Influence of Surface Roughness Lay and Surface Coatings on Galling During Hot Forming of Al-Si Coated High Strength Steel
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
High strength boron steels are commonly used as structural reinforcements or energy absorbing systems in automobile applications due to their favourable strength to weight ratios. The high strength of these steels leads to several problems during forming such as poor formability, increased spring back, and tendency to work-harden. In view of these difficulties, high strength boron steels are usually formed by press hardening at elevated temperatures with a view to facilitate forming and simultaneous hardening by quenching of complex shaped parts.The high strength steel sheets are used with an Al–Si coating with a view e.g. to prevent scaling of components during hot-metal forming. The Al-Si coated high strength steel can lead to problems with galling (i.e. material transfer from the coated sheet to the tool surface) which have a negative influence on the quality of the produced parts as well as the process economy. The available results in the open literature pertaining to high temperature galling are very scarce. With this in view, the friction and wear behaviours of different tool steel coatings and different roughness lay directions sliding against Al–Si-coated high-strength steel at elevated temperatures have been investigated by using a high-temperature reciprocating friction and wear tester at temperature of 900 °C.The results have shown that parallel sliding with respect to the surface roughness lay reduces the severity of galling compared to perpendicular sliding. None of the coatings included in this study have shown beneficial effects in view of galling. The DLC coating experienced less galling compared to the AlCrN and TiAlN. Post polishing of the coated tool steel has resulted in more severe material transfer with higher and more unstable friction.
Place, publisher, year, edition, pages
2011. , 39 p.
Technology, Friction, Galling, Material transfer, High temperature, PVD coatings, Surface roughness
IdentifiersURN: urn:nbn:se:ltu:diva-47706Local ID: 539dee07-5ffd-4366-ac63-847fb2198bc0OAI: oai:DiVA.org:ltu-47706DiVA: diva2:1021034
Subject / course
Student thesis, at least 30 credits
Materials Engineering, master's level
Validerat; 20111022 (anonymous)2016-10-042016-10-042016-10-17Bibliographically approved