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ISIJ International Advance Publication

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. 63 (2023)

    1. No.3
    2. No.2
    3. No.1

  2. Vol. 62 (2022)

    1. No.12
    2. No.11
    3. No.10
    4. No.9
    5. No.8
    6. No.7
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    8. No.5
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    11. No.2
    12. No.1

  3. Vol. 61 (2021)

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    2. No.11
    3. No.10
    4. No.9
    5. No.8
    6. No.7
    7. No.6
    8. No.5
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    10. No.3
    11. No.2
    12. No.1

  4. Vol. 60 (2020)

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    3. No.10
    4. No.9
    5. No.8
    6. No.7
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    8. No.5
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  5. Vol. 59 (2019)

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    5. No.8
    6. No.7
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  6. Vol. 58 (2018)

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    6. No.7
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  7. Vol. 57 (2017)

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  8. Vol. 56 (2016)

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    3. No.10
    4. No.9
    5. No.8
    6. No.7
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    8. No.5
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  9. Vol. 55 (2015)

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  10. Vol. 54 (2014)

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    3. No.10
    4. No.9
    5. No.8
    6. No.7
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  11. Vol. 53 (2013)

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  12. Vol. 52 (2012)

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    3. No.10
    4. No.9
    5. No.8
    6. No.7
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  13. Vol. 51 (2011)

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    3. No.10
    4. No.9
    5. No.8
    6. No.7
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    8. No.5
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    10. No.3
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  14. Vol. 50 (2010)

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    3. No.10
    4. No.9
    5. No.8
    6. No.7
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    8. No.5
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  15. Vol. 49 (2009)

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    3. No.10
    4. No.9
    5. No.8
    6. No.7
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    8. No.5
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  16. Vol. 48 (2008)

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  17. Vol. 47 (2007)

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    3. No.10
    4. No.9
    5. No.8
    6. No.7
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  18. Vol. 46 (2006)

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    3. No.10
    4. No.9
    5. No.8
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  19. Vol. 45 (2005)

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  20. Vol. 44 (2004)

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  21. Vol. 43 (2003)

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  22. Vol. 42 (2002)

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  23. Vol. 41 (2001)

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  24. Vol. 40 (2000)

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  25. Vol. 39 (1999)

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  26. Vol. 38 (1998)

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  27. Vol. 37 (1997)

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  28. Vol. 36 (1996)

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  29. Vol. 35 (1995)

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  30. Vol. 34 (1994)

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  31. Vol. 33 (1993)

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  32. Vol. 32 (1992)

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  33. Vol. 31 (1991)

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  34. Vol. 30 (1990)

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  35. Vol. 29 (1989)

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21 Mar. (Last 30 Days)

ISIJ International Advance Publication

Experimental investigation on the formation mechanism of secondary inclusions in Fe-36mass%Ni alloy using a novel combination analysis technique

Hiroshi Fukaya, Jonah Gamutan, Makoto Kubo, Shintaro Yano, Shigeru Suzuki, Takahiro Miki

DOI:

10.2355/isijinternational.ISIJINT-2022-433

Abstract

Controlling the size, number, and composition of secondary inclusions is vital in the production of high-quality steels. In this study, experimental and computational investigation of the relationship between secondary inclusion formation in Fe-36mass%Ni alloy and cooling rate was carried out. Assuming the case of large ingots, solidification experiments using various cooling rates (0.17 to 128 K/min) were employed and the size, number, composition, and distribution of inclusions were analyzed by SEM-EDS automatic inclusion analysis. Like previous studies, inclusion number density increased with increasing cooling rate, while inclusion size decreased with increase of cooling rate. On the contrary, oxide inclusion area fraction was found to have little relationship with the cooling rate and was instead found related with oxygen content of the sample. As a new attempt to investigate the relationship between microsegregation and secondary inclusion formation, a combination of SEM-EDS analysis and EPMA mapping analysis was carried out. By superimposing information of microsegregation and inclusions, it was found that high-Al2O3 inclusions formed during the early stage of solidification, whereas low-Al2O3 inclusions formed during the later stage of solidification. These findings suggest that Al2O3 inclusions formed in the early stage of solidification reacted with the remaining Si-enriched liquid steel and changed into low-Al2O3 inclusions. Experimental results were also confirmed by thermodynamic calculations. Present work made it possible to understand deeper the relationship between microsegregation and secondary inclusion formation.

