Research on Pattern of Machined Surface of 18CrNiMo7-6 Forging
After normalizing,heat-treatment and machining,local point-like"pattern"appeared on the machining surface of gear forgings produced of 18CrNiMo7-6 continuous casting billet.In order to clarify the formation mechanism of"pattern",a variety of analysis methods were used to study the"pattern"area,and the results showed that there were dark and light areas distributed between the"pattern"area,with a typical morphomorphic dendrite structure,the light area was the dendrite arm,and the elements were evenly distributed in this area,with a microhardness of 174.1HV;the dark area was the typical interdendrite segregation area,with higher carbon content,more carbides,with a microhardness of 217.4HV.Above results show that the coarse dendrites of raw materials and dendrite segregation are the direct causes of machining"pattern".Therefore,avoiding coarse dendrites and reducing dendrite segregation in the continuous casting production process are the key point to solve the surface pattern of forgings.After normalizing,the 18CrNiMo7-6 gear forgings produced by continuous casting billet,a local dotted"pattern"appeared on the machined surface.In order to clarify the formation mechanism of the"pattern",the"pattern"area was studied with a variety of analysis methods.The results show that:in the"pattern"area,there are alternatively distributed dark and light-colored microstructure areas,with typical solidification dendrite characteristics.The light-colored area is the dendritic crystal arm,and all elements are evenly distributed in this area,and the microhardness is 174.1HV.The dark area is the interdendrite segregation area,with high carbon content and more carbides,and a microhardness of 217.4HV.The above research results show that local dendritic crystal thickening and dendrite segregation of continuous casting billet are the direct causes of machined"pattern".Therefore,avoiding coarse dendrites and reducing segregation between dendrites in the process of continuous casting are the key measures to solve the"pattern"of forging.
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