Abstract: Temperature range of non-recrystallization region and dynamic CCT curves of vanadium-free coil-free snail steel bars HRB400E were studied, and the industrial production process of the steel bars was optimized. The results show that when the strain rate is 0.2 s^-1, obvious recrystallization occurs in the HRB400E steel when rolling at 970 ℃, while partially recrystallization or non-recrystallization occur when the rolling temperature is reduced to 850 ℃ and below. The microstructure of the steel is ferrite and pearlite when the cooling rate is less than 3 ℃/s, ferrite+pearlite+bainite when the cooling rate is in the range of 5-15 ℃/s, and pearlite+bainite when the cooling rate is over 15 ℃/s. According to the experiment results, the rolling start temperature, finishing rolling temperature and wire spinning temperature is preset as (950±15) ℃, (870±10) ℃, and (870±10) ℃, respectively, and the opening degree of No.1 to No.4 fans is 90%, 90%, 70% and 70%, respectively. When this optimized process is used in trial production, the yield strength of the steel bar R_p0.2≥409.5 MPa, the difference in the same circle ≤32.6 MPa, the maximum total elongation A_gt≥10.26%, the microstructure is composed of ferrite and pearlite, and the tonnes steel cost in the whole process is reduced by about 16 Yuan.

Key words: non-recrystallization region, CCT curve, microstructure, yield strength, maximum total elongation