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Experimental investigation on the formation mechanism of secondary inclusions in Fe-36mass%Ni alloy using a novel combination analysis technique

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Comparison of crack initiation sites and main factors causing hydrogen embrittlement of tempered martensitic steels with different carbide precipitation states

Naoki Uemura, Takahiro Chiba, Kenichi Takai

DOI:

10.2355/isijinternational.ISIJINT-2023-026

Abstract

The dependence of crack initiation sites and main factors causing hydrogen embrittlement fracture on carbide precipitation states has been investigated for tempered martensitic steels with the same tensile strength of 1450 MPa. Notched specimens charged with hydrogen were stressed until just before fracture and subsequently unloaded. The crack initiation site exhibited intergranular (IG) fracture at 21 μm ahead of the notch tip as observed by scanning electron microscopy (SEM) for 0.28% Si specimens with plate-like carbide precipitates on prior austenite (γ) grain boundaries. This crack initiation site corresponded to the vicinity of the maximum principal stress position as analyzed by a finite element method (FEM). The initiation site corresponded to the triple junction of prior γ grain boundaries as analyzed by electron backscattered diffraction (EBSD). In contrast, the crack initiation site exhibited quasi-cleavage (QC) fracture at the notch tip for 1.88% Si specimens with fine and thin carbide particles in the grains. This crack initiation site corresponded to the maximum equivalent plastic strain site obtained by FEM. Additionally, the crack initiated on the inside of prior γ grain boundaries and propagated along the {011} slip plane with higher kernel average misorientation (KAM) values as analyzed by EBSD. These findings indicate that differences in carbide precipitation states changed the crack initiation sites and fracture morphologies involved in hydrogen embrittlement depending on mechanical factors such as stress and strain and microstructural factors.

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Comparison of crack initiation sites and main factors causing hydrogen embrittlement of tempered martensitic steels with different carbide precipitation states

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Thermodynamic formation and three-dimensional characterization of MnS-MgAl2O4 composite inclusions in steel

Qian Meng, Liying Ju, Tao Li, Min Tan, Xiaopei Guo, Henan Cui, Peidong Xu, Han Guo

DOI:

10.2355/isijinternational.ISIJINT-2022-329

Abstract

The distribution and morphology of inclusions in steel have an important effect on the quality of steel. It has been proved that the oxide inclusions can be modified into small and dispersed spinel inclusions by adding proper amount of Mg in steel. The MnS-MgAl2O4 composite inclusions are formed with the core of MgAl2O4 inclusions during the solidification process of molten steel, which has deforming ability and can improve the properties of materials steel. However, the investigation of the control of the composite inclusions is limited by the lack of understanding structure of the inclusions. In this study, the Mg treated steel samples were prepared by induction furnace in this study. In the experiment, SEM-EDS was used to characterize the samples, and thermodynamic calculations were used to describe the evolution mechanism of inclusions and MnS-MgAl2O4 composite inclusions formed in steel samples with different Mg contents. The atomic mismatch calculated between MnS and MgAl2O4 proves that they can nucleate effectively. The three-dimensional (3D) morphology of the composite inclusion of MnS-MgAl2O4 in steel samples were observed by using the X-ray Micro-CT in the beamline of BL16U2 at Shanghai Synchrotron Radiation Facility (SSRF). It is proved that MnS and MgAl2O4 phases exist in the form of co-associated, which is valuable for the control of composite inclusions in steel. The current work provide a powerful method to analyze the detailed structure of the composite inclusions in the steel.

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Thermodynamic formation and three-dimensional characterization of MnS-MgAl2O4 composite inclusions in steel

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Effect of Nb on grain growth behavior in the heat affected zone of linepipe steels

Daichi Izumi, Nobuyuki Ishikawa, Pello Uranga, Nerea Isasti, Jose M. Rodriguez-Ibabe, Douglas Stalheim, David Jarreta, David Martin

DOI:

10.2355/isijinternational.ISIJINT-2022-556

Abstract

Recrystallization and grain growth during plate rolling are prevented by Nb addition both with the solute drag and the Nb carbide precipitation. Although a fine microstructure is achieved in the base material, welding heat completely changes the microstructure in the heat affected zone (HAZ). In this study, laboratory simulation of the coarse grain HAZ (CGHAZ) thermal cycle of double submerged arc welded linepipe was carried out using low carbon steels containing different Nb contents. Extraction residue analysis of the simulated CGHAZ samples revealed that almost all the Nb remained in solid solution. To clarify the interaction of Nb carbide dissolution and grain growth on overall simulated HAZ microstructure evolution, additional weld HAZ thermal simulations were performed. It was found that Nb carbides remain undissolved at HAZ peak temperatures up to 1200°C and showed significant pinning effect to prevent austenite grain growth. Significant grain growth was seen after continuous fast heating to 1350°C peak temperature, while the higher Nb added steel showed a slower overall austenite grain growth rate, suggesting that grain growth in the HAZ at higher temperature was suppressed by the combined effects of slower coarse Nb carbide dissolution providing some pinning, and the solute drag effect of higher amounts of Nb in solid solution. A pronounced retardation of longer-term isothermal grain growth was identified at 1350°C at higher levels of solute Nb, confirming the influence of Nb solute drag on high temperature resistance to austenite grain coarsening.

