Formation mechanism of ultrafine grains at machined surface of 0.45 % carbon steel under high-speed turning process

• Published in: Journal of manufacturing processes Vol. 113; pp. 171 - 182
• Main Authors: Park, Hyung-Won, Matsuda, Masaki, Ishitaka, Kanji, Funase, Shinichi, Tomizawa, Atsushi, Hosokawa, Akira, Yanagimoto, Jun, Ueda, Takashi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.03.2024
• Subjects: Carbon steel; Cutting temperature; Finite element analysis; High-speed machining; Phase transformation; Surface integrity; Surface integrity; Phase transformation; Carbon steel; Finite element analysis; High-speed machining; Cutting temperature
• ISSN: 1526-6125; 2212-4616
• DOI: 10.1016/j.jmapro.2024.01.071

Turning of 0.45 % carbon steel was performed with an Al2O3 tool at a cutting speed of 64–923 m·min−1 to investigate the cutting behavior, such as cutting temperature, cutting force, and chip formation, and to clarify the formation mechanism of ultrafine grains at the machined surface under high-speed turning process. The principal force exhibited stable behavior at cutting speeds up to 923 m·min−1. The cutting temperature exceeded 760 °C when the cutting speed was over 500 m·min−1 and reached 850 °C when the cutting speed was 923 m·min−1. From the microstructure of machined surface, the shear band at all cutting speeds was observed at a depth of up to 20 μm. Discontinuous and continuous ultrafine ferrite and pearlite layers with nanosized grains at cutting speeds of 509 and 923 m·min−1, respectively, were present at depths of up to 5–8 μm. Additionally, {211}〈111〉 and {110}〈112〉–{110}〈114〉 orientations in the ferrite were observed in an ultrafine layer, which are generally formed by shear-deformed austenites. From the results of finite element analysis at a cutting speed of 923 m·min−1, the severe cutting affected zone was up to 10 μm, where the temperature, strain, and strain rate reached approximately 870 °C, 5, and 2 × 105 s−1, respectively. Therefore, ultrafine ferrite and pearlite with nanosized grains could be formed owing to the α + Fe3C → γ → α + Fe3C phase transformation at the machined surface subjected to ultrahigh-speed and severe-shear thermomechanical processing. [Display omitted] •Turning of 0.45% carbon steel was performed with an Al2O3 tool at a cutting speed of 64–923 m·min−1, cutting depth of 0.5 mm, and feed rate of 0.21 mm·rev−1.•A continuous ultrafine layer at a cutting speed of 923 m·min−1 was present at depths of up to 5–8 μm.•Ultrafine ferrite and pearlite could be formed owing to phase transformation at the machined surface subjected to ultrahigh-speed and severe-shear thermomechanical processing.