大应变冷拉拔珠光体钢丝的力学性能与微观组织

【作者】 丁立；

【导师】 吴锵；

【作者基本信息】 南京理工大学 ， 材料学， 2008， 硕士

【摘要】 随着钢丝拉拔技术的进步,钢丝强度的提高主要通过加大拉丝速度来实现。应此,现代钢丝生产主要是一个高速大应变的塑性变形问题。因此对高速大应变工业生产条件下高碳珠光体钢丝拉拔形变过程进行考察,研究高碳钢丝的组织演变和性能变化就显得尤为重要。本文研究了70~#钢丝从Φ5.5mm冷拉拔至Φ1.8mm左右的变形过程,结果表明:钢丝的抗拉强度与显微硬度均随随拉拔应变量增大而增大,且当应变量较大时,强度增长速度略快于应变量较小阶段,经拉拔后,横截面上的显微硬度略大于纵截面。金相观察显示,70~#钢钢丝经冷拉拔形变后,随着应变量的增大钢丝横截面上晶粒逐渐细化,而在纵截面上晶粒被拉长直至呈纤维状。SEM与TEM对钢丝微观组织观察显示,随着应变量的增大,钢丝组织中珠光体平均片层间距逐步减小,并逐渐向拉丝轴平行的方向上调整;铁素体片层中,位错密度显著增大。钢丝经200℃以下退火30min,组织缺陷减少,但钢丝性能保持稳定,这是因为渗碳体分解造成的强化作用。在更高温度下退火,高强度渗碳体片层发生球化,铁素体片层中位错密度进一步降低,造成钢丝强度下降。更多还原

【Abstract】 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.更多还原