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Effect of Nb on grain growth behavior in the heat affected zone of linepipe steels

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Austenite reversion behavior of maraging steel additive-manufactured by laser powder bed fusion

Naoki Takata, Yuya Ito, Ryoya Nishida, Asuka Suzuki, Makoto Kobashi, Masaki Kato

DOI:

10.2355/isijinternational.ISIJINT-2023-045

Abstract

This study was set to fundamentally investigate the characteristics of austenite reversion occurring in maraging steels additive-manufactured by laser powder bed fusion (L-PBF). The maraging steel samples manufactured under different L-PBF process conditions (laser power P and scan speed v) were subjected to heat treatments at 550 oC for various durations, compared with the results of the austenitized and water-quenched sample with fully martensite structure. The L-PBF manufactured samples exhibited the martensite structure (including localized austenite (γ) phases) containing submicron-sized cellular structures. Enriched alloy elements were detected along the cell boundaries, whereas such cellar structure was not found in the water-quenched sample. The localized alloy elements can be rationalized by the continuous variations in the γ-phase composition in solidification during the L-PBF process. The precipitation of nanoscale intermetallic phases and the following austenitic reversion occurred in all of the experimental samples. The L-PBF manufactured samples exhibited faster kinetics of the precipitation and austenite reversion than the water-quenched sample at elevated temperatures. The kinetics changed depending on the L-PBF process condition. The enriched Ni element (for stabilizing γ phase) localized at cell boundaries would play a role in the nucleation site for the formation of γ phase at 550 oC, resulting in enhanced austenite reversion in the L-PBF manufactured samples. The variation in the reaction kinetics depending on the L-PBF condition would be due to the varied thermal profiles of the manufactured samples by consecutive scanning laser irradiation operated under different P and v values.

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Austenite reversion behavior of maraging steel additive-manufactured by laser powder bed fusion

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Microscopic shear deformation characteristics of the Lüders front in a metastable austenitic transformation-induced-plasticity steel

Naoki Maruyama, Miyuki Yamamoto, Shinichiro Tabata

DOI:

10.2355/isijinternational.ISIJINT-2022-550

Abstract

To elucidate the mechanisms of deformation and a state of plastic stability at the front of Lüders bands during a tensile test, metastable austenitic transformation-induced plasticity (TRIP) steels with different dislocation densities and ferritic steels were characterized via macroscopic-DIC-based stress–strain investigations and scanning electron microscopy (SEM). A direct correlation between stress–strain curves and measured strain distributions in the tensile specimen indicated that the Lüders front represents a transition region from a state of plastic instability to one of stability, whereby a general rule relating the Lüders strain ∆????????∗ and increments in the true stress in the Lüders band ∆????????∗ to a lower yield stress (????????0∗) can be described as ????????0∗=∆????????∗∆????????∗ irrespective of the amount of deformation-induced martensite in the band or crystal structure of the steel. The inclination angle of the Lüders front with respect to the tensile direction changed from 55° to 90° with a reduction in the measured strain ratio (-????????????/????????????) in the Lüders band, and the change agreed with the tendency calculated by the plasticity model, assuming the pure shear occurs under the minimum shear strain criterion. SEM observations of the sheet surface and the front cross-section in the TRIP steel showed the formation of multiple inclined ~20 μm-wide shear deformation zones that accompanied a reduction in thickness. All the observed geometrical characteristics of the Lüders front were qualitatively described by a mechanism involving minimizing the misalignment from the fixed tensile axis caused by ‘shear' deformation.

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Microscopic shear deformation characteristics of the Lüders front in a metastable austenitic transformation-induced-plasticity steel

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3D transient heat transfer simulation and optimization for initial stage of steel continuous casting process

Jian Yang, Zhi Xie, Hongji Meng, Zhenwei Hu, Wenhong Liu, Zhenping Ji

DOI:

10.2355/isijinternational.ISIJINT-2022-479

Abstract

In this paper, a specially designed three dimensional transient heat transfer model has been developed for initial stage of steel continuous casting process. Firstly, a general three dimensional heat transfer model for continuous casting process has been established, and it is discretized by finite volume method and solved by alternative direction implicit method. For transient simulation of initial stage, the fixed-length moving bloom with dummy bar at its bottom experiences time-variant boundary conditions, while the filling process is also equivalent to moving process. Secondly, the transient model has been calibrated by surface temperature measurements by pyrometer and shell-thickness measurements by nail-shooting. Online temperature measurement for verification indicates the calibrated model is reliable as the maximum error between calculations and measurements are within ±28°C, and soon in less than 80s the error will be reduced to within ±5°C. Thirdly, uncertainty caused by dummy bar's length and thermo-physical properties has been studied, and the results indicate that the uncertainty is quite small and acceptable. Finally, the model has been applied to optimizing the secondary cooling water flows and cut length of strand head.

