• Korean Journal of Materials Research
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• v.6 no.8
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• pp.841-851
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• 1996

In a recent investigation, the formation of bainite phase in direct-quenched low carbon non heat-treated steel was reported. In this study the effects of bainite phase on the mechanical properties of direct-quenched microalloying steels were investigated. By isothermal transformation at $480^{\circ}C$ for 7 sec., volume fraction of bainite lath was 15~20%, and the UTS and impact energy were increased. In this case $B_{ll}$ and $B_{lll}$ type bainite was observed and the fractography of impact test specimen showed a ductile fracture tendency. Isothermal transformation for 100sec., yielded 30% volume fraction of granular bainite and the mechanical properties were decreased. The f ractography of impact test specimen showed a brittle fracture tendency. The addition of Mo was more effective than B for improving impact energy because amounts of boron aditions were restricted to considerably lower levels, typically 10~ 30ppm. From this study, it is predicted that 15~20% volume fraction of lath bainite on the direct quenching process is procduced by addition of Mo up to 1.2wt. % and controlling the finish forging proc¬ess at $1000^{\circ}C$ and using oil as direct quenching media. This will improve mechanical properties of the direct- quenched steel.

• Korean Journal of Materials Research
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• v.4 no.3
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• pp.364-375
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• 1994

The microstructure of medium-carbon non-heat treated steels by air-cooling shows ferritepearlite structure. Compared to the conventional Q/T steels, the strength of these steels containing V, Nb and Ti are similar to Q/T steels. However, their toughness are inferior. In this study, the mechanical properties and microstructures of low-carbon Mo bearing steels produced by direct-quenching process were investigated. Especially, the effect of Mo on the direct-quenched steels was examined. The direct-quenched steels containing Mo were found to have higher strength and toughness. Mo seemed to be effective in producing the fine structure and dense precipitates because of decreasing transformation temperature. The best results were 1211 MPa in UTS and 127.5 J in toughness in the oil quenched 0.15C+O.llV+ 0.035Nb+ 1.81Mo steel. Compared to 0.4% C microalloyed steels, this results showed that UTS increased by 45% and toughness by 2 times.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.6
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• pp.12-19
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• 1994

This paper deals with the bending fatigue strength of SNC815 carburized spur gears. The test gears are heat-treated by two different treatments. One is the direct quenching after car-burization. The other is treated by reheating and quenching. The fatigue test at a constant stress amplitude is performed by using an electrohydraulic servo-controlled pulsating tester. The S-N curves are obtained and illustrated. The fatigue strength of direct quenched gears is higher than that of reheated quenched gears. The fatigue strength is estimated from the hardness and the residual stress by using the experimental formula proposed by Tobe and Inoue. The estimated strength is close to the test results, and the validty of the formular is confirmed.

• Korean Journal of Soil Science and Fertilizer
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• v.18 no.4
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• pp.319-324
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• 1985

This study was designed to evaluate the feasibility of direct application of quenched slag, as a silicate fertilizer byproduct of iron and steel industry. A field experiment was conducted on a low silica content paddy soil and its effect was compared to over corresponding air-cooled slag of milled commercial silicate fertilizer on rice plant growth and yields. The yields of rice were slightly higher in the commercial air-cooled slag than in the quenched slag, however, there was no significant statistical difference. The silica content of rice plants at harvest was higher in commercial silicate fertilizer than that of quenched slag. The available soil silica was high in quenched slag at the early growing stage, however, at harvest higher in air-cooled slag, which meant that the quenched slag might release silica quickly in soil. This results indicated that the slag could be considered resource as a silicate fertilizer.

• Korean Journal of Materials Research
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• v.22 no.10
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• pp.513-518
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• 2012

Recently, automobile parts have been required to have high strength and toughness to allow for weight lightening or improved stability. But, traditional micro-alloyed steel cannot be applied in automobile parts. In this study, we considered the influence of quenching temperature and cooling rate for specimens fabricated by vacuum induction furnace. Directly quenched micro-alloyed steel for hot forging can be controlled according to its micro structure and the heat-treatment process. Low carbon steel, as well as alloying elements for improvement of strength and toughness, was used to obtain optimized conditions. After hot forging at $1,200^{\circ}C$, the ideal mechanical properties (tensile strength ${\geq}$ 1,000 MPa, Charpy impact value ${\geq}\;100\;J/cm^2$) can be achieved by using optimized conditions (quenching temperature : 925 to $1,050^{\circ}C$, cooling rate : ${\geq}\;5^{\circ}C/sec$). The difference of impact value according to cooling rate can be influenced by the microstructure. A fine lath martensite micro structure is formed at a cooling rate of over $5^{\circ}C/sec$. On the other hand, the second phase of the M-A constituent microstructure is the cause of crack initiation under the cooling rate of $5^{\circ}C/sec$.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.1
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• pp.21-26
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• 2000

