Discontinuities that originate during the melting and original solidification of the metal are categorized as what?

Discontinuities that originate during the melting and original solidification of the metal are categorized as inherent discontinuities. This classification is important because these types of discontinuities are an intrinsic part of the material's structure. Inherent discontinuities can arise from the solidification process itself, such as porosity, inclusions, and the formation of dendrites. These issues are directly related to the material's properties and behaviors in its initial form, leading to variations that are not a result of external influences or later handling.

Understanding inherent discontinuities helps in assessing the quality of the metal at the time of its manufacture and informs processes like casting or welding where the integrity of the material is critical for the final application. This is foundational knowledge in visual testing and materials science, as it enables engineers and inspectors to recognize and evaluate potential weaknesses in the material before they contribute to failures in service.

The other categories, such as forming discontinuities, process discontinuities, and service-induced discontinuities, typically refer to problems that occur at different stages of the material life cycle, such as in fabricating processes or under service conditions. Those do not directly pertain to the initial solidification phase of the metal.