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3D transient heat transfer simulation and optimization for initial stage of steel continuous casting process

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Mathematical Modeling and Analyses of Integrated Process with Blast Furnace Iron Making and Co-gasification of Coal-COG-BF top gas

Jianpeng Li, Xiaojie Liu, Xin Li, Qing Lyu, Yana Qie

DOI:

10.2355/isijinternational.ISIJINT-2022-505

Abstract

For the blast furnace iron-making process which depends on the coke seriously and is the largest CO2 emission source in iron and steel industry, a novel technology integrated the blast furnace process and co-gasification of coal-COG-BF top gas is investigated and examined its potential of energy conservation and CO2 emission reduction. The mathematical model of the whole integrated process is established based on mass and heat balance principles. And typical operation analyses for the integrated process are demonstrated by this model. The results indicate that it takes about 4 times for the unsteady process caused by the recycling of BF top gas to reach steady. Compared with conventional blast furnace process, the coke ratios in two integrated process cases selected decrease by 33.5kg/tHM and 81.3kg/tHM obviously, and the fuel ratios decrease 1.1% and 8.2% due to the increase of coal ratios by 27.9kg/tHM and 39.1kg/tHM. The energy consumption decreases by 8.3% and 10.8%. And the CO2 emission decreases by 37.0% and 42.9%.

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Mathematical Modeling and Analyses of Integrated Process with Blast Furnace Iron Making and Co-gasification of Coal-COG-BF top gas

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Prediction of Graphitization Behavior during Long-Term Creep in Carbon Steels

Tomotaka Hatakeyama, Kaoru Sekido, Kota Sawada

DOI:

10.2355/isijinternational.ISIJINT-2022-558

Abstract

Carbon steels with ferrite and pearlite microstructures suffer from graphitization by the decomposition of cementite when exposed to elevated temperatures for long periods. Graphitization degrades the mechanical properties of the steels and increases its risk of failure. Therefore, by considering the extended life span of a thermal power plant, where carbon steels are used at elevated temperatures, evaluation of graphitization risk is necessary. This study evaluates the effect of temperature, stress, time, and chemical composition for both elongated and spherical graphitization using logistic regression of previously reported graphitization conditions in long-term creep ruptured specimens and establishes a prediction formula for graphitization occurrence. In addition, the accuracy of the prediction formula was validated by investigating the graphitization behavior of other carbon steels.

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Prediction of Graphitization Behavior during Long-Term Creep in Carbon Steels

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Effects of Cooling Conditions and γ Grain Size on each Behavior of Transformations, 3-Dimensional Thermal Deformation and Stress Generation during Immersion Cooling of Steel Bloom

Kohichi Isobe, Yuga Kumagai, Takumi Satou

DOI:

10.2355/isijinternational.ISIJINT-2023-032

Abstract

To optimize reverse transformation treatment, which is effective in preventing hot rolling cracking in the CC-HCR (Continuous Casting - Hot Charge Rolling) process, three-dimensional metallo-thermo-mechanical analyses were performed. The metallo-thermo-mechanics and a CCT (Continuous Cooling Transformation) diagram estimation method using JMatPro were used to obtain the required cooling time for reverse transformation in immersion cooling with water jet and to elucidate the effects of nonuniform cooling and γ grain size on thermal deformation and stress generation behaviors during cooling and the mechanisms of these events.These analyses clarified the following. When diffusion-controlled transformation occurs during cooling, the required cooling time increases as Dγ (Diameter of γ grain) increases, and becomes substantially constant when only martensitic transformation occurs. In addition, the difference of Dγ causes a difference in the type of transformation that occurs during cooling and the temperature range where transformation occurs during cooling, and these differences produce differences in the amount of transformation expansion, which greatly affects the bloom deformation behavior during cooling. Furthermore, there is a difference in the level of the maximum generated stress during cooling depending on whether the transformation that occurs near the bloom surface layer during cooling is diffusion-controlled transformation or martensitic transformation. In addition, this difference in transformation behavior also causes a difference in the mechanism of maximum stress generation.

