Abstract
For the realization of liquid lubricant free forming processes different approaches are conceivable. The priority program 1676 “Dry forming - Sustainable production through dry machining in metal forming” addresses this issue in the context of metal forming processes. The present study reports results from one subproject of the priority program that employs selective oxidization of tool steel surfaces for the implementation of a dry sheet metal deep drawing process. Within the present study, specimen surfaces of the tool steel (1.2379) were heat-treated to optimize their tribological properties with respect to sliding wear behaviour in contact with drawn sheet metal (DP600+Z). The heat treatment was designed to result in the formation of selective oxide layers that can act as friction reducing separation layers. The heating setup employed an inductive heating under protective gas atmosphere. Selective oxidation was realized by controlling the residual oxygen content. Specifically, the specimens were heated in the near-surface region just above the annealing temperature, thus avoiding the degradation of mechanical properties in the bulk. Evaluation of hardness along cross-sections of each specimen revealed suitable initial temperatures for the inductive heat treatment. Oxide layer systems were analyzed regarding their tribological sliding wear behaviour after selective oxidation, as well as their morphology and chemical composition before and after the sliding wear tests.
Highlights
For modern industrial manufacturing, economic and ecological objectives become more and more significant
Peak temperatures above the annealing temperature of the tool steel can favour surface activation, and selective oxidation processes that are caused by thermal acceleration of diffusion and higher reactivity of the tool steel elements with oxygen
Even short dwell periods at peak temperatures above 620 °C reduced the hardness of the tool steel by nearly 40% in the bulk
Summary
Economic and ecological objectives become more and more significant. Thin oxide layers were generated on the tool steel surfaces using a heat treatment under defined atmospheres.In earlier studies, positive effects of α-Fe2O3 oxide layers on friction and wear behaviour have already been reported. The present study focuses on the wear behaviour of selectively oxidized tool steel specimens (1.2379), which were heat treated inductively under an argon process atmosphere with an oxygen content of 0.03 vol.-%. These process conditions were selected to favour the formation of α-Fe2O3 oxide layer systems, which can act as a friction reducing separation layers. The friction coefficients and wear resistance were determined to compare the systems’ behaviour with results obtained in previous studies using convective tempering methods
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