Notch-Fatigue Properties of Advanced TRIP-Aided Bainitic Ferrite Steels |
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Authors: | Nobuo Yoshikawa Junya Kobayashi Koh-ichi Sugimoto |
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Affiliation: | 1. Graduate School, Shinshu University, 4-17-1, Wakasato, Nagano, 380-8553, Japan 2. Department of Mechanical Systems Engineering, Shinshu University, 4-17-1, Wakasato, Nagano, 380-8553, Japan
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Abstract: | To develop a transformation-induced plasticity (TRIP)-aided bainitic ferrite steel (TBF steel) with high hardenability for a common rail of the next generation diesel engine, 0.2?pct C-1.5?pct Si-1.5?pct Mn-0.05?pct Nb TBF steels with different contents of Cr, Mo, and Ni were produced. The notch-fatigue strength of the TBF steels was investigated and was related to the microstructural and retained austenite characteristics. If Cr, Mo, and/or Ni were added to the base steel, then the steels achieved extremely higher notch-fatigue limits and lower notch sensitivity than base TBF steel and the conventional structural steels. This was mainly associated with (1) carbide-free and fine bainitic ferrite lath structure matrix without proeutectoid ferrite, (2) a large amount of fine metastable retained austenite, and (3) blocky martensite phase including retained austenite, which may suppress a fatigue crack initiation and propagation. |
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