Hosoya, Yoshihiro*; Matsumura, Yuta*; Tomota, Yo*; Onuki, Yusuke*; Harjo, S.
ISIJ International, 60(9), p.2097 - 2106, 2020/09
Islam, M. S.*; Otani, Kyohei; Sakairi, Masatoshi*
ISIJ International, 58(9), p.1616 - 1622, 2018/09
To elucidate the role of Zn on corrosion of coated steel, the effects of metal cations on the corrosion of carbon steel in the concentrated Cl aqueous solutions were studied by immersion tests, surface analysis and electrochemical tests. Among the examined metal cations, Zn showed the significant effect on corrosion inhibition of carbon steel in the Cl aqueous solution at high concentration. XPS analysis results elucidated that Zn can remain on the steel surface after immersed in the solutions with Zn. EIS measurements showed higher impedance in the solution with Zn than other solutions, and the results suggested that Zn reduced the defect points in the thin oxide film by forming a metal cation layer. Based on the experimental results, Zn may form a layer on the oxide film that protects the Cl attack in the solution. The findings demonstrated that the formation of Zn layer on the oxide film is one of the main reason for showing high and longtime corrosion resistance of Zn coated steel substrate.
Sato, Shigeo*; Shobu, Takahisa; Sato, Kozue*; Ogawa, Hiromi*; Wagatsuma, Kazuaki*; Kumagai, Masayoshi*; Imafuku, Muneyuki*; Tashiro, Hitoshi*; Suzuki, Shigeru*
ISIJ International, 55(7), p.1432 - 1438, 2015/07
To characterize the distribution and anisotropy of dislocations in cold-drawn pearlitic steel wires, X-ray diffraction line-profile analysis was performed using synchrotron radiation micro-beams. The plastic shear strain was generally more severe near the surface than the center of the wire, whereas the dislocation density distribution was almost constant from the center to the surface. On the other hand, the dislocation rearrangement, which evolves the dislocation cell structure, progressed closer to the surface. It was also revealed that a difference between the hardness in axial and transverse wire directions could be explained by anisotropic dislocation density. Line-profile analysis based on diffraction data at elevated temperatures was performed. Whereas the cementite recovery progressed at a constant rate, the ferrite phase recovery rate was temperature-dependent, suggesting that the ferrite phase recovery was less related to that of the cementite phase.
Hayashi, Kentaro*; Kasahara, Seiji; Kurihara, Kohei*; Nakagaki, Takao*; Yan, X.; Inagaki, Yoshiyuki; Ogawa, Masuro
ISIJ International, 55(2), p.348 - 358, 2015/02
Reducing coking coal consumption and CO emissions by application of iACRES (ironmaking system based on active carbon recycling energy system) was investigated using process flow modeling to show effectiveness of HTGRs (high temperature gas-cooled reactors) adoption to iACRES. Two systems were evaluated: a SOEC (solid oxide electrolysis cell) system using CO electrolysis and a RWGS (reverse water-gas shift reaction) system using RWGS reaction with H produced by IS (iodine-sulfur) process. Both the effects on saving of the coking coal and reduction of CO emissions were greater in the RWGS system. It was the reason of the result that excess H which was not consumed in the RWGS reaction was used as reducing agent in the BF as well as CO. Heat balance in the HTGR, SOEC and RWGS modules were evaluated to clarify process components to be improved. Optimization of the SOEC temperature was desired to reduce Joule heat input for high efficiency operation of the SOEC system. Higher H production thermal efficiency in the IS process for the RWGS system is effective for more efficient HTGR heat utilization. The SOEC system was able to utilize HTGR heat to reduce CO emissions more efficiently by comparing CO emissions reduction per unit heat of HTGR.
