Carbon steel is cheap, strong, weldable, easy to machine. Stainless steel costs 3-5× more, resists corrosion, and works in food and medical applications. For most designers, the choice is obvious by the application. But edge cases reveal that sometimes "stainless because corrosion" is over-specified, and sometimes "carbon because cheap" ignores real corrosion costs.
| Property | 1018 Carbon Steel | 304 Stainless | 316 Stainless |
|---|---|---|---|
| Tensile strength | 440 MPa | 515 MPa | 515 MPa |
| Yield strength | 370 MPa | 205 MPa | 205 MPa |
| Elongation | 15% | 40% | 40% |
| Hardness (Brinell) | 126 HB | 92 HB | 95 HB |
| Density | 7.87 g/cm³ | 8.00 g/cm³ | 8.00 g/cm³ |
| Corrosion resistance (bare) | Poor (rusts) | Very good | Excellent |
| Magnetic | Yes | Non-magnetic (annealed) | Non-magnetic (annealed) |
| Machinability | Excellent (70%) | Moderate (45%) | Moderate (36%) |
| Weldability | Excellent | Good (use L grade for welds) | Good (use L grade for welds) |
| Cost ($/kg) | $1.20 | $3.80 | $5.00 |
Machine frames, industrial fixtures, structural brackets in factory environments. Painted or powder-coated to prevent rust. Cost is baseline.
If finishing (powder coat, zinc plating, painting) is applied, the base metal corrosion resistance becomes irrelevant. Carbon steel + zinc plating costs 1/3 of stainless equivalent with similar corrosion performance.
Alloy steels (4140, 4340) heat-treated to 40+ HRC provide 1,000+ MPa strength. Stainless grades typically can't match this without specialized precipitation-hardened alloys.
Bolts, screws, nuts indoors. Steel fasteners cost 1/3 of stainless. Plating adds minor cost. For non-corrosive service, easily justifiable.
Tool steels, springs, gears that need hardening above 40 HRC. Stainless options are limited; carbon and alloy steels dominate this space.
FDA requires non-reactive materials. Stainless 304 is the industrial baseline. 316 for high-chloride cleaning environments.
Biocompatibility, sterilizability, inherent cleanability. Stainless (specifically 316L, 17-4 PH) dominates medical applications.
Marine atmosphere attacks carbon steel rapidly. 316 stainless withstands decades of coastal service. The cost premium is negligible compared to replacement cost.
Electropolished 316L for ease of cleaning, validated passivation. Non-negotiable for pharma manufacturing.
Handrails, facades, sculptures. Where painted carbon steel would need maintenance every 5-10 years, stainless requires none. Life-cycle cost often favors stainless.
Most mild acids, solvents, caustic — stainless resists where carbon steel corrodes. For aggressive chemistry, higher grades (duplex, super duplex, Hastelloy) may be needed.
When specifying carbon steel, account for:
When evaluating "carbon steel + paint" vs "stainless":
For infrastructure, long-service equipment, and exposed structural elements, stainless life-cycle cost often wins even though initial cost is higher.
Beyond simple carbon vs stainless choice, mid-range options exist:
Email [email protected] with drawing and service environment. For outdoor/marine/food applications, we'll recommend appropriate stainless. For indoor/coated applications, carbon steel with proper finishing. We machine both grades routinely.
Start a quote →