Effect of isothermal transformation temperature on the microstructure, precipitation behavior, and mechanical properties of anti-seismic rebar

Abstract

The synergy between Nb/Ti strengthening and precise isothermal transformation temperatures has resulted in the optimal microstructure and mechanical properties in Nb/Ti anti-seismic rebars. The microstructure, precipitates, and mechanical properties of experimental steels at different isothermal transformation temperatures were characterized using scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, and universal tensile testing machine. As the isothermal transformation temperature decreased from 700 to 600°C, the ferrite grain size, pearlite interlamellar spacing, and carbon diffusion coefficient of the experimental steel decreased to 6.69 μm, 0.17 μm, and 0.14 cm2·s−1, respectively, while the yield strength and tensile strength increased to 584 and 714 MPa, respectively. At 600°C, the pearlite transformation rate in the experimental steel was the fastest, accompanied by the most rapid precipitation kinetics. The precipitates were (Nb, Ti)C of approximately 50 nm in size, with a mismatch of 14.24% at the matrix/precipitate interface and a screw dislocation angle of 2.07°. The presence of screw dislocation steps may facilitate nucleation of Nb/Ti precipitates, forming semi-coherent interfaces.

Keywords

• nb/ti strengthening
• screw dislocation
• diffusion coefficient
• strengthening mechanism