Based on the reasonable design of chemical composition HRB400E steel (/% ：0. 21 ~0. 25C

0. 40 〜 0. 65Si

1.40 ~ 1. 55Mn

W0. 040P

W0. 0405

0. 015 ~ 0. 025Nb

6. 005 〜0. 008N)

the effects of different heating temperature and controlled rolling and controlled cooling temperature on the mechanical properties

metallographic structure and aging corrosion of steel bar surface are studied. The optimum rolling temperature parameters are： the heating temperature 1 140 ~ 1 170 T

the starting rolling temperature 1040 ~ 1060 °C

the finishing rolling temperature 1000 〜 1030 °C

and the cold bed temperature 870 ~890 V. after the final rolling. Results show that the yield strength of niobium microalloyed HRB400E steel is 450 ~475 MPa

the precipitates in steel are mainly Nb( C

N) with a particle size of 300 ~ 600 nm

which are distributed on the network carbide

the edge of the network carbide and the inside of the grain near the grain boundary.