Effects of different microalloying and controlled cooling technology on microstructure and properties of 500MPa high-strength rebars

摘要

The mechanical properties and microstructures of three different VN, Nb, V-Nb microalloyed rebars were investigated by using tensile testing machine, impact machine, metallographic microscopy, scaning electron microcopy, transmission electron microscopy and X-ray diffraction apparatus. The results showed that the microstructure of V-Nb microalloyed specimen is consisted of ferrite, pearlite and a small amount of fine bainite (6.7wt%), and obvious effect of grain refinement was obtained with more than 10 size grade of ferrite grain, showing optimal comprehensive properties. SEM micrograph of tensile fracture surface for V-Nb microalloyed 500MPa high-strength rebar is dimple and ductile, ductile-brittle transformation temperature is lower than -30°C, which has good plasticity-toughness and impact toughness at low temperature. The results of precipitates have shown that a large number of small and dispersive V(CN) and Nb (CN) precipitates with size of 5～30nm are formed, good effect of precipitation strengthening was achieved in 500MPa high-strength rebars produced by different microalloying and controlled cooling technology.