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ISIJ International Vol. 54 (2014), No. 7

ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559
Publisher: The Iron and Steel Institute of Japan

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  1. Vol. 64 (2024)

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  11. Vol. 54 (2014)

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ISIJ International Vol. 54 (2014), No. 7

Recent Progress on Advanced Blast Furnace Mathematical Models Based on Discrete Method

Tatsuro Ariyama, Shungo Natsui, Tatsuya Kon, Shigeru Ueda, Shin Kikuchi, Hiroshi Nogami

pp. 1457-1471

DOI:

10.2355/isijinternational.54.1457

Abstract

From the backgrounds of the recent trends towards low reducing agent operation of large blast furnaces and application of diversified charging modes for various burdens, an advanced mathematical model of the blast furnace is required. Although conventional models based on the continuum model have been widely used, these models are not sufficient for the recent demands. Discrete models such as discrete element model (DEM) and particle method are expected to enable precisely simulation of the discontinuous and inhomogeneous phenomena in the recent operating conditions. With discrete models, microscopic information on each particle in the packed bed can be obtained in addition to the overall phenomena in the blast furnace. Visual information for understanding in-furnace phenomena can be also obtained with high spatial resolution. Liquid dripping and the movement of fines in the lower part of the blast furnace can be simulated with high accuracy by using DEM and particle methods such as the Moving Particle Semi-implicit Method (MPS). Moreover, the optimum bed structure for low reducing agent operation is being clarified by application of the Eulerian-Lagrangian method. This review summarizes recent progress on the mathematical models based on the discrete model.

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Recent Progress on Advanced Blast Furnace Mathematical Models Based on Discrete Method

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Global Progress on Welding Consumables for HSLA Steel

Tianli Zhang, Zhuoxin Li, Frank Young, Hee Jin Kim, Hong Li, Hongyang Jing, Wolfgang Tillmann

pp. 1472-1484

DOI:

10.2355/isijinternational.54.1472

Abstract

This paper reviews the global progress on welding consumables for high strength low alloy steel. The numerous aspects, such as the toughness and cleanliness of weld metal, the new removal mechanisms of impurity elements and the crack resistance of weld metal, are discussed. To meet increasing environment requirements, the fumes and life cycle assessment of welding consumables are also discussed. Finally, future trends in the development of welding consumables for high strength low alloy steel are pointed out.

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Global Progress on Welding Consumables for HSLA Steel

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Reduction Reactions in Al2O3–C–Fe and Al2O3–Fe2O3–C Systems at 1823 K

Rita Khanna, Muhammad Ikram-Ul-Haq, Seyed Fahandej Sadi, Veena Sahajwalla, Partho Sarathy Mukherjee, Seshadri Seetharaman

pp. 1485-1490

DOI:

10.2355/isijinternational.54.1485

Abstract

With a view to produce Fe–Al alloys for deoxidation during steel refining, chemical reactions were investigated in Al2O3–C–Fe and Al2O3–Fe2O3–C systems at 1823 K. Using a horizontal tube furnace and argon atmosphere, interactions were investigated for time periods up to 2 hours. Two sets of blends were prepared from initial constituents, which were later used to prepare two types of substrates. Alumina and synthetic graphite powders were blended in a 70: 30 proportion (blend I), and in the second set, Fe2O3 was blended with C in a proportion of 75:25 (blend II). In one case, blend I was mixed thoroughly with iron powder (Fe (2.7 pct C)) in a ratio of 80:20; in the second case, blend I was mixed with blend II in the ratio of 70:30. We report significant reduction reactions in both cases. SEM/EDS studies on the Al2O3–C–Fe system showed unambiguous evidence for the pick-up of aluminium by molten iron after 1 hour. Levels of aluminium in molten iron were found to increase significantly with time. Due to in-situ reduction of Fe2O3, the generation of CO gas and associated turbulence, the reactions were quite fast in the Al2O3–Fe2O3–C system. X-ray diffraction studies showed the presence of additional diffraction peaks belonging to Fe3AlC and Fe3Al systems. Molten iron was found to act as a reducing agent and a metallic solvent in both cases. This study provides evidence for the carbothermic reduction of alumina at 1823 K and for the formation of ferroalloys directly from mixed oxides of aluminium and iron.

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Reduction Reactions in Al2O3–C–Fe and Al2O3–Fe2O3–C Systems at 1823 K

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Effect of P2O5 Addition on the Viscosity and Structure of Titanium Bearing Blast Furnace Slags

Yongqi Sun, Kai Zheng, Junlin Liao, Xidong Wang, Zuotai Zhang

pp. 1491-1497

DOI:

10.2355/isijinternational.54.1491

Abstract

This study provided a fundamental analysis of the viscosity and structure of titanium bearing blast furnace slags modified by different levels of P2O5 addition. The viscosity of slag melts was obtained by rotating cylinder method, which is a significant factor for blast furnace process and utilization of slags. The results showed that the slag viscosity was greatly influenced by basicity. Slag viscosity decreased and the calculated apparent activation energy for viscous flow also decreased with increasing basicity, which indicated the breakdown of melt structure. The addition of P2O5 substantially increased the slag viscosity at each basicity, and the increasing trend was most pronounced at basicity 0.5. To connect the viscosity changes of slags to the slag melt structure, Fourier transformation infrared (FTIR) and Raman spectral spectroscopy analysis were performed in this study. FTIR results clearly indicated that the added P2O5 increased the degree of polymerization of slags, corresponding to the increase of slag viscosity. Based on Raman and FTIR curves, it can be concluded that P2O5 acted as a characteristic network former in the melts.

