Large Strain Cold Drawing Of The Mechanical Properties And Microstructure Of Pearlitic Steel Wire

With the development of steel wire drawing technology, accelerating drawing speed is used as the main method to strengthen the steel wire. The manufacture of steel wire nowadays mainly adopts the process of high speed severe plastic deformation. Therefore, it is of equal importance to investigate the details of high-carbon pearlite steal drawing with high speed severe plastic deformation, as well as the microstructure evolution and properties transform of high-carbon steel wire.In this paper, deformation process of 70~# steel wire, drawn fromΦ5.5mm toΦ1.8mm, was studied. The results showed that tensile strength and micro-hardness of steel wire were improved with the increase of drawing strain. In addition, rate of strength increase was a little faster when the drawing strain accreted. Finally, after drawing, the micro-hardness of cross section was higher than that of profile section appreciably.OM analysis indicated that with the increase of strain, grains were gradually refined on the cross section, while those on the profile section were elongated to fibrous morphology; SEM and TEM micrographs showed that as drawing strain increased, the average pearlite interlaminar spacing decreased, and it gradually modified to the direction parallel to drawing axis. Besides, dislocation density in lamellar ferrite increased significantly.Moreover, microstructure defect of steal wire tempered at 200℃for 30min reduced, and the properties of steal wire remained stable, because of the strengthening effect caused by dissolution of cementite. However, when tempered at a higher temperature, the strength of steel wire reduced. It was because high strength lamellar cementite spheroidized, ferrite experienced recovery and recrystallization, and therefore, dislocation density in lamellar ferrite further decreased, which was the main reason of the strength reduction.