金属切削过程中，剧烈的大剪切变形可以产生具有超细晶结构的切屑从而使其获得了比本体材料更高的硬度和强度。本文对比了不同的金属和合金在各种刀具前角和切削速度条件下，切屑上产生的剪应变、切屑的微结构及其硬度的变化规律。实验结果显示随着刀具前角的减小切屑的微结构得到显著细化，其硬度随之得到极大地提高；而切削速度的减小提高了切屑的硬度但其微结构的变化不甚明显；采用负前角刀具在较低的切削速度下能加工出具有超细晶结构和高硬度的切屑材料，而切削速度的提高将使大剪切变形引起的硬度增长减弱。

During the metal cutting process, ultrafine-grained chips may form owing to the severe shear deformation, thus resulting in higher hardness and strength for the chips. In this paper, the variations of the shear strain imposed on the chips as well as on the microstrueture and the hardness of chips under the condition of different tool rake angles and various cutting velocities are investigated for different metals and alloys. Experimental results indicate that   with the decrease of the tool rake angle, the microstructure of chips are significantly refined and the hardness of chips is greatly improved;   the effect of the cutting velocity on the microstructure and the hardness is opposite to that of the tool rake angle ;   ultrafine-grained chip materials with high hardness can be obtained by cutting with a negative tool rake angle at a lower cutting velocity; and   the increase in cutting velocity alleviates the improvement of hardness owing to the large shear deformation.