Suzuki, Katsuki*; Hayashi, Kentaro*; Kurihara, Kohei*; Nakagaki, Takao*; Kasahara, Seiji
ISIJ International, 55(2), p.340 - 347, 2015/02
Use of the Active Carbon Recycling Energy System in ironmaking (iACRES) has been proposed for reducing CO emissions. To evaluate the performance of iACRES quantitatively, a process flow diagram of a blast furnace model with iACRES was developed using Aspen Plus, a chemical process simulator. CO emission reduction and exergy analysis were performed by using mass and energy balance obtained from simulation results. The following CO reduction methods were evaluated as iACRES: solid oxide electrolysis cells (SOEC) with CO capture and separation (CCS), SOEC without CCS, and a reverse water-gas shift reactor powered by a high-temperature gas-cooled reactor. iACRES enabled CO emission reduction by 3-11% by recycling CO and H, whereas effective exergy ratio decreased by 1-7%.
Ebihara, Kenichi; Iwamoto, Takashi*; Matsubara, Yukio*; Yamada, Hiroki*; Okamura, Tsukasa*; Urushihara, Wataru*; Omura, Tomohiko*
ISIJ International, 54(1), p.153 - 159, 2014/01
For understanding the mechanism of hydrogen embrittlement that is one cause of stress corrosion cracking, it is necessary to identify the location of hydrogen segregation (hydrogen existing state) in steels. The thermal desorption spectrum of hydrogen that is obtained by measuring hydrogen desorbing from specimens heated at a constant rate is a useful data for identifying the hydrogen existing state. In the paper, using the numerical simulation, we examined the difference of the thermal desorption spectra between two specimens of pre-strained high-strength steel, one was charged with hydrogen by the method used widely in laboratories, the other was by the method simulating hydrogen penetration in real environment. As a result, it was found that the difference results from the difference of the initial hydrogen distribution caused by the amount of charged hydrogen. If the amount of charged hydrogen is small, the thermal desorption spectrum is more sensitive to the initial distribution.
Tsuchida, Noriyuki*; Kawahata, Takuji*; Ishimaru, Eiichiro*; Takahashi, Akihiko*; Suzuki, Hiroshi; Shobu, Takahisa
ISIJ International, 53(7), p.1260 - 1267, 2013/07
To investigate the tensile deformation behavior of a lean duplex stainless steel (S32101) from the viewpoints of plastic deformability among phases or grains, we performed static tensile tests, in situ neutron diffraction, and white X-ray diffraction experiments at room temperature. From the experimental results of synchrotron radiation white X-ray diffraction experiments, the hard phase of S32101 was changed from the ferrite phase to austenite one during tensile deformation. This led to a larger stress partitioning between the phases at the latter stage of deformation. From the experimental results of in situ neutron diffraction, it was found that the stress partitioning of the phase in the S32101 was the largest among the present results. Therefore, the larger work hardening rate of S32101 can be explained by the large stress partitioning of the phase, that between and phases and volume fraction.
Onizawa, Takashi; Asayama, Tai; Kikuchi, Kenji*
ISIJ International, 53(6), p.1081 - 1088, 2013/06
The applicability of high chromium (Cr) steel as the main structural material in fast breeder reactors (FBR) has been explored to enhance the safety, the credibility and the economic competitiveness of FBR power plants. Vanadium (V) and Niobium (Nb) are believed to improve the high-temperature strength of high Cr steels by precipitating as carbides and/or nitrides, namely fine MX particles, although the long-term efficiency and stability of such precipitation strengthening mechanisms resulting from the fine MX particles have not been clarified yet. The effects of V and Nb on degradation of creep properties were investigated under FBR operating conditions, e.g., at 550 C for 500,000 h, and the relationship between the long-term creep properties and microstructural changes was investigated considering the MX particles and the Z-phase. It was found that the optimal V and Nb contents for excellent high Cr steel of FBR grade are 0.2 mass% and 0.01 mass%, respectively, under FBR operating conditions.
