A36 and A572 are two of the most important types of structural steel adhering to ASTM International standards. They both serve similar purposes in construction and fabrication, but each has distinct qualities that make them suitable for specific tasks. Both engineers and designers need to understand their differences in strength and composition to allow them to make wise and informed decisions. Read further and let us explore the world of steel to determine each grade’s unique strengths and capabilities!
What is an A36 steel?
A36 steel is a low-carbon mild steel utilized in various structural applications. Highly regarded for its cost-effectiveness, good weldability, formability, and machinability, its key feature is a minimum yield strength of 36,000 pounds per square inch (psi). This makes it suitable for a variety of construction and engineering applications.
What is A572 steel?
A572 steel is a high-strength low-alloy (HSLA) steel that comes in different grades. ASTM A572 Gr.50 is the most commonly used grade, which offers a minimum yield strength of 50,000 psi (345 MPa). The combination of certain alloys in A572 improves its overall strength and corrosion resistance.
Key differences Between A36 and A572
Tensile Strength
A36
ASTM A36 steel’s ultimate tensile strength (UTS) ranges between 58,000 to 80,000 pounds per square inch (psi), which is roughly equivalent to 400 to 550 megapascals (MPa). This strength varies depending on several factors such as the specific chemical composition and the manufacturing processes used in the steel’s production.
A572
A572 Steel is available in various grades, and each one is defined by its minimum tensile strength. Grade 50 steel, the most common grade of A572, has a tensile strength of 65,000 psi, allowing it to withstand a greater pulling force when compared to A36 steel.
Yield Strength
A36
A36 steel has a minimum yield strength of 36,000 pounds per square inch (psi), which is equivalent to 250 megapascals (MPa).
A572
Grade 50 Steel is a type of metal that can handle a lot of pressure. It has a minimum strength of 50,000 psi (which is about 345 MPa). This means it can take more stress than A36 steel before it starts to bend or change shape.
Impact Resistance
A36
A36 steel is a mild, low-carbon steel known for its excellent malleability. It can bend and deform without breaking, and this property allows it to be the ideal choice for absorbing impacts due to its lower carbon content, which enhances its toughness. In colder environments, A36 can become more brittle, resulting in decreased impact resistance.
A572
A572 steels, particularly the higher grades, are renowned for their excellent impact resistance, often exceeding that of A36. This strength is possible due to their fine-grain structure and carefully controlled alloys. In most cases, A572 steels also become more brittle when exposed to colder temperatures, like A36.
Weldability
A36
A36 steel is known for its outstanding weldability, making it suitable for all standard welding processes. Some common welding techniques used in A36 steel include shielded metal arc and gas metal arc welding. The lower carbon content of the material helps in reducing the occurrence of cracks during the welding process.
A572
A572 steel is also good for welding, but as its grade increases and becomes stronger, the risk of cracking also slightly increases due to the steel’s higher alloy content. For higher grades of A572 steel, preheating the material and carefully monitoring the temperatures between welding passes is the best approach as these steps help reduce the risk of hydrogen-induced cracking and result in strong welds.
Corrosion Resistance
A36
A36 is a plain carbon steel that consists of both manganese and silicon as its alloys. It has limited corrosion resistance when compared to alloyed steels that contain higher levels of chromium and nickel, which are commonly found in stainless steel. Without additional protective measures such as paint or galvanizing, A36 is prone to rust when exposed to moisture and air.
A572
ASTM A572 steel is engineered to provide increased resistance to atmospheric corrosion when compared to other standard carbon steels, such as A36. The various alloying elements in A572 allow the formation of a more stable oxide layer on the surface, which helps reduce the rate of corrosion.
Cost
A36
A36 steel, with its characteristics, is more affordable than ASTM A572 steel. Its simpler chemical composition and classification as a standard, as well as its widely produced mild carbon steel, make it the more economical choice. The price of A36 steel plates usually ranges between approximately $350 to $810 per ton, all depending on several factors such as the supplier, thickness, and quantity.
A572 Steel
ASTM A572 steel is known as a high-strength, low-alloy steel that incorporates additional elements to enhance its properties. Due to this, this type of steel has a higher price point compared to standard steel. The cost fluctuates depending on various factors, including the specific grade (which can be 42, 50, 55, 60, or 65), thickness, and supplier. To give an idea, prices for A572 steel plates typically range between US$ 480 to US$ 1460 per ton or even higher.
Availability
A36 Steel
A36 is one of the most popular and widely used structural steel grades globally, and because of this, it is commonly utilized in both construction and manufacturing. It is almost always in stock with steel suppliers and distributors. If you need plates, bars, angles, channels, or other structural shapes, A36 is always easy to find in a variety of sizes and thicknesses.
A572 Steel
A572 steel, like A36 is also easy to find, especially the common grades like Grade 42 and Grade 50. You will observe that it is always stocked at most major steel suppliers and service centers. However, higher strength grades like 60 and 65, or less common thicknesses, might not be as widely available, resulting in longer lead times.
Chemical Compositions
| Chemical Alloy | A36 Steel | A572 Grade 50 |
| Carbon Max | 0.25% | 0.23% |
| Manganese | 0.80-1.20% | 1.35% |
| Phosphorus Max | 0.03% | 0.03% |
| Sulfur Max | 0.03% | 0.03% |
| Silicon | 0.40% MAX | 0.15-0.40% |
| Copper Min | 0.20 % | 0.20 % |
Applications
A36 Steel
As stated, A36 steel is widely used in both construction and manufacturing because of its strength and characteristics. It is usually the favored material for frames and structural components in low to mid-rise buildings due to its cost, weldability, and ease of handling. It is also commonly used in the fabrication of brackets, supports, base plates, and components for machinery. Moreover, it is also becoming popular in agricultural equipment and temporary road plates, showcasing a strong balance between strength and versatility.
A572
ASTM A572 steel is the better choice for projects requiring both high-strength and lightweight materials. A572’s improved efficiency is thanks to its great strength-to-weight ratio allowing it to be widely used in various heavy-duty applications, such as long-span bridges, critical load-bearing components in high-rise buildings, and construction equipment such as cranes and excavators. Moreover, it is also the preferred material for transmission towers and wind turbine structures, where strength and durability are crucial.
Conclusion:
The main difference between A36 steel and A572 steel is their strength. A572 possesses significantly higher yield and tensile strength compared to A36, making it more suitable for heavy-duty projects. In terms of cost, A36 is more economical and is ideal for everyday construction where moderate strength and ease of welding are sufficient. Though A572 has a higher initial cost, it provides long-term value in projects where reducing weight without sacrificing strength is crucial.
