Ferrite Grain Refinement by Large Reduction per Pass in Non-recrystallization Temperature Region of Austenite

• Published in: ISIJ International Vol. 36; no. 5; pp. 603 - 610
• Main Authors: Kojima, Akihiko, Watanabe, Yoshiyuki, Terada, Yoshio, Yoshie, Atsuhiko, Tamehiro, Hiroshi
• Format: Journal Article
• Language: English
• Published: Tokyo The Iron and Steel Institute of Japan 01.01.1996; Iron and Steel Institute of Japan
• Subjects: annealing twin boundary; Applied sciences; austenite; Cross-disciplinary physics: materials science; rheology; deformation band; Exact sciences and technology; ferrite; ferrite nucleation; grain refinement; grain size; hot deformation; low carbon steel; Materials science; Metals. Metallurgy; non-recrystallization temperature; Other heat and thermomechanical treatments; Physics; reduction per pass; Treatment of materials and its effects on microstructure and properties; Hot deformation; Grain size; Compression; Nucleation; Low carbon steel; Experimental study; Ferrite; Optical microscopy; Grain refining; Austenite; Thermomechanical treatments; SEM; Microstructure
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.36.603

In order to clarify the effects of reduction per pass in non-recrystallization temperature region of austenite (γ ) on ferrite (α) grain size of low carbon steels, isothermal hot compression tests have been performed. The hot deformations have been carried out by the constant reduction per pass of 10, 20 or 30% under the cumulative reduction of 30 or 50% in the non-recrystallization region. The α grain size is decreased about 15% with increasing the reduction per pass from 10 to 30% under the cumulative reduction of 50%. At this time, the α nucleaton site density, which is defined as the number of γ grain boundaries, deformation bands and annealing twin boundaries per unit length of deformation direction, is increased about 30%. It is estimated that the increase in the α nucleation site density is caused by the increase in deformation bands. Furthermore, the number of α nuclei per unit length of γ grain boundaries is increased about 10% with increasing the reduction per pass from 10 to 30% under the cumulative reduction of 30%. It has been clarified by the calculation that the α grain refinement by the large reduction per pass is mainly caused by the increase in the α nucleation site density, which is led by the increase in deformation bands.