## 1 Introduction  
Rolling bearings play a crucial role in machinery design, demanding high durability and reliability to ensure continuous operation, minimizing the need for maintenance shutdowns [1; 2]. They must exhibit a high service life irrespective of the environmental conditions they are exposed to [1; 3; 4; 5]. Among the several alloys explored within bearing steels, only two categories of steels find widespread application: steels that are hardened throughout their sections into a martensitic or bainitic condition and steels with soft cores but hard surface layers achieved by case or induction hardening [3; 6]. Bearing steels are usually subjected to heat treatment to develop martensitic microstructures, delivering the required high hardness crucial for effective resistance to rolling contact fatigue [7]. Hypereutectoid through-hardening steels exhibit fatigue and wear resistance, along with dimensional stability. Hence, they are suitable for crafting bearing components. The EN 100 Cr6 type is the typically adopted bearing steel (e.g., ball and roller bearings, spinning tools, punches, and dies), employed in both hardened and tempered states, renowned for its high hardness, compressive strength, and abrasion resistance. Among the thermal treatment operations developed to promote specific microstructure and, in turn, enhance the mechanical properties of steel components, martempering and austempering are two interrupted quenching procedures widely adopted for bearing steels [8; 9; 10; 11]. Martempering in industrial practice is performed by quenching the steel to slightly above the martensite start temperature Ms, then holding it to promote a uniform temperature throughout the piece, and finally air-cooling it to room temperature [12]. This slow cooling rate prevents the generation of residual stress and distortion akin to those induced by quench hardening [13]. Furthermore, austempering involves quenching from the austenitizing temperature into a molten salt bath, typically held between 200 \({}^{\circ}\)C and 400 \({}^{\circ}\)C, until the austenite transforms into bainite. The austempering makes it possible to successfully harden challenging geometries that are impossible to harden with conventional quenching [12]. The obtained lower bainite microstructure exhibits a balance of ductility, strength, and toughness, though the austempering route requires more careful control than hardening by conventional quenching [8; 9; 12; 14]. To date, most applications rely on martensitic hardening procedures. However, a bainitic microstructure is more suitable for large components where the precise control of the transformation strain is crucial for minimizing machining costs. Furthermore, bainitic microstructures exhibit superior performance compared to martensitic ones under conditions of hydrogen embrittlement or in impact scenarios where increased toughness is needed [9]. As a result, austempering is preferred when machining costs increase due to distortion issues [15]. Thus far, several studies have attempted to evaluate the impact of temperature/time heat treatment parameters on the microstructural characteristics and associated mechanical behavior of bearing steels [9; 10; 16; 17; 18; 19]. [PERSON] et al. [10] explored the impact of austempering and martempering treatments on AISI 52100 bearing steel and argued that austempered steel demonstrated the highest impact strength, which increased with soaking time. On the contrary, the martempered samples exhibited the lowest wear rate in both abrasion and dry sliding wear tests. Notably, the annealed steel exhibited the lowest hardness and was more susceptible to wear, but the average friction coefficient in dry sliding wear was the lowest and increased in martempered and austempered samples. [PERSON] et al. [9] sought to ascertain the optimum austempering process window (temperature, time, and heating/cooling rate) for SAE 52100 steel to develop a duplex bainitic + martensitic microstructure.