Yes, carbon fiber is generally stronger than steel. Both its specific strength and absolute tensile strength generally are significantly higher than those of steel. Therefore, the short answer is that steel is stronger than carbon fiber in some ways — but that comparison is not as straightforward as it seems.
The use of steel and carbon fiber offers endless possibilities for engineers.
Tensile strength refers to a material’s ability to resist pulling loads without breaking. However, this can be a tricky question to answer, since these two materials are fundamentally different. Their mechanical behavior depends on many factors, and a direct, absolute comparison is not entirely fair. Let’s take a closer look at their characteristics.
Comparison Between Steel and Carbon Fiber
| Material Type* | Density ρ (kg/m³) | Tensile Strength σᵤ (GPa) | Elastic Modulus E (GPa) | Breaking Length σᵤ/(ρg) (km) |
| Carbon Fiber (Standard) | 1760 | 3.53 | 230 | 205 |
| Carbon Fiber (High Strength) | 1820 | 7.06 | 294 | 396 |
| Carbon Fiber (High Modulus) | 1870 | 3.45 | 441 | 188 |
| Steel (S355) | 7850 | 0.50 | 210 | 6 |
| Steel (Wire) | 7850 | 1.77 | 210 | 23 |
*These are average, representative values for each type of material, as there are special grades of steel and carbon fiber composites that can differ widely.
Summary:
Per unit of weight, carbon fiber composites are far stiffer and stronger than steel. Even the standard carbon fiber grade shows an order of magnitude higher breaking length, which means it can sustain far more load relative to its weight before failing.
Why Is It So Hard to Define Which Material Is Stronger?
First, both belong to very broad families of materials. Steel properties vary considerably depending on the type — whether it’s carbon steel, stainless steel, or high-strength alloy steel.
The same applies to carbon fiber: there are numerous types of fibers and resins, and every combination results in a composite with unique mechanical properties.
Carbon fiber and its composites are anisotropic, meaning they have very high strength along the direction of the fibers but much lower strength transversely. This is especially relevant for unidirectional composites, where the load direction determines the performance. That’s why many woven carbon fabrics include layers oriented at 0° and 90° to balance mechanical behavior and improve overall performance.
So… Is Carbon Fiber Stronger Than Steel?
The short answer: yes — because carbon fiber generally has a much higher specific strength and absolute tensile strength than steel.
But when you analyze it more deeply, there are many variables that influence the outcome, and a simple direct comparison is not truly representative.
When Is It Better to Use Carbon Fiber, and When Is Steel the Right Choice?
As we’ve seen, these materials are so different that one cannot be said to be universally “better” than the other without considering the application.
- Carbon fiber is the better choice when weight reduction is a key factor, thanks to its unmatched strength-to-weight ratio.
- Another reason why steel is often the more convenient choice is its behavior in the event of catastrophic failure, which is more favorable than that of composites for many applications.
- Steel tends to perform better when components must endure compressive loads or high-impact conditions.
Each material comes with its own advantages and drawbacks, so the right choice depends on the application and the specific requirements for each part.
How to Compare Carbon Fiber with Steel in Real Life
Metals and composites are so different that they should not be seen as substitutes for one another. At Managing Composites, we believe that focusing solely on mechanical test data only shows part of the picture. The true potential of these materials lies in the specific design and the intended function of the part. Composites enable designs that metals simply cannot achieve. Therefore, they should not be understood as a replacement, but rather as a distinct material category — one with its own design logic, advantages, and engineering possibilities.
TL;DR
- Carbon fiber outperforms steel in strength-to-weight and stiffness-to-weight ratios.
- Steel remains superior in toughness, ductility, catastrophic failure behavior and thermal stability.
- A direct comparison between carbon fiber and steel is very complex, since these are two very different families of materials, each with variants that have widely diverse characteristics.
- Choosing between them depends entirely on the design, load case, and purpose of the part.