Simulation And Experimental Study On Temperature Field And Stress Field Of Ductile Iron Electron Beam Surface Quenching

Ductile Iron (DI) is being widely used in the machinery manufacturing industry,especially producing the large and complex loading parts, because of their low cost andproperties like low melting point, good fluidity and cast-ability, excellent machinability.But its hardness and wear resistance is relatively low and its application is limited towearing, corrosion and fatigue failure. Therefore surface modification is necessary. Thehardness, wear resistance and corrosion resistance can be improved by the electron beamsurface quenching technology. It is difficult to directly determine the distribution oftransient temperature field and stress field by using experimental method and is necessaryto be studied.In this paper, the physical foundation of temperature field and stress field formation ofsurface quenching by electron beam is analyzed. A finite element model is established todescribe the temperature field for DI surface quenching by electron beam，according to theactual experimental condition of the electron beam heat treatment installation andsimulation theory. Calculated results of the temperature field model are verified by theexperimental results. A finite element model is established to describe the stress field forDI surface quenching by electron beam, based on the temperature field model. The changerules of the temperature field and stress field are analyzed. The effects of processingparameters, such as beam current, scanning speed, beam diameter and sample effectivethickness, on the temperature field, are discussed by the model. Simulation andexperimental results shows that the temperature and stress field distribution of electronbeam surface quenching process are both an unsteady state. The ends hardened layerdistribution rule is gotten by simulation and trial research of endwise hardened size(containing depth and width)，which is that enter-end size is less than that of middle-area，and exit-end size is more than that of middle-area. The surface hardness of DI increases to3~4times of the matrix hardness, because the surface hardened layer is composed ofspherical graphite and martensite shell by electron beam surface quenching. The followingresults are obtained with other parameters unchanged. The width and depth of hardenedlayer increases and the maximum temperature of specimen surface increased linearly withbeam current increasing. The martensite shell is thicker and the surface hardness hasimproved with beam current increasing. The width and depth of hardened layer decline andthe maximum temperature of specimen surface declines hyperbolic curve with scanningspeed increasing. The martensite shell is thinner and the surface hardness has fallen with scanning speed increasing. The beam diameter has impacted strongly on the temperaturefield. The energy of small bean diameter is more centralized than that of large. Theeffective thickness of sample has also impacted on the temperature field of electron beamquenching. The temperature field for the thicker samples has less infect by under surfacecooling condition. The regularity of thermal stress distribution is basically the same to thatof temperature field. The electron beam scanning area is mainly compressive stress. Itspeak is between the matrix and hardening layer and moving with the heat source.The research of electron beam surface quenching provides reference and directivesignificance for the further research and enterprise application of the electron beam surfacemodification.