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Effect of P2O5 Addition on the Viscosity and Structure of Titanium Bearing Blast Furnace Slags

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Deoxidation Mechanism of Al-Killed Steel during Industrial Refining Process

Zhiyin Deng, Miaoyong Zhu

pp. 1498-1506

DOI:

10.2355/isijinternational.54.1498

Abstract

Deoxidation is a key step for steel refining, and it would influence the cleanliness of final product. In present study, the measured and calculated oxygen activities in Al-killed bulk steel were compared according to industrial trails, and the Fe–O equilibrium at the interface between slag and steel was also concerned by thermodynamic analysis. Finally, the deoxidation mechanism of Al-killed during industrial refining was proposed. It is found that the activity of oxygen in bulk steel is controlled by Al content, since the activity of oxygen in bulk steel is very close to the equilibrium value as the activity of Al2O3 is treated as unity. In order to keep low oxygen in molten steel, a certain Al content needs to be guaranteed. At slag-steel interface, the activity of oxygen is controlled by FeO, which is much larger than that of bulk steel, so the oxygen would transfer from slag into bulk steel. Slagging therefore presents its importance for deoxidation to reduce the oxygen transfer. Besides, the essence of SiO2 supplying oxygen is Al consumption in bulk steel, which gives rise to the increase of dissolved oxygen. So, stable refining slag is also very important to obtain low oxygen steel, and the slag basicity needs to be no smaller than 3 to reduce the Al consumption caused by SiO2 reduction. In present study, the basicity of 3–4 is recommended to refine low oxygen Al-killed steel.

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Deoxidation Mechanism of Al-Killed Steel during Industrial Refining Process

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Numerical Simulation on Gas-liquid Flow in Mechanical-Gas Injection Coupled Stirred System

Pin Shao, Ting-an Zhang, Zimu Zhang, Yan Liu

pp. 1507-1516

DOI:

10.2355/isijinternational.54.1507

Abstract

Based on Euler–Euler approach, a mathematical model is established to describe gas and liquid two-phase flow in the mechanical-gas injection coupled stirred system for steelmaking, and the effects of different location and rotation speed of impeller, and gas flow rate on the bubble dispersion, gas total volume and mixing time in the bath were studied. The results show that the predicted bubbles dispersion and mixing time agree well with the experimental photos and measured data. With the increasing of impeller eccentricity, the bubbles dispersion become more better, and the mixing time decreases, while the gas total volume first decreases and then increases. With the increasing of rotation speed of impeller, the bubble dispersion becomes better, and the gas total volume the mixing efficiency also increases. But these effects become weak when the rotation speed exceed 200 rpm. With the increasing of gas flow rate, the bubble dispersion remain basically unchanged, and the gas total volume gradually increase, but the mixing time would rapidly increase. It is recommended to use the impeller placed at radial position of 0.4 R (R is the radius of bath), rotation speed of 200 rpm, and gas flow rate not exceeding 2.0 Nm3/h for present system.

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Numerical Simulation on Gas-liquid Flow in Mechanical-Gas Injection Coupled Stirred System

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Prediction of Heap Shape in Blast Furnace Burden Distribution

Samik Nag, Ankit Gupta, Sananda Paul, Dharm Jeet Gavel, Binayak Aich

pp. 1517-1520

DOI:

10.2355/isijinternational.54.1517

Abstract

Estimation and prediction of the stock profile in the radial direction of the furnace is essential for controlling ore and coke distribution and permeability distribution. In this paper, based on experiments carried out in different scaled model of blast furnace with different material, a general purpose methodology to estimate the stock profile in blast furnace burden distribution is proposed.

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Prediction of Heap Shape in Blast Furnace Burden Distribution

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Numerical Study on Pulverized Biochar Injection in Blast Furnace

Agung Tri Wijayanta, Md. Saiful Alam, Koichi Nakaso, Jun Fukai, Kazuya Kunitomo, Masakata Shimizu

pp. 1521-1529

DOI:

10.2355/isijinternational.54.1521

Abstract

The possibility of injecting pulverized biochar instead of conventional pulverized coal in blast furnace ironmaking was investigated numerically. More detailed reactions including the water-related reactions were considered here. The combustion process from the tuyere to the raceway of a blast furnace was simulated. Oak char (volatile matter wt.% dry basis, VM = 27.11 wt.%-db) provided a lower temperature than Taiheiyo coal (VM = 44.60 wt.%-db). Increasing the O2 concentration from 23 to 27 wt.% resulted in a higher combustibility of both solid fuels. However, the effect of increasing oxygen concentration was still insufficient for the Oak char at high injection rates because of its inadequate volatile content. Biochar properties become increasingly important as the injection rate increases. Compared with Oak char that provided a combustibility of 68% at an injection rate of 200 [(kg solid fuel)/(1000 Nm3 feed gas)] and hot blast of 27 wt.% O2 concentration, Oak char 1 (VM = 32.09 wt.%-db) had a higher combustibility of 71%.

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Numerical Study on Pulverized Biochar Injection in Blast Furnace

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Metal-slag Separation Behaviors of Pellets Consisted of Iron, Graphite and CaO–Al2O3 Based Slag Powders

Ji-Ook Park, In-Hyeon Jeong, Sung-Mo Jung, Yasushi Sasaki

pp. 1530-1538

DOI:

10.2355/isijinternational.54.1530

Abstract

In-situ observations of metal-slag separation behaviors between CaO–Al2O3 based slag, iron and graphite powder mixed pellets by a confocal laser-scanning microscope (CLSM) have been carried out to find the effective way to use high Al2O3 iron ore in CCA reduction processes. Since a particular type of high Al2O3 iron ore such as laterite contains small amount of NiO and Cr2O3, the effect of NiO and Cr2O3 on the metal-slag separation behaviors were also studied. The observed metal-slag separation behaviors were analyzed based on the equilibrium phase fractions calculated by FactSage and carbon diffusion simulation in an iron sphere particle with a spot carbon source condition. Based on these in-situ observations and carbon diffusion results, starting temperature of metal-slag separation was found to correspond to the eutectic temperature of CaO–Al2O3 based slag. The iron carburization was initiated by slag melting and most of iron particles were melted within about 20 s after slag melting. The rapid carburization after slag melting was introduced by the good wettability between solid iron and molten slag. NiO and Cr2O3 additions did not change the fundamental behaviors of metal-slag separation at least up to about 3 mass%. Based on these results, it was confirmed that high Al2O3 content iron ore can be used in CCA reduction process by using CaO–Al2O3 based slag.

