磨削用量对球墨铸铁QT400磨削淬硬层及其均匀性的影响

Effect of grinding parameter on grinding-hardened case and its uniformity of nodular cast iron QT400

采用逆磨+顺磨的双程平面磨削方式对球墨铸铁QT400进行磨削淬硬试验,研究了磨削深度a_(p)和试样进给速度v_(w)对淬硬层及其均匀性的影响。结果表明,磨削后试样表层存在熔化、完全相变淬硬和未完全相变淬硬等3种情况,其中,熔化层组织为二次渗碳体、残留奥氏体和碳化物,完全相变淬硬层组织为针状马氏体、残留奥氏体和球状石墨,未完全淬硬层组织为针状马氏体、铁素体、残留奥氏体和球状石墨。显微硬度分布曲线中高硬度区的平均硬度值在850~950 HV0.2之间,与基体(190~230 HV0.2)相比,显微硬度提高近3倍。随着磨削深度a_(p)的增大或试样进给速度v_(w)的减小,试样表层呈现“完全未淬硬→未完全淬硬→完全淬硬→熔化”的变化规律,显微硬度分布曲线中高硬度区的范围也变宽,淬硬层的深度也增大且均匀性良好。

Grinding-hardening was done on nodular cast iron QT400 by using two-passes grinding up-grinding+down-grinding on a surface grinder.The influence of depth of cut a_(p) and table speed v_(w) on grinding-hardened case and its uniformity was studied.The results show that there are three case of the hardened surface of the specimen,which are melted layer,completely hardened case and incompletely hardened case.Among them,the structure of the melted layer is secondary cementte,retained austenite and carbides.The microstructure of the complete transformation hardened case is acicular martensite,retained austenite and spheroidal graphite,and the structure of the incompletely hardened case is acicular martensite,ferrite,retained austenite and spheroidal graphite.The average value of the high hardness region in the microhardness distribution curve is between 850-950 HV0.2.Compared with the matrix(190-230 HV0.2),the microhardness is increased by nearly 3 times.With the increase of grinding depth a_(p) or the decrease of feed speed v_(w),the surface layer of the specimen shows the changing order of"completely unhardened→incompletely hardened→completely hardened→melted",the range of the high hardness region in the microhardness distribution curve also becomes wider,the depth of the grinding-hardened case is also increased and the uniformity is better.