What type of discontinuity is indicative of rolled bar stock?

• A. Blow holes
• B. Shrinkage laps
• C. Cracks or seams
• D. Insufficient penetration

Answer: (C)

The type of discontinuity that is indicative of rolled bar stock is characterized by the presence of cracks or seams. Cracks can result from various factors during the manufacturing process, including excessive stress or rapid cooling, leading to internal flaws in the material. Seams are often formed due to the joining of metal during the rolling process and can be seen on the surface or internally.

In rolled bar stock, the process of rolling can introduce these defects as the material is manipulated under high pressure and temperature. This means that any discontinuities present, such as seams or cracks, can impact the structural integrity of the material and hence are critical for inspection.

Other types of discontinuities mentioned, such as blow holes, shrinkage laps, and insufficient penetration, tend to relate to different manufacturing processes or stages. For example, blow holes are typically linked to casting processes, while shrinkage laps often occur in poured steel. Insufficient penetration is usually a concern in welding applications. These distinctions help highlight why cracks or seams are specifically relevant to rolled bar stock.