Osugi, Takeshi; Sukenaga, Sohei*; Inatomi, Yosuke*; Gonda, Yoshiyuki*; Saito, Noritaka*; Nakashima, Kunihiko*
ISIJ International, 53(2), p.185 - 190, 2013/02
Understanding the changes in viscosity due to the different oxidation states of iron ions is important for simulating phenomena related to molten slags and also for understanding the structure of iron-oxidecontainingsilicate melts. However, these viscosity changes are not well understood. Here, we show the viscosity changes of RO-SiO-FexO (R = Li, Na, or K) melts due to changes in the oxidation states of the iron ions by systematically varying the oxygen partial pressure using several Ar-based gases at 1773 K. Not only the oxidation state of the iron ions but also the coordination structure of Fe may be important for understanding the viscosity.
Kasahara, Seiji; Inagaki, Yoshiyuki; Ogawa, Masuro
ISIJ International, 52(8), p.1409 - 1419, 2012/08
Flow sheet model evaluation of nuclear hydrogen steelmaking (NHS) and nuclear hydrogen partial reduction steelmaking (NHPRS) systems applying VHTR-IS (Very high temperature reactor and iodine-sulfur process) was carried out. Heat input and CO emissions of these systems were analyzed. Total net heat input to the NHS system was 28.4 GJ/t-high quality steel (HQS), including material production, material transportation, and power generation. This value was much larger than that of blast furnace steelmaking (BFS) system of 17.6 GJ/t-HQS. Reduction of hydrogen consumption in the shaft furnace and electricity consumption in the electric arc furnace were desired for lowering the heat input. Total net heat input of the NHPRS system was 31.9 GJ/t-HQS. Optimization of operation parameters such as reduction ratio of partial reduced ore (PRO) and PRO input ratio to the blast furnace is desired to decrease the heat input. CO emissions from the NHS and the NHPRS systems were 9% and 50% of that from BFS system. Substitution of hydrogen for coal and reduction of transportation weight contributed to the reduction. Steelmaking cost was also evaluated. When steelmaking scale of each system was unified to one million t-HQS/y, NHS was economically competitive to the BFS and Midrex steelmaking. And NHS was advantageous at higher cost of resources.
Inagaki, Yoshiyuki; Kasahara, Seiji; Ogawa, Masuro
ISIJ International, 52(8), p.1420 - 1426, 2012/08
The merit assessment of the nuclear hydrogen steelmaking (NHS) was performed for reduction of CO emissions from the steelmaking process. The NHS process is composed of the steelmaking process by hydrogen reduction and hydrogen production process, namely IS process, using a very high temperature reactor (VHTR). VHTR has the excellent safety features outstanding as compared with the other nuclear reactors that the reactor can be shut down inherently and cooled down passively using natural heat radiation from outside of the reactor pressure vessel even in a loss of coolant flow accident caused by loss of power and so on. Therefore, hydrogen can be supplied directly to a shaft furnace using piping from VHTR installed near the steelmaking plant. The NHS process with VHTR and IS process can decrease the CO emissions by approximately 9% of those of the conventional blast furnace process, and be economically competitive to the blast furnace and the shaft furnace processes.
Ebihara, Kenichi; Kaburaki, Hideo
ISIJ International, 52(2), p.181 - 186, 2012/02
In the study of hydrogen embrittlement, it is indispensable to identify the hydrogen trapping state in steels. The hydrogen thermal desorption profile, which is obtained from the thermal desorption analysis (TDA) and is the relation between temperature and the amount of desorbed hydrogen of a specimen heated at a constant rate, is effective. Since various factors such as the specimen size, the heating rate, the hydrogen diffusion and the trapping effect of defects affect the desorption profile, however, it is necessary to model the process of the hydrogen desorption from the specimen. This paper reviewed the present model which can simulate the desorption profile by categorizing them according to the rate-determining process of the hydrogen desorption. The historical background and the range of validity of the models were also mentioned.
