HEAT TREATMENT EFFECT ON HIGH-STRENGTH CAST IRON MACHINABILITY

Problem. The use of ductile cast iron (DCI) in engineering is constrained by its insufficient cutting ability. There is a problem of improving the machinability of cast iron by performing heat treatment. Goal. The aim of the work is to study the effect of heat treatment on DCI machinability. Method. The research has been carried out on the basis of high-strength cast iron chemistry widely used in industry. Cast iron is heterogeneous in structure and distributing chemical elements. The hardness and microhardness of cast iron, average values and oscillations of the cutting force have been studied. Results. Structural and chemical inhomogeneity of cast iron determines its machinability, causes shock loads on the tool and intensifies its wear. The heterogeneity coefficient was used as a complex characteristic of inhomogeneity. It is determined by instantaneous values of the cutting force. The coefficient of relative machinability has been defined on the basis of the heterogeneity coefficient. The machinability of gray cast iron is taken as 1. Taking into account the machinability factor the cutting speed has been calculated with the stability of 60 min for hexanite-R while high-strength cast iron turning. The heterogeneity of such cast irons has been changed by heat treatment according to different modes. Scientific novelty. Heat treatment allows to change structural and chemical heterogeneity of cast irons and to effect on their machinability. That is, DCI machinability depends on the degree of cast iron heterogeneity determined by the heterogeneity coefficient. Practical significance. The technique for determining the heterogeneity and machinability of ductile cast iron has been suggested. The research of the heat treatment effect (heterogeneity) on machinability has been carried out. The studies have shown that after double normalizing cast iron is characterized not only by a high level of cutting ability but also by a sufficiently high level of mechanical properties – hardness. This fact allows to recommend this mode as the final heat treatment.