## 1 Introduction  
Hard turning is a machining technique that focuses on the cylindrical surface of heat-treated steel with a hardness that varies between 45 and 68 HRC. It entails the use of a variety of single-point turning tools. The technique is difficult, owing to the material's extreme hardness, which results in greater cutting forces, cutting temperature, tool wear, and probable damage to the finished surface. Hard turning, on the other hand, has advantages such as shorter cycle times and lower costs as compared to grinding processes [1; 2; 3]. Dry hard turning has faced countless challenges like the generation of high cutting temperature, high tool wear, and poor surface quality. Therefore, to overcome these issues, many researchers have focused on improving the machinability of hard turning using various sustainable cooling technologies. In the modern machining scenario, a cleaner advanced technological machining process can develop the technical, economical, and environmental viability of traditional methods, resulting in human-centered, sustainable, and compatible machining [4]. The use of nanofluids with hybrid-type nanofluids surpass other types of cooling and lubrication methods. The use of nanofluids and hybrid nanofluids improves the surface quality and decreases the cutting temperature, cutting tool wear, and cutting force during the machining process [5]. Hard machining has captured the interest of many researchers as a potential substitute for many conventional finish grinding techniques because of its high productivity, ease of adjusting to complicated part forms, lack of cutting fluids, high-quality surface quality, and minimal investment in machine equipment. The intense heat created by the cutting zone, on the other hand, always mandates the use of premium cutting tools and limits the cutting environment. The MQL process for severe machining aids in increasing cutting performance while ensuring environmental friendliness [6]. More efficient hard machining methods have seen a significant increase in demand in recent years, not just for enhanced productivity, but also for environmental friendliness. The greatest challenges remain higher hardness strength, and a significant cutting temperature. To address these issues, NFMQL (nanofluid minimum quantity lubrication)-assisted hard part machining has emerged as a viable process [7]. Because of environmental concerns about the use and disposal of cutting fluids during machining, the MQL approach was developed, which necessitates the use of specialized fluids with better qualities. Nano-lubricants have been found to meet the qualities of cutting fluids employed in MQL. The primary difficulties in hard machining technology continue to be friction and extremely high temperatures, both of which have a considerable impact on cutting competence. The employment of nanoparticles in the MQL technique to advance the cooling lubrication capabilities of cutting oil (base) has been demonstrated to be a feasible solution [8]. Based on the findings [9], the implementation of nano-cutting fluids in turning operations has demonstrated a notable enhancement in surface finish, as well as a substantial reduction in tool wear, cutting force, and cutting zone temperature. To know the current advancement in hard turning research, a detailed literature review was carried out as follows. [PERSON] et al. [10] experimentally explored the impacts of CuO and ZnO nanofluids on process variables for MQL-assisted turning. Experimentation revealed that a CuO-assisted nanofluid provides the most effective cooling conditions when compared to a ZnO-based nanofluid. [PERSON] et al. [11] developed experimental models for energy and cost consumption under different cooling conditions, which is the proposed hybrid energy-cost models and their experimental validations. [PERSON] et al. [12] observed that when compared to dry cutting and machining with traditional cutting fluid, using nano-cutting fluid minimizes cutting force, tool wear, workpiece surface roughness, and chip thickness.