# Effect of Austenitizing on the Microstructure and Mechanical Properties of Gray Cast Iron
## 3 Results and Discussion
As shown in Figure 6, which depicts the hardness of different gray cast iron specimens, the hardness of the specimens gradually increases with the rise in the austenitizing temperature, increasing from 187.3 HBW in the as-cast state to 408.3 HBW for At 900. Figure 7 shows the friction coefficients of gray cast iron under different heat treatment conditions. There is little difference in the friction coefficients between the as-cast specimen and At 810, and the friction coefficient of At 850 is slightly better than that of At 900. The as-cast gray cast iron needs to enter the running-in state in the early stage of friction; therefore, the friction coefficient first decreases and then tends to be stable. For At 810, the surface is not damaged in the early stage of friction, resulting in a low friction coefficient at the beginning of the experiment. As time goes on, the friction coefficient increases rapidly. This is because the hardness difference between ferrite and ausferrite in the matrix is relatively large, causing the friction coefficient to fluctuate unstably under high-frequency friction. The matrices of At 850 and At 900 are both composed of ausferrite, which has a high and uniform hardness. Therefore, their friction coeffici  
Figure 5: Mechanical property diagrams of different gray cast iron specimens. The three-dimensional morphology of the wear surface after the wear test described in the experimental method was reproduced using laser confocal microscopy, and further wear resistance analysis was conducted. As shown in the 3D topography and 2D profile in Figure 8, both the wear width and depth gradually decrease with increasing heat treatment temperature. However, specimens treated at 850 \({}^{\circ}\)C and 900 \({}^{\circ}\)C exhibit comparable wear dimensions (depth and width). Although the coefficient of friction (COF) of the as-cast specimen is similar to that of the 810 \({}^{\circ}\)C-treated sample, the latter demonstrates a shallower wear depth and a narrower wear width, with the as-cast specimen displaying a significantly larger wear volume. Figure 7 reveals that the 850 \({}^{\circ}\)C-treated specimen has a lower COF than the 900 \({}^{\circ}\)C-treated specimen, yet no distinct differences in wear volume are observed between them based on 3D topography and 2D cross-sectional profiles. Magnified analysis indicates that both 850 \({}^{\circ}\)C and 900 \({}^{\circ}\)C specimens exhibit wear widths of 500-550 \(\upmu\)m and wear depths of 1.75-2.0 \(\upmu\)m.  
Figure 6: Hardness diagrams of different gray cast iron specimens. Figure 7: Friction coefficients of different gray cast iron specimens. In order to conduct an in-depth comparative analysis of the wear states of gray cast iron under different heat treatment conditions, the wear surface was carefully observed, and the results are shown in Figure 9. Moreover, the wear types of different specimens were analyzed. The wear surface of the Ht zt specimen exhibits large-scale delamination and transverse cracks. The presence of oxygen elements on the surface indicates that it is atypical adhesive wear. Meanwhile, due to the surface oxidation caused by frictional heat and the easy peeling of the brittle oxide film, it is also accompanied by oxidative wear. The delamination phenomenon on the wear surface of the At 810 specimen is reduced, and the crack size is decreased. This is attributed to the increase in the hardness of the matrix, which makes the surface less likely to be damaged. However, the wear types are still adhesive wear and oxidative wear, although the degree of oxidative wear is weakened. This is because the partial formation of ausferrite has improved the matrix's ability to resist plastic deformation and has inhibited the peeling of the oxide film. The wear surface of the At 850 specimen is relatively smooth, with only shallow furrows and fine abrasive particles embedded. Moreover, the edges of the graphite are intact without significant deformation.