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Tetsu-to-Hagané Advance Publication

ISIJ International
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575
Publisher: The Iron and Steel Institute of Japan

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  1. Vol. 110 (2024)

    1. No.13
    2. No.12
    3. No.11
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  2. Vol. 109 (2023)

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  3. Vol. 108 (2022)

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  4. Vol. 107 (2021)

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  5. Vol. 106 (2020)

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  6. Vol. 105 (2019)

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  7. Vol. 104 (2018)

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  8. Vol. 103 (2017)

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  9. Vol. 102 (2016)

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  10. Vol. 101 (2015)

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  11. Vol. 100 (2014)

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  12. Vol. 99 (2013)

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  13. Vol. 98 (2012)

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  14. Vol. 97 (2011)

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  15. Vol. 96 (2010)

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  16. Vol. 95 (2009)

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  17. Vol. 94 (2008)

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  18. Vol. 93 (2007)

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  19. Vol. 92 (2006)

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  20. Vol. 91 (2005)

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  21. Vol. 90 (2004)

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  22. Vol. 89 (2003)

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  23. Vol. 88 (2002)

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  24. Vol. 87 (2001)

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  25. Vol. 86 (2000)

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  26. Vol. 85 (1999)

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  27. Vol. 84 (1998)

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  28. Vol. 83 (1997)

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  29. Vol. 82 (1996)

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  30. Vol. 81 (1995)

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  31. Vol. 80 (1994)

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  32. Vol. 79 (1993)

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  33. Vol. 78 (1992)

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  34. Vol. 77 (1991)

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  35. Vol. 76 (1990)

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  36. Vol. 75 (1989)

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  37. Vol. 74 (1988)

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  38. Vol. 73 (1987)

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  39. Vol. 72 (1986)

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  40. Vol. 71 (1985)

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  41. Vol. 70 (1984)

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  42. Vol. 69 (1983)

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  43. Vol. 68 (1982)

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  44. Vol. 67 (1981)

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  45. Vol. 66 (1980)

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  46. Vol. 65 (1979)

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  47. Vol. 64 (1978)

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  48. Vol. 63 (1977)

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  49. Vol. 62 (1976)

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  50. Vol. 61 (1975)

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  51. Vol. 60 (1974)

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  52. Vol. 59 (1973)

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  53. Vol. 58 (1972)

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  54. Vol. 57 (1971)

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  55. Vol. 56 (1970)

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  56. Vol. 55 (1969)

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  57. Vol. 54 (1968)

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  58. Vol. 53 (1967)

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  59. Vol. 52 (1966)

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  60. Vol. 51 (1965)

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  61. Vol. 50 (1964)

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  62. Vol. 49 (1963)

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  63. Vol. 48 (1962)

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  64. Vol. 47 (1961)

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  65. Vol. 46 (1960)

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  66. Vol. 45 (1959)

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  67. Vol. 44 (1958)

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  68. Vol. 43 (1957)

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  69. Vol. 42 (1956)

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  70. Vol. 41 (1955)

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    12. No.1

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24 Oct. (Last 30 Days)

Tetsu-to-Hagané Advance Publication

Yielding Behavior of Low Carbon Martensitic Steel Sheet Containing Retained Austenite

Junya Tobata, Hidekazu Minami, Yuki Toji, Shinjiro Kaneko

DOI:

10.2355/tetsutohagane.TETSU-2024-107

Abstract

Quenching and Partitioning (Q&P) steel sheets, which utilize the transformation induced plasticity (TRIP) effect of retained austenite to improve the elongation of high strength steel sheets, are expected to become an important material for next-generation automotive structural parts. Although it has been reported that the yield strength (YS) of the Q&P steels consisting of tempered martensitic microstructure with retained austenite (hereafter ”Q&P steels” in this study) is affected by retained austenite, the mechanism has not yet been discussed in detail. The purpose of this study is to clarify the effect of the carbon content in retained austenite on the yielding behavior of the Q&P steels. The chemical composition of the model steel used here was 0.18%C-1.5%Si-3.0%Mn (mass%). The steels were annealed at 1143 K, then cooled to 473 K, followed by holding at the temperatures between 523 K and 673 K for 600 s. The increased carbon content in retained austenite increased the YS of the Q&P steels. It was found that the yielding of the Q&P steels was caused by the stress-induced transformation of retained austenite when the critical stress for the stress-induced transformation was lower than the elastic limit of tempered martensitic matrix. This result revealed that the increased carbon content in retained austenite was able to achieve the higher elastic limit of martensitic steels containing retained austenite.

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Yielding Behavior of Low Carbon Martensitic Steel Sheet Containing Retained Austenite

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Quantitative Understanding of Solute Concentration Distribution by Microsegregation During Solidification

Sakiko Kawanishi, Shingo Terashima, Yuki Tsukahara, Sohei Sukenaga, Hisao Esaka, Hiroyuki Shibata

DOI:

10.2355/tetsutohagane.TETSU-2024-098

Abstract

Microsegregation of solute components during the solidification process causes solute pile-up in the liquid phase, which strongly affects the formation behavior of inclusions. However, there is no quantitative evaluation of solute concentration distribution during dendritic growth. In this study, we established an in-situ observation method for quantitative evaluation of solute concentration distribution using model materials with fluorescent reagents to clarify how the solute pile-up progresses due to microsegregation. In addition to evaluating the physical properties of the model materials necessary for this study, a quantitative evaluation of solute concentration distribution during dendritic growth was successfully achieved. Numerical analysis, taking into account the equilibrium partition of solute components and solute diffusion in each phase, reproduced the measured solute concentration distribution in the liquid phase. Thus, the solute concentration distribution was evaluated by the actual measurement and numerical analysis, and it was clarified that a relatively simple model can represent the progress of microsegregation.

