# Effect of Austenitizing on the Microstructure and Mechanical Properties of Gray Cast Iron
## 1 Introduction  
Within the operational environment of coal mines, a significant concentration of combustible gases, dust, and other flammable or explosive substances is widely distributed. To ensure safe underground production, explosion-proof equipment is utilized. This specialized equipment is engineered to endure electric sparks, arcs, and localized high-temperature conditions, thereby preventing any potential ignition that could lead to an explosion within the external production environment [1, 2, 3]. Gray cast iron exhibits excellent mechanical properties, superior wear resistance, and outstanding casting characteristics. Additionally, its straightforward production process offers a significant low-cost advantage. This material is extensively utilized in complete units or components of explosion-proof electrical equipment for coal mines, including flameproof motors, explosion-proof travel switches,explosion-resistant frequency converters, integrated explosion-proof lighting protection systems, and flameproof junction boxes [4; 5; 6; 7]. Nonetheless, in the underground operational environments of coal mines, explosion-proof equipment may encounter geological hazards such as coal seam subsidence and roof collapse. During enclosure disassembly for maintenance procedures, flameproof surfaces are susceptible to damage. This consequently stricter requirements on the strength, hardness, and wear resistance of explosion-proof equipment housings in mining applications to be imposed [8]. To meet the performance demands of explosion-proof housings and their components in underground mining environments, it is critical to further enhance the comprehensive properties of gray cast iron. To enhance the performance of gray cast iron, scholars have conducted alloying and austempering treatments on gray cast iron castings [9; 10; 11]. [PERSON] et al. [12] added elemental Cu to gray cast iron. As a result, the content of pearlite in the gray cast iron matrix increased, and the pearlite lamellar spacing decreased significantly. This led to a slight increase in the hardness of gray cast iron and a 30% reduction in wear weight loss. [PERSON] [13] incorporated elemental B into gray cast iron. When the content of added B reached 0.02%, the formation of carbides led to an elevation in both the tensile strength and hardness values of the gray cast iron. Nevertheless, once the addition amount surpassed 0.02%, type B and type D graphite would come into being. Consequently, this caused the tensile strength and hardness values to exhibit a downward-trending tendency. [PERSON] et al. [14] investigated the influence of Mo on the properties of gray cast iron. After the addition of Mo, the eutectic structure of gray cast iron was refined, the proportion of the area of primary austenite increased, and the tensile strength was enhanced by 15%. [PERSON] et al. [15] added V to gray cast iron. As the V content increased, the pearlite content increased, the inter-lamellar spacing of the pearlite decreased, and the size of the eutectic structure decreased. When the V content reached 0.77 wt%, the tensile strength reached 336 MPa, representing a 29% increase compared with the specimens without V. [PERSON] et al. [16] added Nb to gray cast iron. The results showed that an appropriate amount of Nb could refine the graphite and pearlite matrix and increase the friction coefficient. [PERSON] [17] fabricated gray cast iron containing V and Cr, which led to an 89% reduction in wear mass loss. Moreover, the hardness also increased due to the presence of chromium- and vanadium-containing carbides in the pearlite matrix. [PERSON] et al. [18] added Cr to gray cast iron. The formation of chromium carbide improved the wear resistance of the gray cast iron. [PERSON] et al. [19] added Cr, Mo, Ag, and rare earth elements to gray cast iron. After alloying, the graphite morphology in the gray cast iron changed from type C to type A, and the graphite size also significantly decreased. The pearlite content decreased, and the pearlite lamellar spacing was smaller.