Tooling constitutes a significant part in the economical investment of the hot stamping process. Significant benefits in production economy and environmental benefits can be attained by improving the tribological performance in hot forming operations of automotive components. The main idea of this project is to create tailored tool surfaces on dies made from cheaper and easier to manufacture tool steel for the hot stamping of ultra-high strength steels.
The approach of the project is to select high performance powder materials and thermal spray it on tool steel substrates with lower hardness compared to normal hot forming tools. Thus, the thermal spray coating provides a functional surface that protects the softer substrate material from wear and enables robust friction.
Three different thermal spray coatings (Rockit 701, Tribaloy T400 and WOKA 7504) were deposited on a prehardened hot forming tool steel (Toolox33) by high velocity air-fuel (HVAF) technique. The powders and coatings were characterised in terms of microstructure, chemical composition, hardness and tribological performance in order to select a suitable coating for semi-industrial scale tests.
All coatings had good adhesion to the substrate but a relatively rough surface that required subsequent polishing. All coatings also showed stable friction when sliding against Al-Si coated high-strength steel. Material transfer was slightly reduced and, in case of the WOKA coating, weakly bonded to the surface. Semi-industrial tests were carried with one uncoated tool and one coated with Rockit 701. Both tools showed transfer of Al-Si from the workpiece material at the radii and further work to optimise the surface topography is required to improve the performance of the coated tools.
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