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Effects of Cooling Conditions and γ Grain Size on each Behavior of Transformations, 3-Dimensional Thermal Deformation and Stress Generation during Immersion Cooling of Steel Bloom

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Comprehensive Evaluation Method for Cooling Effect on Process Thermal Dissipation Rate during Continuous Casting Mold

Kai-tian Zhang, Zhong Zheng, Jian-hua Liu, Liu Zhang, Da-li You

DOI:

10.2355/isijinternational.ISIJINT-2022-478

Abstract

Cooling in the continuous casting mold is the essential process of the molten steel solidifying into a slab shell. The synergistic relationship of casting state, process operation, continuous casting equipment, and other factors is complex and has a significant influence on thermal transfer in the mold. Therefore, a concept of "process thermal dissipation rate" defined by mold system thermal input and output was proposed in this work. The thermal input of molten steel was calculated through the casting temperature, and the slab residual thermal at the outlet of the mold was calculated by the solidification heat transfer model. Consequently, the thermal dissipation rate was calculated to quantify the multi-factor cooperative relationship of mold. The industrial case reflected that the thermal dissipation rates of three stable castings were 12.5%, 14.3%, and 18.8%, respectively, and all of them were obviously abnormal in unsteady casting such as start casting, changing tundish, and end casting. The results above indicated that the thermal dissipation rate could characterize the mold cooling target under the cooperation of complex factors and provide a new method for the dynamic evaluation of the mold system cooling effect with different casting states. Accordingly, the correlation analysis between superheat, casting speed, cooling water flow, and thermal dissipation rate revealed the synergistic influence law of multi-operation on mold cooling effect, which provided a new idea for the precise control of multi-process collaboration in continuous casting.

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Tetsu-to-Hagané Vol.41(1955), No.1

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Comprehensive Evaluation Method for Cooling Effect on Process Thermal Dissipation Rate during Continuous Casting Mold

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Application of Variable Gauge Rolling Technology for Plate to Reduce the Head Impact

Zhijie Jiao, Chunyu He, Shiwen Gao, Xu Wang, Yongxiang Zhang, Lei Hao

DOI:

10.2355/isijinternational.ISIJINT-2022-438

Abstract

The Variable Gauge Rolling (VGR) technology is adopted for plate rolling. Two passes are treated as a group, with reducing the head reduction, increasing the tail reduction, to reduce the peak impact torque of the head, and give full play to the equipment capacity in the stable rolling stage to increase the pass reduction. The prediction models of plate width and length, rolling force and torque in VGR process are established. The using strategy of VGR are determined, and two methods for increasing reduction are put forward. The main body and head and tail sections of the rolled plate are calculated separated. The reduction corresponding to the target rolling torque is calculated by Newton iterative method, and pass schedule distribution of VGR process is shown. The VGR technology is applied for plate rolling process. The practical application shows that the influence of head impact in the plate rolling process can be reduced by using VGR. The torque amplification coefficient decreases linearly with the increase of gauge variation, and rolling passes number can be reduced through reasonable pass schedule distribution. The practical application shows that VGR can reduce the influence of head impact in the plate rolling process.

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Application of Variable Gauge Rolling Technology for Plate to Reduce the Head Impact

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Optimum Water Content Estimation for Wet Granulation of Iron Ore Powders with Quicklime Binder

Shota Yokokawa, Hideya Nakamura, Tomotaka Otsu, Shuji Ohsaki, Satoru Watano, Shohei Fujiwara, Takahide Higuchi

DOI:

10.2355/isijinternational.ISIJINT-2022-498

Abstract

Wet granulation plays an important role in the processing of fine ore powder. Water content is a critical process parameter that determines the granule properties during wet granulation. However, in the ironmaking industry, various types of iron ore powder imported from different regions are blended, quicklime powder is added as a binder, and used as raw materials. Therefore, the physicochemical properties of the raw powders are not always consistent, which makes it difficult to determine the optimum water content. In this study, we present a method to determine the optimum water content using the agitation torque of wet ore powder blended with quicklime. First, we investigated the agitation torque for blending of various types and ratios of ore powders and quicklime. Two types of torque profiles were observed: a unimodal torque profile (Type I) and a torque profile with a plateau region (Type II). From the agitation torque profile, the characteristic water content (????torque) for estimating the optimum water content (????optexp) was individually defined for the types I and II. The ????torque was well correlated with the ????optexp, regardless of the type and blending ratio of the original ore powders and quicklime. Finally, the optimum water content was estimated using the ????torque. The estimated water content was confirmed to be in good agreement with the experimental results, demonstrating that the optimum water content for the wet granulation of fine ore powder with quicklime can be determined using agitation torque.