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Quantitative Understanding of Solute Concentration Distribution by Microsegregation During Solidification

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Characterization of Crack Growth Acceleration of V-added Precipitation-strengthened High-Mn Austenitic Steel in High-pressure Gaseous Hydrogen Environment

Tatsuya Iwano, Atsushi Saji, Kodai Miura, Yukio Tachi, Osamu Takakuwa

DOI:

10.2355/tetsutohagane.TETSU-2024-093

Abstract

To verify the crack growth resistance of the V-added precipitation-strengthened high-Mn austenitic steel subject to a static and dynamic loading in a hydrogenated environment, the fracture toughness test and two types of fatigue crack growth (FCG) test, i.e., stress intensity factor range ΔK-increasing and ΔK-constant tests were performed under high-pressure gaseous hydrogen environment under the pressure of 95 MPa. The fracture toughness dramatically decreased from 95 to 35 MPa･m1/2 by hydrogen occlusion. The fracture surface consists of intergranular fracture aspects in gaseous hydrogen despite being covered by the dimples tested in air. The FCG acceleration was also pronounced: more acceleration emerged as the ΔK became higher. When changing the loading frequency f as 1, 0.1, 0.01, and 0.001 Hz under constant ΔK of 30MPa･m1/2, the relative FCG rate in gaseous hydrogen to that in air became higher as f decreased, i.e., the dependency of FCG acceleration on the crack opening time. However, the acceleration did not completely depend on the crack opening time, which means a part of FCG acceleration was dominated by crack tip plasticity under cyclic loading. The scanning electron microscopy (SEM) characterization, including the electron-channeling contrast (ECC) imaging and the electron backscatter diffraction (EBSD) analysis, demonstrated that the crack preferentially propagates along grain boundary in the hydrogenated environment. The micro-void and/or micro-crack ahead of the primary FCG crack initiated at the M23C6 carbides precipitated at the grain boundary, which triggered the dramatic acceleration of FCG under 95 MPa gaseous hydrogen.

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Characterization of Crack Growth Acceleration of V-added Precipitation-strengthened High-Mn Austenitic Steel in High-pressure Gaseous Hydrogen Environment

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Direct Observation of Atomic Arrangement in Multicomponent Calcium Ferrite Using Scanning Transmission Electron Microscopy

Kenta Takehara, Kohei Ikeda, Takashi Kawano, Takahide Higuchi

DOI:

10.2355/tetsutohagane.TETSU-2024-080

Abstract

To reduce the reducing agent ratio and CO2 emissions in blast furnace operation, it is important to control the material structure of sintered ore, which affects its metallurgical and mechanical properties. Multicomponent calcium ferrites (also called CF or SFCA (silico-ferrite of calcium and aluminum)), which is a type of melting and solidification structure, has attracted considerable interest recently, and the chemical composition and crystal structure of each CF have been researched. Although the crystal structure of CF has conventionally been analyzed mainly by XRD, the atomic arrangement could not be observed directly. Therefore, in this study, CF was investigated at the atomic level by scanning transmission electron microscopy (STEM). This research revealed that acicular CF, which was previously understood to be SFCA-I, has a SFCA (≠ SFCA-I)structure. It was also found that columnar CF had a non-periodic SFCA structure induced with a magnetite-like structure. Furthermore, a CF in which SFCA and SFCA-I were alternately stacked repeatedly was also discovered. This research clarified the fact that CF has a non-periodic structure at the atomic level.

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Direct Observation of Atomic Arrangement in Multicomponent Calcium Ferrite Using Scanning Transmission Electron Microscopy

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Effect of Initial Microstructures on Grain Refinement by Burnishing

Yoshinori Amano, Takahisa Suzuki, Kaori Kawano

DOI:

10.2355/tetsutohagane.TETSU-2024-086

Abstract

The development of ultrafine grained microstructures under severe plastic deformation by burnishing process was investigated using spherical cementite-ferrite (SA) steel and pearlite (P) steel of AISI 52100. Microstructures were analyzed using FE-SEM, FE-TEM and EBSD observations. In the SA steel, equiaxed ultrafine ferrite grains were formed at the burnished surface where the equivalent strain was about 3.9. These ultrafine grains were formed by continuous dynamic recrystallization because they consisted of high angle grain boundaries. On the other hand, in the P steel, the initial lamellar structure was maintained even at the equivalent strain about 4.3, and ferrite grains with a large aspect ratio were formed. These ferrite grains were considered to be non-recrystallized grains because the KAM value within these grains was high. In addition, many dislocation contrasts in the same direction were observed within a ferrite grain by FE-TEM observation. These results suggested that active dislocation slip system in these ferrite grains is limited by lamellar structure. As the strain increased by repeated burnishing process, these ferrite grains of P steel became coarse and the KAM value within these grains decreased. In addition, several dislocation contrasts in multiple directions were observed within a ferrite grain. It can be concluded that the limitation of active dislocation slip system in these ferrite grains were relaxed, and dynamic recovery was occurred in these ferrite grains.

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Effect of Initial Microstructures on Grain Refinement by Burnishing

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Influence of Silicon Contents on the Microstructure and Tensile Properties of Quenching and Partitioning (Q&P) Processed Low Carbon Steel

Chang Jae Yu, Chang-Hyo Seo, Young-Roc Im, Dong-Woo Suh

DOI:

10.2355/tetsutohagane.TETSU-2024-088

Abstract

The microstructure and corresponding tensile properties were examined in quenching and partitioning (Q&P) processed low carbon steels, depending on the silicon content ranging from 0.1–2.0 wt.%. The silicon content and process temperature generated a highly interactive influence on the evolution of final microstructure, including the fraction of constituent phases and their characteristics such as solute carbon content in each phase. The yield strength was nearly unchanged or slightly decreased even with the silicon addition for a given Q&P condition. The change of yield strength showed a reasonable correlation with the loss of solute carbon in martensite or bainite caused by the carbide precipitation and the carbon partitioning into austenite, which depended on the silicon content. High partitioning temperature enhanced the yield strength for a given silicon content and quenching condition, because of the tempering effect on the martensite matrix. Although the fraction and stability of retained austenite were still critical for improving ductility, the intrinsic properties of the martensite matrix, such as the occurrence of tempered martensite embrittlement, governed the ductility of Q&P steels in situations where the role of retained austenite was limited due to low fraction or poor mechanical stability.

