• 한국재료학회지
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• 제14권2호
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• pp.126-132
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• 2004

The high strength steel sheets has been widely used as the automobile parts to reduce the weight of a vehicle. The aim of this research is to develop the TRIP aided high strength low carbon steels using reverse transformation process. The 0.15C-4Mn and 0.15C-6.5Mn steel sheets were reversely transformed by slow heating to intercritical temperature region and air cooling to room temperature. The stability of retained austenite depends on the enrichment of carbon and manganese by diffusion during the reverse transformation. The amount of retained austenite formed after reversely transformed at $645^{\circ}C$ for 12 hrs. was about 46vol.% in hot rolled 0.lC-6.5Mn steel. The change in volume fraction of retained austenite with a holding temperature was consistent with the changes in elongation and the strength-ductility combination. The tendency of tensile strength to increase with increasing the holding temperature was due to the decrease of retained austenite after cooling from the higher temperature of $670 ^{\circ}C$. The maximum strength-ductility combination was about 4,250 kg/$\textrm{mm}^2$ㆍ% when the hot rolled 0.lC-6.5Mn steel was reversely transformed at $645^{\circ}C$ for 12 hrs.

• 대한치과보철학회지
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• 제40권3호
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• pp.296-305
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• 2002

The main disadvantage of cement-retained implant restorations is their difficulty in retrievability. Advocates of cemented implant restorations frequently state that retrievability of the restoration can be maintained if a provisional cement is used. The purpose of this study was to find the optimal properties of provisional luting cements and the surface treatment of abutments in single implant abutment system. 30 prefabricated implant abutments, height 8mm, diameter 6mm, 3-degree taper per side, with light chamfer margins were obtained. Three commercially available provisional luting agents which were all zinc oxide eugenol type ; Cavitec, TempBond and TempBond NE were evaluated. No cement served as the control. TempBond along with vaseline, a kind of petrolatum (2:1 ratio) was also evaluated. Ten out of thirty abutments were randomly selected and abutment surfaces were sandblasted with $50{\mu}m$ aluminum oxide. Another ten abutments were sandblasted with $250{\mu}m$ aluminum oxide. A vertical groove, 1 mm deep and 5mm long was cut in each twenty abutments. Ten of them were sandblasted with $50{\mu}m$ aluminum oxide. The full coverage casting crowns were cemented to the abutments with the designated provisional luting agent. Specimens were stored in distilled water at $37^{\circ}C$ for 24 hours. Each specimen was attached to a universal testing machine. A crosshead speed of 0.5mm/min was used to apply a tensile force to each specimen. Within the limitations of this in vitro study, the following conclusions were drawn: 1. Tensile bond strength of provisional luting cements in no surface treatment decreased with the sequence of TempBond NE, TempBond, Cavitec, TempBond with vaseline, no cement. 2. Tensile bond strength more increased by surface treatment. Sandblasting with $250{\mu}m$ aluminum oxide exhibited the highest tensile bond strength in the abutment cemented with TempBond NE and sandblasting with $50{\mu}m$ aluminum oxide exhibited the highest tensile bond strength in cemented with TempBond. 3. In the aspect of a groove formation, tensile bond strength significantly increased in TempBond with vaseline only and the others had no significant effect on tensile bond strength.

• 한국주조공학회지
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• 제18권4호
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• pp.340-348
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• 1998

C/V graphite iron has superior tensile strength, toughness and ductility than grey iron, and better castability than ductile iron. The retained austenite content of C/V graphite iron by austempering treatment affects on the mechanical properties such as ductility, hardness, wear properties and machinability. C/V graphite iron alloyed with Cu and Mo were carried out on the austenitizing at $900^{\circ}C$ for 1 hour, and the austempering at $240{\sim}400^{\circ}C$ for 1 hr. And then the mechanical and wear properties of austempered C/V graphite iron have been investigated by the retained austenite content. In consequence, the retained austenite content was found to be 18.2% in austempering temperature at $240^{\circ}C$, and was increased 39.2% at $400^{\circ}C$. Tensile strength and hardness of austempered C/V graphite iron were decreased as the retained austenite content increased, but elongation was increased. The rolling wear loss were increased as the retained austenite content increased. The wear surface of as-cast became to be rough. The microstructure of austempered C/V graphite iron was became to be acicular ausferrite in austempering at $240^{\circ}C$, and feathery ausferrite at $400^{\circ}C$.

• 열처리공학회지
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• 제10권2호
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• pp.109-120
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• 1997

Microstructure and mechanical properties of Fe-Si-Mn-P high strength steel sheet have been investigated by controlling the cooling rate. Bainite and ferrite were obtatined by annealing in the ferrite pluse austenite region, and ferrite and austenite were obtatined after annealing in the fully austenite region. Ferrite and pearlite were obtained when the cooling rate was controlled from the annealing temperature above $760^{\circ}C$ and bainite showed with increasing cooling rate, however below $760^{\circ}C$ ferrite and bainite were obtained. Tensile strengths and hardness nearly unchanged with increasing cooling rate after control the cooling rate from the temperature above $760^{\circ}C$, while tensile strengths increased and elongation decreased with increasing cooling rate when the cooling rate was controlled from the tempeature below $760^{\circ}C$. Without regard to annealing temperature, tensile strength increased and elongation decreased with increasing cooling rate. Tensile strengths and elongation values heat treated in the ferrite plus austenite region were higher than those in the fully austenite region. Retained austenite and strength-elongation balance showed the maximum value at $780^{\circ}C$ and decreased with increasing annealing temperature. Strength-elongation balance value was controlled by the retained austenite.

