고질소 오스테나이트계 스테인리스강의 고온 석출 거동

김성준 ( Sung Joon Kim ),이태호 ( Tae Ho Lee ),오창석 ( Chang Seok Oh ),박익민 ( Ik Min Park ),방해중 ( Hae Jung Bang ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 대한금속·재료학회지 Vol.45 No.5

Time-temperature-precipitation (TTP) characteristics of high nitrogen austenitic Fe-18Cr-18Mn-2Mo-0.9N stainless steel (all in weight percent) were investigated in terms of precipitation behavior, and crystallographic features of the second phases. The precipitation reactions can be categorized into three stages, i.e. (i) high temperature region (above 950℃): mainly coarse grain boundary (intergranular) Cr2N; (ii) nose temperature region: intergranular Cr2N→cellular Cr2N→intragranular Cr2N+sigma(σ); (iii) low temperature region (below 750℃): intergranular Cr2N→cellular Cr2N→intragranular Cr2N+σ+chi(χ)+M7C3 carbide, respectively. Based on the analyses of selected area diffraction (SAD) patterns, the crystallographic features of the second phases were determined: (i) Cr2N (trigonal, P31m)-[001]y∥[1100]Cr2N,(111)y∥(0001)Cr2N; (ii)χ(b.c.c., I43m)-K-S orientation relationship; (iii) M7C3 (orthorhombic, Pnma)-[001]γ∥[101]M7C3,(111)y∥(131)M7c3.

Construction of OH sites within MIL-101(Cr)-NH2 framework for enhanced CO2 adsorption and CO2/N2 selectivity

The Ky Vo,Pham Van Vu,Van Cuong Nguyen,김진수 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.8

The MIL-101(Cr)-NH2 framework was effectively modified by 2,5-dihydroxyterephthalic acid ((HO)2BDC) guest molecules to obtain (HO)2BDC-incorporated MIL-101(Cr)-NH2 adsorbent, namely (HO)2BDC@CrN. The CO2- temperature programmed-desorption (TPD) analysis indicated that the incorporation of (HO)2BDC into the MIL- 101(Cr)-NH2 framework generated new OH sites besides unsaturated Cr- metal sites and NH2 sites. The formed OH sites improved CO2 adsorption and separation on the prepared adsorbent. The highest CO2 uptake capacity of ~3.58mmol g1 obtained over the novel (HO)2BDC@CrN adsorbent was higher 40% than that of the parent MOF, and also surpasses that of other previously reported adsorbents, including activated carbon, nitrogen-doped hollow carbon, zeolite, ZIF-68, MOF-5, ZIF-8, UiO-66(Zr), and MIL-100(Cr). The highest ideal adsorbed solution theory (IAST) CO2/ N2 selectivity of ~67 was obtained over the (HO)2BDC@CrN adsorbent at 100 kPa. The achieved selectivity was six times greater than that of pure MIL-101(Cr)-NH2. In addition, the synthesized (HO)2BDC@CrN adsorbent displayed good regenerability after six consecutive adsorption-desorption cycles.

고질소 오스테나이트계 스테인리스강에서 Cr2N 석출상의 결정학적 특성 (5): 5. Cr2N 규칙격자에 대한 중성자 회절 분석

이태호 ( Tae Ho Lee ),김성준 ( Sung Joon Kim ),신은주 ( Eun Joo Shin ),고목절웅 ( Setsuo Takakj ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 대한금속·재료학회지 Vol.44 No.8

In the fifth part of this study, the ordered structure of Cr2N precipitate was investigated utilizing high-resolution neutron powder diffractometry (HRPD). Based on the Rietveld refinement of neutron diffraction patterns, the ordered Cr2N superstructure was confirmed to be an ordered h.c.p. or trigonal structure (space group: P(-)3 1m) with lattice parameter of a = 4.800 and c = 4.472 Å, as suggested in our previous TEM studies (part Ⅱ ~ Part Ⅳ). Even in perfect ordered state, a partial disordering of nitrogen atoms along caxis was detected, and the occupancies of nitrogen atoms in four different crystallographic position (l(a), 1(b), 2(d) and 2(c) Wyckoff sites) were determined to be 1.00(5), 0.0, 0.74(9) and 0.12(3), respectively. The accurate position of metal atoms was specified to be x = 0.346(8), y = 0 and z = 0.244(6), corresponding to deviation from ideal positions (x = 0.333, y = 0 and z = 0.250). This had a drastic effect on the scattering intensities of (11/33(0)) -type superlattice reflection, whereas the other two types of superlattice reflections were not significantly affected by deviation of metal atoms. The comparison between ideal and measured crystal structure of Cr2N was discussed using computer simulation of selected area diffraction (SAD) patterns.

