• Corrosion Science and Technology
• /
• 제23권2호
• /
• pp.104-112
• /
• 2024

Al-Zn-Mg-Si alloy coatings have been developed to inhibit corrosion of cold rolled steel sheets, and an understanding of the alloy system helps prevent coating defects. We used a Bridgman furnace to characterise the nature and formation mechanisms of the phases present in the quaternary system with 0.4 wt% Fe. In the directional solidification experiments we imposed steep temperature gradients and varied the pull rate. After the samples were quenched in the furnace, detailed characterization of the samples was carried out by electron microscopy (SEM/EDS). From the dT/dt vs T plots of the cooling curves of the alloys, the solidification path was determined to be $Liquid{\longrightarrow[80]^{544-558}}{\alpha}-Al{\longrightarrow[80]^{453-459}}Al/Mg_2Si{\longrightarrow[80]^{371-374}}Al/Zn{\longrightarrow[80]^{331-333}}Zn/mgZn_2$. The formation mechanisms of the Mg and Zn containing phases and their morphology was discussed together with the effects of the cooling rate. Key findings include the lengthening of the mushy zone in directionally solidified samples remelted against a positive temperature gradient, as well as an enrichening of the α-Al phase by Zn through remelting. Mg₂Si and other Si based phases were observed to adopt a much finer faceted microstructure in favour of a script-like microstructure when exposed to the higher cooling rate of coolant quenching.

• Advances in materials Research
• /
• 제13권3호
• /
• pp.183-194
• /
• 2024

D3 tools steel and 440C stainless steel (SS) are normally being employed for application such as knife blade and cutting tools. These steels are iron alloys which have high carbon and high chromium content. In this study, lab work focused on the microstructural and corrosion behavior of D3 tools steel and 440C SS after went through heat treatment processes. Heat treatments for both steels were started with normalizing at 1020 ℃, continue with hardening at 1000 ℃followed by oil quenching. Cryogenic treatment was carried out in liquid nitrogen for 24 hours. The addition of cryogenic heat treatment is believed to increase the hardness and corrosion resistance for steels. Both samples were then tempered at two different tempering temperatures, 160 ℃ and 426 ℃. For corrosion test, the samples were immersed in NaCl solution for 30 days to study the corrosion behavior of D3 tool steel and 440C SS after heat treatment. The mechanical properties of these steels have been investigated using Rockwell hardness machine before heat treatment, after heat treatment (before corrosion) and after corrosion test. Microstructure observation of samples was carried out by scanning electron microscopy. The corrosion rate of these steels was calculated after the corrosion test completed. From the results, the highest hardness is observed for D3 tool steel which tempered at 160 ℃(54.1 HRC). In terms of microstructural analysis, primary carbide and pearlite in the as-received samples transform to tempered martensite and cementite after heat treatment process. From this research, for corrosion test, heat treated 440C SS sample tempered with 426 ℃possessed the excellent corrosion resistance with corrosion rate 0.2808 mm/year.

• 대한기계학회논문집B
• /
• 제38권6호
• /
• pp.465-474
• /
• 2014

본 연구에서는 비등 열유속 분배 모델의 예측 정확성을 검증하기 위하여 수직평판 자연대류 과냉 비등에서 기화, 급랭, 및 단상대류 열전달 기구에 대한 열유속 분배 특성을 실험적으로 조사하였다. 비등 열유속의 분배를 위해 적외선 열화상 기법과 전반사 가시화 기법을 동기화하여 비등 표면의 열유속 분포와 액상-기상 분포를 동시에 측정하여 분석하는 실험을 수행하였다. 실험은 대기압 조건에서 과냉도 $10^{\circ}C$를 가지는 물을 이용하여 수행하였으며, 벽면과열도 $12^{\circ}C$ 및 평균 열유속 $283kW/m^2$ 조건에 대한 실험 결과를 분석에 활용하였다. 실험을 통해 획득된 열유속 분배 결과는 상관식을 이용한 예측 결과와 큰 차이를 보였으며, 기포이탈직경과 기포이탈 시 주변의 과열액체층이 함께 뜯겨져 나가는 효과를 고려한 기포영향인자가 차이를 만드는 주요 원인들로 파악되었다.

• Journal of Welding and Joining
• /
• 제33권5호
• /
• pp.53-60
• /
• 2015

Laser surface Melting Process is getting hardening layer that has enough depth of hardening layer as well as no defects by melting surface of substrate. This study used CW(Continuous Wave) Yb:YAG and STD11. Laser beam speed, power and beam interval are fixed at 70mm/sec, 2.8kW and 800um respectively. Hardness in the weld zone are equal to 400Hv regardless of melting zone, remelting zone overlapped by next beam and HAZ. Similarly, microstructures in all weld zone consist of dendrite structure that arm spacing is $3{\sim}4{\mu}m$, matrix is ${\gamma}$(Austenite) and dendrite boundary consists of ${\gamma}$ and $M_7C_3$ of eutectic phase. This microstructure crystallizes from liquid to ${\gamma}$ of primary crystal and residual liquid forms ${\gamma}$ and $M_7C_3$ of eutectic phase by eutectic reaction at $1266^{\circ}C$. After solidification is complete, primary crystal and eutectic phase remain at room temperature without phase transformation by quenching. On the other hand, microstructures of substrate consist of ferrite, fine $M_{23}C_6$ and coarse $M_7C_3$ that have 210Hv. Microstructures in the HAZ consist of fine $M_{23}C_6$ and coarse $M_7C_3$ like substrate. But, $M_{23}C_6$ increases and matrix was changed from ferrite to bainite that has hardness above 400Hv. Partial Melted Zone is formed between melting zone and HAZ. Partial Melted Zone near the melting zone consists of ${\gamma}$, $M_7C_3$ and martensite and Partial Melted Zone near the HAZ consists of eutectic phase around ${\gamma}$ and $M_7C_3$. Hardness is maximum 557Hv in the partial melted zone.

