Abstract: Effect of annealing time on the microstructure evolution and mechanical properties of warm rolled 45 steel with pseudoeutectoid type initial microstructure was studied by means of scanning electron microscopy, electron backscatter diffraction and tensile test. The results show that the microstructure of the warm rolled steel is of multiphase and multiscale, and the cementite is fragmented. With the increase of annealing time, the cementite gradually spheroidizes, grows up and gradually distributes evenly, and the multiphase and multiscale structure is weakened. With the annealing time increases from 15 min to 120 min, the average ferrite grain size increases from 2.32 μm to 5.62 μm, the proof strength, plastic extension decreases from 1057 MPa to 662 MPa, and the uniform elongation reaches the maximum when annealed at 120 min. Overall, the comprehensive mechanical properties of the tested steel reaches the best when warm rolled at 500 ℃, then annealed at 600 ℃ for 15 min.

Key words: pseudoeutectoid 45 steel, warm rolling, annealing, microstructure evolution, mechanical properties