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준안정 오스테나이트계 Fe-18Cr-10Mn-N 합금의 연성-취성 천이 거동에 미치는 Cu와 Ni의 영향
황병철,Hwang, Byoungchul 한국재료학회 2013 한국재료학회지 Vol.23 No.7
The influence of Cu and Ni on the ductile-brittle transition behavior of metastable austenitic Fe-18Cr-10Mn-N alloys with N contents below 0.5 wt.% was investigated in terms of austenite stability and microstructure. All the metastable austenitic Fe-18Cr-10Mn-N alloys exhibited a ductile-brittle transition behavior by unusual low-temperature brittle fracture, irrespective of Cu and/or Ni addition, and deformation-induced martensitic transformation occasionally occurred during Charpy impact testing at lower temperatures due to reduced austenite stability resulting from insufficient N content. The formation of deformation-induced martensite substantially increased the ductile-brittle transition temperature(DBTT) by deteriorating low-temperature toughness because the martensite was more brittle than the parent austenite phase beyond the energy absorbed during transformation, and its volume fraction was too small. On the other hand, the Cu addition to the metastable austenitic Fe-18Cr-10Mn-N alloy increased DBTT because the presence of ${\delta}$-ferrite had a negative effect on low-temperature toughness. However, the combined addition of Cu and Ni to the metastable austenitic Fe-18Cr-10Mn-N alloy decreased DBTT, compared to the sole addtion of Ni or Cu. This could be explained by the fact that the combined addition of Cu and Ni largely enhanced austenite stability, and suppressed the formation of deformation-induced martensite and ${\delta}$-ferrite in conjunction with the beneficial effect of Cu which may increase stacking fault energy, so that it allows cross-slip to occur and thus reduces the planarity of the deformation mechanism.
지방분해에 따른 혐기성 소화조 메탄가스 함량 및 미생물 군집 변화
황병철,한규성,이준엽,황석환 한국폐기물자원순환학회 2014 젊은 연구자 학술연구발표회 Vol.13 No.0
혐기성 소화의 최종 산물인 메탄 가스는 유기물이 혐기 미생물에 의해서 분해되는 과정을 거쳐 발생한다. 메탄 가스는 여러 장소에서 에너지원으로 사용되므로, 높은 함량의 메탄 가스를 얻는다면 별도의 정제과정이 필요 없어 경제적이고 편리할 것이다. 따라서 본 연구에서는 높은 함량의 메탄가스를 얻기 위한 기초연구로 메탄 순도와 연관관계가 있는 변수를 찾아내고자 하였다. 실규모 혐기소화조의 물리화학적 측정항목과 미생물, 그리고 메탄 순도간의 상관관계를 살펴보았을 때, 전체 소화된 기질의 지방 비율이 높을수록 높은 메탄 순도가 나타났으며, 그 때 수소이용성 메탄균 (Hydrogenotrophic methanogen)이 아세트산 이용성 메탄균 (Aceticlastic methanogen) 보다 우점 하는 것을 확인하였다. 지방이 분해되어 메탄이 되는 과정에서 어떤 중간과정이 메탄 순도 향상에 영향을 미치는 지 확인하기 위하여 실험실 규모 실험을 수행하였으며, 그 결과 기질 내 지방이 많을수록 수소가스 발생량이 증가하고, 이는 베타 산화과정에 의해서 지방이 탄소수가 많은 지방산으로 분해되면서 생성되는 것으로 밝혀졌다.
황병철 한국수자원학회 2004 한국수자원학회논문집 Vol.37 No.4
댐(dam)은 물의 흐름을 조절하고, 저장한 물을 활용하기 위해 시내나 강, 혹은 강 하구를 가로질러 건설한 둑을 의미하며, barrage라는 표현으로 사용되기도 한다. 우리말로는 제언, 또는 보, 언막 이라는 용어가 쓰이는데 보나 언막이는 논맡에 물을 대기 위해서 하천에 둑을 방아 만든 저수시설을 의미하므로 용어의 의미나 규모에 있어서 댐보다는 작은 것을 의미하는 것으로 통용되고 있다.(중략)
황병철,Hwang, Byoungchul 한국재료학회 2014 한국재료학회지 Vol.24 No.9
The effect of tungsten (W) addition on the hardenability of low-carbon boron steels was investigated using dilatometry, microstructural observations and secondary ion mass spectroscopy. The hardenability was discussed with respect to transformation behaviour aspects depending on the segregation and precipitation of boron at austenite grain boundaries. A critical cooling rate producing a hardness corresponding to 90 % martensite structure was measured from a hardness distribution plot, and was used as a criterion to estimate hardenability at faster cooling rates. In the low-carbon boron steel, the addition of 0.50 wt.% W was comparable to that of 0.20 wt.% molybdenum in terms of critical cooling rate, indicating hardenability at faster cooling rates. However, the addition of 0.50 wt.% W was not more effective than the addition of .0.20 wt.% molybdenum at slower cooling rates. The addition of 0.20 wt.% molybdenum completely suppressed the formation of eutectoid ferrite even at the slow cooling rate of $0.2^{\circ}C/s$, while the addition of 0.50 wt.% W did not, even at the cooling rate of $1.0^{\circ}C/s$. Therefore, it was found that the effect of alloying elements on the hardenability of low-carbon boron steels can be differently evaluated according to cooling rate.
저탄소 보론강의 경화능에 미치는 Nb 첨가와 오스테나이트화 온도의 영향
황병철,Hwang, Byoungchul 한국재료학회 2015 한국재료학회지 Vol.25 No.11
The present study is concerned with the influence of niobium(Nb) addition and austenitizing temperature on the hardenability of low-carbon boron steels. The steel specimens were austenitized at different temperatures and cooled with different cooling rates using dilatometry; their microstructures and hardness were analyzed to estimate the hardenability. The addition of Nb hardly affected the transformation start and finish temperatures at lower austenitizing temperatures, whereas it significantly decreased the transformation finish temperature at higher austenitizing temperatures. This could be explained by the non-equilibrium segregation mechanism of boron atoms. When the Nb-added boron steel specimens were austenitized at higher temperatures, it is possible that Nb and carbon atoms present in the austenite phase retarded the diffusion of carbon towards the austenite grain boundaries during cooling due to the formation of NbC precipitate and Nb-C clusters, thus preventing the precipitation of $M_{23}(C,B)_6$ along the austenite grain boundaries and thereby improving the hardenability of the boron steels. As a result, because it considerably decreases the transformation finish temperature and prohibits the nucleation of proeutectoid ferrite even at the slow cooling rate of $3^{\circ}C/s$, irrespective of the austenitizing temperature, the addition of 0.05 wt.% Nb had nearly the same hardenability-enhancing effect as did the addition of 0.2 wt.% Mo.