In construction steel, yield strength marks the all-important point where steel stops springing back to its original form and instead starts to bend or stretch for good. Think of it like a tipping point, which, for steel, is permanent.
Yield strength tells us exactly how much stress steel can handle before it’s changed for good, and this knowledge is critical when designing structures with steel. A skyscraper or a bridge, as examples, need to handle heavy loads and endure fierce weather, and steel’s yield strength gives engineers a clear-cut measure of its resilience, so the right type and formulation can be used.
Yield strength by steel grade
Different steel grades have different yield strengths depending on their carbon content and alloying elements. Here are the most common structural and mild steel grades used in Australian construction, with minimum yield and tensile strength values in MPa.
| Steel grade | Yield strength (MPa) | Tensile strength (MPa) | Typical use |
| Grade 250 (mild steel) | 250 MPa | 410 MPa | General structural work, beams, columns |
| Grade 350 (high-strength) | 360 MPa | 480 MPa | Heavy commercial and industrial structures |
| Grade 450 (high-strength) | 450 MPa | 520 MPa | Long-span structures, crane rails, heavy plate |
| Grade 304 stainless | 210–310 MPa | 520–720 MPa | Corrosion-resistant applications, coastal builds |
| Grade 316 stainless | 220–320 MPa | 530–730 MPa | Marine, chemical, and food industry environments |
Steel is not a one-size-fits-all material
Different types of steel come with different strengths, dictated by their makeup and how they’re processed. For example, adding more carbon can boost a steel’s yield strength, while elements like manganese can fine-tune other characteristics.
Yield strength is just one piece of the puzzle in steel fabrication, though. Tensile strength the point at which steel outright breaks, as opposed to just deforming is another vital metric to understand how the particular steel you have selected for your project will perform in real-world conditions.
Steel’s yield strength can vary across types
Depending on the type, steel’s yield strength can range from around 200 MPa for mild steel, ideal for less load-intensive applications, to over 2000 MPa for high-strength alloys suited for demanding structures where extreme durability is essential.
Mild Steel
Mild steel is the go-to material for many everyday construction projects. Its yield strength typically sits on the lower end, around 200 MPa, making it a suitable option for structures that don’t face constant heavy stress but benefit from some give and flexibility. This can be beams or columns in residential apartment buildings, where its affordability and ease of use make it a popular choice for many builders.
Stainless Steel
Stainless steel is chosen for its corrosion resistance, but its yield strength can vary depending on the specific subtype:
- Austenitic Stainless Steels (e.g., Stainless Steels 304 and 316)
High corrosion resistance for environments exposed to moisture or chemicals with a yield strength from 200 to 300 MPa – moderately strong while highly resistant to rust, ideal for coastal constructions and kitchen applications.
- Martensitic Stainless Steels (e.g., Stainless Steel 410)
Yield strengths of around 400 to 600 MPa, often chosen for applications where durability is more important than corrosion resistance, like in tools and certain industrial components.
- Duplex Stainless Steels
Offering a higher yield strength (typically 500 to 700 MPa) and solid corrosion resistance, ideal for heavy-duty environments, like chemical plants or marine settings.
High-Strength Alloy Steels
These steels are engineered to take on substantial loads without bending or breaking, with yield strengths reaching over 2000 MPa. These steels are used in specialised applications like high-rise buildings and heavy infrastructure.
Steel’s highest yield strength
There is no one-size-fits-all maximum yield strength; some steels are designed to reach high resistance levels well above 2000 MPa. Some of the strongest steels and their applications include:
- Maraging steels with strength that exceeds 2000 MPa, ideal for aerospace components and precision tooling
- Ultra-high-strength steels which include varieties like martensitic and dual-phase steel also hit the 2000 MPa mark, and are often used in automotive and defence applications
- Tool steels cover a spectrum ranging from around 500 MPa to over 2000 MPa and are used in manufacturing tools
High-yield steels are expensive and often require specialised processing, but they’re essential in industries where performance and safety are non-negotiable.
Steel’s behaviour under stress
Steel is either being pulled apart (tension) or pushed together (compression). This difference comes down to how materials fail under these two forces. In general, steel and many other materials can withstand higher stresses under compression than under tension before they reach their yield point. Understanding tensile and compressive yield strengths is essential for selecting the right steel for a project, ensuring durability and safety under varying stress conditions.
Tensile yield
Tensile yield strength is the stress level where steel starts to deform permanently under tension. For example, M2 tool steel has a tensile yield strength of around 2200 MPa. Under tensile stress, steel will eventually stretch and thin out, which leads to permanent deformation if it surpasses its yield strength. Tensile yield strength is particularly relevant in applications where steel components are under pulling forces, such as in cables or beams under load.
Compressive yield
Compressive yield strength is the point where steel deforms plastically under compression. Steel can typically handle greater compressive forces; for instance, M2 tool steel’s compressive yield strength can reach around 3250 MPa. This strength is crucial in structures or applications where components face compressive forces like columns in warehouses or buildings to avoid deformation and maintain stability.
Compressive yield strength vs tensile yield strength
For structural steel, compressive yield strength and tensile yield strength are equal, both sit at the same MPa value for a given grade. This is a key property of ductile metals, and it is why engineers can design steel columns and beams using the same yield value regardless of whether the member is in compression or tension. For Grade 250 mild steel, that value is 250 MPa in both directions.
Choosing the right option with Kelly Steel
At Kelly Steel, we bring together our skills, experience, and expertise to handle industrial, commercial, and residential steel fabrication projects of any scale.
We’re committed to delivering quality steel fabrications and to building lasting relationships through our professionalism, approachable team, reliability, innovative solutions, and adaptability. We’ll make sure you have the right steel for your project. Let’s chat today.
Frequently asked questions about steel yield strength
What is the yield strength of steel?
Yield strength is the stress level, measured in megapascals (MPa), at which steel permanently deforms rather than returning to its original shape. The most common structural steel in Australia, Grade 250 mild steel, has a yield strength of 250 MPa. Higher grades like 350 and 450 have proportionally higher yield strengths, used where loads are heavier or spans longer.
What is the yield strength of mild steel in MPa?
Mild steel (Grade 250 to AS/NZS 3678) has a minimum yield strength of 250 MPa for sections up to 17 mm thick. Yield strength drops to 240 MPa for sections between 17 mm and 40 mm, and 230 MPa for sections over 40 mm thick. Thicker sections have slightly lower yield strength, a factor engineers account for in design.
What is the yield stress of steel?
Yield stress and yield strength are the same thing, both refer to the stress at which a material begins to deform plastically. For structural steel, yield stress is measured in megapascals (MPa) and varies by grade: 250 MPa for mild steel, up to 450 MPa and above for high-strength grades used in heavy industrial and long-span applications.
Is compressive yield strength the same as tensile yield strength for steel?
Yes. Unlike brittle materials, structural steel has equal yield strength in compression and tension. For Grade 250, both compressive and tensile yield strength are 250 MPa. This symmetry is one of the primary reasons steel is so versatile as a structural material, the same grade performs reliably whether a member is a beam in bending or a column in compression.
What is the maximum yield strength of steel?
Standard structural steel grades used in Australian construction cap out around 450–500 MPa. Specialised high-strength steels used in aerospace and defence can exceed 2,000 MPa, though these are not used in commercial or industrial building construction. For most structural projects, Grade 350 or Grade 450 covers the upper range of practical requirements.