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Optimum Water Content Estimation for Wet Granulation of Iron Ore Powders with Quicklime Binder

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A novel way refining the partially reverted globular austenite in reversion from martensite

Xianguang Zhang, Huan Liu, Yingjie Ren, Wenchao Yang, Jiajun Chen, Peng Shi, Goro Miyamoto, Tadashi Furuhara

DOI:

10.2355/isijinternational.ISIJINT-2022-503

Abstract

Refining of the partially reverted globular austenite grain is of great importance to obtain high mechanical property of advanced high strength steels and a new approach for such refining, pre-tempering of initial martensite, is proposed in this study. The pre-tempering results in precipitation of the coarse and alloying-elements partitioned cementite particles in an Fe-2.5Mn-1.5Si-0.35C alloy. The cementite particles with Mn and Si partitioning enhanced the nucleation of globular austenite grains but suppressed its growth during continuous heating. The enhancement in nucleation and restriction in growth of globular austenite resulted in the refinement of partially reverted globular austenite grains and fully transformed austenite grains after reversion. This provides a new strategy to control the growth of partially reverted globular austenite by tailoring coarse and partitioned cementite particles.

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A novel way refining the partially reverted globular austenite in reversion from martensite

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Effect of microstructure on mechanical properties of quenching & partitioning steel

Yuki Toji, Tatsuya Nakagaito, Hiroshi Matsuda, Kohei Hasegawa, Shinjiro Kaneko

DOI:

10.2355/isijinternational.ISIJINT-2022-508

Abstract

The microstructure and mechanical properties of a low-carbon steel produced via the quenching & partitioning (Q&P) heat treatment was investigated, with particular focus on the hole expansion ratio, which is an index of the stretch-flange-formability. 0.19mass%C-1.5mass%Si-2.9mass%Mn steel was annealed at 850 ˚C, then cooled to 150~400 ˚C (QT: quench temperature), followed by holding at 400˚C for 1100 s. Yield strength and hole expansion ratio drastically increased when the QT was below the Ms (martensite start) temperature. The steel with QT of 300 ˚C exhibited not only a higher elongation, which has been well documented, but also a higher hole expansion ratio, when compared to the conventional TRIP steel with QT of 400 ˚C having equal tensile strength around 1200 MPa. The micro-void formation during deformation was suppressed in the steel with QT of 300 ˚C due to the smaller volume fraction of large blocky martensite compared to the TRIP steel. These excellent mechanical properties are attributed to its unique microstructure consisting of a certain amount of tempered martensite, lath-shaped retained austenite and bainitic ferrite, which was generated via the Q&P heat treatment.

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Effect of microstructure on mechanical properties of quenching & partitioning steel

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Influence of the Slag Rim on the Heat Transfer Behavior of a Mold

Wang Xingjuan, Guo Yinxing, Xiao Pengcheng, Zhu Liguang, Di Tiancheng

DOI:

10.2355/isijinternational.ISIJINT-2022-390

Abstract

To explore the influence of the slag rim on the heat transfer behavior of a mold, a slag rim was extracted from a stainless steel production factory for high-temperature continuous casting simulation experiments. The 2DIHCP (Two-Dimensional Inverse Heat Conduction Problem) two-dimensional inverse problem calculation model was used to analyze the heat transfer characteristics in the mold, and the temperature and heat flux distribution of the hot surface of the mold copper wall under different working conditions were investigated. The results showed that under a casting speed of 0.5 Â m/min, vibration frequency of 2 Hz, and amplitude of 10 mm, the seepage flow of the mold flux was 9.314 and 6.326 g with and without the slag rim, respectively, the thickness of the slag film was 2.1 and 1.3 mm, respectively, the temperature of the mold hot surface was 118.24 and 134.83 °C, respectively, and the maximum heat flux density of the mold was 0.98 and 1.95 MW/m2, respectively. Through data comparison, when there is a slag rim, the amount of slag infiltration decreased by 32%, the thickness of the slag film decreased by 38%, the temperature of the hot surface of the mold increased by 14%, the heat flux density increased by 99%, and the internal crystal morphology of the slag film was complete. This indicates that the slag rim affects the heat transfer behavior in the mold by restricting the inflow of the mold flux and affecting the formation of the slag film.

