kinetics at Coarsened Grain Heat Affected Zone(CGHAZ) on the basis of Johnson-Mehl-Avrami equation(JMA equation) was proposed. In this model, the effect of prior austenite grain size on the transformation and the morphological changes of ferrite were considered. Isothermal dilatometer tests were performed to determine the effect of prior austenite grain size (AGS) on the austenite decomposition to ferrite and pearlite in a plain carbon steel. By comparing the calculated volume fraction with measured data, the reliability of the developed model was discussed.