铌微合金化HRB400E高强钢筋CCT曲线测定及应用

为了研究分析铌微合金化HRB400E高强钢筋不同冷速下转变组织，达到现场精细化的生产管理的目的，利用LINSEIS L78热膨胀仪及AutoCCT软件，结合组织和硬度测定并绘制了CCT曲线。分析结果为，过冷奥氏体在冷速小于3.5 ℃/s时发生F+P转变；在冷速为3.5 ℃/s时析出B；在冷速约为20 ℃/s时无P析出，组织为B+少量F；在冷速约为32 ℃/s时发生M相变，此时无F析出；在冷速约为80 ℃/s时全部转变为M。随着冷速的增大，F晶粒逐渐变小，而硬度逐渐增大且约到80 ℃/s时趋于平缓。根据测得的CCT曲线制定现场轧制工艺为开轧温度为（1 040±30） ℃，上冷床温度为规格小于25 mm时（950±30） ℃，规格不小于25 mm时（990±30） ℃，轧后冷速为2.2~3.0 ℃/s，可得到F+P组织且性能良好的高强钢筋。

Measurement and application of CCT curve of Nb #br# microalloyed HRB400E high strength rebar

 In order to study and analyze the transformation structure of Nb microalloyed HRB400E high strength rebar at different cooling rates, and achieve the purpose of fine production management in the field, the CCT curve was drawn with the help of LINSEIS L78 thermal expansion instrument and AutoCCT software combined with the microstructure and hardness measurement. The results showed that F+P transformation occured at the cooling rate of the undercooled austenite less than 3.5 ℃/s, B was precipitated at the cooling rate of 3.5 ℃/s, no P was precipitated at the cooling rate of about 20 ℃/s, and the micro structure was B with a small amount of F. M phase transition occured at the cooling rate of about 32 ℃/s, and no F precipitates at this time, and all of them change to M at the cooling rate of about 80 ℃/s. With the increase of the cooling rate, the F grains became smaller, while the hardness increased and tended to be flat at the cooling rate of about 80 ℃/s. According to the measured CCT curve, the field rolling process was that the open rolling temperature was (1 040±30) ℃, the upper cold bed temperature was (950±30) ℃, and (990±30) ℃ for the size of less than 25 mm and more than 25 mm, respectively, the cooling rate after rolling was 2.2 3.0 ℃/s. And, high strength rebar with F P structure and good performance can be obtained.