Effect of Nb content and cooling rate on the microstructure transformation and mechanical properties of hot-rolled rebar

In this study, the synergistic effect of the Nb content and cooling rate on the microstructural transformation, precipitation behavior, and mechanical properties of hot -rolled rebar was studied using a Gleeble-3800 thermal simulation machine, scanning electron microscopy, transmission electron microscopy, and a universal tensile testing machine. The results showed that the synergistic effect of Nb content and cooling rate could optimize the microstructure and precipitation behavior of rebar, promote ferrite and pearlite transformation, and reduce the ferrite grain size, pearlite lamellar spacing, and precipitated phase size, thereby improving the strength and plasticity of Nb-containing rebar. When the cooling rate was 3 degrees C/s and the Nb content was 0.035 wt%, the ferrite grain size decreased to 21.45 mu m, the pearlite lamellar spacing refined to 0.222 mu m, and the particle size of the (Nb, Ti, V) C precipitates reduced to 5 nm. Accordingly, the yield and tensile strength increased to 779 +/- 6 MPa and 973 +/- 8 MPa, respectively, the elongation at fracture increased to 16.35%, and the microhardness increased to 311.39 +/- 8.0 HV.