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Metal-slag Separation Behaviors of Pellets Consisted of Iron, Graphite and CaO–Al2O3 Based Slag Powders

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Reduction Behavior of Cold-bonded Briquettes under Simulated Blast Furnace Conditions

Antti Kemppainen, Mikko Iljana, Eetu-Pekka Heikkinen, Timo Paananen, Olli Mattila, Timo Fabritius

pp. 1539-1545

DOI:

10.2355/isijinternational.54.1539

Abstract

Recycling of fine sized iron-rich by-products back to blast furnace (BF) process in the form of cement-bonded briquettes has become a common procedure in steel plants. Replacing part of the cement by Ground Granulated Blast Furnace Slag (GGBFS) is also a common method to reduce cement consumption. When the briquettes are subjected to high temperature and reducing atmosphere in the BF, the cement phases decompose and the iron oxides undergo a series of phase transformations. To avoid early disintegration and to improve the performance of the briquettes, it is necessary to study these reactions during the reduction. In the present study the reduction behavior of the BF briquette samples was studied by experimental methods in a laboratory scale furnace, which simulates the conditions of the BF shaft in a CO–CO2–N2 atmosphere. With interrupted experiments the composition of the briquette was studied in different reduction stages of the BF shaft. The effect of GGBFS as a binder material on the reduction was studied with GGBFS containing briquette samples. The reduction of briquettes was compared to an olivine pellet which was used as a reference sample. Considerably higher reduction rate was detected with the briquettes compared to the pellet at 1100°C when reduced to metallic iron. 25–50 vol-% swelling in the briquette samples was detected during the wüstite-iron reduction step at 900–1000°C. X-ray diffraction (XRD) was used to observe the phase transformations in the Fe–Fe2O3–CaO system of the briquette and the results are in agreement with the theory.

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Reduction Behavior of Cold-bonded Briquettes under Simulated Blast Furnace Conditions

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Reduction Potential Evaluation Index of Various Reducing Agents in Blast Furnace

Akihiko Shinotake

pp. 1546-1551

DOI:

10.2355/isijinternational.54.1546

Abstract

In blast furnace operation, reducing agent ratio (RAR) is an important index. The RAR is defined only as a sum of weights, without considering the kind of reducing material. Here the author proposes a new reducing potential index, ReP, which considers the difference of reducing material composition under the real blast furnace condition that gas utilization ratios (ηCO and ηH2) are 50%. Namely, ReP is set as
C = 3, H = 0.5, O = –2, (N = 0) (ReP/kmol).
This index evaluates reduction potentials of various reducing materials in a uniform manner. Latter part of this report includes an example of blast furnace operation analysis using ReP. Extended case studies that concern utilization of partially reduced ore, utilization of mixture of ferrous and carbonous materials, and gas utilization ratio changes far from 50%, are performed. When gas utilization ratios change from 50%, ReP is available if extended ReP is set as C = 2 + 2ηCO, H = ηH2, O = –2, (N = 0) (ReP/kmol).

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Reduction Potential Evaluation Index of Various Reducing Agents in Blast Furnace

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Enhanced Carburization of Iron by CH4-containing Gas at 1573 K

Woo-Il Park, In-Hyun Jeong, Sung-Mo Jung

pp. 1552-1559

DOI:

10.2355/isijinternational.54.1552

Abstract

The carburization rate of iron by N2-11 vol% CH4 gas was investigated at 1573 K employing an induction furnace in order to minimize the pre-decomposition of methane. Unlike the carburization of iron by CO or CO+H2 gases, the carburization rate of iron by CH4-containing gas was controlled not by chemical reaction at the surface, but by diffusion of carbon in the liquid phase of Fe–C. The carburization rate by CH4 was about 30 times faster than that by 50 vol% CO. The effects of H2 addition and change in CH4 concentration supported that the chemical reaction do not control the total carburization rate. The formation of graphite rods confirmed that the surface had a very high carbon concentration and the chemical reaction rate is sufficiently fast. Numerical simulation of the carbon diffusion in the spherical iron estimated the diffusivity of carbon () in liquid iron at 1573 K to be 3 × 10–9 m2/s. In addition, the moving mechanism of liquid/solid interface was schematically proposed.

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Enhanced Carburization of Iron by CH4-containing Gas at 1573 K

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Mathematical Model for Decarburization Process in RH Refining Process

Jiongming Zhang, Liang Liu, Xinyu Zhao, Shaowu Lei, Qipeng Dong

pp. 1560-1569

DOI:

10.2355/isijinternational.54.1560

Abstract

A three-dimensional mathematical model for natural decarburization process of ultra-low carbon Al killed steel during RH refining has been established. The decarburization behavior in RH degasser was discussed on the basis of a comparison between simulation data and the actual plant trials ones. The effects of the different initial carbon content, initial oxygen content, the lift gas rate and inside diameter on decarburization were investigated. The results showed that when the dissolved oxygen concentration was 0.08% in the molten steel, the flow rate of gas injected through the up-leg was 120 Nm3/h, the inside diameter of up and down-leg was 650 mm, under these conditions, the initial carbon content was 0.03%, 0.023% and 0.015%, respectively, after about 25 minute, the average carbon content in molten steel was 0.011%, 0.01% and 0.0008%. The final dissolved carbon content is related to the initial dissolved oxygen content in molten steel. The average carbon concentration and the decarburization rate of the molten steel will decrease with the increasing of the initial dissolved oxygen content. The effects of different inside diameter of up and down-leg were also compared, it shows that the increasing of the diameter of up/down-leg will promote decarburization effectively, which can increase the circulation flow rate and promote the reaction rate.

