The production process flowsheet of Φ22~25 mm steel reinforced bar HRB400 (/% : 0.20~0.25 C

0.25~0.43Si

0.90~1.15Mn) and Φ18~28 mm high strength steel reinforced bar HRB500 (/% : 0.20~0.25C

0.50~0.65Si

1.38 ~ 1.53Mn

0.05~0.07V) is 100 t top and bottom combined blowing converter-deoxidizing and alloying during tapping-ladle bottom argon blowing- 160 mm X 160 mm billet casting-continuous rolling. By observation on structure of reinforced bar HRB400 and high strength reinforced bar HRB500 the precipitation behavior and the effect of V and Nb carbide precipitation on properties of steel are analyzed

and the strengthening measures including to control the self-tempering structure layer at surface of HRB400 steel reinforced bar less than 1 mm and using V-Nb composite micro-alloying for HRB500 steel reinforced bar are put forward. With controlling carbon content in steel 0. 18% ~0. 23%

increasing steel bar temperature after water cooling to 700 ℃from original 650 ℃

and using V + Nb =0.05%〜0.07% to com- posite-strengthen for HRB500 steel bar

the yield and tensile strength of Φ22 ~25 mm bar of HRB400 steel decreases respectively from 460~510 MPa and 580 ~610 MPa to 440~490 MPa and 570~620 MPa

and the yield and tensile strength of of Φ18~28 mm bar of HRB500 steel increases respectively from 560~610 MPa and 670~700 MPa to 570~620 MPa and 680~710 MPa obviously to increase the comprehensive mechanical properties of steel.