Metallurgical characterization and performance of high speed steel tool materials used in metal cutting applications

Rousseau, A 2016, Metallurgical characterization and performance of high speed steel tool materials used in metal cutting applications, Masters by Research, Applied Sciences, RMIT University.


Document type: Thesis
Collection: Theses

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Title Metallurgical characterization and performance of high speed steel tool materials used in metal cutting applications
Author(s) Rousseau, A
Year 2016
Abstract The introduction of hard ceramic coatings has significantly improved the performance of high speed steel (HSS) cutting tools. However, failure mechanisms such as plastic deformation of the HSS substrate (beneath a ceramic coating) remain and motivate further research into vacuum heat treatment (VHT). This thesis describes investigations into the hardening response and carbon content of HSS before and after VHT. Poor hardening response of HSS was found to correlate with a loss of carbon in VHT. Full hardening response was achievable by removing surface oxide scale (predominantly Fe2O3 and Fe3O4) prior to VHT. Further investigation revealed an almost linear relationship between the surface oxide thickness pre-VHT and the post-VHT carbon content and hardening response. With surface oxide present, CO evolution and sample mass loss were observed during VHT of HSS above ~800 ℃. With the surface oxide removed, full hardening response was achieved and there was no measurable loss in carbon content post-VHT

To exploit the fully hardened HSS in a coated tool, plasma nitriding followed by steered cathodic arc evaporation TiAlN ceramic coating process was performed (with no break in vacuum) in an industrial scale deposition chamber. Bright plasma nitriding at ~480 ℃ resulted in a fracture tough diffusion zone with no evidence of a compound layer or grain boundary precipitation. M2 HSS coupons and M2 ¼-inch jobber drills were similarly tested microstructurally and mechanically in untreated, plasma-nitrided, coated-only and duplex. The ¼-inch jobber drills were subjected to accelerated drill testing into D2 tool steel which revealed a significant increase in cutting performance of the duplex treatment compared with un-treated tools. Electron microscopy of the sectioned tools indicated that this improved performance was due to increased toughness of the cutting edge coupled with an increase in adhesion at the substrate-TiAlN coating interface.
Degree Masters by Research
Institution RMIT University
School, Department or Centre Applied Sciences
Subjects Physical Sciences not elsewhere classified
Keyword(s) Plasma nitriding
Physical vapour deposition
Carbon evolution
High speed steel
Vacuum heat treatment
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Created: Fri, 12 Aug 2016, 11:49:38 EST by Keely Chapman
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