Estimation of glass lubricant viscosity for hot extrusion of Cr-Ni steel and Ni alloy tubes

Abstract

Purpose. Estimation of optimal viscosity of a glass lubricant for chromium-nickel steel tube extrusion depending on the deformation resistance, chemical composition of metal and the temperature, degree and rate of deformation. Methodology. To determine the force conditions for tube extrusion, a complex factor of deformation resistance was used, which consists in estimating the value of deformation resistance under the basic process parameters of extrusion plants and its refinement depending on the deviations of heating temperature and wall thickness of billets as well as the degree and rate of deformation from the base conditions. Findings. The dependence of basic values of deformation resistance on the percentage of alloying elements (Ni + Cr) in steels has been found. With the addition of hardening alloying elements (Mo, W, V, Nb) into the alloy steel, its deformation resistance increases in proportion to their percentage. Analytical expressions for calculating the base values of deformation resistance for different extrusion plants have been obtained. Originality. For the first time, the principles governing estimation of the optimal viscosity of glass lubricants based on the chemical composition of steel to be formed, its temperature and the degree and rate of deformation of the blank, thickness of the lubricating layer and geometric dimensions of the tool (die) in hot extrusion of tubes have been established. Practical value. The use of the results of calculation according to the developed method will make it possible to increase the surface quality of tubes manufactured by extrusion and reduce the volume of their subsequent machining.