Effect of Cold Drawing Deformation and Heat Treatment on Microstrcture and Mechanical Properties of 55SiCr Spring Steel Wire

55SiCr spring steel wire with a diameter of 5.5 mm was coarsely drawn to the diameter of 5.00 mm, and then was subjected to cold drawing with ten passes to obtain the wire with the linear diameter of 1.81 mm. The cold drawing deformations were successively 4.94, 8.91, 13.34, 19.54, 25.97, 34.75, 42.52, 55.44, 69.55, 82.34 cm. The effect of cold drawing deformation on microstructure and mechanical properties of the cold-drawn steel wire was studied. The cold-drawn steel wire was quenched in oil after holding at 920 ℃ for 1.5 min, and then tempered at 435 ℃ for 1 min. The microstructure and mechanical properties of the steel wire after quenching and tempering treatment were studied. The results show that the microstructures of the cold-drawn spring steel wire were all composed of pearlite and ferrite. With the increase of cold drawing deformation, the microstructure changed from equiaxed crystals to slender strip silk texture, and the grain size decreased; the tensile strength and hardness increased, and the percentage reduction of area decreased. After quenching and tempering treatment, the microstructure of the steel wire was transformed into a tempered troostite structure composed of ferrite matrix and dispersed fine-grained cementites; the ferrite still maintained the needle-like quenched martensite orientation and morphology. Compared with those before quenching and tempering treatment, the tensile strength and hardness of the steel wire after quenching and tempering treatment increased by 17.5% and 23.0%, respectively, and the percentage reduction of area only decreased by 1.96%.