High temperature tribological behaviour of additively manufactured tool material for applications in press hardening

Abstract

In hot sheet metal forming, minimising material transfer and ensuring homogenous cooling of the workpiece are important for quality and productivity reasons. The development of additive manufacturing (AM) opens up possibilities for novel tooling concepts by tailoring the tool material (new chemistries, microstructure, and size/distribution of hard phases) and producing conformal cooling channels. Implementing surface functionality for improved tribological performance is another advantage of AM. Research pertaining to high temperature tribological behaviour of AM tool materials is, however, very limited.The aim of this work is to study the high temperature friction and wear behaviour of AM produced maraging steel and compare this to a conventional hot-work tool steel. The AM maraging steel was post-machined to different surface conditions (milled, ground and shot blasted).The tribological behaviour was evaluated using a hot-strip drawing tribometer and the counter surface was an Al–Si coated 22MnB5 steel. The temperatures of the Al–Si coated steel strips were 600 and 700 °C during the tribological tests.The results have shown that the friction behaviour of the maraging steel and the hot-work tool steel at 600 °C was stable and very similar. At 700 °C, the maraging steel showed more unstable friction and early failure of the tests due to high friction compared to the hot forming tool steel. This was associated with increased material transfer and embedment of FeAlSi intermetallics from the workpiece surface.The maraging steel experienced material removal and development of transfer layers composed of debris from both surfaces in contact. Comparable wear behaviour was observed at both temperatures, but its severity increased with temperature. The milled and ground surfaces showed similar wear mechanisms including ploughing and delamination of material, as well as embedment of FeAlSi particles. The shot blasted surface showed less build-up of transferred material but instead more deformation and folding of asperities leading to entrapment of FeAlSi particles in the near surface region.