• Proceedings of the Materials Research Society of Korea Conference
• /
• 2009.11a
• /
• pp.36.1-36.1
• /
• 2009

최근 각종 환경 규제와 자동차의 안전성 증대를 위해 고장력 자동차 강판의 수요가 증대되고 있다. 차량의 많은 강판 비중을 차지하는 외판재의경우 안전성과 경량화를 위해서는 고장력강판이 유리하지만, 일반적으로 강도가 증가함에 따라 성형성이 감소되어 자동차 생산에 커다란 문제를 야기 시킬 수 있다. 따라서 본 연구에서는 자동차용 고장력강판의 집합조직 제어를 통해 강도의 변화없이 성형성을 증대시키고자, 고장력 자동차용 강판의 집합조직의 특징을 알아보는데 목적이 있다. 강판은 $\gamma$-fiber (ND//[111]) 조직이 증가할수록 성형성의 증대를 가져올 수 있으며, 이는 압연과 열처리등의 공정 조건에 의해 제어된다. 자동차용 고강도강판의 열처리는 연속소둔방식으로 행하였으며, XRD와 EBSD 등을 통한 집합조직과 기계적인 특성을 분석하였다.

• Korean Journal of Materials Research
• /
• v.6 no.9
• /
• pp.871-877
• /
• 1996

가스터빈용 단결정 주조 블레이드는 기포 및 Freckle등과 같은 주조결함이 없어야 하며, 수지상, ${\gamma}$'크기와 모양에 따라 화학조성이 다르며, 기지와 공정조직을 각각 2영역 및 3영역으로 분류할 수 있었다. 또한, Ti는 첨가원소호서 조직제어에 매우 중요한 역할을 하였다.

• Journal of the Korean Society for Heat Treatment
• /
• v.32 no.5
• /
• pp.195-200
• /
• 2019

For expanding the applications and workability of TiAl alloy, elongation is very important property. Fine microstructure is needed for elongation and physical properties of TiAl alloys. In this study, The effects of cyclic heat treatment process for fine microstructure of Ti-46Al-Nb-W-Cr-Si-C alloy, which was made by VAR (vacuum arc remelting) and VIM(vacuum induction melting) centrifugal casting process, was investigated. Cycle heat treatment process was very effective for recrystallization of this TiAl system, which has microstructure size of $50{\sim}100{\mu}m$ through pre-heat treatment, cyclic heat treatment in ${\alpha}+{\gamma}$ phase region and solution heat treatment respectively. Refined grain size was finally confirmed by photos of optical microscope and scanning electron microscope.

• Journal of the Korean Society for Heat Treatment
• /
• v.32 no.5
• /
• pp.201-211
• /
• 2019

Low carbon steel (S20C steel) and SPCC steel sheet have been austenitic nitrided at $700^{\circ}C$ in a closed pit type furnace by changing the flow rate of ammonia gas and heat treating time. When the flow rate of ammonia gas was low, the concentration of residual ammonia appeared low and the hardness value of transformed surface layer was high. The depth of the surface layer, however, was shallow. With increasing the concentration of residual ammonia by raising up the ammonia gas flow, both the depth of the surface layer and the pore depth increased, while the maximum hardness of the surface layer decreased. By introducing a large amount of ammonia gas in a short time, a deep surface layer with minimal pores on the outermost surface was obtained. In this experiment, while maintaining 10~12% of residual ammonia, the flow rate of inlet ammonia gas, 7 liter/min, was introduced at $700^{\circ}C$ for 1 hour. In this condition, the thickness of the surface layer without pores appeared about $60{\mu}m$ in S20C steel and $30{\mu}m$ in SPCC steel plate. Injecting additional methane gas (carburizing gas) to this condition played a deteriorating effect due to promoting the formation of vertical pores in the surface layer. For $1^{st}$ transformed surface layer for S20C steel, maintaining 10~12% residual ammonia condition via austenitic nitriding process resulted in ${\varepsilon}$ phase with relatively high nitrogen concentration (just below 4.23 wt.%N) among the mixed phases of ${\varepsilon}+{\gamma}$. The ${\varepsilon}$ phase was formed a specific orientation perpendicular to the surface. For $2^{nd}$ transformed layer for S20C steel, ${\gamma}$ phase was rather dominant (just above 2.63 wt.%N). For SPCC steel sheet, there appeared three phases, ${\gamma}$, ${\alpha}(M)$ and weak ${\varepsilon}$ phase. The nitrogen concentration would be approximately 2.6 wt.% in these phases condition.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2007.04a
• /
• pp.118-119
• /
• 2007