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Influence of the Slag Rim on the Heat Transfer Behavior of a Mold

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Improved cross-tension strength of a friction-element-welding joint by tempering treatment using electric heating

Sho Matsui, Kohsaku Ushioda, Hidetoshi Fujii

DOI:

10.2355/isijinternational.ISIJINT-2022-535

Abstract

Resistance spot welding is widely used in automobile assembly, but reduction of the cross-tension strength (CTS) is inevitable when using high-strength steel sheets. Therefore, we focused on joining high-strength steel sheets using friction element welding (FEW), which is mainly used to join steel sheets and aluminum alloy sheets, to improve the CTS. However, even when using FEW, the CTS decreases at the joint, when a high-carbon-content steel sheet is used as the lower sheet. This CTS decrease is presumed to be due to the low local ductility caused by the large hardness difference (ΔHn) between martensite (M) and ferrite (α) in the inter-critically annealed and quenched area during joining. The local ductility of the material having complex structure with hard and soft phases is affected by the structural morphology and ΔHn. Therefore, we attempted to improve the CTS by creating joints whose α of the inter-critically annealed and quenched area was equiaxed or acicular, and performed tempering treatment using electric heating to reduce ΔHn of this part. The results showed that ΔHn decreased at the annealed joint and the CTS improved. Furthermore, the highest CTS was observed at the joint having acicular α when tempering was performed. It was inferred that the reduction of ΔHn using electric heating improved the local ductility and CTS of the area. Furthermore, it was considered that the local ductility and CTS are also influenced by the α morphology.

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Improved cross-tension strength of a friction-element-welding joint by tempering treatment using electric heating

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Influence of High Concentration Vacancy-Type Defects on the Mobility of Edge Dislocation in α-Iron: An Atomistic Investigation

Sunday Temitope Oyinbo, Ryosuke Matsumoto

DOI:

10.2355/isijinternational.ISIJINT-2022-356

Abstract

Many vacancy-type defects (vacancy, vacancy clusters, and hydrogen-vacancy complexes) are generated in metals by plastic deformation in hydrogen environments. In this study, we use extensive molecular dynamics calculations based on a highly accurate interatomic potential to examine how vacancy-type defects affect the mobilities of edge dislocations in α-iron at a temperature range of 300–500 K and a dislocation speed ????d range of 0.1–10 m/s. Under all conditions, the edge dislocation absorbs the vacancies along the slip plane and causes them to migrate with the edge dislocation. Although the necessary shear stress to glide edge dislocation in α-iron containing vacancy increases with dislocation speed, the effect is small compared to the hydrogen effects. The dislocation absorbs the hydrogen-vacancy complex along the slip plane and causes the hydrogen and the jog to migrate with the edge dislocation at low dislocation velocity regimes (????d ≤ 0.1 m/s). Therefore, the hydrogen-vacancy complex exerts a continuous drag effect on the dislocation. At higher dislocation speeds (???????? ≥ 1 m/s), hydrogen does not migrate with the dislocation, resulting in the formation of isolated hydrogen detached from the dislocation and diffused into the material; only vacancy is absorbed. When multiple hydrogen-vacancy complexes are arranged along the slip plane, the dislocation absorbs them if they interact with dislocation at different points rather than at a single point to avoid the formation of a large jog at the colliding segment, and the required shear stress increases as the hydrogen atoms in the dislocation core increase.

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Influence of High Concentration Vacancy-Type Defects on the Mobility of Edge Dislocation in α-Iron: An Atomistic Investigation

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Effects of Normalizing Temperature on the Precipitation of Fine Particles and Austenite Grain Growth during Carburization of Al- and Nb-Microalloyed Case-Hardening Steel

Genki Saito, Norihito Sakaguchi, Kiyotaka Matsuura, Taichi Sano, Takuya Yamaoka

DOI:

10.2355/isijinternational.ISIJINT-2022-429

Abstract

This paper deals with the precipitation behaviors of AlN and Nb(C, N) particles during normalizing of hot-forged Al- and Nb-microalloyed case-hardening steel, and investigates the effects of the number density and volume fraction of these particles on the grain growth behavior of austenite (γ) during the subsequent high-temperature carburization. When the sample was cooled from the hot forging temperature at 16 °C/min, AlN did not precipitate at all and was completely supersaturated in the matrix, although fine Nb(C, N) particles precipitated during cooling. When reheated to the normalizing temperature, AlN particles started precipitation at approximately 620–640 °C on the grain boundaries of the bainitic ferrite matrix and the interfaces between the cementite particles and the matrix, and the AlN particles contained Cr and Mn, and had an NaCl structure and Bain orientation relationship with the matrix. The AlN structure changed from NaCl type into wurtzite type at approximately 800 °C. AlN particles grew during reheating to the normalizing temperature and holding at the temperature. Both the number density and volume fraction of the AlN particles were dramatically increased by reducing the normalizing temperature from 1070 to 900 °C. The distribution of these particles strongly affected the ( grain structure formed during carburization. As the normalizing temperature was reduced from 1070 to 950 and 900 °C, the  grain structure became finer. Some abnormally large grains were formed near the carburized surface, when normalized at 1070 °C. However, no abnormal grain was found when normalized below 950 °C.

