## 1 Introduction  
Gray cast iron (GI) is a common ferrous material with the presence of graphite flakes in the matrix. It has been reported that GI has high machinability, high vibration adsorption, and high castability. In industry, GI has been widely utilized in the production of gears, guide rails, and cylinder liners for diesel engines [1; 2; 3]. These GI engineering parts frequently are required to withstand direct surface contacts with applied pressure and relative movement. Superior wear resistance is required to ensure good working performance and long service life. Thus far, surface-hardening treatments and heat treatments are considered as the common strengthening methods to improve the anti-wear performance of ferrous mechanical components [4; 5; 6]. Austempering heat treatment has received considerable attention in the past two decades due to the formation of a unique ausferritic structure with high strength-weight ratio, fracture toughness, ductility, and good tribological performance [7; 8; 9; 10]. In the austempering heat treatment, fully austenitized cast iron is quickly transferred to a salt bath furnace and maintained for a certain time period. The austempering temperatures should be controlled within the range between the temperatures at which pearlite and martensite form. Quench-tempering heat treatment is a conventional heat treatment to increase the strength and hardness of cast irons and steels. During the quench-tempering process, the as-quenched martensite decomposes to tempered martensite with the precipitation of cementite particles or islands. Additional tempering can decrease the amount of retained austenite and release the internal residual stress caused by the rapid cooling rate in the quenching step [11; 12]. The wear properties of GI have been significantly improved by the use of austempering and quench-tempering heat treatments. [PERSON] et al. [8] investigated the wear resistance of hypereutectic gray cast iron after receiving austempering and quench-tempering heat treatments. The austempered gray cast iron (AGI) had the best wear performance, which was related to the Transformation induced plasticity (TRIP) effect, and the quench-tempered gray cast iron (QTGI) had moderate wear resistance, which was attributed to fine carbides. [PERSON] et al. [10] determined the effects of austempering heat treatment on the microstructure, wear, and mechanical properties of AGI alloyed with copper. The amount of retained austenite increased, the hardness and tensile strength decreased, and the ductility and wear depth increased with higher austempering temperature. Laser surface hardening treatment is an effective approach to lower the wear loss and extend the fatigue life of cast iron and steel components. During the laser-hardening process, the top surface of cast irons or steels is heated above A\({}_{\text{cm}}\) or the eutectic critical temperature to transform the original microstructure into an unstable austenite or liquid state. Then, the top surface in the fully austenitized or liquid state is cooled by air and self-quenches to the adjacent cold substrate. Currently, laser surface hardening treatment is often applied to small components with complicated geometry [13; 14; 15; 16]. [PERSON] et al. [17] applied laser glazing treatment to GI. The surface hardness was significantly improved due to the far-from equilibrium phase transformation. It was experimentally observed that the central fusion regions containing dendritic structure and cementite plates, and the heat-affected region containing bainite with graphite flakes was formed after laser glazing. [PERSON] et al. [18] investigated the effects of surface temperature and scanning speed on the characteristics of the hardened layers of gray cast iron such as microstructure and hardness profile by using a high-power diode laser. It was found that a homogeneous microstructure with hardness ranging from 700 HV to 800 HV was formed in the laser-hardened zone, which was not dependent on the temperature and scanning speed.