Electrical Wire Explosion of Cr-Coated Ti Wire in N₂ Gas

Kim, Wonbaek,Lee, Sujeong,Suh, Chang-yul,Cho, Sung-wook,Ryu, Taegong,Park, Je-shin,Shon, In-Jin The Japan Institute of Metals 2010 MATERIALS TRANSACTIONS Vol.51 No.11

<P>Cr-coated Ti wire was electrically exploded in N<SUB>2</SUB> gas. The diameter of Ti wire was 0.289 mm and the thickness of Cr coating was 0.033 mm, which corresponds to the average composition of about 25 at% Cr. X-ray diffraction and FE-TEM study revealed that the explosion products consisted of cube-shaped TiN, sphere-shaped Cr<SUB>2</SUB>N, and clusters of extremely fine particles. The average particle size of TiN and Cr<SUB>2</SUB>N was about 35 and 38 nanometers, respectively. The size of the fine particles was small as a few nanometers and clustered heavily. Therefore, it was not possible to examine individually. The particles contained about 28 at% Cr. In some part of the high resolution TEM image, cubic structure could be recognized. The lattice parameter of the particles calculated assuming cubic structure was smaller than TiN and larger than CrN. As a result, it was concluded that the fine particles are (Ti,Cr)N.</P>

Evaluation of TiO2/V2O5 and N,F-doped-TiO2/V2O5 nanocomposite photocatalysts toward reduction of Cr(VI) and oxidation reactions by OH radicals

A. Giannakas,F. Bairamis,I. Papakostas,T. Zerva,I. Konstantinou 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.65 No.-

V2O5/TiO2 photocatalysts, with V2O5 particles supported on TiO2 (TV), N-TiO2 (NTV) and N/F-TiO2 (NFTV), were prepared with 5% wt. V2O5 loading and 450, 550 °C as calcination temperatures. XRD analysis showed the formation of anatase TiO2 and very small peaks of V2O5. DRS UV–vis spectra showed that V2O5 coupling extended the absorption edge into the visible light region. Photocatalysts calcined at 450 °C exhibited higher rates of Cr(VI) reduction and OH radical photogeneration than photocatalysts calcined at 550 °C. For catalysts at 450 °C, photocatalytic reduction of Cr(VI) follows the trend ΤV450 > ΝΤV450 > ΝFTV450 while the OH generation followed the reverse trend.

Modelling of Cr₂N Age-precipitation in High Nitrogen Stainless Steels by Neural Networks

Reddy, N. S.,Dzhebyan, I.,Lee, Jae Sang,Koo, Yang Mo The Iron and Steel Institute of Japan 2010 ISIJ international Vol.50 No.2

<P>It is very important to study the incubation time of alloys as it has direct relation to precipitation kinetics and affects morphology of structure. In spite of many efforts of scientists to develop methods to find incubation time, it is still difficult to measure experimentally. In addition, there is need to develop an approach to analyze existing data for many steels. On the other hand, high nitrogen steels have received a lot of attention for their unique properties, however, there is no clear model developed to predict its precipitation kinetics. In present work, Cr<SUB>2</SUB>N age-precipitation in high nitrogen austenitic steels is simulated using neural network (NN) analysis. The feed forward neural network with a back propagation algorithm was built to obtain the constitutive relation of Cr<SUB>2</SUB>N age precipitation with alloying elements and aging temperature. The simulated results show that the NN model can correctly reproduce the precipitation behavior of the steel. An analysis of model predictions and experimental data is presented.</P>

Enhanced photoactivity of N-doped TiO2 for Cr(VI) removal: Influencing factors and mechanism

Shu Qin Wang,Wen Bo Liu,Peng Fu,Wei Liang Cheng 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.5

To further enhance the photoactivity of virgin TiO2, we prepared N-doped TiO2 (N-TiO2) by sol-gel method and used it to remove Cr(VI) ions from water under visible light. The catalysts were characterized by TEM, XRD, BET and UV-vis techniques. Better crystalline structure, larger specific surface area and decreased band-gap width were obtained after the insertion of N atoms into TiO2 lattice. Several influencing factors were also investigated. The removal efficiency of Cr(VI) increases with the decrease of initial Cr(VI) concentration or the increase of catalyst dosage. Addition of glucose or some inorganic ions (Mg2+, Al3+) can promote the photoreduction process by improving the quantum efficiency. The kinetics and mechanism were discussed as well.

