Which point on the hysteresis curve represents the residual field value?

The point on the hysteresis curve that represents the residual field value is indeed represented as Point C. This point corresponds to the level of magnetization retained in a ferromagnetic material after an external magnetic field is removed.

During the magnetization process, as a material is exposed to increasing levels of magnetic intensity, it becomes progressively magnetized. When the external magnetic field is removed, the material does not return completely to a state of zero magnetization; instead, it retains some magnetization, which is the residual magnetism. This residual magnetism is critical in magnetic particle testing, as it indicates how much magnetism remains in the part, influencing the detectability of discontinuities.

Point C, on the hysteresis curve, identifies this residual field, which is significant for evaluating the magnetic properties of materials and understanding how they behave under testing conditions.