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Influence of Silicon Contents on the Microstructure and Tensile Properties of Quenching and Partitioning (Q&P) Processed Low Carbon Steel

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Modeling of Steel Production Sub-Processes by Probabilistic Time Automaton and Assessing The Risk of Deviation from Stability in The Manufacturing Facility Environment

Riku Hashimoto, Gaku Kondo, Haruto Murakami, Kazutoshi Sakakibara, Masaki Nakamura

DOI:

10.2355/tetsutohagane.TETSU-2024-046

Abstract

In the steelmaking industry in recent years, requirements such as mixed production of various types of products and short delivery times have led to a demand for efficient operation methods that allow for efficient production while tolerating the risk of disruptions to stable operations. However, the steelmaking process is a complex supply chain, and even a localized change in one element can cause the entire system to fail.

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Modeling of Steel Production Sub-Processes by Probabilistic Time Automaton and Assessing The Risk of Deviation from Stability in The Manufacturing Facility Environment

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Simultaneous Determination of Transformation Plasticity Coefficients of Bainite and Martensite Transformations by Oil Quenching of Steel Sheet for Machine Structural Use and Accurate Prediction of Distortion by Oil Quenching

Keisuke Watanabe, Motohiro Nishikawa, Morihiko Nakasaki, Ryo Matsumoto, Hiroshi Utsunomiya

DOI:

10.2355/tetsutohagane.TETSU-2024-090

Abstract

The dimensional accuracy of power train parts depends on the distortion caused by oil quenching. The parts are manufactured from steels for machine structural use, and the steel transforms from austenite to bainite and martensite during the quenching. For accurately predicting the distortion, it is important to know the accurate transformation plasticity coefficients of both bainite and martensite transformations. Transformation plasticity is a phenomenon caused by the stress due to transformation expansion, resulting in large plastic deformation of the steel. In this paper, a method was proposed to determine both the coefficients of bainite and martensite transformations by fitting the distortions in numerical analyses of the quenching process to oil quenching experiments. In this method, assuming that the transformation plasticity of both bainite and martensite transformations does not interact, two steel sheets with different thicknesses were used. In the previous study, by using this method for a thin sheet of Cr-Mo steel (consisting of martensite), the coefficient of martensite was determined as 21x10-5 MPa-1. Thereafter, the coefficient of bainite was determined as 11x10-5 MPa-1 by using a thick sheet (consisting of bainite and martensite). An experiment using a heat treatment oil with different cooling capacity was conducted to check the accuracy of the obtained coefficients. The numerical analysis results of cooling curve and microstructure were verified by comparing with the experimental results. The predicted deflection using the obtained coefficients was in good agreement with the experimental result. Thus, this method enabled to accurately predict the distortion caused by quenching.

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Simultaneous Determination of Transformation Plasticity Coefficients of Bainite and Martensite Transformations by Oil Quenching of Steel Sheet for Machine Structural Use and Accurate Prediction of Distortion by Oil Quenching

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Hydrogen Content Dependence of the Contribution of Dislocation-slip Stability and Carbide Precipitation Morphology to the Hydrogen Embrittlement Property of High-strength Martensitic Steels

Kei Saito, Kenichi Takai

DOI:

10.2355/tetsutohagane.TETSU-2024-091

Abstract

The contribution of dislocation-slip stability and carbide precipitation morphology to the hydrogen embrittlement (HE) property of tempered martensitic steels with low and high silicon contents (L-Si and H-Si) and oil-quenched martensitic steel (As-OQ), was evaluated by conducting slow strain rate tests. The order of dislocation-slip stability was the H-Si specimen > L-Si specimen > As-OQ specimen. The H-Si and As-OQ specimens had finely dispersed carbides inside prior austenite (γ) grains, whereas the L-Si specimen had coarsely dispersed carbides inside prior γ grains and on the boundaries. Notched specimens were charged with hydrogen in a range of low (0.19–0.31 ppm), medium (1.04–1.49 ppm), and high (2.17–2.33 ppm) hydrogen contents. The H-Si specimen had the highest HE property under the three hydrogen charging conditions. With the low and medium hydrogen charging conditions, the HE property of the L-Si specimen was higher than that of the As-OQ specimen, whereas their HE properties markedly declined to a similar level under the high hydrogen charging condition. The HE property of the L-Si specimen with increased dislocation-slip stability by applying stress relaxation was equivalent to that of the L-Si specimen under the high hydrogen charging condition. These results revealed that increasing dislocation-slip stability improved the HE property in the range of low to medium hydrogen charging. Under the high hydrogen charging condition, dislocation-slip stability did not contribute to improving the HE property, but it was found that the carbide precipitation morphology, particularly coarse carbides precipitated on prior γ grain boundaries, influenced the HE property.

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Hydrogen Content Dependence of the Contribution of Dislocation-slip Stability and Carbide Precipitation Morphology to the Hydrogen Embrittlement Property of High-strength Martensitic Steels

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Effect of Binder Adsorption Characteristics of Coal on Cold Strength for Ferro-coke Briquette

Mikiya Nagayama, Hidekazu Fujimoto, Takashi Anyashiki, Takashi Matsui, Tetsuya Yamamoto

DOI:

10.2355/tetsutohagane.TETSU-2024-085

Abstract

In the ferro-coke production process, the molded briquettes are carbonized as they are to become ferro-coke, and the quality of ferro-coke is greatly reduced when the briquettes deteriorate during transportation to the shaft furnace. Therefore, briquette strength is one of the most important characteristics in ferro-coke production.

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Effect of Binder Adsorption Characteristics of Coal on Cold Strength for Ferro-coke Briquette

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Solidification Characteristics and TiC Formation Behaviour in Alloy 800H

Shigeo Fukumoto, Yuto Sakaizawa, Shigeru Kaneko, Nobuhisa Ebihama

DOI:

10.2355/tetsutohagane.TETSU-2024-083

Abstract

It is known that the size distribution of inclusions in steels have a significant effect on material properties. The solidification characteristics and TiC formation behavior of alloy 800H were evaluated both by experiment and simulation in this work. The relationship between dendrite arm spacing and the cooling rate was estimated. TiC particles were observed at the interdendritic region. The size distribution of TiC particles was affected by solidification cooling rate. Solidification analysis using the MPF (Multi-Phase Field) method revealed that TiC formation begins at a solid fraction of 0.79, and solidification accelerates due to TiC formation. It was thought that TiC particles generated in the latter part of solidification aggregate and coalesce without engulfment by the solidified shell. The size distribution of TiC particles was also affected by heat treatment after solidification.