• Fibers and Polymers
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• 제6권1호
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• pp.72-78
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• 2005

The impact of fiber friction, yarn twist, and splicing air pressure on mechanical and structural properties of spliced portion have been reported in the present paper. The mechanical properties include the tensile and bending related properties and, in the structural properties, the diameter and packing density of the splices are studied. A three variable three level facto­rial design approach proposed by Box and Behnken has been used to design the experiment. The results indicate that there is a strong correlation between retained spliced strength (RSS) and retained splice elongation (RSE) with all the experimental variables. It has been observed that RSS increases with the increase in splice air pressure and after certain level it drops, whereas it consistently increases with the increase in yarn twist. The RSE increases with the increase in both fiber friction and yarn twist. It has also been observed that the yarn twist and splicing air pressure have significant influence on splice diameter, percent increase in diameter and retained packing coefficient, but the fiber friction has negligible influence on these parame­ters. Yarn twist and splicing air pressure has a strong correlation with splice flexural rigidity, where as poor correlation with retained flexural rigidity.

• 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.

• 한국전기전자재료학회논문지
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• 제19권3호
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• pp.287-291
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• 2006

This paper describes mechanical and electric properties of ACSR $410\;mm^2$ conductor from many of older overhead conductor. Samples of conductors itemized two division according to operation sector, green area, salt and pollution area. Samples of conductors operated various environment conditions have undergone laboratory metallurigical investigation and tensile strength torsional ductility and electrical performance. The steel core were found to have retained their original properties to a large degree in both tensile strength and the number of turns to failure. On the other hand the aluminum conductor showed reductions in tensile strength. To determine the remaining useful life of aged conductor, an unacceptable deterioration level has to established for each diagnostic procedure.

• 한국주조공학회지
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• 제15권2호
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• pp.146-155
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• 1995

This study was performed to investigate the effect of austempering temperature on the mechanical properties and fracture characteristics of the ductile cast iron with Cu, Mo and Cu, Mo, Ni. The results obtained from this study are summarized as follows; Microstructures of Cu-Mo and Cu-Mo-Ni ductile cast iron by austempering were obtained low bainite with some martensite at $250^{\circ}C$, mixture structure of upper and low bainite obtained at $300^{\circ}C$ and upper bainite obtained at $350^{\circ}C$. Tensile, impact and fracture toughness properties were remarkably controlled by retained austenite. With increasing austempering temperature, tensile and yield strength, hardness decreased, while the elongation and impact absorption energy, fracture toughness increased. With adding Ni, tensile and yield strength increased and elongation, facture toughness and impact absorption energy decreased. Retained austenite increased with increasing austempering temperature and the fracture surface were shown mixture structure of fibrous and dimple.

• 동력기계공학회지
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• 제12권1호
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• pp.47-52
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• 2008

This study was investigated the effect of subzero treatment in austempered ductile cast iron. Retained austenite transformed to martensite by subzero treatment and strain. With decreasing subzero treatment temperature and increasing strain, retained austenite transformed more to martensite and transformed 30% above by subzero treatment at $-196^{\circ}C$. With decreasing subzero treatment temperature, the value of strength and ratio of increasing of strength, hardness and ratio of increasing of hardness increased but the value of elongation and ratio of decreasing of elongation decreased. With decreasing subzero treatment temperature, impact value and ratio of decreasing of impact value decreased. In case of subzero treatment at $-196^{\circ}C$, hardness value increased about 18% and impact value decreased above 20%. We could find that in subzero treated specimens had a little of effect on the tensile properties but had very much effect on the hardness and value of the impact.

• 한국주조공학회지
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• 제13권2호
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• pp.187-193
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• 1993

In this study, it was examined the relationship between the microstructure, fatigue properties, mechanical properties and retained austenite volume of Mo-Ni ADI corresponding to various austempering temperatures. When the austempering temperature is increased to $370^{\circ}C$, acicular bainite structure was found to be transformed to feathery bainite structure. But at the austempering temperature of $420^{\circ}C$, the dissolved bainite lath was showned. Up to the austempering temperature of $370^{\circ}C$, the volume of retained austenite was increased. However at the austempering temperature of $420^{\circ}C$ a large amount of retained austenite was decreased. In this study, the retained austenite volume was determined by XRD(X-ray diffraction). It was observed that the optimum fatigue properties can be obtained at the condition of austempering temperature $370^{\circ}C$. Under the such conditions, fatigue limit determined as the value of 290 MPa, tensile strength 877MPa elongation 6%, hardness 285(BHN), impact values(CVN) 9.2J and retained austenite volume 30.3%, respectively.