This study deals with effects of heat-treatment on the fatigue strength of SNC815 spur gears. The test gears are heat-treated by two different treatments. After carburization, one group of the test gears is quenched directly, while the other group is fumace cooled, reheated then quenched. The fatigue test at a constant stress amplitude is performed by using an electrohydraulic servo-controlled pulsating tester. The S-N curves are obtained and illustrated. By comparing the estimated strength with the experimental results, the validity of the previous experimental formula, presented by the author for estimating the fatigue strength of carburized gears, was discussed on these tested gears.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.431-434
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• 2008

In the present study, direct quenching of alloyed steel after hot forging was simulated using commercial finite element program, $FORGE^{TM}$. A typical heat treatment of alloyed steels consists of quenching for hard martensite and subsequent tempering for toughness. In the practice, forgings which cool down to room temperature are heated to temperature of austenite regime. As investigated in the present study, direct quenching of hot forged stock would be beneficial in terms of energy saving. This process has already been propose and termed as ausforging or forged hardening. However, it is well known that quenching temperature would be the most critical factor to control heat treated forging properties. And it is very difficult to control quenching temperature when forged stock gets directly quenched after forging. In this study, we have calculated final forging temperature of stock. Also, quenching simulation was conducted using a series of material parameter which were also calculated using JMATpro, a commercial program for physical properties of materials.

• Korean Journal of Materials Research
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• v.7 no.11
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• pp.999-1006
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• 1997

0.14wt.%C-0.82wt.%Mn-0.20wt, %Si-0.10wt.%V-0.03wt.%Nb의 조성을 갖는 직접 소입강에 몰리브데늄을 각각 0.30wt.%, 0.58wt.% 첨가하여 기계적 성질을 조사하고 투과 전자 현미경을 이용하여 각각의 미세 조직을 관찰하여 석출물을 분석하였다. 직접 소입시의 석출물은 M$_{2}$C, MC의 비평형 상태의 석출물이 생성되었고 석출물들은 마르텐사이트 래스내의 침상형탄화물, 구형의 M$_{2}$C탄화물, 직사각형 형태의 MC탄화물이 관찰되었다. 유냉시에는 래스내의 침상형 탄화물만 관찰되었으며 수냉시에는 M$_{2}$C 탄화물이 관찰되었다. 0.58wt.%의 몰리브데늄의 첨가된 강에서는 MoN이 관찰되었으며, 이 강의경우 강도의 손실 없이 인성이 증가하는 경향을 나타내었다.

• Bulletin of the Korean Chemical Society
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• v.35 no.9
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• pp.2749-2752
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• 2014

Recent studies have shown that single-stranded DNA adsorbed onto graphene oxide is protected from DNase I cleavage. However, double-stranded DNA bound to graphene oxide and could be digested by DNase I. To elucidate whether single-stranded DNA is protect from DNase I in the presence of graphene oxide, this study conducted DNase I digestion using single-stranded DNA and single-stranded DNA containing the duplex region in the presence of graphene oxide. Addition of DNase I resulted in restoration of the fluorescence emission that had been quenched when DNA was adsorbed to graphene oxide. It indicates that DNase I cleaved the adsorbed single-stranded DNA onto graphene oxide, which was sufficient for the detection of DNase I activity.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.191-191
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• 2012

InP quantum dot (QD) - organosilicon nanocomposites were synthesized and their photoluminescence quenching was mainly investigated because of their applicability to white LEDs (light emitting diodes). The as-synthesized InP QDs which were capped with myristic acid (MA) were incompatible with typical silicone encapsulants. Post ligand exchange the MA with a new ligand, 3-aminopropyldimethylsilane (APDMS), resulted in soluble InP QDs bearing Si-H groups on their surface (InP-APDMS) which allow embedding the QDs into vinyl-functionalized silicones through direct chemical bonding, overcoming the phase separation problem. However, the ligand exchange from MA to APDMS caused a significant decrease in the photoluminescent efficiency which is interpreted by ligand induced surface corrosion relying on theoretical calculations. The InP-APDMS QDs were cross-linked by 1,4-divinyltetramethylsilylethane (DVMSE) molecules via hydrosilylation reaction. As the InP-organosilicon nanocomposite grew, its UV-vis absorbance was increased and at the same time, the PL spectrum was red-shifted and, very interestingly, the PL was quenched gradually. Three PL quenching mechanisms are regarded as strong candidates for the PL quenching of the QD nano-composites, namely the scattering effect, Forster resonance energy transfer (FRET) and cross-linker tension preventing the QD's surface relaxation.