Analysis of oxidized hot working tool steel tribological behavior in tube piercing

Abstract

Abstract. In this paper the tribological behavior of the oxide layer present on the mandrel used in rotary piercing tube manufacturing operations has been analyzed. A hot upsetting sliding test campaign has been carried out in order to analyze the hot working steel oxide layer under different contact conditions. Optical microscopy, profilometry and XRD have been used to establish the type of contact and oxides generated, respectively. Results show abrasive sliding contact between mandrel and tube materials. Oxide transfer from the tube material to the mandrel material occurs in all the tested conditions. Regarding friction, the coefficient of friction COF is reduced by the presence of the oxide layer, confirming its lubricity. It has been observed how COF decreases with the increase of contact pressure and relative velocity. The value of COF is reduced from 0.42 to 0.18 if the contact pressure is increased from 165 to 200 MPa and the relative velocity is increased from 200 to 450 mm/s.