Abstract: Effect of 650-730 ℃ warm rolling temperature on microstructure evolution and mechanical properties of a 0.46%C medium carbon steel was studied by means of TEM, SEM, room temperature tensile test. The results show that after 90% rolling deformation, a large amount of intragranular dislocations are introduced in the ferrite of the tested steel, the cementite lamella produces stress concentration, which causes the lamellar cementite to bend, kink, and shear into granules. With the decrease of warm rolling temperature, the dislocation multiplication is obvious, the spheroidization rate of cementite increases and the distribution becomes more and more uniform, the strength and the elongation increase overall. At the warm rolling temperature of 650 ℃, the cementite is greatly spheroidized, the tensile strength is 877 MPa, and the elongation after fracture is 16.0%, the tested steel has the best comprehensive mechanical properties. The tensile fracture results show that with the decrease of warm rolling temperature, the fracture mechanism of the tested steel changes from ductile and brittle mixed fracture to ductile fracture, and the ductility increases.

Key words: medium carbon steel, warm rolling temperature, dislocation density, microstructure, mechanical properties