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Solidification Characteristics and TiC Formation Behaviour in Alloy 800H

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Effects of Inclination of Strip Entering into Roll-Bite on Warpage Behavior in Rolling

Daisuke Kasai, Atsushi Ishii, Hiroshi Utsunomiya

DOI:

10.2355/tetsutohagane.TETSU-2024-084

Abstract

Rolling experiments were conducted to investigate strip warpage behavior after rolling where the strip was inclined before a roll-bite with the roller guide. Direction of the strip warpage was explained by the shape factor Γ (contact arc length / mean thickness). The relationship between inlet inclination and outlet warpage of the strip was divided into four typical categories, by the shape factor Γ; 1) Γ < 1.0; a positive relation, 2) 1.0 < Γ < 1.9; a negative relation, 3) 1.9 < Γ < 3.1; a positive relation and 4) 3.1 < Γ; a negative relation. In other words, the sign of the warpage changes at three times with increasing the shape factor Γ. These experimental results were predicted by the two-dimensional rigid plastic steady-state finite element analyses. The analyses numerically showed that shear bands are initiated at the entrance of the roll-bite with the shear stress field, and that the intensity and configuration of the shear bands determine strip warpage behavior.

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Effects of Inclination of Strip Entering into Roll-Bite on Warpage Behavior in Rolling

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Process of White Etching Cracks Formation in Carburized Bearing Steel under Rolling Contact Fatigue

Daisuke Takazaki, Masato Yuya, Yutaka Neishi, Makoto Kosaka, Yuji Sakiyama, Tomohiko Omura, Kaori Kawano

DOI:

10.2355/tetsutohagane.TETSU-2024-078

Abstract

The purpose of this study is to investigate the mechanism of the premature failure of bearing steels in rolling contact fatigue (RCF), with a particular focus on the process of the white etching cracks (WECs). A two-roller type rolling contact fatigue test was carried out using a carburized SAE5120 steel, which successfully provides systematic sequences leading to the WECs under a contact pressure of 2700 MPa with 3.0×107 RCF cycles. The process of WECs consisted of crack initiation at prior austenite grain boundaries, crack propagation accompanied by WECs formation, and crack propagation without WECs. The initial stage of the RCF test resulted in the formation of acicular structures, which were caused by {110}<111> slip driven by cyclic shear stress. However, these acicular structures were found to be unnecessary for crack initiation or the formation of white etching area (WEA). Instead, it was observed that crack initiation occurred at the boundaries of the prior austenite grains. After the crack initiation, the WEA was formed around the cracks, indicating that rubbing of the crack surfaces leads to WEA formation. Stress analysis revealed that a mode-Ⅰ crack was formed due to cyclic compressive stress applied by RCF. Furthermore, it was found that the crack initiation was suppressed with low amount of hydrogen content. This suggests that hydrogen accelerate the crack initiation at prior austenite grain boundary.

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Process of White Etching Cracks Formation in Carburized Bearing Steel under Rolling Contact Fatigue

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The Crystal Structure of As-quenched Fe–C Martensite

Bevis Hutchinson, Peter Lynch, Sitarama Kada, Jun Wang

DOI:

10.2355/tetsutohagane.TETSU-2024-087

Abstract

Confusion exists in the literature as to whether the crystal structures are cubic or tetragonal in lath martensites of Fe–C alloys and low-alloy steels. Steels with a range of carbon contents have been quenched and examined by synchrotron x-ray diffraction. The presence of dislocations and residual local strains complicates the analysis since peak splitting of tetragonal lines is obscured by the broadening. Asymmetry of the 200,020/002 lines has been examined and synthesised using model peak functions. A new approach has been to study the 222 peaks which are unique (not split) for both cubic and tetragonal crystals. For low carbon steels (<~0.2%C) the structures are fully or almost completely cubic. Above about 0.7%C the martensite has tetragonal symmetry. Intermediate, medium carbon, steels consist of mixtures of cubic and tetragonal structures.

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The Crystal Structure of As-quenched Fe–C Martensite

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Influence of Nitrogen Introduced by Solution Nitriding on Microstructure and Room-temperature Mechanical Properties of Grade 91 Steel

Shuntaro Ida, Kyosuke Yoshimi

DOI:

10.2355/tetsutohagane.TETSU-2024-064

Abstract

The effect of nitrogen introduced by solution nitriding on microstructure and mechanical properties of modified 9Cr-1Mo (Gr. 91) steel at room temperature was investigated. The nitrogen concentration at the sample surface was 0.164 wt% and nitrogen diffused at least 5000 mm after solution nitriding heat treatment at 1200ºC for 48 hours. The martensite with a small amount of MX carbonitride with cF8 structure and retained austenite was formed on 100 mm from the sample surface. The Cr2N phase with hP9 structure containing V, Nb and Mo and Cr23C6 phase with cF116 structure precipitated by tempering. Solute nitrogen improved the hardness, yield strength, ultimate tensile strength and uniform elongation. However, the nitride formation did not contribute to the improvement of hardness and decreased yield strength and ultimate tensile strength. It suggests that the contribution of solid solution strengthening by Cr, V, Nb and Mo is larger than that of precipitation strengthening by nitride at room temperature.

