Primary mill products — minimum cross-section classified as a bloom In steel rolling terminology, which of the following minimum square sizes is generally classified as a bloom (as opposed to a billet or slab)?

Introduction / Context:
Ingots are broken down into primary mill products: blooms, billets, and slabs. The classification is based on cross-sectional dimensions and dictates the next rolling operations (rails, structural shapes, bars, or plates).

Given Data / Assumptions:

• Square cross-sections considered.
• Industry-conventional dimensional thresholds.
• Terminology used in steel plants and rolling mills.

Concept / Approach:
Blooms are larger than billets. A common rule of thumb is that blooms have a minimum square section of about 150 mm × 150 mm (15 cm × 15 cm) or larger. Billets are smaller (often below 150 mm square), and slabs are wide, rectangular, with small thickness relative to width.

Step-by-Step Solution:

Verification / Alternative check:
Training references for rolling mills use 150 mm square as the typical dividing line between blooms and billets.

Why Other Options Are Wrong:

• 5 cm × 5 cm and 10 cm × 10 cm: billet sizes.
• 20 cm × 20 cm and 25 cm × 25 cm: still blooms but not the minimum threshold.

Common Pitfalls:
Confusing slabs with blooms; slabs are wide rectangles used for plate and strip rolling.

Final Answer: