Article
Materials Science, Multidisciplinary
Tomohiko Hojo, Yutao Zhou, Junya Kobayashi, Koh-ichi Sugimoto, Yoshito Takemoto, Akihiko Nagasaka, Motomichi Koyama, Saya Ajito, Eiji Akiyama
Summary: The effects of thermomechanical processing on the microstructure and hydrogen embrittlement properties of ultrahigh-strength, low-alloy, TRIP-aided bainitic ferrite (TBF) steels were investigated. The study found that thermomechanical processing can refine the microstructure, improve the characteristics of retained austenite, and enhance the strength of the material. Additionally, it was found that thermomechanical processing improves the hydrogen embrittlement resistance of the TBF steels.
Article
Materials Science, Multidisciplinary
Madhumanti Mandal, Warren J. Poole, Matthias Militzer, Laurie Collins
Summary: There is a growing interest in establishing quantitative correlations between microstructures and mechanical properties (yield stress and ductile-brittle transition temperature) for the weld heat-affected zone of pipelines. In this study, two line pipe steels with different carbon contents were subjected to thermal treatments to create specific microstructures. The microstructure was characterized using optical metallography and electron backscatter diffraction mapping. Tensile and impact tests were conducted over a range of temperatures, and microstructure-property models were developed for yield strength and cleavage stress. These findings provide a framework for predicting mechanical properties based on microstructural characteristics.
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
(2023)
Article
Nanoscience & Nanotechnology
Yutao Zhou, Tomohiko Hojo, Motomichi Koyama, Saya Ajito, Eiji Akiyama
Summary: The mechanical properties of TRIP-aided steel with a bainitic ferrite matrix in the presence of hydrogen were investigated. It was found that hydrogen charging slightly increased the yield strength and deteriorated the uniform elongation. In the hydrogen-uncharged and hydrogen-charged specimens, the transformation ratio of retained austenite increased with a decrease in the deformation temperature, but hydrogen charging decreased the transformation ratio.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2022)
Article
Nanoscience & Nanotechnology
G. Yang, X. Y. Long, Y. Zhang, F. C. Zhang, G. J. Du, Z. L. Liu, Y. G. Li
Summary: The influence of monotonic mechanical properties on the low-cycle fatigue lifetime of carbide-free bainitic steel is investigated. It is found that an increase in dislocation density and a decrease in bainitic ferrite lath size lead to an increase in tensile strength, while a decrease in retained austenite volume fraction leads to a decrease in elongation. The mathematical analysis of fatigue lifetime in terms of tensile strength, elongation, and static toughness can effectively predict the variation of the LCF lifetime for different grades of bainitic steels.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2022)
Article
Metallurgy & Metallurgical Engineering
Junya Kobayashi, Ryo Sakata, Naoya Kakefuda, Goroh Itoh, Tomohiko Hojo
Summary: This study aims to investigate the role of retained austenite in hydrogen embrittlement of TRIP-aided bainitic ferrite steel (TBF steel), revealing that hydrogen embrittlement of TBF steel sheet is suppressed with increasing austempering time.
ISIJ INTERNATIONAL
(2021)
Article
Metallurgy & Metallurgical Engineering
Virendra Kumar Verma, Motomichi Koyama, Bakuya Kumai, Tomohiko Hojo, Eiji Akiyama
Summary: The study found that pre-strain significantly affects the hydrogen embrittlement resistance of transformation-induced plasticity-aided bainitic ferrite steel, improving the crack growth resistance of hydrogen-charged specimens. Additionally, high levels of pre-strain can result in high hydrogen concentration and subsequent strain-age-hardening, leading to decreased crack initiation resistance and crack growth resistance.
ISIJ INTERNATIONAL
(2021)
Article
Metallurgy & Metallurgical Engineering
Akihiko Nagasaka, Tomohiko Hojo, Yuki Shibayama, Masaya Fujita, Takumi Ohashi, Mako Miyasaka, Eiji Akiyama
Summary: The effect of retained austenite characteristics on V-bending in ultrahigh-strength TRIP-aided steel sheets with bainitic ferrite matrix (TBF steel) for automotive applications was investigated. It was found that the 0.2C-1.5Si-1.5Mn TBF steel sheets performed V-bending through strain-induced martensitic transformation of TRIP effect, while the ferrite-martensite dual-phase (MDP0) steel sheet of 900 MPa grade was not able to perform 90-degree V-bending due to crack initiation in tension area. Additionally, the TBF375 steel sheet, produced by specific heat treatment, enabled 90-degree V-bending and controlled the amount of springback.
ISIJ INTERNATIONAL
(2022)
Article
Nanoscience & Nanotechnology
I Burda, K. Zweiacker, A. Arabi-Hashemi, P. Barriobero-Vila, A. Stutz, R. Koller, H. Roelofs, L. Oberli, M. Lembke, C. Affolter, C. Leinenbach
Summary: Controlling the grain size of steels has a significant impact on their mechanical properties. This study successfully achieved microstructural refinement of a low-alloyed TRIP-assisted bainitic steel through a new industrial thermomechanical treatment. Fatigue tests showed the influence of this treatment on crack propagation behavior. Electron backscatter diffraction, vibrating sample magnetometry, and high-energy synchrotron X-ray diffraction were used to analyze the microstructure near the fatigue crack tip and assess the contribution of martensitic transformation to fracture toughness.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2022)
Article
Nanoscience & Nanotechnology
Feng Cai, Mingxing Zhou, Junyu Tian, Guang Xu
Summary: This investigation examines the role of niobium (Nb) in ferritic and bainitic steels, and explores its influence on the transformation kinetics, microstructure, and mechanical properties of these steels. The study finds that increasing Nb content inhibits and then accelerates the transformation kinetics of both ferrite and bainite. However, the effects of Nb on ferritic and bainitic transformations are different. Additionally, the strengthening mechanisms of Nb differ between ferritic and bainitic steels, with precipitation strengthening predominant in ferritic steels and dislocation strengthening and phase transformation strengthening being major sources in bainitic steels. Moreover, the addition of Nb reduces the work hardening capacity of both ferritic and bainitic steels.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2022)
Article
Nanoscience & Nanotechnology
Yutao Zhou, Tomohiko Hojo, Motomichi Koyama, Eiji Akiyama
Summary: The study investigated the effects of austempering treatment on Fe-0.4C-1.5Si-1.5Mn TRIP-aided bainitic ferrite steel, finding that the suppression of crack propagation and improvement in mechanical properties and ductility at optimal austempering time are attributed to the effective transformation of metastable retained austenite. Formation of bainitic ferrite and retained austenite play a crucial role in the mechanical properties of the steel.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2021)
Article
Materials Science, Multidisciplinary
Tianyu Zhang, Jun Hu, Chenchong Wang, Yu Wang, Weina Zhang, Hongshuang Di, Wei Xu
Summary: The study examines the impact of DCT on multiphase steel, revealing the transformation of blocky RA and the competitive relationship between bainitic transformation and nanoscale carbide precipitation during tempering. The yield strength of the DCT-treated steels is significantly increased due to the precipitation of nanoscale carbides and the elimination of unstable RA, showing the correlation between thermal and mechanical stabilities of RA during DCT and tensile strain.
MATERIALS CHARACTERIZATION
(2021)
Article
Materials Science, Multidisciplinary
Guhui Gao, Rong Liu, Yusong Fan, Guian Qian, Xiaolu Gui, R. D. K. Misra, Bingzhe Bai
Summary: This study investigates the fatigue crack initiation behavior of advanced bainitic steels during high cycle fatigue/very high cycle fatigue regimes and the role of retained austenite in crack initiation and propagation. The study identifies multiple micro-mechanisms responsible for fatigue crack initiation and discusses the formation of fine grains that assist crack advancement. The findings provide insights into the cyclic response of multiphase structures and the mechanisms of fatigue crack initiation during very high cycle fatigue.
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY
(2022)
Article
Materials Science, Multidisciplinary
Ravi Ranjan, Hossein Beladi, Peter D. Hodgson, Shiv Brat Singh
Summary: Thermo-mechanical treatments were used to study the effects of recrystallisation and deformation induced ferrite transformation (DIFT) in a low-carbon, low alloy CMnSiAl TRIP-aided steel. The study showed that the prior transformation of retained austenite to martensite does not necessarily lead to brittle failure, and that the deformation of a composite microstructure plays a significant role in the improved mechanical properties of TRIP-aided steels compared to conventional high strength steels. The findings provide insights for the design of alloy composition and subsequent thermo-mechanical treatments.
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
(2021)
Article
Materials Science, Multidisciplinary
Yusong Fan, Xiaolu Gui, Miao Liu, Xi Wang, Chun Feng, Guhui Gao
Summary: The study focuses on the high-cycle fatigue behaviors of medium-carbon bainitic steels. Two crack initiation modes, inclusion-induced crack initiation (IICI) and noninclusion-induced crack initiation (NIICI), were identified after fatigue failure. Predictions of fatigue strength and life were made based on fracture surface analysis.
Article
Materials Science, Multidisciplinary
Avanish Kumar, Aparna Singh
Summary: Nanostructured bainitic steels exhibit ultra-high strength and good ductility, suitable for various engineering applications. By tailoring the microstructure, their performance can be further enhanced. A fundamental understanding of the correlation between microstructure and properties is crucial for research in nanostructured bainitic steels.