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Influence of Nitrogen Introduced by Solution Nitriding on Microstructure and Room-temperature Mechanical Properties of Grade 91 Steel

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Evaluating the Cognitive Framework for Resilient Slab Yard Control Decision Process

Hajime Mizuyama, Kohei Nakamizo, Shota Suginouchi

DOI:

10.2355/tetsutohagane.TETSU-2024-063

Abstract

A slab yard within a steel factory comprises multiple Last-In, First-Out (LIFO) buffers, typically managed by a crane operator in a dynamic environment. The efficacy of decision-making in controlling the slab yard hinges on the operator’s cognitive grasp of the task. Therefore, it is crucial to evaluate various cognitive frameworks to enhance and stabilize performance, bolster resilience, and adequately support the operator. This study presents a framework integrating feature variables that convey information about the due dates of slabs, intended for use by and provision to the operator. Subsequently, it employs a combination of behavioural and computational methodologies to assess this framework, utilizing a serious game model of the task for testing purposes. The findings confirm that the effective representation for conveying due date information depends on yard congestion, with the provision of such information potentially backfiring when the yard is crowded. This observation holds true for both computational experiments using a reinforcement learning agent and behavioural experiments using human subjects. Moreover, the consistency of results across both experiments suggests that a reinforcement learning agent could be valuable for formulating plausible hypotheses regarding the suitable cognitive framework for individuals tasked with this responsibility.

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Evaluating the Cognitive Framework for Resilient Slab Yard Control Decision Process

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Effect of Tensile Loading on the Residual Stress Relaxation Behavior of Induction Hardened SCM440 Steel with a Shallow Hardened Layer

Tomofumi Aoki, Motoaki Hayama, Shogo Takesue, Atsushi Ezura, Masahiro Tsukahara, Yoshitaka Misaka, Shoichi Kikuchi, Jun Komotori

DOI:

10.2355/tetsutohagane.TETSU-2024-072

Abstract

Fatigue tests under axial loading were conducted on steel with a shallow hardened layer induced by induction hardening, and in situ X-ray stress measurements were performed to investigate the relaxation of residual stresses during fatigue. The residual stresses were relaxed owing to tensile loading and not compressive loading. The two conditions that bring about this phenomenon are (i) a high peak of tensile residual stress just below the hardened layer, and (ii) the hardened layer coinciding with the compressive residual stress field that prevents the yielding of the compressive residual stress field under compressive loading. In this case, tensile yielding occurred just below the hardened layer under tensile loading, the residual stresses are redistributed, and the compressive residual stress on the material surface is relaxed. The experimental results also showed that the fatigue fracture morphology changed depending on the residual stress relaxation behavior.

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Effect of Tensile Loading on the Residual Stress Relaxation Behavior of Induction Hardened SCM440 Steel with a Shallow Hardened Layer

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Effect of Liquid Fraction on Reaction Rate of Molten Steel Desulfurization Using Solid-Liquid Coexisting Slag

Akihiro Matsuzawa, Hiroshi Harada

DOI:

10.2355/tetsutohagane.TETSU-2024-082

Abstract

In the high purification refining processes, a CaO-containing flux or slag is used commonly for the desulfurization of molten steel. Because the slag generated during the actual process is not always a homogeneous liquid, the quantitative relation between the liquid fraction of the slag and its mass transfer coefficient must be clarified. Therefore, to elucidate the effects of the liquid fraction on the desulfurization rate and the mass transfer coefficient in the slag phase, kslag, desulfurization experiments were performed on molten steel using a resistance heating furnace with solid CaO-liquid coexisting slag corresponding to the CaO-Al2O3 and CaO-CaF2 systems. The overall mass transfer coefficient and sulfur partition ratio at the slag-metal interface were evaluated based on the regression analysis of the experimental data using the reaction rate equation, and kslag could be determined. It was found that kslag decreased slightly with a decrease in the liquid fraction of the slag for both the CaO-Al2O3 and CaO-CaF2 systems. This is because the effective diffusion coefficient decreased with the decrease in the liquid fraction. Two empirical equations for kslag for the solid-liquid coexisting compositions were formulated; these were based on a previously reported equation for the effective diffusion coefficient and the regression analysis of the experimental data obtained in this study. The threshold value of the liquid fraction between the equations for kslag was determined to be 0.87. This is possibly because the state of the solid in the slag changes because of the percolation transition.

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Effect of Liquid Fraction on Reaction Rate of Molten Steel Desulfurization Using Solid-Liquid Coexisting Slag

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Effect of Alumina on the Phase Equilibria of the Iron-rich Corner of the CaO-SiO2-Fe2O3 System at 1240°C in Air

Amane Takahashi, Yukihiro Uchisawa, Hirokazu Sato, Takashi Watanabe, Rie Endo, Masahiro Susa, Miyuki Hayashi

DOI:

10.2355/tetsutohagane.TETSU-2024-079

Abstract

The effect of Al2O3 on the compositional region of silico-ferrite of calcium and aluminum (SFCA) and the liquid phase and the phase equilibria, including SFCA, was investigated in a CaO-SiO2-Fe2O3-5mass%Al2O3 system at 1240 °C in air. To obtain the desired composition, reagent-grade CaCO3, SiO2, Fe2O3, and Al2O3 powders were weighed, mixed, and equilibrated at 1240 °C in air. Each obtained sample was divided into two parts: one was pulverized into a powder and analyzed by XRD, and the other was subjected to microstructural observation and compositional analysis using EPMA. The results revealed that the compositional region of SFCA lies on the CF3-CA3-C4S3 plane and is C/S = 2.77–7.60 for 5 mass% Al2O3. Compared with the SFC composition region for 0 mass% Al2O3, the compositional range of SFCA extended in the CF3-C4S3 direction, suggesting that the addition of Al2O3 contributes to the stability of SFCA. Furthermore, the liquid-phase region was divided into a ferrite melt with a high Fe2O3 concentration and a silicate melt with a high SiO2 concentration, both of which shifted to the lower Fe2O3 side compared to the liquidus isotherm in the CaO-SiO2-Fe2O3 system. Unlike CaO-SiO2-Fe2O3, SFCA-I (SFC-I) was observed in the CaO-SiO2-Fe2O3-5mass%Al2O3 system, thus indicating that the addition of Al2O3 contributes to the stability of SFCA-I.

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Effect of Alumina on the Phase Equilibria of the Iron-rich Corner of the CaO-SiO2-Fe2O3 System at 1240°C in Air

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Equation of Cleavege Fracture and Grain Boundary Fracture Stress Based on Brechet-Louchet Model

Katsutoshi Hyodo, Yosuke Nonaka, Kazuma Itoh, Tetsuya Namegawa

DOI:

10.2355/tetsutohagane.TETSU-2024-074

Abstract

New fracture process model of cleavage fracture initiated from cementite crack was proposed. In addition, the equation of propagation of cementite crack into the ferrite grain was developed based on the Brechet-Louchet model. This equation can reproduce not only ferrite size dependence of cleavage fracture stress that the Petch model can reproduce but both of test temperature dependence and strain rate dependence of fracture stress. Furthermore, in exchanging surface energy for grain boundary cohesive energy in the equation, grain boundary fracture stress can be also estimated.

