## 1 Introduction  
As a medium-carbon alloy structural steel, 45 steel is widely used in machinery manufacturing and automobile manufacturing due to its moderate carbon content and good workability [1; 2; 3]. In practice, friction and wear are caused by the relative motion of parts made of 45 steel under the action of external forces [4; 5; 6; 7]. The accumulation of such wear directly affects their performance and service life. Therefore, improving its material properties is essential to extend the service life of mechanical parts. In order to meet the requirements of hardness, strength, and wear resistance of metal parts, the hardening-tempering process is widely used. The enhancement of material properties through heat treatment processes primarily involves the modulation of the microstructure [8; 9; 10]. Quench-tempering stands out as a prevalent heat treatment method for carbon steel, aiming to attain a uniform microstructure by controlling the heating temperature and holding time. This process effectively improves the material's strength and hardness. [PERSON] et al. [11] optimized the hardening-tempering process of 34 CrNi3 MoV steel box body and found that optimizing the tempering temperature can improve the product quality. [PERSON] et al. [12] compared the friction and wear properties of 45 steel and 40 Cr under different heat treatment conditions, and concluded that the heat treatment process of 45 steel varies under different conditions of use. [PERSON] et al. [13] carried out the hardening-tempering treatment in the hot rolling process of Q345 steel, which is the material of the pressure vessel, and through the tempering treatment, the strength and toughness of the hot-rolled plates were improved, which in turn improved the performance of the pressure vessel. The hardening-tempering process consists of two steps: quenching and tempering, i.e., rapid cooling (quenching) is performed to obtain high-hardness martensite, followed by high-temperature tempering to reduce the brittleness of the material and enhance its toughness and plasticity [14; 15; 16; 17]. However, different quenching media have a significant effect on the effectiveness of the tempering process. In the carbon steel tempering process, water quenching can significantly improve the hardness and strength of the material due to its fast cooling rate, but it is also prone to causing the cracking phenomenon, which restricts its popularization in practical applications. Although oil quenching can effectively reduce the risk of cracking due to its slower cooling rate, it can cause environmental pollution during its use, which triggers concerns about environmental protection. In view of these problems, it is particularly important to find a new quenching process that avoids cracking and reduces environmental pollution. [PERSON] et al. proposed the intensive quenching process [18; 19; 20]. Rapidly cooling the specimen in a salt solution at a rate greater than 600 \({}^{\circ}\)C/S is a process that leads to high compressive stress on the surface of the specimen and reduces the possibility of quench cracking and deformation [21]. This process is characterized by low energy consumption, non-pollution and a \"superstrengthening\" of the material [22]. At the same time, they proposed a general formula for calculating the heating and cooling times in the quenching process, which accelerated the widespread application of strengthened quenching in the heat treatment industry [23; 24]. Furthermore, [PERSON] et al. [25] completed a study on the weight reduction of heavy truck components and concluded that the intensive quenching process is superior to the oil quenching process in terms of both residual stress and strength. However, high-temperature tempering can adjust the residual stresses in the microstructure and improve the toughness and fatigue resistance of the material. Therefore, through a rational design of the heat treatment process and intensive quenching and high-temperature tempering, carbon steel can be improved in some aspects of performance.