In the present study, room temperature tensile behaviors of duplex stainless steels with the low Ni content were investigated to examine the effect of nitrogen addition. For this purpose, nitrogen of 0.1~0.3 wt.% was added to the steels. The steels were cold rolled (~70 % reduction) and then annealed at 1100 C for 5 min. Both strength and ductility increased with increasing the N content. Especially, in the case of the steel containing 0.3 wt.% N, tensile strength exhibited ~1000 ㎫, and the elongation became ~50 %. Deformation of austenite in the present duplex stainless steel was dominated by transformation induced plasticity, and greatly affected the overall deformation.
본 연구는 20일 동안 TBTO 노출에 의한 참굴의 생존율 및 hemolymph 내의 무기성분과 효소활성의 변동을 조사하였다. TBTO 노출에 의한 참굴의 생존율은 실험 20일 동안 10㎍/L이하의 농도에서 90%이상을 나타냈다. 그러나 참굴의 생존율은 TBT농도가 증가함에 따라 감소하기 시작하여 실험 10일째 TBT농도 80㎍/L이상, 실험 20일째는 50㎍/L이상의 농도에서 유의한 감소가 관찰되었고, 100㎍/L에서는 실험 16일째 전 개체가 사망하였다. 참굴의 hemolymph의 calcium 농도는 10일째 대조구를 포함한 TBTO 5∼10㎍/L 농도에서 유사한 값을 나타냈으나 50㎍/L 이상의 TBTO 농도에서는 급격히 증가하여 대조구에 비해 유의한 증가가 관찰되었다. 또한 20일째 calcium 농도는 10일째 보다 전반적으로 증가하였으며, 대조구와 비교하여 20일㎍/L 이상의 농도에서 유의한 증가를 나타냈다. GPT활성은 실험 전 기간을 통해 모든 농도구에서 뚜렷한 변화를 보이지 않았다. 그러나 GOT는 실험 10일째 이상의 20㎍/L이상의 농도에서 유의한 증가를 나타냈다.
시안의 만성적 조건에서 이스라엘 잉어의 생존, 섭이 및 성장에 미치는 독성영향을 파악하기 위하여 유수식방법에 의해 6주 동안 실험을 실시하였다. 시안의 만성적 조건하에 노출시킨 이스라엘잉어의 생존율은 시안농도 $151{\mu}$ g/ $\ell$ 이상에서 유의한 감소를 나타내었고, 실험종료시 시안농도 151, $289{\mu}...
PCBs 농도 3.0㎍ L^(-1) 노출에 따른 넙치의 혈액학적 변동을 조사하기 위하여 60일간 침지실험을 실시하였다. PCBs에 노출된 넙치의 무기성분 중에 혈장 magnesium과 inorganic phosphorus는 유의적 변동이 없었으나, calcium은 대조구에 비해 유의한 감소를 보였다. 또한 유기성분 중에 total protein과 albumin은 노출 20일째부터 유의한 감소를 보여 실험 종료시까지 이러한 감소는 지속되었고, glucose는 노출 40일 이후 유의한 증가를 나타내었다. 혈장 ALP와 GPT의 활성도는 노출 20일 이후부터 대조구에 비해 유의한 증가를 나타내었고, GOT는 노출 40일 이후 유의한 증가를 나타내었다. 이상의 결과는 해양에 3.0㎍L^(-1)의 PCBs 농도가 존재할 경우 넙치의 혈액학적 변동을 야기할 수 있음을 의미한다.
산업활동의 증가로 인해 해양에 유입되는 수은 (Hg)이 저서성 연안정착 어류인 넙치, Paralichthys olivaceus 치어의 생존, 성장, 사료효율 및 산소소비에 미치는 영향을 조사하였다. 6주 동안 0~0.13mg/L의 아치사 농도에서 넙치를 사육하며 Hg 독성에 대한 영향을 조사하였다. Hg 농도와 노출기간이 증가할수록 생존육은 감소했으며 6주 후, 0.05mg/L 이상의 농도 구에서 생존율이 급격히 감소했다. 성장률과 사료효율 또한, 각각 0.028mg/L (P<0.01)와 0.05mg/L (P<0.01) 이상의 농도 구에서 현저하게 감소하였다. 산소소비율은 0.05mg/L와 0.13mg/L의 농도구에서 각각 대조 구에 비해 25(P<0.01)와 32% (P<0.01) 감소해, 유의적인 차이를 나타내었다.
