*2.2. Image Calibration*

The metallographic images were distributed to experts to determine the sorbite region and sorbite content in each image using the grid truncation method. The sorbite area (dark zone) was then labeled using LabelMe software version 5.1.1. Figure 1 shows an example of the sorbite labeling in a single metallographic image. For this study, 2500 valid metallographic images and their labeling files were collected, with an image size of 2048 × 1536.

**Figure 1.** Example of sorbite content labeling. (**a**) Original image; (**b**) Labeling image.
