Effect of Nb content and thermal deformation on the microstructure and mechanical properties of high-strength anti-seismic rebar

Rebar is the most important material in large-scale engineering structures, and its fine structure determines the strength and seismic resistance of rebar. The objective of this study is to investigate the effect of Nb content on the microstructure and mechanical properties of high-strength anti-seismic rebar under the condition of thermal deformation. The Gleeble-3800 thermal simulator was used to simulate the continuous rolling process, which analyzed that effect of precipitation behavior of Nb on the microstructure and mechanical properties of rebar. Scanning electron microscope (SEM), transmission electron microscope (TEM) and universal tensile testing machine were used to characterize the microstructure, precipitation and mechanical properties of high-strength anti-seismic rebar. Under the condition of process I or process II, when the Nb content changed from 0.012 wt% to 0.020 wt%, the microstructure of the experimental steel was mainly composed of ferrite and pearlite, resulting in relatively low the tensile strength and good the plasticity, and the tensile fracture belonged to ductile fracture. Under the condition of process I or process II, when the Nb content changed from 0.035 wt% to 0.060 wt%, the microstructure of the experimental steel was mainly composed of ferrite, pearlite and bainite, resulting in relatively high the tensile strength, which reached 995.30±5 MPa and low the plasticity, and the tensile fracture belonged to shear fracture. Whether under the condition of process I or process II, when the Nb content changed from 0.012 wt% to 0.060 wt%, TEM confirmed that the main precipitates of the experimental steels were mainly (Ti, Nb) C, (Ti, Nb, V) C, (Nb, Ti, V) C, respectively. These carbides were mainly distributed on the ferrite grains or grain boundaries, and the shapes were elliptical, square, strip, respectively. The average particle size of these carbides was less than 50 nm, and the crystal structure of these carbides belonged to the cubic structure.