Citation: Binali, R.; Demirpolat, H.; Kunto ˘ glu, M.; Salur, E. Different Aspects of Machinability in Turning of AISI 304 Stainless Steel: A Sustainable Approach with MQL Technology. Metals 2023, 13, 1088. https://doi.org/10.3390/ met13061088 Academic Editor: Shoujin Sun Received: 24 May 2023 Revised: 31 May 2023 Accepted: 6 June 2023 Published: 8 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). metals Article Different Aspects of Machinability in Turning of AISI 304 Stainless Steel: A Sustainable Approach with MQL Technology Rüstem Binali 1, * , Havva Demirpolat 1 , Mustafa Kunto ˘ glu 1 and Emin Salur 2 1 Mechanical Engineering Department, Technology Faculty, Selcuk University, Konya 42130, Turkey; hdemirpolat@selcuk.edu.tr (H.D.); mkuntoglu@selcuk.edu.tr (M.K.) 2 Metallurgical and Materials Engineering Department, Technology Faculty, Selcuk University, Konya 42130, Turkey; esalur@selcuk.edu.tr * Correspondence: rustem.binali@selcuk.edu.tr Abstract: Machining of AISI 304 austenitic stainless steel is considered to be difficult due to its structural aspects and low thermal conductivity, which leads to increased temperatures during machining. To overcome the challenges of machining AISI 304 stainless steel, several cooling and lubricating techniques have been developed. The main objective of this experimental study is to evaluate the different turning conditions of AISI304 stainless steel under dry and minimum quantity lubrication (MQL) environment conditions. The machining experiments were conducted using a two-level full factorial design method and utilized a TiC-coated cutting tool. The tool-tip temperature, cutting force and surface roughness were analyzed regarding three cutting parameters namely, cutting speed, feed rate and cutting depth. Also, chip macro-morphology was investigated to define the interaction at the tool-chip-workpiece region. The cutting medium affects the surface roughness significantly (more than 100%) for all cutting parameter values. In some environmental cutting conditions, high cutting speed provides 10% lesser surface roughness than low cutting speed parameters. Also, the cutting force decreases by 20% in low feed rate machining conditions. However, the effect of this parameter disappeared for cutting forces in high feed rates and low cutting depth conditions in both MQL and dry environments. Cutting speed was observed as the most influential factor on surface roughness, followed by feed rate. The depth of cut was the main parameter that caused the temperature to increase in the dry machining environment. Keywords: turning; AISI 304; surface roughness; temperatures; chip shape; cutting force 1. Introduction Stainless steel materials are widely used in the biomedical, construction, food, phar- maceutical, petrochemical, aerospace, and aviation industries due to their superior physical and mechanical properties. It contains alloying elements such as Cr (at least 10.5% accord- ing to the European standard EN 10088), Ni, Mo, and N [1]. The physical and mechanical properties of stainless steel vary with the chemical composition of alloying elements. In ad- dition, the Chromium content ensures the formation of a protective oxide film that provides corrosion resistance while the nickel content improves the use in harsher environments conditions with its stabilized austenitic structure [2]. Stainless steel can be divided into five main groups: martensitic, ferritic, austenitic, and precipitation. hardening and austenitic- ferritic (duplex) [3]. Martensitic grades are designated as (Fe-Cr-C-(Ni-Mo)) alloy systems and this steel family can be hardened by heat treatment [4]. Tempered martensitic alloys are the most easily machined type of stainless steel family with low carbon content [5]. Ferritic stainless steels are designated as Fe-Cr-(Mo) alloy systems where carbon contains limited low levels. Ferritic grades are generally nickel-free but some of the super-alloyed ferritic grades may contain nickel to improve the ductile-to-brittle transition (DBTT) [6]. Duplex types which consist of austenite and ferrite microstructure are stronger than both of the Metals 2023, 13, 1088. https://doi.org/10.3390/met13061088 https://www.mdpi.com/journal/metals