Corten Steel vs Mild Steel: What Is the Difference?
Corten steel (weathering steel) and mild steel look similar when new but behave very differently over time. The key difference is that corten forms a stable, self-protecting rust layer while mild steel corrodes continuously until it fails. This distinction determines lifespan, maintenance cost and suitability for outdoor use.
Comparison table
| Property | Corten Steel (A588/S355J2WP) | Mild Steel (A36/S235) |
|---|---|---|
| Corrosion behavior | Forms protective oxide layer, self-healing | Corrodes continuously, flakes off |
| Outdoor lifespan (unpainted) | 50–100+ years | 5–15 years before structural loss |
| Maintenance | None (after patina stabilizes) | Requires painting every 3–5 years |
| Cost (raw material) | 15–25% more than mild steel | Baseline |
| Total lifecycle cost | Lower (no repainting) | Higher (paint + labor every cycle) |
| Appearance | Rich rust-brown patina | Flaking orange rust (unattractive) |
| Weldability | Good (needs weathering-grade filler) | Good (standard filler) |
When to choose corten over mild steel
- Outdoor permanent installations: Planters, screens, edging, sculptures, facades — anywhere paint maintenance is impractical or expensive.
- Design intent: When the rust aesthetic is desired as a feature.
- Lifecycle budgeting: Projects where 20+ year maintenance-free performance justifies higher upfront cost.
When mild steel is acceptable
- Indoor use (no corrosion risk)
- Painted or powder-coated products where the coating provides protection
- Temporary installations (under 5 years)
- Budget-constrained projects where repainting is acceptable
For outdoor landscape products, corten is almost always the better long-term investment. Browse our corten product range for maintenance-free options designed for 50+ year service life.
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