Plain-carbon steels are divided into four categories:
- Low-carbon steel (0.005% - 0.30%C) for such items as automobile frames and bodies, structural shapes (I-beams, channels, angles) and the like.
- Medium-carbon steel (0.30% - 0.60%C) for machined parts, tools and the like.
- High-carbon steel (0.60% - 1.0%C) for springs, dies, railroad rail and the like.
- Ultra-high-carbon steel (1.0 – 1.2%C) for knives, axles or punches.