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Mathematical Model for Decarburization Process in RH Refining Process

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Sulphide Capacity and Mineralogy of BaO and B2O3 Modified CaO–Al2O3 Top Slag

Pengcheng Yan, Pinxu Nie, Shuigen Huang, Bart Blanpain, Muxing Guo

pp. 1570-1577

DOI:

10.2355/isijinternational.54.1570

Abstract

BaO and B2O3 were used to improve the metallurgical properties and valorisation potential of CaO–Al2O3 based top slag. The sulphide capacity of BaO–B2O3 modified CaO–Al2O3 based top slag was measured and compared with calculated values using the FactSage software. The effect of slag basicity (CaO + MgO)/(Al2O3 + B2O3) = 0.6–1.4 and BaO content on sulphide capacity was discussed. The mineralogy of the slag after experiments was observed. The crystallisation path of the slag during cooling was predicted based on a Scheil-Gulliver model. Consequently, the effect of the slag basicity and B2O3 on slag mineralogy and glass formation ability was discussed. It is found that the sulphide capacity is mainly influenced by slag basicity. BaO addition improves the slag sulphide capacity only for slag with low basicity (< 1.2). B2O3 addition enlarges the liquid region at 1600°C but decreases the slag sulphide capacity. High basicity and B2O3 addition benefit the glass formation and would improve the slag valorisation potential in applications where the glass content is important.

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Sulphide Capacity and Mineralogy of BaO and B2O3 Modified CaO–Al2O3 Top Slag

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Effect of Carbon on Nitrogen Solubility and AlN Formation in High Al Alloyed Liquid Steels

Jung-Mock Jang, Seok-Hyo Seo, Young-Dae Kim, Hyo-Jong An, Jong-Jin Pak

pp. 1578-1583

DOI:

10.2355/isijinternational.54.1578

Abstract

The nitrogen solubility and the AlN solubility product in liquid Fe–C–Al–N alloys containing a wide composition range of carbon and aluminum were measured in the temperature range of 1773–1873 K. Aluminum and carbon both decreased the nitrogen solubility in liquid iron. The simultaneous effect of aluminum and carbon on nitrogen solubility in liquid iron was determined. The AlN solubility product in liquid iron decreased significantly with carbon addition primarily due to the large effect of carbon on nitrogen solubility. Using the Wagner’s formalism, the experimental results were thermodynamically analyzed to determine the interaction parameters among carbon, aluminum and nitrogen in liquid iron as follows:

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Effect of Carbon on Nitrogen Solubility and AlN Formation in High Al Alloyed Liquid Steels

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Efficiency of Inclusion Absorption by Slags during Secondary Refining of Steel

Bruno Henrique Reis, Wagner Viana Bielefeldt, Antônio Cezar Faria Vilela

pp. 1584-1591

DOI:

10.2355/isijinternational.54.1584

Abstract

One of the functions of secondary refining in steelmaking is to remove non-metallic inclusions produced through deoxidation of the steel bath during the process. Removal of these inclusions occurs in three fundamental stages: flotation, separation and dissolution of the inclusions in supernatant slag. Given that dissolution is subject to the action of slag, this study aims to clarify the inclusion absorption capacity of industrial slags and factors that influence slag properties in absorbing inclusions, as well as the impact of each factor on the cleanliness of the steels analyzed. To that end, the results of industrial steel and slag samples collected during the different stages of secondary refining were analyzed. The amount and chemical composition of the inclusions was determined by SEM/EDS (scanning electron microscopy coupled with energy-dispersive spectroscopy). The chemical composition of slag samples was measured by XRF (X-ray fluorescence) and subsequently submitted to thermodynamic simulations using FactSage 6.4 software. Calculations were made with the SlagViscosityPredictor, which uses FactSage 6.2 software. This made it possible to establish the chemical composition and proportion of the solid phase in the slags and inclusions, as well as the effective viscosity of the slags. The efficiency of absorption inclusion by the industrial slags was found to be greater in the presence of high thermodynamic driving force between slags and inclusions, low slag effective viscosity and when inclusions were not liquid.

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Efficiency of Inclusion Absorption by Slags during Secondary Refining of Steel

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Mechanism Analysis of Free-Surface Vortex Formation during Steel Teeming

Hong-Xia Li, Qiang Wang, Hong Lei, Jia-Wei Jiang, Zhan-Cheng Guo, Ji-Cheng He

pp. 1592-1600

DOI:

10.2355/isijinternational.54.1592

Abstract

To develop an effective technology to prevent vortex forming in ladles, the mechanism underlying vortex formation during steel teeming must be studied. For simulations using the numerical simulation software Fluent, a geometric model of the ladle was generated, and initially water teeming in the ladle was simulated for different initial tangential velocities. The results obtained help to verify the validity of the numerical computations. Similar simulation conducted for steel showed that the tangential velocity increases from the liquid level to the bottom of the ladle, and the flow at the bottom is related to vortex formation. The inference is that vortex formation begins from the ladle bottom. Causes for vortex formation during teeming are discussed to help lay a theoretical basis for ladle design in preventing vortex formation during steel teeming.

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Mechanism Analysis of Free-Surface Vortex Formation during Steel Teeming

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Phase Field Simulation of Equiaxed Microstructure Formation during Semi-solid Processing of A380 Al Alloy

Prosenjit Das, Sudip Kumar Samanta, Pramod Kumar, Pradip Dutta

pp. 1601-1610

DOI:

10.2355/isijinternational.54.1601

Abstract

A phase field modelling approach is implemented in the present study towards simulation of microstructure evolution during cooling slope semi solid slurry generation process of A380 Aluminium alloy. First, experiments are performed to evaluate the number of seeds required within the simulation domain to simulate near spherical microstructure formation, occurs during cooling slope processing of the melt. Subsequently, microstructure evolution is studied employing a phase field method. Simulations are performed to understand the effect of cooling rate on the slurry microstructure. Encouraging results are obtained from the simulation studies which are validated by experimental observations. The results obtained from mesoscopic phase field simulations are grain size, grain density, degree of sphericity of the evolving primary Al phase and the amount of solid fraction present within the slurry at different time frames. Effect of grain refinement also has been studied with an aim of improving the slurry microstructure further. Insight into the process has been obtained from the numerical findings, which are found to be useful for process control.

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Phase Field Simulation of Equiaxed Microstructure Formation during Semi-solid Processing of A380 Al Alloy

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Effect of the Induced Ferrite and Precipitates of Nb–Ti Bearing Steel on the Ductility of Continuous Casting Slab

Guoyu Qian, Guoguang Cheng, Zibing Hou

pp. 1611-1620

DOI:

10.2355/isijinternational.54.1611

Abstract

The hot ductility of Nb–Ti bearing ship plate steel has been obtained using the Gleeble 1500 thermal-mechanical simulator, the results showed that the ductility trough of the reduction of area (R.A) curve of Nb–Ti bearing ship plate steel is wider than other steels without Nb. In order to investigate the reasons of the loss of the ductility, a series of studies have been done. It was found that Nb(C,N) particles with a mean size of 9 nm precipitate at 950°C and induce the formation of the nuclei of grain boundary ferrite, which could lead to strain concentration at grain boundaries as well as the poor uniformity of ferrite films thickness. This causes rapid decrease of the R.A values with the temperature cooling from 1000 to 950°C. When the temperature falls to 900°C, a large number of Nb(C,N) particles precipitate, which promote further formation of the grain boundary ferrite films. Therefore, the thickness of ferrite films formed at different time makes a difference and presents a poor uniformity. As the temperature down to 850°C, hot ductility further reduces because of the worse uniformity of ferrite films thickness which leads to strain concentration at the grain boundary. When temperature is close to Ae3 (816°C), the formation and growth of ferrite films become faster due to austenite-ferrite phase transformation, which leads to the uniformity of ferrite film thickness at worst, so that the R.A value exhibits a rapid decrease. After the temperature is lower than Ae3, ferrite films are markedly thickened, which compensate parts of adverse effects from the poor uniformity of ferrite films thickness and reduce the strain concentration at grain boundaries. In this way, ductility begins to recover.

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Effect of the Induced Ferrite and Precipitates of Nb–Ti Bearing Steel on the Ductility of Continuous Casting Slab

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On Melting of Electrodes during Electro-Slag Remelting

Abdellah Kharicha, Andreas Ludwig, Menghuai Wu

pp. 1621-1628

DOI:

10.2355/isijinternational.54.1621

Abstract

In this paper a numerical investigations on the thermal state and on the tip shape of a melting electrode during electro-slag remelting are presented. In the first part the heat necessary to melt an electrode with a flat tip shape is calculated. It is shown that to keep a constant melting rate, the heat supplied to the electrode must be continuously changed. The results for different electrode descend rates, corresponding to different melting rates, are presented. In the second part the melting process was simulated with the help of a numerical model which takes into account simultaneous action of magneto-hydrodynamics, and thermal and phase changes phenomena. The model assumes no mould current. Simulations were performed with constant applied current and electrode descend velocity. The simulations have shown that the coupling between the melting rate and the Joule heat release process is very unstable. One result showing a stable electrode tip is presented and discussed in details.

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On Melting of Electrodes during Electro-Slag Remelting

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Mathematical Model for Cluster-Inclusion’s Collision-Growth in Inclusion Cloud at Continuous Casting Mold

Hong Lei, Yan Zhao, Dian-Qiao Geng

pp. 1629-1637

DOI:

10.2355/isijinternational.54.1629

Abstract

The inclusion’s morphology and size play a strong role in the steel product quality, so it is very important to have a deep insight into the inclusion’s collision-growth in the continuous caster. In order to describe the formation of the cluster-inclusion, a mathematical model and the related source code are developed to trace the inclusion’s movement and collision-growth in the inclusion cloud. Such a model includes two sub-models. Firstly, the spatial distribution of turbulent flow and the inclusion’s number density and the characteristic radius after Stokes collision and turbulent collision are obtained by Eulerian approach. Secondly, the inclusion’s trajectory and the related inclusion fractal growth are predicted by Lagrangian approach. Numerical results show that the spatial distributions of the inclusion volumetric concentration, number density and characteristic radius have some features of the upper and lower recirculation zone due to the fluid flow. For an inclusion particle, the bigger inclusion has more chances to catch other inclusions and forms a more complex cluster-structure. Among the forces acting on the inclusion, the pressure gradient force, Basset history force, the visual mass force, the gravitational force and the buoyancy force should be considered in order to describe the inclusion’s exact motion. Furthermore, the pressure gradient force, the Basset force, the visual mass force follow the same variation rule along with the inclusion’s trajectory.

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Mathematical Model for Cluster-Inclusion’s Collision-Growth in Inclusion Cloud at Continuous Casting Mold

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Strip Steel Surface Defect Recognition Based on Novel Feature Extraction and Enhanced Least Squares Twin Support Vector Machine

Maoxiang Chu, Anna Wang, Rongfen Gong, Mo Sha

pp. 1638-1645

DOI:

10.2355/isijinternational.54.1638

Abstract

Feature extraction and classification are two important steps in the process of strip steel surface defect recognition. Traditional methods of defect feature extraction are not of scale and rotation invariance. Moreover, traditional methods of defect classification have a conflict between efficiency and accuracy in. In order to solve the above two problems, a novel recognition method is proposed in this paper. On one hand, the novel defect feature extraction scheme is realized by building sampling benchmark scale (SBS) information for training dataset and using gradient magnitude and gradient orientation co-occurrence matrix (GMGOCM), gray level and gradient orientation co-occurrence matrix (GLGOCM), and moment invariant features. On the other hand, K-nearest neighbor and R-nearest neighbor algorithms are used to prune training dataset, and amplification factors of pruned samples are used to improve least squares twin support vector machine (LSTWSVM) classifier in efficiency and accuracy. The experimental results show that the novel recognition method can not only realize defect feature extraction with scale and rotation invariance but also realize defect classification with high efficiency and accuracy.

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Strip Steel Surface Defect Recognition Based on Novel Feature Extraction and Enhanced Least Squares Twin Support Vector Machine

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Finite Element Investigation for Edge Wave Prediction in Hot Rolled Steel during Run Out Table Cooling

Hoon-Hwe Cho, Yi-Gil Cho, Dong-Wan Kim, Se-Jong Kim, Won-Beom Lee, Heung Nam Han

pp. 1646-1652

DOI:

10.2355/isijinternational.54.1646

Abstract

A three-dimensional numerical model is developed here to predict the edge wave behavior of hot rolled steel during run out table cooling based on a finite element (FE) method. The edge wave of the hot rolled steel is reproduced successfully using the FE simulation considering proper thermo-mechanical boundary conditions. The simulation results demonstrate that the edge wave could be caused by the strain gradient due to the temperature difference between the edge and center regions. The maximum amplitude of the edge wave is used as a parameter of the degree of edge wave for quantitative comparison. The effect of the edge mask width and the checkers on the edge wave is examined through a series of process simulations. The measured temperatures agree fairly well with the predicted data.

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Finite Element Investigation for Edge Wave Prediction in Hot Rolled Steel during Run Out Table Cooling

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Effect of Preadsorption of Organic Additives on the Appearance and Morphology of Electrogalvanized Steel Sheets

Hiroaki Nakano, Takashi Ura, Satoshi Oue, Shigeo Kobayashi

pp. 1653-1660

DOI:

10.2355/isijinternational.54.1653

Abstract

Zn electrodeposition was performed galvanostatically on steel sheets at 1500 A/m2 in an agitated sulfate solution at 40°C to investigate the effect of preadsorption of organic additives on the lightness and morphology of Zn. The organic additives employed were classified into two types: 1) polyethylene glycol (PEG), gelatin, and stearyl dimethylbenzyl ammonium chloride (SDBAC) (Type I), which exhibit a polarization effect for Zn deposition; and 2) saccharin and sodium lauryl sulfate (Type II), which exhibit no polarization effect for Zn deposition. The platelet crystals of deposited Zn were reduced in size with preadsorption of all the organic additives considered. The observed decrease in the size of Zn platelet crystals with preadsorption is attributed to both an increase in the overpotential for Zn deposition and a decrease in the epitaxial growth of Zn on steel substrates. The preferred orientation of the {0001} Zn basal plane significantly decreased because of an increase in Zn deposition overpotential owing to preadsorption of PEG and gelatin, and the orientation slightly decreased with saccharin and sodium lauryl sulfate in spite of the absence of a polarization effect on Zn deposition. The surface roughness of deposited Zn decreased with preadsorption of organic additives with the exception of SDBAC. This is due to a decrease in the size of Zn platelet crystals. The lightness of deposited Zn was increased by preadsorption of organic additives with the exception of SDBAC. Because Zn deposited nonuniformly with preadsorption of SDBAC, the surface roughness of Zn increased and the lightness decreased.

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Effect of Preadsorption of Organic Additives on the Appearance and Morphology of Electrogalvanized Steel Sheets

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Coloration by Zinc–Nickel Composite Films Electrodeposited from a Chloride Solution

Hiroaki Nakano, Syota Kataoka, Satoshi Oue, Shigeo Kobayashi

pp. 1661-1666

DOI:

10.2355/isijinternational.54.1661

Abstract

Zn–Ni composite films were electrodeposited under coulostatic (515–5145 C·m−2) and galvanostatic (5 A·m−2) conditions onto brass plates with a Ni precoating in an unagitated chloride solution at 23°C to investigate the color and structure of the deposited films. The chromaticity of the deposited Zn–Ni composite films changed in a clockwise direction in each quadrant of the a*b* diagram of the L*a*b* color space with increasing amount of charge. The deposited films contained S, Zn, and Ni, and their content decreased in the order of S > Zn > Ni. X-ray photoelectron spectroscopy revealed that the deposited films were primarily composed of ZnS, ZnO, and Ni and contained small amounts of Zn(OH)2 and Zn. The color of the deposited films is attributed to interference of light, and the index of refraction of the deposited films composed of ZnS, ZnO, and Ni is assumed to be large. When Ni was excluded from the electrolytic solution, ZnS did not codeposit and the amount of Zn deposited in the metallic state increased. This result suggests that the Ni deposition induces the codeposition of ZnS.

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Coloration by Zinc–Nickel Composite Films Electrodeposited from a Chloride Solution

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A Study of Carbide Precipitation in a H21 Tool Steel

Meilinda Nurbanasari, Panos Tsakiropoulos, Eric J. Palmiere

pp. 1667-1676

DOI:

10.2355/isijinternational.54.1667

Abstract

Carbide precipitation in a H21 tool steel during conventional heat treatment was studied. The aim of this work was to study the exact microstructure and for better understanding of carbide formation during double tempering process of the H21 tool steel. The steel was austenised either at 1100°C or 1250°C for 1 hour, and water quenched. Double tempering was performed at 650, 750 and 800°C for 1 hour with air cooling in the first and second temper for each austenising temperature. The results showed that the double tempered microstructure consisted of tempered martensite, lower bainite and carbides. The current study confirmed previous findings and contributed to existing knowledge that depending on the tempering temperature, the types of carbide formed during double tempering were M2C, Fe3C, M6C and M23C6 carbides. The present study findings add substantially to our understanding of the carbide formation sequence in the H21 tool steel during double tempering. No secondary peak hardening was observed, and the highest hardness (505 HV) was obtained after austenising at 1250°C and double tempering at 650°C, which implies that the double tempering of the H21 tool steel should be carried out below 650°C.

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A Study of Carbide Precipitation in a H21 Tool Steel

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Dissolution Behaviour of NbC during Slab Reheating

Hongyeob Lee, Kyong-Su Park, Jung Hyeung Lee, Yoon-Uk Heo, Dong-Woo Suh, Harshad Kumar Dharamshi Hansraj Bhadeshia

pp. 1677-1681

DOI:

10.2355/isijinternational.54.1677

Abstract

It is common practice to reheat continuously cast slabs prior to hot-rolling. Here we examine the dissolution of niobium carbide precipitates present in the cast slabs, as a function of the temperature during heating at a typical rate. The initial condition of precipitates in slab is quantified with transmission electron microscopy. Kinetic simulations and interrupted quenching experiments indicate that the precipitates persist well beyond the equilibrium dissolution temperature. The coarsening of the precipitates during heating, as opposed to a general lowering in the mean size due to dissolution, occurs only at heating rates some two orders of magnitude slower than typical.

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Dissolution Behaviour of NbC during Slab Reheating

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An Approach to Predict the Depth of the Decarburized Ferrite Layer of Spring Steel Based on Measured Temperature History of Material during Cooling

Sangwoo Choi, Youngseog Lee

pp. 1682-1689

DOI:

10.2355/isijinternational.54.1682

Abstract

An approach is proposed to predict in sequence the phase transformation behavior, scale thickness, and depth of the decarburized ferrite layer of spring steel during cooling process once the measured temperature history of the spring steel were provided. This proposed approach successively couples a set of mathematical models describing the temperature evolution, phase transformation, oxidation, and decarburization. The dilatometry experiment was performed to verify the proposed method. Results reveal that the measured depth of the decarburized ferrite layer agreed well with the predicted depth. The predicted pearlite volume fraction nearly coincided with the measured value as well.

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An Approach to Predict the Depth of the Decarburized Ferrite Layer of Spring Steel Based on Measured Temperature History of Material during Cooling

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Crystal Orientation Relationships between Acicular Ferrite, Oxide, and the Austenite Matrix

Hidenori Nako, Hitoshi Hatano, Yoshitomi Okazaki, Ken Yamashita, Minoru Otsu

pp. 1690-1696

DOI:

10.2355/isijinternational.54.1690

Abstract

Crystal orientation relationships between acicular ferrite (AF), oxide and the austenite matrix have been investigated in low carbon steel weld by the submerged arc welding process. In particular, this study focused on the formation mechanism of the crystal orientation relationships. The AF microstructure was observed in weld metal containing titanium. Oxide particles were composed of MnTi2O4, amorphous phase and TiO2. The AF nucleated on MnTi2O4 having the Baker-Nutting (B-N) orientation relationship with the MnTi2O4 and Kurdjumov-Sachs (K-S) orientation relationship with the austenite matrix. This result implies that the MnTi2O4 had a rational orientation relationship with the austenite matrix. The orientation relationship is considered to be (001)MnTi2O4//(111)γ, [100]MnTi2O4//[211]γ from the viewpoint of the lattice coherency. It is supposed that the MnTi2O4 can be formed within oxide particles having this orientation relationship with the austenite matrix at high temperature during welding process. This mechanism allows the coexistence of both B-N and K-S orientation relationships, which lowers the AF/MnTi2O4 and AF/austenite interfacial energies. This results in the decrease of the activation energy for AF nucleation.

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Crystal Orientation Relationships between Acicular Ferrite, Oxide, and the Austenite Matrix

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Effect of Nb Addition on the Growth and Coarsening of Cu-particles in Ferritic Stainless Steel

Sengo Kobayashi, Takafumi Takeda, Takeshi Oe, Jun-ichi Hamada, Norihiro Kanno, Yoshiharu Inoue, Kiyomichi Nakai, Tatsuaki Sakamoto

pp. 1697-1704

DOI:

10.2355/isijinternational.54.1697

Abstract

The growth and coarsening of Cu-particles in 18%Cr–1.5%Cu ferritic stainless steels as a function of Nb content was investigated quantitatively. The samples were solution-treated at 1250°C and then isothermally aged at 700°C for up to 86400 s. Fine, spherical Cu-particles nucleated and grew during aging. The radius of the Cu particles increased in proportion to the one-third power of the aging time in all the stainless steels. The radius of the Cu particles in the Nb-added stainless steels was always smaller than that in the Nb-free stainless steel. The normalized standard deviation of the size distribution of the Cu particles increased and reached saturation at a certain value during aging. The increase in the standard deviation during aging was delayed by the addition of Nb. The volume fraction of Cu particles increased and reached saturation at a certain value during aging. The addition of niobium delayed the saturation of the volume fraction of the Cu particles. The slow growth of Cu particles in Nb-added stainless steels is thought to be owing to the slow diffusion of Nb atoms from the Cu particles.

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Effect of Nb Addition on the Growth and Coarsening of Cu-particles in Ferritic Stainless Steel

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Carbonitride Dissolution and Austenite Grain Growth in a High Cr Ferritic Heat-resistant Steel

Xingang Tao, Jianfeng Gu, Lizhan Han

pp. 1705-1714

DOI:

10.2355/isijinternational.54.1705

Abstract

Dissolution of carbonitrides and growth of austenite grain in X12CrMoWVNbN10-1-1 steel under various austenitizing conditions were investigated. The experimental results showed that the carbonitrides existing in after-forging heat treated state were mainly Cr23C6 and small amounts of NbN and Cr2N. However, Cr23C6 and Cr2N precipitates were dissolved completely after austenitization at 1070°C for 60 min or at 1200°C for 15 min, only the NbN particles left. The state of dissolution of NbN particles was also studied in detail as a function of austenitization holding time (tA) at different temperatures. Initially, the NbN particles dissolved with increasing tA at 1070°C. When tA reached over 360 min, the amount of NbN remained approximately constant. On the contrary, during the process of austenitization at 1010°C, no NbN particles dissolved into matrix. Starting from the fine and uniform grains, abnormal grain growth was observed after austenitizing at 1010°C for 960 min or at 1070°C for 180 min due to the heterogeneous distribution of NbN particles. The plot of grain size against tA indicated that the NbN particle with mean diameter of 117 nm and volume fraction of 3.1×10–4 would be sufficient to inhibit the austenite grain size effectively. Finally, the EBSD measurements demonstrated that the high energy grain boundaries whose misorientation range is 20–45° might be responsible for abnormal grain growth.

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Carbonitride Dissolution and Austenite Grain Growth in a High Cr Ferritic Heat-resistant Steel

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Back Stress Work Hardening Confirmed by Bauschinger Effect in a TRIP Steel Using Bending Tests

Hiroyuki Kato, Richard Moat, Tsutomu Mori, Kazuaki Sasaki, Philip Withers

pp. 1715-1718

DOI:

10.2355/isijinternational.54.1715

Abstract

Martensite formed in TRIP steels causes large work hardening. The expectation that this is due to the back stresses induced into the ferrite by the hard martensite was examined by the Bauschinger effect after room temperature tensile straining of a TRIP steel into which the martensite had been introduced by prior straining at –50°C. Bending tests were employed to detect the Bauschinger effect. The tests showed that the compressive flow stress became much smaller than the tensile flow stress and confirmed the expectation.

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Back Stress Work Hardening Confirmed by Bauschinger Effect in a TRIP Steel Using Bending Tests

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Observation and Quantification of Crack Nucleation in Ferrite-Cementite Steel

Kazuki Shibanuma, Shuji Aihara, Shigeru Ohtsuka

pp. 1719-1728

DOI:

10.2355/isijinternational.54.1719

Abstract

It is known that a cracking of brittle phase such as cementite works as a trigger of cleavage fracture initiation. This study shows a microscopic observation of cracked cementite and its quantitation of the cracking nucleation in ferrite-cementite steels. Seven steels with various sizes of microstructures are produced by laboratory scale vacuum melting and rolling. The cementite particle thickness was measured by a SEM observation and an image analysis. Tensile tests using circumferential notched round bar specimens were conducted. A trace analysis of cleavage surface of cementite using the EBSD analysis indicated a possibility that the cleavage surface coincides with (010) plane. Distributions of cementite particle crack lengths were measured for various strain and stress conditions. In order to understand a microscopic internal stress of cementite particle, a finite element analysis was carried out. An estimation formula of internal stress of the cementite particle from macroscopic stress and strain was developed based on the numerical results. A nucleation of cementite cracking should be quantitated based on a stochastic framework because of its uncertainties such as distribution, shape, orientation and so on. The measured distributions of cementite particle thickness and crack length were approximated by introducing a distribution function considering upper limit. Probability of nucleation of cementite cracking was formulated as a function of cementite particle thickness and macroscopic stress and strain, based on the approximated distribution function and the estimation formula of internal stress of the cementite particle.

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Observation and Quantification of Crack Nucleation in Ferrite-Cementite Steel

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Transition of Deformation Mechanism with Grain Refinement in Interstitial-Free Steel

Shun Itoh, Kasane Nakazawa, Tetsuya Matsunaga, Yoshitaka Matsukawa, Yuhki Satoh, Hiroaki Abe

pp. 1729-1734

DOI:

10.2355/isijinternational.54.1729

Abstract

To examine effects of the grain boundary (GB) and dislocation on the deformation mechanism for ultrafine-grained (UFG) and coarse-grained (CG) interstitial-free (IF) steels at room temperature, tensile tests and several types of microscopy were conducted for each steel. Atomic force microscopy revealed that the contribution of grain-boundary sliding (GBS) on deformation increased more prominently in UFG region than in CG region. Moreover, transmission electron microscopy revealed that dislocation motion was dominant in CG steel, where cell structure was formed with increasing strain. On the other hand, although dislocations moved in UFG steel, they did not tangle and piled up at GB, where interaction between GB and dislocation occurred markedly, causing significant GBS. Therefore, the dominant deformation mechanism changed from dislocation motion to GBS by decreasing grain size in IF steel.

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Transition of Deformation Mechanism with Grain Refinement in Interstitial-Free Steel

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Decrease in the Brittle-to-ductile Transition Temperature in Cu Added Nickel-free Austenitic Stainless Steels

Masaki Tanaka, Tatsuro Onomoto, Chihiro Furusho, Toshihiro Tsuchiyama, Kenji Higashida

pp. 1735-1740

DOI:

10.2355/isijinternational.54.1735

Abstract

Brittle-to-ductile transition (BDT) in Cu added Ni-free austenitic stainless steel was investigated. Temperature dependence of apparent fracture toughness was measured using four-point bending tests, indicating that the BDT temperature was decreased with the increase in the Cu content. The activation energy was obtained from the deformation rate dependence of BDT temperatures. It was found that the values of the activation energy was decreased with the increase in the Cu content, suggesting that the dislocation mobility in austenitic stainless steels was increased by Cu addition. The increase in the dislocation mobility induces the decrease in the BDT temperature. The values of the activation energy are deviated from the regression line drawn on the data which obtained from the materials with high Peierls potentials. Temperature dependence of 0.2% proof stress indicated that the effective stress was nearly independent from the Cu content while the values of activation volume were decreased with the increase in the Cu content. A model for dislocation glide was proposed to explain the both decrease in the activation energy and the activation volume with the increase in the Cu content.

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Decrease in the Brittle-to-ductile Transition Temperature in Cu Added Nickel-free Austenitic Stainless Steels

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Mechanism of Suppression of Sulfide Ion in Seawater Using Steelmaking Slag

Akio Hayashi, Satoshi Asaoka, Tetsuya Watanabe, Ryoko Kaneko, Katunori Takahashi, Yasuhito Miyata, Kyunghoi Kim, Tamiji Yamamoto, Ryo Inoue, Tatsuro Ariyama

pp. 1741-1748

DOI:

10.2355/isijinternational.54.1741

Abstract

In Japan, 15 million tons of steelmaking slag is produced annually as a by-product of the steelmaking process. It is known that steelmaking slag has specific properties to decrease hydrogen sulfide in seawater. To date, however, the specific mechanism is still unknown. This is the first report that explains the process of the slag reducing the hydrogen sulfide level.
We added slag to the artificial seawater containing sulfide ion and obtained fine particles. We analyzed the reaction products with X-ray absorption fine structure (XAFS) and scanning electron microscopy-energy dispersive X-ray detector (SEM-EDX) and confirmed corresponding peaks of FeS, FeS2, sulfur and sulfate.
We also measured the oxidation-reduction potential (ORP) and found that a shift to oxidizing atmosphere was promoted by adding slag, which oxidized sulfide ion to sulfuric acid ion.
These data suggested that hydrogen sulfide level in seawater is reduced not only by the reaction of sulfide with iron contained in steelmaking slag but also by oxidation of sulfide in seawater with steelmaking slag. These results imply that effective utilization of steelmaking slag in coastal areas has a capability to improve the surrounding marine environment.

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Mechanism of Suppression of Sulfide Ion in Seawater Using Steelmaking Slag

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