A machinability evaluation based on the thermal and mechanical properties of two engine valve steels
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ORIGINAL ARTICLE
A machinability evaluation based on the thermal and mechanical properties of two engine valve steels Marta Regina Delle Donne Carvalho 1 & Armando Ítalo Sette Antonialli 2
&
Anselmo Eduardo Diniz 1
Received: 19 June 2020 / Accepted: 15 September 2020 / Published online: 21 September 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract Iron-based superalloys are difficult to machine because of their thermal and mechanical properties provided by alloying elements as nickel, chromium, titanium, and aluminum. However, parts made with this kind of material has to be machined during their production processes. In this work, two different automotive engine valve steel grades, VAT 30® and VAT 36®, were compared in terms of machinability, considering cutting power consumption, roughness of the machined surface, and tool life, besides the identification of the main tool wear mechanisms that have led to the end of tool life. The main goal of this work is to understand the difference in these machining outputs based on the thermal and mechanical properties of these two materials. In order to reach this goal, turning tests were held using two different cooling conditions, conventional and high-pressure coolant. Also, two PVDcoated carbide inserts were applied, one with negative rake angle and another neutral. Finally, cutting speed was tested in two levels, providing a full 24 factorial planning. Results show that VAT 30® has shown higher machinability in terms of tool life in almost every condition, although this steel presents higher hardness, mechanical strength, and strain hardening coefficient, besides lower thermal conductivity. However, it also presents lower ductility and abrasiveness, features that retarded abrasion and attrition as tool wear mechanisms, in such a way that tool life could have been lengthened. Keywords Turning . Cutting speed . Cutting tool geometry . High-pressure coolant
1 Introduction Alloy design and improvements of austenitic steels for exhaust valve applications have taken place since the 1980s. Steel alloys 23-8N and modified 21-4N are still used today in some applications, although their mechanical properties are clearly inferior to alloys with intermediate Ni content and Nibased superalloys, in part due to the significantly lower cost of the previous compared to the last. Because of that, recent developments of intermediate Ni-based alloys, which contain lower amounts of costly Ni, utilize novel alloy design strategies to provide similar or greater mechanical properties than some Ni-based superalloys [1].
* Armando Ítalo Sette Antonialli [email protected] 1
Faculty of Mechanical Engineering, University of Campinas, Campinas, Brazil
2
Center for Exact Sciences and Technology, Federal University of São Carlos, São Carlos, Brazil
UNS N07751 and UNS N07080 alloys, for example, present high hot hardness and resistance to oxidation, corrosion, and creep, but also present low wear resistance and high cost due to the high nickel contents. New Ni-based
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