Deposition of (Ti,Cr,Zr)N-MoS₂ Thin Films by D.C. Magnetron Sputtering

Sun Kyu Kim,Pham Van Vinh 한국표면공학회 2006 한국표면공학회지 Vol.39 No.6

As technology advances, there is a demand for development of hard solid lubricant coating. (Ti,Cr,Zr)N-MoS₂ films were deposited on AISI H13 tool steel substrate by co-deposition of MoS₂ with (Ti,Cr,Zr)N using a D.C. magnetron sputtering process. The influence of the N2/Ar gas ratio, the amount of MoS₂ in the films and the bias voltage on the mechanical and structural properties of the films were investigated. The highest hardness level was observed at the N₂/Ar gas ratio of 0.3. Hardness of the films did not change much with the increase of the MoS₂ content in the films. As the substrate bias potential was increased, hardness level of the film reached maximum at ?150 V. Surface morphology of these films indicated that high hardness was attributed to the fine dome structure

Hot working behavior of a nitrogen-alloyed Fe-18Mn-18Cr-N austenitic stainless steel

Moon, J.,Lee, T.H.,Shin, J.H.,Lee, J.W. Elsevier Sequoia 2014 Materials science & engineering. properties, micro Vol.594 No.-

The hot workability of a nitrogen-alloyed Fe-18Mn-18Cr-N austenitic stainless steel was investigated through hot compression tests using a Gleeble simulator in a temperature range of 700-1100<SUP>o</SUP>C and at strain rates of 0.01-5s<SUP>-1</SUP>. From stress(σ)-strain(ε) curves obtained in the hot compression tests, a processing map was established to estimate the hot workability, based on the dynamic material model (DMM). The processing map predicted that the optimum hot working regimes are in the temperature range from 1050<SUP>o</SUP>C to 1100<SUP>o</SUP>C at strain rate of 0.01s<SUP>-1</SUP>. After the hot compression tests, intergranular cracking arose under most conditions, except for the optimum hot working condition predicted by the processing map. This study discusses the cause of the intergranular cracking in terms of the precipitation of intergranular Cr<SUB>2</SUB>N particles. In addition, hot ductility tests were carried out for a better understanding of the decrease in the hot workability, and a significant loss of ductility was observed with intergranular Cr<SUB>2</SUB>N precipitation.

질소 보호 가스 첨가가 하이퍼 듀플렉스 스테인리스 밀봉용접재의 마모부식 저항성에 미치는 영향

김혜진 ( Hye Jin Kim ),전순혁 ( Soon Hyeok Jeon ),김순태 ( Soon Tae Kim ),이인성 ( In Sung Lee ),박용수 ( Yong Soo Park ) 한국부식방식학회(구 한국부식학회) 2014 Corrosion Science and Technology Vol.13 No.2

Duplex stainless steels with nearly equal fraction of the ferrite(α) phase and austenite(γ) phase have been increasingly used for various applications such as power plants, desalination facilities due to their high resistance to corrosion, good weldability, and excellent mechanical properties. Hyper duplex stainless steel (HDSS) is defined as the future duplex stainless steel with a pitting resistance equivalent (PRE= wt.%Cr+3.3(wt.%Mo+0.5wt.%W)+30wt.%N) of above 50. However, when HDSS is welded with gas tungsten arc (GTA), incorporation of nitrogen in the Ar shielding gas are very important because the volume fraction of α-phase and γ-phase is changed and harmful secondary phases can be formed in the welded zone. In other words, the balance of corrosion resistance between two phases and reduction of Cr2N are the key points of this study. The primary results of this study are as follows. The addition of N2 to the Ar shielding gas provides phase balance under weld-cooling conditions and increases the transformation temperature of the α-phase to γ-phase, increasing the fraction of γ-phase as well as decreasing the precipitation of Cr2N. In the anodic polarization test, the addition of nitrogen gas in the Ar shielding gas improved values of the electrochemical parameters, compared to the Pure Ar. Also, in the erosion-corrosion test, the HDSS welded with shielding gas containing N2 decreased the weight loss, compared to HDSS welded with the Ar pure gas. This result showed the resistance of erosion-corrosion was increased due to increasing the fraction of γ-phase and the stability of passive film according to the addition N2 gas to the Ar shielding gas. As a result, the addition of nitrogen gas to the shielding gas improved the resistance of erosion-corrosion.