切削大变形对材料微结构及硬度的影响

在金属切削过程中,剧烈的大剪切变形可以产生具有超细晶结构的切屑,从而使其获得比本体材料更高的硬度和强度.文中比较了不同的金属和合金在各种刀具前角和切削速度下,切屑上产生的剪应变、切屑的微结构及硬度的变化规律.实验结果显示:随着刀具前角的减小,切屑的微结构显著细化,其硬度随之极大提高;切削速度的减小提高了切屑的硬度,但对其微结构的影响不甚明显;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变缓.

Effect of Large Cutting Deformation on Microstructure and Hardness of Material

Large shear strains imposed during chip formation in machining are found to produce significant microstructure refinement in the chip, resulting in higher hardness compared to the bulk. The effect of rake angle and cutting velocity on the shear strain imposed in the chips, microstructure and hardness of chips are highlighted in a variety of metals and alloys. The experimental results indicated that the microstructure of chips are significantly refined and the hardness of chips are increased with decreasing rake angle, but the hardness of chips are increased while the microstructure of chips are not refined significantly with decreasing cutting velocity. Chip materials with ultrafine grained and high hardness can be produced during the chip formation by machining with more negative tool rake angle at some lower cutting velocity. While the increasing cutting velocity not only can alleviate the increase of hardness produced by decreasing rake angle but can lead to the decrease of hardness.