오스테나이트계 스테인리스 AISI304L강을 저온 플라즈마 분위기에서 표면에 C와 N을 주입하면 내식성의 저하 없이 표면경도를 증가 시킬 수 있다. 이 공정에서 온도에 따른 영향을 조사하기위해 $380^{\circ}C{\sim}430^{\circ}C$의 온도 범위에서 20시간 동안 실시하였다. 경화층의 두께는 $7{\sim}16\;{\mu}m$정도였으며, N의 농도가 높은 영역과 C의 농도가 높은 영역으로 나뉘어 형성되었고, N이 풍부한 영역이 표면층에 형성되고 그 아래에 C의 농도 높은 영역이 형성되었다. 표면층은 질소에 의해 확장된 오스테나이트(${\gamma}_N$)상을 가지며 고온에서 처리한 경우 석출물이 형성되었다. 표면경도는 약 $900\;HV_{0.01}{\sim}1200\;HV_{0.01}$로 측정되었다.

• Microbiology and Biotechnology Letters
• /
• v.38 no.4
• /
• pp.420-427
• /
• 2010

A process for manufacturing virally-safe bovine amniotic membrane(BAM) has been developed for biological dressing. BAM was harvested from a healthy bovine placenta, and then the epithelium was removed. The remaining stromal layer was consecutively disinfected with 70% ethanol and 0.05% sodium hypochlorite. The stromal layer was incubated in a decellularization solution containing 0.25%(w/v) trypsin to remove the cellular components. The resulting acelluar BAM was lyophilized to preserve its biochemical and structural integrity. The BAM was packed and exposed to 25 kGy of gamma irradiation for sterilization purpose. Histological, electron microscopical, and biochemical observations showed that the acellualr BAM had intact structural integrity of three dimensional collagen fibers and contained several growth factors, accelerating wound healing, such as EGF (Epidermal growth factor), KGF (Keratinocyte growth factor), and FGF (Fibroblast growth factor). Bovine herpes virus (BHV), bovine viral diarrhoea virus (BVDV), bovine parainfluenza virus type 3 (BPIV-3), and bovine parvovirus (BPV) were chosen as the biological indicators for validation of viral safety of the acellular BAM. Samples from relevant stages of the production process were spiked with each virus and subjected to viral inactivation processes. Viruses were recovered from the samples and then titrated immediately. All the viruses tested were completely inactivated to undetectable levels within 1 h of 70% ethanol treatment. Enveloped viruses such as BHV, BVDV, and BPIV-3 were more effectively inactivated than BPV by 0.05% sodium hypochlorite treatment. BHV, BVDV, and BPIV-3 were completely inactivated to undetectable levels by 25 kGy of gamma irradiation. Also BPV was effectively inactivated by 25 kGy of gamma irradiation. The cumulative log reduction factors of BHV, BVDV, BPIV-3, and BPV were ${\geq}$13.30, ${\geq}$14.32, ${\geq}$15.22, and ${\geq}$7.57, respectively. These results indicate that the production process for acelluar BAM has a sufficient virus-reducing capacity to achieve a high margin of the virus safety.

• Journal of Radiation Protection and Research
• /
• v.4 no.1
• /
• pp.14-20
• /
• 1979

For accurate and easily shielding irregular shaped organ, its minimized penumbra region and a low melting point alloy 'Lead Y' and synchronizing instrument have been developed. The 'Lead Y' is the quaternary eutectic alloy and it is composed of Lead 30.0% Tin 11.5% Bismuth 48 5% Cadmium 10.0% The density of its at $22^{\circ}C$ is $9.8g/cm^3$ and the melting temperature has $40^{\circ}C\;to\;68^{\circ}C$. The thickness of 'Lead Y' for perfect shielding of Co-60 gamma ray and LINAC 10MeV x-ray is 6cm and 7cm respectively. The 'Lead Y' shielding block is casted directly on the styrofoam from which is cut with hot wire of synchronizer device. The special features and advantages of the Lead Y shielding block could be summarized as follows; 1. The shielding block for radiotherapy is rapidly processed only with boiling water and styrofoam. 2. It is not injure one's health and not danger of a fire, because of not generating of any metals vapor and evil smelling. 3. It is very effective to minimize secondary penumbra for the protection of healthy tissue from unnecessary ionizing radiation regardless of the magnification source to skin distance. 4. The HVL of the Lead Y is 1.2cm for Co-60 gamma ray and it's shielding effect is almost same as the pure lead block. 5. The hardness of Lead Y is 1.5 times higher than lead block. 6. It's reavailability is higher than lead block and then one block of Lead Y is reavailable about 30 to 40 times. 7. It is usefull for shielding of x-ray, gamma ray, beta-ray, electron and neutron radiation. 8. The materials for Lead Y are easy to acquire with reasonable price and tractable.