이상의 결과로부터 Hg 독성은 넙치의 성장, 사료효율 및 산소소비와 같은 생리적 기능을 저해해 생존율을 감소시키는 것으로 나타났다.
This study was carried out to examine the effects of bis (tribytyltin)oxide (TBT), endocrine disrupting compounds (EDCs), on the changes of survival, growth and oxygen consumption rate in the oliver flounder, Paralichthys olivaceus. Oliver Flounders were exposed to sublethal concentration of TBT (0, 1.67, 3.20, 6.30 and 12.50㎍/L) during 6 weeks. Survival rate was decreased in a concentration and exposure period-dependent way and suddenly the reduction of more than 20% occurred at TBT concentration greater than 3.20 IlglL after exposure 6 weeb. GroWth rate and feed efficiency significantly decreased at concentration greater than 3.20 ㎍/L, Oxygen consumption rate was also decreased in a concentration-dependent way and significantly decreased to 17,48 and 67% than that of the control at the TBT concentration of 3,20, 6.32 and 12.50 ㎍/L, respectively. This study revealed that high TBT concentration (≥ 3.20 ㎍/L) reduced growth and oxygen consumption rates of the juvenile oliver flounder suggesting potential influence on the natural mortality of Paralichthys olivaceus in the coastal areas.
Experiments were carried out to examine the effects of the different levels of oxygen, ammonia and hydrogen sulfide on survival, specific growth rate (SGR) and feed conversion ratio (FCR) of juvenile shrimp, Fenneropenaeus chinensis. Survival of the shrimp exposed to the hypoxia with ≤2.5 ㎎/L dissolved oxygen for 24 days were significantly affected. SGR and FCR of the shrimp exposed to ≤3.0 ㎎/L dissolved oxygen were significantly reduced than those of shrimp reared at 6.8 ㎎/L dissolved oxygen concentration. Survival of the shrimp exposed to ≥2.0 ㎎/L of ammonia levels for 24 days was significantly affected. Moreover, compared to the control group significant decrease of SGR and FCR of the shrimp has been observed with ≥1.0 ㎎/L and ≥0.5 ㎎/L of ammonia concentrations. In case of hydrogen sulfide, ≥0.5 ㎎/L was the critical level showed its significant negative effect on survival rate of shrimp exposed for 24 days. While, the group exposed with ≥0.07 ㎎/L and ≥0.05 ㎎/L hydrogen sulfide levels had a lower SGR and FCR values than did the control group in the same stipulated time of exposure.
The effects of nitrogen addition on the strain induced martensitic transformation (SIMT) behavior of duplex stainless steel (D-STS) with the low nickel content were examined in a wide range of strain by means of cold rolling. Nitrogen of 0.1，0.2 and 0.3 wt.% was added into Fe-20Cr-5Mn-0.2Ni D-STS (in wt.%) and cold rolling was conducted up to the effective strain of ~1.45 after annealing at 1100 C for 30 min. In the as-annealed state, the austenite fraction increased with increasing the N content. Regardless of the N content, the ferrite grain size was coarser than that of austenite. The stacking fault energy of austenite of the present D-STSs inferred by the element partitioning analysis was low enough so that SIM transformation is available. Accordingly, during cold rolling, SIMT occurred in austenite with a sequential manner of austenite → e martensite → α’ martensite with increasing strain. By contrast, the deformed microstructure of ferrite was dominated by dislocation cells.
Bars of OFHC Cu with the diameter of 45 mm were processed by equal channel angular pressing up to 16 passes via route B(c), and homogeneity of their microstructures and mechanical properties was examined at every four passes which develop the equiaxed ultrafine grains. In general, overall hardness, yield strength and tensile strength increased by 3, 7, and 2 times respectively compared with those of unECAPed sample. Cross-sectional hardness exhibited a concentric distribution. Hardness was the highest at the center of bar and it decreased gradually from center to surface. After 16 passes, overall hardness decreased due to recovery and partial recrystallization. Regardless of the number of passage, yield strength and tensile strength were quite uniform at all positions, but elongation showed some degree of scattering. At 4 passes, coarse and ultrafine grains coexisted at all positions. After 4 passes, uniform equiaxed ultrafine grains were obtained at the center, while uniform elongated ultrafine grains were manifested at the upper half position. At the lower half position, grains were equiaxed but its size were inhomogeneous. It was found that inhomogeneity of grain morphology and grain size distribution at different positions are to be attributed to scattering in elongation but they did not affect strength. The present results reveal the high potential of practical application of equal channel angular pressing on fabrication of large-sized ultrafine grained bars with quite homogeneous mechanical properties.
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