How to Identify Defects in Forgings

How to Identify Defects in Forgings

Further refining the classification based on the sequence of operations in the forging process, defects can be categorized as follows: defects from cutting, heating, forging, cooling, and cleaning processes.

Different operations may produce different forms of defects; however, the same form of defect can also come from various processes. Since the causes of forging defects are often related to the raw material production process and post-forging heat treatment, it’s crucial not to analyze the causes of forging defects in isolation.

If we classify forging defects by their manifestation, they can be divided into external, internal, and performance-related defects.
External defects include issues with geometry dimensions and shape; surface cracks, folds, missing material, misalignment; insufficient die forging, surface pitting, surface bubbles, and orange peel-like surfaces. These defects are exposed on the exterior of the forging, making them relatively easy to detect or observe.

Internal defects can be further divided into macro defects and micro defects. Macro defects include internal cracks, shrinkage holes, looseness, white spots, disordered forging flow, segregation, coarse grains, rock-like fractures, and non-metallic inclusions; micro defects include decarburization, carburization, banding, residual casting structures, and carbide segregation not meeting requirements. Internal defects, residing within the forging and often complex, are difficult to identify and can significantly hinder production.

Defects affecting performance may include inadequacies in room temperature strength, plasticity, toughness, or fatigue properties; or high-temperature instantaneous strength, enduring strength, permanent plasticity, and creep strength not meeting requirements. Performance defects can only be precisely identified after conducting performance tests.

It’s noteworthy that there is often an inseparable link between internal, external, and performance-related defects. For instance, overheating and burning often manifest externally as cracks, internally as grain coarsening or decarburization, and in terms of performance as a reduction in plasticity and toughness. Therefore, to accurately determine the cause of forging defects, it’s essential not only to identify their form and characteristics but also to explore the intrinsic connections between them.