• Journal of Powder Materials
• /
• v.26 no.5
• /
• pp.421-431
• /
• 2019

In this study, the formation, microstructure, and wear properties of Colmonoy 88 (Ni-17W-15Cr-3B-4Si wt.%) + Stellite 1 (Co-32Cr-17W wt.%) coating layers fabricated by high-velocity oxygen fuel (HVOF) spraying are investigated. Colmonoy 88 and Stellite 1 powders were mixed at a ratio of 1:0 and 5:5 vol.%. HVOF sprayed self-fluxing composite coating layers were fabricated using the mixed powder feedstocks. The microstructures and wear properties of the composite coating layers are controlled via a high-frequency heat treatment. The two coating layers are composed of ${\gamma}-Ni$, $Ni_3B$, $W_2B$, and $Cr_{23}C_6$ phases. Co peaks are detected after the addition of Stellite 1 powder. Moreover, the WCrB2 hard phase is detected in all coating layers after the high-frequency heat treatment. Porosities were changed from 0.44% (Colmonoy 88) to 3.89% (Colmonoy 88 + ST#1) as the content of Stellite 1 powder increased. And porosity is denoted as 0.3% or less by inducing high-frequency heat treatment. The wear results confirm that the wear property significantly improves after the high-frequency heat treatment, because of the presence of well-controlled defects in the coating layers. The wear surfaces of the coated layers are observed and a wear mechanism for the Ni-based self-fluxing composite coating layers is proposed.

• Food Science and Preservation
• /
• v.11 no.3
• /
• pp.394-399
• /
• 2004

The effects of gamma irradiation to improve the hygienic quality and microbiological shelf stability of whole baked egg were investigated by comparison with autoclaving process. The contamination levels of coliform, total aerobic bacteria and fungal group in a fresh egg were 10$^{5}$ CFU/g, 10$^{2}$ CFU/g and 10$^{1}$ CFU/g, respectively. After baking process, total aerobic bacteria and fungi were not exceeded to 10$^{1}$ CFU/g. Also, coliform was not detected under the aseptic process. However, cell counts of the baked egg after packaging reached to 10$^{4}$ CFU/g of total aerobic bacteria, 10$^{1}$ CFU/g of coliform, and 10$^{2}$ CFU/g of fungi. Therefore, it was assumed that microbial contamination of baked and packaged egg was mainly originated from an environmental uptake during packaging process. Microbiological shelf stability of the non sterilized control was about a week. Whereas, the baked eggs irradiated at more than 5 kGy were stable over 12 weeks at ambient condition as like those being autoclaved. Analytical texture profIle was stable within 10 kGy, but it became hardened in the sample treated with autoclaving. About 67$\%$ of panelists identified a sensory difference between non-irradiated and 10 kGy-irradiated sample. The baked egg irradiated at 10 kGy and autoclaved had lower acceptability than the control or samples irradiated lower than 5 kGy. Therefore, it was considered that optimal irradiation dose for radiation sterilization of baked and packaged egg was 5 kGy. At that point, it was recommended that appropriate microbiological shelf-life was 12 weeks at ambient condition.

• Applied Biological Chemistry
• /
• v.29 no.3
• /
• pp.288-293
• /
• 1986

The washed fresh ginsengs packed with air, vaccum and nitrogen gas were irradiated at the levels of 1,2 and 3kGy gamma radiation and then stored at $4{\sim}5^{\circ}C$ for 90days to investigate the effects of gamma radiation on microbial inactivation, eelworm disinfestation and physicochemical changes. After a 90 day storage, $2{\sim}3kGy$ irradiated groups showed 20% of weight loss and 10% of rot while non-irradiated group 100% and 20% or more, respectively. Also the irradiated groups showed somewhat lower values of specific gravity, color density and hardness immediately after irradiation, thereafter higher value of them with storage time than those of non-irradiated group. The irradiation increased the yields of ginseng extract and crude saponins but no effects on the proximate composition and TLC and HPLC patterns of saponin. The food-borne microorganisms decreased in viable cell counts by $2{\sim}3$ log cycles with $2{\sim}3kGy$ radiation and the eelworms were completely disinfested with 1 kGy radiation.