Research And Application Of High-Rigidity Low-Stress Ductile Iron

The material rigidity, residual stress and deformation of lathe bed castings are important factors that effecting the dimensional accuracy and precision of retention. In this study, QT600-3ductile iron material used for machine tool was selected as the research object. Tensile test, metallographic test, scanning electron microscope analysis and massive residual stress measurement were done. Effect of alloy elements (Cu、Mn、Sn、Cr、Ni), silicon-carbon ratio, carbon equivalent and aging treatment on elastic modulus and residual stress of ductile iron were systematically studied. The chemical composition formula and production technology of high-rigidity low-stress QT600-3ductile iron was developed. T lathe bedway samples were poured for production verification and the production of beam castings was done. The research results are listed as follows.1) Alloy elements, silicon-carbon ratio and pearlite all have significant effects on elastic modulus of ductile iron. The elastic modulus of ductile iron samples are147-182GPa, which has a larger range and most of it below160GPa. By0.5-0.7%Cu,0.04-0.06%Sn,0.4-0.6%Mn compouned alloying under high silicon-carbon ratio(0.55-0.60), high-rigidity QT600-3ductile iron can be obtained The tensile strength is above600MPa, and the elastic modulus is above160GPa.2) The higher the carbon equivalent, the lower the residual stress of ductile iron. Lower shakeout temperature can help to reduce the residual stress. The maximum residual stress of as-cast ductile iron samples are53-146GPa. The range is larger and all of it exceed50GPa, which can cause the deformation of castings."Multistep temperature rising/falling" heat aging treatment can significantly eliminate the residual stress. The residual stress of QT600-3ductile iron can be reduced to be below50MPa after the heat aging.3) It is an effective technology to obtain high-rigidity low-stress QT600-3ductile iron by0.5-0.7%Cu-0.04-0.06%Sn-0.4-0.6%Mn compouned alloying, lower shakeout temperature (≤300℃) and "multistep temperature rising/falling" heat aging treatment under higher carbon equivalent (4.40～4.60%) and higher silicon-carbon ratio (0.55-0.60) condition. QT600-3ductile iron castings obtained by this technology can stably achieve the mechanical indicators "Rm≥600MPa, E≥160GPa, σi≤50MPa".4) Ductile iron T lathe bedway samples obtained by the above technology have both high tensile strength (705MPa) and high elastic modulus (176GPa). The hardness and elongation respectively is HB234and3.0%. The pearlite content is98%. The maximum residual stress is26.3MPa. The mechanical properties have exceed the indicators of QT600-3ductile iron. The high-rigidity low-stress QT600-3ductile iron beam casting is successfully producted.