The present work investigates the lubricant capabilities at room and hot-forging temperatures (>1400 K) of three types of lubricants with two different graphite concentrations (8% and 12%). These lubricants are distinguished by measuring the percentage of chemical elements and average size of graphite particles. Later, two standardized methods, i.e., pin-on disc and ring test, are utilized to assess the main friction differences under laboratory and real industry conditions, respectively. The results exhibit that the friction values at room temperature are lower for lubricant B, no matter which type of graphite concentration is used, whereas at hot-forging temperatures, greater percentage of graphite enhances lower frictional values when higher deformations are assessed. Additionally, the ring tests performed at hot-forging temperatures show significant tribology differences when the degree of deformation reaches 50%. Particularly, the lubricant B shows the lowest values of friction coefficients of 0.22 and 0.21 for 8% and 12% of graphite concentration, respectively. Therefore, it can be concluded that the selection of a proper type of lubricant (regarding chemical composition and size of solid suspension) and the graphite concentration are sensitive parameters, when it comes to achieve different bulk deformations combined with extreme temperatures like in hot-forging process.
Graphitic lubricant Extreme temperatures Friction coefficients Ring test Hot-forging
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CRAFMSA S.A. is acknowledged for their support and contribution to this work. We give thanks to Soledad Pereda from INTI-Mecánica for the valuable support with the electronic microscopy and X-ray spectroscopy analysis.
This work is supported by the Ministry of Economy and Competitiveness of Spain (reference project: FJCI-2016-29297), the National Council for Scientific and Technological Development of Chile (Fondecyt project 3180006), and the Aeronautics Advanced Manufacturing Center (CFAA) of Bilbao.
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Conflict of interest
The authors declare that they have no conflict of interest.
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