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Equation of Cleavege Fracture and Grain Boundary Fracture Stress Based on Brechet-Louchet Model

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Optimization Model for Resource-Buffer Scheduling toward Resilient Steel Production

Haruhiko Suwa, Daisuke Morita

DOI:

10.2355/tetsutohagane.TETSU-2024-041

Abstract

Steel manufacturing often needs to improve its stability margin due to logistics delays, increased manufacturing costs, and sudden production halts. Keeping a certain level of stability margin in steel production is a practical policy to avoid serious deviation from a steady state in operation. This paper proposes a resource-buffered scheduling method based on Critical Chain / Buffer Management (CC/BM) and its fundamental mathematical models. In this study, we consider a planning decision-making chain from raw material blend planning to hot-roll scheduling through cast scheduling in a steel plant. A series of computational experiments demonstrate the proposed method as a decision-making process enhancing "resiliency" in steel-making operations.

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Optimization Model for Resource-Buffer Scheduling toward Resilient Steel Production

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Analysis of Factory Automated Guided Vehicles Systems by using Multi-agent System and Contract Net Protocol

Daimotsu Kato, Setusya Kurahashi

DOI:

10.2355/tetsutohagane.TETSU-2024-047

Abstract

Automated Guided Vehicles (AGVs) are utilized in flexible job-shop production systems. In these systems, the most crucial issue is the proper scheduling of jobs. Moreover, AGVs in the factory are constrained to follow predetermined transportation routes, leading to potential spatial interference between AGVs. This paper investigates an analytical model of AGV flow using a multi-agent system and contract net protocol. Our model enables the AGV assignment and job manager agents to collaborate and make decisions based on traffic information feedback. This system allows for continuous monitoring of AGV density and ensures the maintenance of an appropriate distance between AGVs. As a result, it effectively mitigates traffic flow fluctuations, thereby enhancing the efficiency and stability of the AGV flow.

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Analysis of Factory Automated Guided Vehicles Systems by using Multi-agent System and Contract Net Protocol

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Corrosion Risk Prediction of Carbon Steels by Hyperspectral Analysis

Hideki Katayama, Yuto Yoshida, Takaya Akashi, Mariko Kadowaki, Yoshiharu Murase, Yusuke Tsutsumi

DOI:

10.2355/tetsutohagane.TETSU-2024-076

Abstract

The utility of hyperspectral measurement was assessed as a means of predicting the corrosion risk of steel materials based on surface information. Carbon steels exposed to outdoor conditions in Choshi and Miyakojima were used as the test specimens. Exposure tests were conducted every six months for a duration of two and a half years. Corrosion loss was calculated by comparing the weight of specimens before exposure test and after removing corrosion products from the surface. Hyperspectral measurements were conducted on these specimens, with corrosion products identified through SAM (Spectral Angle Mapper) analysis. α-FeOOH, β-FeOOH, γ-FeOOH, and Fe3O4 were employed as reference data for SAM analysis. In both Choshi and Miyakojima test sites, γ-FeOOH was predominantly detected on the specimens after ordinary exposure tests, whereas Fe3O4 was prevalent on the specimens exposed to sheltered environments. The correlation between the proportion of each corrosion product identified through SAM analysis and the amount of corrosion change for one year was explored. α-FeOOH exhibited a positive correlation with the amount of corrosion change, whereas the amount of corrosion change tended to decrease with an increase in β-FeOOH fraction.s

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Corrosion Risk Prediction of Carbon Steels by Hyperspectral Analysis

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Phase Stability and Thermal Expansion Properties of Additive Manufactured Super Invar alloy

Senlin Cai, Ryota Nagashima, Yaw Wang Chai, Naoki Sakaguchi, Nobuo Nakada

DOI:

10.2355/tetsutohagane.TETSU-2024-066

Abstract

Super invar alloy, Fe–32%Ni–5%Co, is widely utilized in precision instruments due to its remarkably low thermal expansion coefficient. Additive manufacturing holds promise for fabricating complex-shaped components with this alloy. This study investigated the phase stability and thermal expansion properties of super invar alloy fabricated via Laser Powder Bed Fusion (AM sample), comparing them to those of conventionally cast material (Re-melt sample). Microstructural analysis indicates that the AM sample has a more stable austenitic structure, attributed to minimal micro-segregation. Furthermore, it was observed that the thermal expansion coefficient decreases consistently with higher cooling rates within the temperature range of 400-300 K. As a result, AM sample exhibits lower expansion coefficient and it maintains at lower temperatures.

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Phase Stability and Thermal Expansion Properties of Additive Manufactured Super Invar alloy

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Evaluation of Corrosion on Steel Surface Using Image Processing

Takahiro Igarashi, Yu Sugawara, Kyohei Otani, Takahito Aoyama

DOI:

10.2355/tetsutohagane.TETSU-2024-058

Abstract

Using two types of image processing techniques without machine learning, edge extraction processing and keypoint extraction processing, progressively corroded regions under the rust layer from images of corroded steel surfaces was extracted. We found that there was a relatively good correlation between the keypoint strength obtained from the keypoint extraction processing for HSL transformed and histogram flattened corroded surface images and the corrosion depth after rust removal.

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Evaluation of Corrosion on Steel Surface Using Image Processing

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Properties at Corrosion Sites Formed on Pure Iron during Wet-dry Cycling Test and on Steel during Exposure Test

Soshiro Yamazaki, Fuka Kawamura, Koki Saito, Makoto Chiba

DOI:

10.2355/tetsutohagane.TETSU-2024-062

Abstract

Steels are widely used as a structural material for infrastructure, such as bridges. However, some of bridges built in Japan, have passed more than 50 years, since construction. Thus, these bridges will need to be reconstruction, because atmospheric corrosion of these materials will occur in this condition. However, there are numerous bridges in Japan, and reconstruction of these bridges would need much cost. Therefore, it is necessary to establish the technique for selection of the bridges with severe damage by atmospheric corrosion. To establish a new non-destructive and non-contact techniques for identifying the sites of atmospheric corrosion occurred in steel, used as structural materials for bridges, the relation between corrosion site and color of corrosion product, surface morphology or distribution of surface potential of the pure iron and steel after corrosion test were evaluated.

