Effect of Cr-RE alloying on corrosion resistance of HRB400 reinforcing bars

HRB400 reinforcing bars are susceptible to erosion by aggressive ions such as Cl^- during service, which causes the rupture of the passive film and subsequent corrosion of the bars. To improve the corrosion resistance of reinforcing bars, this study carried out a Cr-RE (Cr-rare earth) alloying design based on the commercial HRB400 reinforcing bars and prepared six types of corrosion-resistant reinforcing bars. Mechanical property tests, microstructure and inclusion characterization, and alternating wet-dry cyclic tests under simulated industrial atmospheric environments were conducted to rapidly screen the experimental steels. According to the corrosion resistance gradient, three types of corrosion-resistant reinforcing bars were further selected for corrosion resistance verification in a chloride-containing simulated concrete environment. The results show that compared with conventional HRB400 reinforcing bars, the developed corrosion-resistant reinforcing bars exhibit reduced pearlite content and significantly refined inclusions. The main inclusions in HRB400 reinforcing bars are MnS and MnO-MgAl₂O₄. The addition of RE transforms strip-shaped MnS and irregular MnO-MgRE₂O₃-(Al, Ca, Si)_xO_y inclusions into spherical MnS-RE₂O₃-(Al, Ca, Si)_xO_y composite inclusions. In the simulated industrial atmospheric environment, the corrosion rate reduction rates of corrosion-resistant reinforcing bars (mass fraction)with 0.51%Cr and 0.81%Cr are 56.0% and 68.8%, respectively, in comparison with HRB400 reinforcing bars. On this basis, with composite addition of RE(mass fraction)(0.51%Cr+ 0.018%RE and 0.81%Cr+0.018%RE), the corrosion rate reduction rates of the corrosion-resistant reinforcing bars reach 73.2% and 89.5%. In the chloride-containing simulated concrete pore solution environment, the corrosion-resistant reinforcing bars with a Cr mass fraction of 0.50% achieve a corrosion rate reduction rate of 81.74%. After the composite addition (mass fraction) (0.51%Cr+ 0.018%RE and 0.81%Cr+ 0.018%RE).The corresponding corrosion rate reduction rates of the corrosion-resistant reinforcing bars reach 92.24% and 94.16%, respectively. The results indicate that Cr-RE alloying can synergistically improve the corrosion resistance of HRB400 reinforcing bars through microstructure refinement, inclusion modification and pitting corrosion inhibition, while ensuring that the mechanical properties meet the requirements of GB/T 1499.2-2024. This study provides a theoretical basis for the development of novel corrosion-resistant reinforcing bars.