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Effects of Normalizing Temperature on the Precipitation of Fine Particles and Austenite Grain Growth during Carburization of Al- and Nb-Microalloyed Case-Hardening Steel

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Iron ore granulation for sinter production: Developments, progress, and challenges

Lele Niu, Jianliang Zhang, Yaozu Wang, Jian Kang, Sida Li, Changdong Shan, Zhen Li, Zhengjian Liu

DOI:

10.2355/isijinternational.ISIJINT-2022-460

Abstract

Iron ore granulation is an indispensable process in the production of sinter that can influence and regulate the yield, efficiency and quality. Although a great deal of research has been done on the granulation process over the past decades, we still need to think about the current and future development of this process, as sinter is still an essential raw material for ironmaking blast furnace today. This paper begins with a review of particle agglomeration theory development for sintering granulation, followed by a summary of existing granulation evaluation methods and indexes. The roles of iron ore, fuel, fluxes, and moisture in sintering granulation are also analyzed, and finally advanced granulation equipment and processes for industrial production, as well as their applications, are summarized. Correspondingly, the challenges in sintering granulation field are proposed to include: (1) Development of iron ore sintering industry; (2) Ore blending optimization based on synergistic coupling of granulation and sintering; (3) Optimization of granulation process and equipment; (4) Methods and tools for granulation scientific research. These issues will be tackled and overcome in the future by both steel enterprises and academic researchers, generating suggestions for future development in the field of sintering granulation.

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Iron ore granulation for sinter production: Developments, progress, and challenges

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State of Deadman in Blast Furnace Hearth and Its Internal Phase Distribution Characteristics

Yong Deng, Ran Liu, Dequan Wang, Kexin Jiao, Yanjun Liu, Ziyu Guo, Sai Meng, Mingbo Song, Zhixin Xiao

DOI:

10.2355/isijinternational.ISIJINT-2022-363

Abstract

The state of deadman in hearth is important for the long campaign life of blast furnace (BF). In order to clarify the influence of deadman on sidewall erosion, the corresponding relationship between the shape of deadman and sidewall erosion was studied, the fundamental reason for the difference of sidewall erosion was analyzed, the influence mechanism of slag-coke interface and iron-coke interface on the coke in deadman was explored based on the phase distribution in deadman. The results show that: The shape of circumferential bulge at the root of deadman is a common feature of BFs, this feature is the main reason for the serious erosion of sidewall, and the serious erosion area of sidewall corresponds to the root position of deadman. The deadman shows a dynamic evolution law of sinking and floating under the action of force in the smelting process of BF, the depth of slag and iron level in hearth has the greatest influence on the deadman. The difference of central voidage of deadman is the fundamental reason for the difference of sidewall erosion for BFs in which the deadman is in the same floating state. Slag-coke interface and iron-coke interface commonly exist in hearth. The dissolution reaction at iron-coke interface makes carbon in coke continuously migrate into molten iron, which makes the graphitization degree of coke increase, the coke is easy to pulverize, this is the main mechanism of coke deterioration and renewal in deadman. The enrichment of harmful element K at slag-coke interface makes the coke expand and crack, the coke matrix is easier to peel off, which accelerates the deterioration process of coke.

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State of Deadman in Blast Furnace Hearth and Its Internal Phase Distribution Characteristics

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Estimation of Material Constants of Hot Coke under Inert Atmosphere

Yasuhiro Saito, Takumu Higo, Chiho Tsukamoto, Shinji Kudo, Jun-ichiro Hayashi

DOI:

10.2355/isijinternational.ISIJINT-2022-190

Abstract

The strength, pore structure, and material constants of coke prepared from caking coal (Coke A) and non- or slightly caking coal (Coke C) were experimentally and numerically investigated with a particular focus on those values at high temperatures. Coke A showed higher strength and lower porosity than Coke C. The pore structure imaged by X-ray computed tomography was translated to the finite element mesh with the image-based modeling, and the stress analysis based on the finite element method was performed to calculate the mode value of maximum principal stress at different Young's modulus and Poisson's ratio. Young's modulus of Coke A and Coke C at a constant Poisson's ratio decreased and increased, respectively by heating. When the temperature increased, the compression stress of Coke A increased. The result indicated that the coke strength could be increased by heating because of the decrease in apparent Young's modulus, accompanied by the occurrence of creep.

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Estimation of Material Constants of Hot Coke under Inert Atmosphere

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