PROGRESSO
Aço laminado a quente versus aço laminado a frio: Superfície, Strength and Cost
Aço laminado a quente versus aço laminado a frio: Superfície, Strength and Cost
Hot rolled and cold rolled are the two basic ways steel sheet and plate are produced. The difference is not cosmetic — it changes the surface finish, dimensional tolerance, strength and price. This guide explains the two processes, compares the products, and shows when to specify each for fabrication, structures and sheet metal work.
The Process Difference
Hot rolled steel is rolled at over 1700°F (925°C), above the recrystallization temperature. The steel is soft and malleable, so it can be rolled into thick sections quickly and cheaply. The surface has mill scale — a black oxide layer that forms when hot steel meets air. Cold rolled steel is hot rolled first, then pickled to remove scale, then cold rolled at room temperature. The cold work hardens the steel, increases strength, and produces a smooth, bright surface with tight dimensional tolerance. Veja nosso Barra plana Q235B.
| Propriedade | Laminado a quente | Cold rolled |
|---|---|---|
| Rolling temp | > 925°C | Room temp |
| Superfície | Black mill scale | Brilhante, suave |
| Thickness tolerance | ±0.2 mm | ±0,05 mm |
| Força de rendimento | 235 MPa | 280 – 350 MPa |
| Thickness range | 1.5 – 200 milímetros | 0.3 – 4 milímetros |
| Cost index | 1.0 | 1.3 – 1.5 |
Surface and Tolerance
Hot rolled has a black, scaly surface that must be cleaned (tiro disparado, pickled or ground) before painting. The thickness tolerance is loose — ±0.2 mm on a 3 mm sheet. Edges are irregular and may have camber. Cold rolled has a smooth, bright surface that is ready for painting or powder coating. The thickness tolerance is tight — ±0.05 mm on 1 mm sheet. Edges are square and straight. For sheet metal fabrication, cold rolled is the default because it bends cleanly and has a finish that does not require extra cleaning.
Strength and Formability
Cold rolling work-hardens the steel: a 1.0 mm cold rolled sheet has a yield strength of 280 – 350 MPa, comparado com 235 MPa for hot rolled. This makes cold rolled stronger but less formable. Hot rolled is softer and bends more easily. For structural applications, hot rolled is standard — the strength is adequate and the cost is lower. For stamped parts, cold rolled is standard — the smooth surface and tight tolerance produce consistent parts. For heavy bending, hot rolled is more forgiving.
When to Use Which
Use hot rolled for: aço estrutural, pratos, beams, bares, tubos, and any part that will be welded, painted or galvanized. It is cheaper and stronger in thick sections. Use cold rolled for: sheet metal enclosures, mobília, automotive body panels, appliance panels, and any part that needs a smooth surface or tight tolerance. Hot rolled is sold by weight and used for structure; cold rolled is sold by weight or sheet and used for visible parts. For parts that need to be painted, cold rolled saves the cost of shot blasting. For parts that are hidden or structural, hot rolled is the cheaper choice.