Doshida, Tomoki*; Suzuki, Hiroshi*; Takai, Kenichi*; Oshima, Nagayasu*; Hirade, Tetsuya
ISIJ International, 52(2), p.198 - 207, 2012/02
Hydrogen behavior and hydrogen-enhanced lattice defect formation under elastic stress of tempered martensitic steel were clarified with respect to dislocations and vacancies by thermal desorption analysis (TDA) using hydrogen as a probe of defects and a positron probe microanalyzer (PPMA). The relationship between hydrogen embrittlement and lattice defects associated with hydrogen was also investigated. The amount of lattice defects increased gradually with increasing time of applied stress. The specimen fractured under elastic stress. The enhanced vacancies due to interactions between dislocations and hydrogen under elastic stress directly caused ductility loss. Even though hydrogen was completely removed by degassing the vacancies remain. Besides hydrogen content and applied stress, the time of formation and accumulation of vacancies are also concluded to be important factors causing hydrogen embrittlement.
Ebihara, Kenichi; Kaburaki, Hideo; Suzudo, Tomoaki; Takai, Kenichi*
ISIJ International, 49(12), p.1907 - 1913, 2009/12
We present a systematic benchmark study on different numerical models for analyzing hydrogen thermal desorption spectra, by focusing on the adoption of the local equilibrium hypothesis in these models. We find that the direct numerical method of the full set of the extended mass conservation equations is only able to predict the experimental behavior of thermal desorption spectra for pure iron in the thin specimen limit, while other models incorporating the local equilibrium hypothesis fail to predict this behavior.
Ebihara, Kenichi; Suzudo, Tomoaki; Kaburaki, Hideo; Takai, Kenichi*; Takebayashi, Shigeto*
ISIJ International, 47(8), p.1131 - 1140, 2007/08
In thermal desorption analysis(TDA), a hydrogen desorption profile, which represents the relation between the amount of desorbed hydrogen and specimen temperature, can be obtained by heating the specimen including hydrogen with a certain rate. We can estimate the amount of sites trapping hydrogen in the specimen, such as vacancies, dislocations and interfaces of phases from the profile. We have developed a numerical model to simulate the hydrogen desorption profiles for pure iron and eutectoid steel. Our model incorporates the equation of McNabb and Foster, which is a kind of rate equation, without the hydrogen diffusion term combined with the Oriani's local equilibrium theory, which describes the hydrogen trapping state. It is found that the present numerical model successfully simulates the profile both for pure iron and for eutectoid steel. We further verify the model by discussing the trapping site concentration and the effect of hydrogen diffusion.
Holden, T. M.*; Suzuki, Hiroshi; Carr, D. G.*
ISIJ International, 46(7), p.959 - 965, 2006/07
In the last decade a more sophisticated understanding of how to calculate the macroscopic stress from strains measured in neutron diffraction experiments has developed. Strains measured with the aid of a particular reflection may have a component corresponding to the stress field as well as a component corresponding to a type-2 or intergranular stress. The latter originates in inhomogeneous plastic deformation among different grain orientations. One approach is to cut small reference coupons from the component, small in size compared with the variation of the stress field. Cutting destroys the stress field but leaves any chemistry and intergranular effects intact since they are on the scale of the grain size. The difference between the intact sample and the coupon then gives an approximation to the strain associated with the macroscopic stress. Examples of how the intergranular and macroscopic strains and stresses are superposed, are presented for the cases of slightly bent and severely bent steam generator tubing, and for a deformed pressure tube. Welds often represent a situation where plastic deformation has occurred on cooling. In addition, microstructural and compositional changes are often associated with melting, so it is important to have reference coupons as a function of position through the weld zone. Examples of austenitic stainless steel and Zr-alloy welds are presented.
Onizawa, Kunio; Suzuki, Masahide
ISIJ International, 37(8), p.821 - 828, 1997/08
no abstracts in English
S.Chi*; Suzuki, Masahide; Nishi, Hiroshi; Eto, Motokuni; I.Kim*
ISIJ International, 32(4), p.545 - 552, 1992/04
no abstracts in English
Nakajima, Hideo; Yoshida, Kiyoshi; Shimamoto, Susumi
ISIJ International, 30(8), p.567 - 578, 1990/08
no abstracts in English
Shindo, Masami; Nakajima, Hajime
ISIJ International, 29(9), p.793 - 795, 1989/09
no abstracts in English