Classification of Discontinuities

Inclusions: Non-metallic impurities, such as sand, slag, oxides, and sulfides that are present in the original ingot. Rolling of raw material into billets or bar stock, these impurities form “stringers”, or lines. When rolled plate it form lamination.

These discontinuity is objectionable, when they occur in critical areas, on highly-stressed surfaces, or in unusual numbers.

Porosity: Gas bubbles being trapped in the material prior to solidification. Bubbles generally round or spherical in shape.