• Journal of Radiation Protection and Research
• /
• 제23권4호
• /
• pp.237-242
• /
• 1998

생체나 공기 등 일반 환경시료의 방사성탄소 측정을 위한 액체섬광측정기술의 최적화에 연구의 목적을 두었다 일반 환경시료의 경우 $CO_2$ 직접흡수법을 적용하였으며, 이산화탄소 흡수제 Carbosorb $E^{TM}$와 섬광용액 Permafluor $V^{TM}$기 혼합비율을 1:1로 결정하였다. 이 20 ml 혼합용액에 포화 흡수되는 이산화탄소의 양은 평균 2.35 g 이며, 포집에 소요되는 시간은 약 40 분이었다 백그라운드 계수율은 1.88±0.06 cpm 이었으며, NIST 옥살산표준시료 측정결과 계측효율은 58.8±1.4 % 이었다. 이산화탄소 흡수량에 따른 계측효율을 보정하기 위하여 소광보정곡선을 구하였다. 자연준위 시료의 경우 4시간 계측시 비방사능 측정에 따른 전반적인 오차는 95 % 신뢰도상 약 7 %이었다. 이 측정방법에 대하여 2주 동안 시료의 안정성을 조사한 결과 계측효율과 백그라운드 계수율의 안정성을 의심할 만한 현상은 발견되지 않았다.

• 한국대기환경학회지
• /
• 제3권1호
• /
• pp.27-33
• /
• 1987

삼중수소 ($^{3}H$) 에 관한 환경 및 생물학상의 연구는 1950년대 중반부터 선진국에서 수행되오고 있다. 삼중소소에 대한 잠재적 노출의 경우 통상적 처리절차는 삼중수소의 신체부하량이라고 일컬어지는 이른바 신체내에 축적된 삼중수소의 양을 결정하기 위하여 삼중수소수로서 오줌속에 포함되는 삼중수소 방사능의 생리분석이다. 전신에 있어서 삼중수소의 최대허용신체부하량은 신체조직에 대하여 약 $30{\mu}Ci/{\ell}$ 이다. 생리분석에서 오줌속에 삼중수소를 검출하는데 가장 보편적인 조사준위(照射准尉)는 최대허용신체부하량의 1/10 이다. 이러한 생리분석 연구계획을 위해서는 소광보정(消光補正) 곡선을 그리는 것이 가장 우선적이다. 이것은 검뇨용 오줌의 색깔이 일정하지 않기 때문에 필요한 것이다. 이 경우에서 소광효과는 주로 오줌시료에 의한 섬광빛의 흡수에 기인된다. 소광보정곡선으로 판단된 공식은 통계적 근거에서 최소자승법에 의하여 Y (%) = 0.771 + 1.836 ${\tmes}10^{-4}$X(count)로 얻어졌다. 여기서 Y는 섬광계수 효율로서 약 12%에서 31% 범위의 값으로 나타났다. 본 논문에서는 삼중수소의 생물학적 반감기와 신체계통적으로 분포된 삼중수소에 적용되고 있는 정체(停滯) 공식에 관한 간략한 이론에 관하여 서술된다.

• Journal of Radiation Protection and Research
• /
• 제45권3호
• /
• pp.142-146
• /
• 2020

Background: Tritium (³H) analysis in groundwater was difficult because of its low activity. Therefore, the electrolytic enrichment method was used. To improve the detection limit and for performing simple analysis, a high-volume counting vial with the available liquid scintillation counter (LSC) was investigated. Further, it was compared with a conventional 20-mL counting vial. Materials and Methods: The LSC with the electrolytic enrichment method was used ³H analysis in groundwater. A high-volume 145-mL counting vial was compared with a conventional 20-mL counting vial to determine the counting characteristics of different LSCs. Results and Discussion: When a Quantulus LSC was used, the counting window between channels 35 and 250 was used. The background count was approximately 1.86 cpm, and the counting efficiency increased from 8% to 40% depending on the mixing ratio of the volume of sample and cocktail solution. For LSC-LB7, the optimum counting window was between 1 and 4.9 keV, which was selected by the factory (Hitachi Aloka Medical Ltd., Japan) by considering quenching using a standard external gamma source. The background count of LSC-LB7 was approximately 3.60 ± 0.29 cpm when the 145-mL vial was used and 2.22 ± 0.17 cpm when the 20-mL vial was used. The minimum detectable activity (MDA) of the 20-mL vial was greater for LSC-LB7 than for Quantulus. The MDA with the 145-mL vial was improved to 0.3 Bq/L when compared with the value of 1.6 Bq/L for the 20-mL vial. Conclusion: The counting efficiency when using the 145-mL vial was 27%, whereas it was 18% when using the 20-mL vial. This difference can be attributed to the vial volume. The figure of merit (FOM) of the 145-mL vial was four times greater than that of the 20-mL vial because the volume of the former vial is approximately seven times greater than that of the latter. Further, the MDA for ³H decreased from 1.6 to 0.3 Bq/L. The counting efficiency and FOM of LSC-LB7 was slightly less than those of Quantulus when the 20-mL vial was used. The background counting rate of the Quantulus was lower than that of the LSC-LB7.