Which of these cracks may appear as an irregular, checked, or scattered pattern of fine lines usually caused by local overheating?

The correct answer pertains to grinding cracks, which manifest as an irregular, checked, or scattered pattern of fine lines. These cracks typically result from local overheating. During the grinding process, excessive heat may be generated due to friction between the grinding wheel and the material being worked on. If the heat exceeds the material's tolerance, it can lead to microstructural changes and the formation of fine surface cracks.

These characteristics are distinct to grinding cracks, as they specifically arise from the thermal effects of grinding operations rather than mechanical fatigue or other sources of stress. In contrast, fatigue cracks result from repetitive loading and unloading cycles, crater cracks occur due to localized melting, and HAZ (Heat Affected Zone) cracks stem from the heat treatment process and its effects on the material structure adjacent to welded or heated areas.