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Properties at Corrosion Sites Formed on Pure Iron during Wet-dry Cycling Test and on Steel during Exposure Test

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Effect of BN Surface Segregation on Coatability in Hot-dip Galvanizing of B-added Steel

Daisuke Tahara, Katsuya Hoshino, Shoichiro Taira

DOI:

10.2355/tetsutohagane.TETSU-2024-052

Abstract

Boron (B) is frequently used as additives to improve the hardenability of advanced high strength steel. It has been reported that B in steel reacts with atmospheric N2 during annealing at low oxygen potential (low dew point) to form boron nitride (BN) by the thermodynamical calculation. In this study, the effect of BN formation on the steel surface on the coatability during hot-dip galvanizing was investigated, experimentally. B-free specimens and specimens containing 15 or 30 ppm B were annealed at various temperature and dew point, and then hot-dip galvanized. The annealed specimens were also prepared and analyzed with GD-OES, XPS, SEM-EDX and TEM-EELS to investigate the oxide and nitride formation on the steel surface during annealing. As results, coatability deteriorated as the amount of B in steel and the annealing temperature increase, and as the dew point decrease. These trends were not correlated with the amount of oxide but the amount of BN formation, suggesting that BN formation deteriorated the coatability. The surface and cross-sectional analysis revealed that BN formed around the oxide to cover the steel surface. This would lead the deterioration of the coatability because most of the steel surface was covered with BN as well as oxide, which are known to have low wettability with molten Zn.

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Effect of BN Surface Segregation on Coatability in Hot-dip Galvanizing of B-added Steel

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Color Tone of Corrosion Products and Estimation of Rust Composition by Image Processing

Kenta Fujihashi, Wataru Oshikawa

DOI:

10.2355/tetsutohagane.TETSU-2024-067

Abstract

Appropriate maintenance and maintenance of infrastructures that has been used for a long time is required because there is the concern that safety will deteriorate due to atmospheric corrosion. However, the cost of maintenance and management is also increasing, and there is required to save labor and improve efficiency of maintenance and management. Therefore, the purpose of this study was to easily estimate the rust composition by the image processing of image of steel surface corroded by the outdoor exposure test. The outdoor exposure test was conducted in Choshi City and those conditions were open exposure and shelter exposure for 2.5 years. The　compositions of those corrosion products measured by X-ray diffraction. Exposed test pieces were photographed RAW with the digital camera. Those photographs were developed and trimmed. The obtained images were converted from RGB images to La*b* and LCh images. The histograms of hue were fitted to the Gaussian function to determine the peak position and the spread of the histogram. As a result, it was indicated that the peak position shown in the histogram of hue shifted to the low-angle side due to the increase in FeFe2O4. In addition, it was indicated that the composition ratio of α-FeOOH, β-FeOOH, γ-FeOOH and FeFe2O4 can be estimated by the shape, spread and peak position of the histogram of hue. As shown in the graphical abstract, the composition ratio of the corrosion products measured by RIR method and estimated by image processing was in good agreement.

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Color Tone of Corrosion Products and Estimation of Rust Composition by Image Processing

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Effect of Re-ignition Method on Sinter Yield Through Improving Carbon Combustion Ratio at Upper Layer of Sinter Packed Bed

Masaru Matsumura, Ryota Kosugi, Yuichiro Yamamoto, Junji Nagata, Kenichi Higuchi

DOI:

10.2355/tetsutohagane.TETSU-2024-031

Abstract

Conventionally, it has been known that the product yield of the upper part of the sintering layer is extremely low, because of the heat loss caused by transferring heat toward the space above sintering layer, and of the large amount of unburned carbon in upper sintering layer.

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Effect of Re-ignition Method on Sinter Yield Through Improving Carbon Combustion Ratio at Upper Layer of Sinter Packed Bed

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Application of Admittance Analysis for Corrosion Rate Evaluation of Carbon Steel with Rust Layer in Electrochemical Impedance Spectroscopy

Yusaku Akimoto, Yoshinao Hoshi

DOI:

10.2355/tetsutohagane.TETSU-2024-059

Abstract

This paper describes an evaluation method for corrosion rate of carbon steel covered with rust layer by admittance analysis in electrochemical impedance spectroscopy. The polarization resistance, Rp, is often estimated from the impedance spectrum of carbon steel to determine the corrosion rate. The Rp can be determined from the impedance spectrum when the low frequency impedance is converted to the real axis on the Nyquist diagram. Because the impedance spectrum of carbon steel covered with rust layer often describes a part of loop in the low frequency range, it is difficult to determine the Rp by extrapolating the low frequency impedance to the real axis. In the present study, an admittance analysis was employed to determine the Rp from the admittance spectrum of carbon steel covered with rust layer. The admittance is plotted as the reciprocal of impedance on the complex plane. In this case, the Rp can be determined from the admittance spectrum when the low frequency admittance is converged to the real axis. The admittance spectrum of carbon steel with rust layer indicated that the low frequency admittance was converted to the real axis, namely, the Rp could be determined from the admittance spectrum. The corrosion rate of carbon steel with rust layer could be estimated from the Rp by admittance analysis, demonstrating that the value was corelated to that estimated from corrosion loss. The impedance and admittance simulations were performed using an equivalent circuit to discuss the time constant observed in the low frequency range.

