A36 Carbon Steel: Uses, Composition, Properties
A36 steel is a steel composition formulated by ASTM (American Society for Testing and Materials). It is mild steel, also known as low-carbon steel, with a carbon content of 0.25%–0.3%. A36 steel also has roughly 1% manganese. This chemical composition gives A36 steel a well-rounded set of properties with good strength, weldability, and malleability at a low cost. For this reason, A36 steel is widely found in structural applications in the construction, automotive, and oil & gas industries.
A36 carbon steel was developed by ASTM International and is one of the most used carbon steels for structural applications. A36 steel exhibits excellent welding properties and is well-suited for punching, grinding, drilling, tapping, and machining. The properties of A36 make this steel suitable for a wide scope of applications when compared to other high-performing alloys. A36 steel is a paramagnetic material which means it is a good conductor of magnetic fields, therefore A36 steel is fairly opaque to electromagnetism.
A36 carbon steel is a material with a wide scope of applications due to its low cost and wide range of desirable properties including: weldability, formability, strength, and toughness. Most applications for A36 steel are structural such as in bridges and buildings. A36 steel also finds applications in the automotive, construction, heavy machinery, and oil & gas industries.
A36 carbon steel is made by mixing the molten metals together and then hot rolling them. This process is similar to most carbon steels, and the only real difference is the chemical composition.
The first step is melting iron ore in a furnace with coal and then burning away the impurities. Next, the alloying elements including manganese and carbon are added. The molten metal is solidified into ingots before finally being hot rolled. Hot rolling is a process in which ingots are rolled into a final dimension at an elevated temperature.
A36 carbon steel, as with every steel, is mainly made up of iron. For A36 steel, iron makes up 98% of its composition, manganese makes up 1.03%, and carbon makes up 0.25%–0.29% of its composition. Any steel with a carbon content lower than 0.3% is classified as low-carbon steel. Table 1 below shows the other elements that are added to make A36 carbon steel by weight:
The carbon content of A36 steel is 0.25%–0.29%. Steels less than 0.3% carbon are considered low-carbon steels. Low-carbon steels are renowned for their ductility, malleability, and weldability. However, they have a lower strength-to-weight ratio and less corrosion resistance than high-carbon steels.
Yes, A36 is low-carbon steel as it has less than 0.3% but more than 0.05% carbon by weight. A36 is a very popular low-carbon steel. Other popular low-carbon steels created by ASTM are A572 Grades 42 and 50 as well as A830-1020.
To find the volume fraction of carbon in A36 steel, you must divide the volume of the carbon by the volume of all of the other elements. The formula below can be used to calculate the volume fraction:
Volume fraction formula.
The machinability rating of A36 steel is 72% machinable. The average cutting speed of A36 steel is 120 ft per minute. While this is a good rating, it is not as easy to machine as 1018 and may be a reason to choose 1018 vs. A36.
A36 carbon steel has a melting point in the range of 2,590–2,670 °F. It also has a specific heat capacity of 0.11 Btu/lb Fahrenheit and a thermal conductivity of 348 Btu-in/hr-ft2 F.
A36 carbon steel is used for a wide variety of applications as it has a versatile range of properties including good hardness, strength, malleability, weldability, ductility, and machinability. These properties, coupled with their low cost, cause A36 steel to be widely used in structural applications, especially in the civil construction industry to build buildings and bridges. A36 steel is also used in the automotive, construction, heavy machinery, and oil & gas industries.
Common forms of ASTM A36 carbon steel are listed below:
A36 sheet metal is between 0.018” and 0.250” thick. A36 sheet steel is used for automotive bodywork or to form walls/bulkheads or build tanks.
A36 steel bars are used for structural applications. One of their most common uses is reinforcement in concrete. This is because concrete has a very high compressive strength but a low tensile strength.
A36 steel plates are equal to or more than 0.25” in thickness. Whereas A36 sheet steel is mainly used for aesthetic functions, A36 steel plates are used to provide structural integrity. The A36 plate is mostly used in structural applications in buildings, bridges, and oil rigs, as well as in automotive and agricultural applications.
The most common form of A36 steel is hot rolled, which creates a surface finish that is rougher. Hot rolling of A36 steel is carried out at 1,562–2,192 °F. The process of hot rolling imparts a strain on the steel which will increase the dislocation density of the microstructure resulting in work hardening. The process also creates grain elongation. Hot-rolled A36 steel is cheaper than the less common cold-rolled A36 as the hot-rolling process is less labor intensive.
Annealing of A36 steel is carried out at 1,550–1,600 °F. The annealing of A36 steel, which involves heating the steel and then cooling it at a specific rate, removes impurities and decreases its brittleness. However, by annealing the steel its hardness is also reduced. The annealing process affects the steel's microstructure by recrystallization. The formation of new grains happens at a temperature just below A36’s melting point and the specific cooling rate controls the growth of these new grains. This process limits the internal stresses produced in the A36 steel. By annealing A36, the hardness of the metal can be brought down, reducing the wear on tools used to machine it.
The process of cold drawing steel is similar to hot rolling, just at a lower temperature. Cold-drawn A36 is stronger and harder than hot-rolled steel. Cold-drawn steel will also have a better finish. Cold-drawn A36 forms shape like bars, tubes, spindles, and wires. Cold-drawn A36 is mostly used to create shafts and products which require an aesthetic finish.
The biggest advantage A36 carbon steel has is its versatility. It is applicable for a range of applications at a low cost. Some of A36’s main advantages are listed below:
- Easy to weld
- High strength
A big limitation of A36 steel is its limited protection from corrosion. This is because this steel has no nickel or chromium added. Other disadvantages are listed below:
- Low strength-to-weight ratio.
- Lower strength than similar 1018 steel.
- Hard to accurately obtain its precise carbon content.
It is hard to exactly match A36 steel using different standards. Each standard will be slightly different in composition and therefore will have slightly different properties. However, Table 3 shows some comparable grades:
A36 and 1018 steel are very chemically similar. The main difference is 1018 has a lower carbon content of around 0.18%. 1018 is usually chosen over A36 for two reasons: because it is more easily machinable, and because it performs better in rotating parts including shafts, spindles, and rods. A36, on the other hand, is more likely to be chosen for applications that require I-beams and cables. A36 steel is generally cheaper than 1018 steel as A36 is usually hot rolled and 1018 is cold rolled which is more labor intensive. This means that A36 would generally be a better choice if high strength and machinability are not required.
A36 and A572 are both steels created by ASTM, however, they vary in the amount of alloying elements they contain. A572 contains more phosphorus, manganese, and silicon which makes it stronger than A36 steel. A572 is regarded as a high-strength low-alloy (HSLA) steel, meaning it is able to bear more weight than A36 steel. The difference in chemical composition changes properties such as the yield point and tensile strength. It is specifically the addition of more manganese and silicon that makes A572 stronger and increases its yield point.
This article presented A36 carbon steel, explained it, and discussed its various uses and properties. To learn more about A36 carbon steel, contact a Xometry representative.
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