硬态车削工艺对18CrNiMo7-6钢表层硬度及微观组织的影响

Impact of Hard Turning Process on Surface Hardness and Microstructure of 18CrNiMo7-6 Steel

为了探究18CrNiMo7-6钢硬态车削工艺参数对加工硬化及金相组织的影响,采用PCBN刀具对18CrNiMo7-6钢漏斗形疲劳试样硬态车削圆弧段时的主轴转速n、背吃刀量a_(p)和进给速度v_(f)进行了单因素实验研究。运用显微硬度计和超景深三维显微系统表征了试样在不同工艺条件下的表层硬度、加工硬化影响深度及微观组织。研究结果表明:硬态车削为漏斗形疲劳试样的圆弧段造成了一定的加工硬化,硬化影响层深度为120~200μm,加工硬化程度为4.31%~8.27%。在试验条件下,随着n的增大,试样的硬化程度先增大后减小,硬化影响层深变化不大;随着a_(p)增大,试样的硬化影响层深和硬化程度都逐渐增大;v_(f)对试样的加工硬化程度先增大后减小,对硬化影响层深没有明显规律;随着径向深度的增加,试样金相组织发生变化,且硬度值逐渐下降,车削工艺参数对试样表层金相组织的影响很小;当n、a_(p)及v_(f)分别为1 200 r/min、0.15 mm、 50 mm/min时,试样表层出现软化现象,高碳马氏体转化为硬度较低的回火屈氏体。该研究为18CrNiMo7-6淬硬钢的硬态车削工艺制定提供了参考依据。

In order to explore the impact of hard turning process parameters of 18 CrNiMo7-6 steel on work hardening and metallographic structure,PCBN tool was used to hard turning of the arc section of the 18 CrNiMo7-6 steel funnel-shaped fatigue sample.The spindle speed n and the turning back a_(p) and feed rate v_(f) were carried out a as single factor experimental study.The surface hardness,work hardening depth of influence and microstructure of the samples under different process conditions were characterized by a microhardness tester and super depth of field 3 D microscopy system.The research results showed that hard turning introduced a certain amount of work hardening to the arc segment of the funnel-shaped fatigue specimen,the depth of the hardened layer was 120~200μm,and the degree of work hardening was 4.31%~8.27%.In the experiment conditions,with the increase of n,the degree of hardening of the sample first increased and then decreased,and the depth of the hardened layer did not change much;with the increase of a_(p),the depth of the hardened layer and the degree of hardening of the sample increased gradually;v_(f) increased the degree of work hardening of the sample first and then decreased,and there was no obvious rule for the depth of the hardened layer;with the increase of the radial depth,the metallographic structure of the sample changed,and the hardness gradually decreased,and turning parameters had little effect on the metallographic structure of the surface of the sample;when n,a_(p) and v_(f) were 1200 r/min,0.15 mm and 50 mm/min,respectively,the surface of the sample softens,and the high-carbon martensite is transformed into a lower hardness tempered troostite.The finding of this study costed extra light on the formulation of hard turning process for 18 CrNiMo7-6 hardened steel.