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Application of Admittance Analysis for Corrosion Rate Evaluation of Carbon Steel with Rust Layer in Electrochemical Impedance Spectroscopy

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Identification of Rusts Formed on Steels by Image Analysis with HSV Color Space

Hiroo Ishii, Masatoshi Sakairi

DOI:

10.2355/tetsutohagane.TETSU-2024-055

Abstract

Corrosion products formed on steel in various environments were identified with image analysis, Raman spectroscopy, and X-ray diffraction (XRD). The results of Raman spectroscopy showed that γ-FeOOH exhibits bright yellow color and β-FeOOH exhibits gray color. Main corrosion products composition formed on the steels by XRD analysis was γ-FeOOH. Using proper threshold of HSV color space, makes it possible to identify corrosion products formed on steel. Comparison of corrosiveness of exposed environments and formed corrosion products, α-FeOOH is preferentially formed in mild corrosive environments, while β-FeOOH was formed in severe corrosive environments.

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Identification of Rusts Formed on Steels by Image Analysis with HSV Color Space

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Composition Analysis of Corrosion Products on Steel by Machine Learning of Optical Microscopic Images

Yuki Tsuji, Kota Hirasawa, Sunao Shoji, Yuichi Kitagawa, Yasuchika Hasegawa, Koji Fushimi

DOI:

10.2355/tetsutohagane.TETSU-2024-056

Abstract

Analysis of the corrosion distribution and composition of corrosion products on steel surfaces using supervised machine learning of optical microscopic images was investigated. The accuracy of the artificial intelligence in evaluating the composition of iron compound reference samples was affected by the illumination intensity and surface roughness during image capture. The evaluation accuracy was high for compounds with a wide distribution of R value such as Fe2O3 and FeOOH, but low for compounds with a narrow distribution such as Fe3O4. The results of wet-dry cycling tests on weathering steel with NaCl particles on the surface showed that the transition of corrosion products during the corrosion progress can be analyzed from optical microscope images.

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Composition Analysis of Corrosion Products on Steel by Machine Learning of Optical Microscopic Images

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Relation between Surface Appearance and Corrosion Depth Distribution of Carbon Steel under Atmospheric Corrosion Environment

Yu Sugawara, Takahiro Igarashi

DOI:

10.2355/tetsutohagane.TETSU-2024-061

Abstract

Degradation due to atmospheric corrosion is an important problem for steel structures such as bridges. In order to maintain steel structures safely over a long period of time, there is a need for a low-cost and easy-to-use method to evaluate corrosion degradation. In this study, corrosion morphology under atmospheric corrosion environment was focused on. The relation between the surface appearance and the distribution of corrosion depth of the carbon steel specimen after atmospheric exposure was analyzed, and the prediction of corrosion morphology under rust layers by surface observation of steel specimens was examined. It was found that deeply-corroded areas were possible to be located within the dark brown regions in the rusted specimen after the atmospheric exposure. As the exposure period increased, the correspondence between the dark brown regions in the rusted specimen and deeply-corroded areas became clearer. Since the corrosion progressed more locally as the exposure period increased, it is considered that the surface appearance of the rusted specimen showed traces of the deeply-corroded areas.

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Relation between Surface Appearance and Corrosion Depth Distribution of Carbon Steel under Atmospheric Corrosion Environment

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Mechanical Properties and Microstructure of High Strength Steel for Fracture Suppression and High Absorbed Energy in Automobile Collision

Shinsuke Komine, Tatsuya Nakagaito, Shinjiro Kaneko, Yuki Toji, Tomohiro Sakaidani, Kentaro Sato

DOI:

10.2355/tetsutohagane.TETSU-2024-035

Abstract

A fundamental study on the axial crush performances of HSS (High Strength Steel) was carried out to clarify the effects of microstructure and mechanical properties on crashworthiness. Axial crush tests were performed to evaluate the crush performances of the HSS with different microstructures and mechanical properties and identify the fracture origins. The cracks in the press formed area were observed and the cracks led to the fractures. The high λ (Hole expansion ratio) steel showed excellent crush performances by crack suppression. Crash deformation in the press formed area was simulated by the ORB (Orthogonally Reverse Bending) fracture tests and the crack suppression factors were investigated. Through the ORB fracture test, it was clarified that the reduction of the hardness gaps between phases and the refinement of the hard phases (Fresh martensite) were effective for suppressing cracks in the press formed area. These microstructures were occurred by the Q&P (Quenching & Partitioning) process for increasing λ. Therefore, it was found that the microstructural design for increasing λ also contributed to excellent crush performances.

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Mechanical Properties and Microstructure of High Strength Steel for Fracture Suppression and High Absorbed Energy in Automobile Collision

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Year-round Monitoring of Temperature and Humidity using a Sensor Network installed in the Hokkaido Centennial Memorial Tower

Kazuhisa Azumi, Masatoshi Sakairi, Koji Fushimi, Takashi Sato, Ken Mikami, Masazumi Miura

DOI:

10.2355/tetsutohagane.TETSU-2024-007

Abstract

Daily and seasonal changes in temperature (T) and relative humidity (RH) were monitored using a sensor network system installed in the Hokkaido Centennial Memorial Tower, built more than 50 years ago using weathering steel, to investigate its corrosion condition. Five T-RH sensors were set at the south side wall, inside the south tower, in the semi-open central area, inside the north tower, and on the north side wall on the 4th, 14th, and 24th floors. The T changed as a function of altitude, location in the floor, season, weather, solar radiation, diurnal cycle, distance from the wall, etc. The highest T of the south wall at daytime in the winter season could rise more than 30 °C even if the outer temperature was below 0 °C due to solar radiation causing the repetition of ice or snow melting in the daytime and freezing of water at night. The change in RH and T inside the tower followed a Tomashov-type RH-T curve (high RH at low T in the morning and evening). In winter, however, T and RH distribution, i.e., high-RH (> ca.60%) area below the freezing point and low-RH area with the high-T, caused air transportation inside the tower, condensation (and freezing) in the low-T area, and drying in the high-T area. In the visual inspections, severe corrosion, such as blistering and peeling, has been observed at the bottom of the tower, where snow has accumulated, and rainwater has stayed for a long time, especially at welds and joints.

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Year-round Monitoring of Temperature and Humidity using a Sensor Network installed in the Hokkaido Centennial Memorial Tower

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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/tetsutohagane.TETSU-2024-018

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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Formation Mechanism of Secondary Inclusions in Fe-36mass%Ni Alloy Using a Novel Combination Analysis Technique

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