If you’re looking for low-carbon steel that’s suitable for welding, two of the most commonly available types on the market are ASTM A36 and SAE/AISI 1018. Both 1018 and A36 are low-carbon or mild steels. Each has its particular advantages and disadvantages that will help you determine which one you should use. My goal in this article is to help you understand those properties so that you can make the right choice.
What is the Difference between 1018 steel and A36 steel? The difference between 1018 steel and A36 steel is in the finish, yield strength, and price. A36 is favored for structural purposes, while 1018 is used for machining and finishing purposes. While both 1018 and A36 come in hot-rolled or cold-rolled forms, hot-rolled A36 steel and cold-rolled 1018 steel are the most common.
To help you gain a better understanding of which steel you may need to use, let’s take a closer look at a36 vs 1018. By evaluating the hot and cold rolling processes as well as the chemical and mechanical properties of these metals, you will gain a better understanding of which is better for your application.
What are Hot-Rolled and Cold-Rolled Steels?
Both hot-rolling and cold-rolling involve running steel through a series of dual rollers that squeeze the metal into a predetermined shape. Machine operators will run the metal through roll forming machines that apply pressure to the metal as many times as need until the desired form is obtained. The forms produced can range from simple flat sheet metal to more complex forms like I-beams (Capital Steel & Wire Inc., 2009).
The Hot Rolling Process
Hot-rolling is a process that takes place with the temperature of the metal over 1700 degrees Fahrenheit. This is above the metal’s temperature of recrystallization, which makes the metal easier to form. As a result, the roller mills can handle the steel in larger sections and produce higher volumes of material. The ease and quickness with which the steel is formed at high temperatures make hot-rolled steels cheaper than cold-rolled steels (Capital Steel & Wire Inc., 2009, 2015).
Since the metal is allowed to cool after the high temperature rolling process, the finish on hot-rolled steel is not as polished as cold-rolled steel. During this process, the steel warps slightly ending in a product that is not as straight and has less predictable measurements (Capital Steel & Wire Inc., 2015).
The rough finish on the outside of hot-rolled steel is the result of an oxide called mill scale. A treatment known as pickling is used to reduce this mill scale by dipping the steel into a mix of hydrochloric or sulfuric acid for steels with less than six percent carbon (nationalmaterial.com). Another process that reduces mill scale is referred to as the smooth clean surface (SCS) process, which runs the metal through a series of roller brushes. Each additional process raises the price.
The Cold Rolling Process
Cold-rolled or cold-finished steel is initially hot-rolled before the additional process of cold rolling in cold reduction mills (Metal Supermarkets, 2014). Cold-rolled steel is produced at near room temperature, below the temperature for recrystallization. This process is more time consuming and handles lower volumes of materials, which results in a higher price tag (Capital Steel & Wire Inc., 2013).
The advantage of cold-rolling is that there is much less warping done as the metal cools, creating a smoother finish and making its dimensions more predictable and accurate. Rolling the steel below the recrystallization temperature also makes it less likely to fracture under pressure (Capital Steel & Wire Inc., 2013).
The cold rolling process hardens the steel through a process called work hardening or strain hardening. As the crystals in the metal are forced together the metal becomes stronger and more resistant to further deformation. Since cold rolling operates with smaller volumes of material than hot rolling, it comes in smaller sheets, bars, and rods.
What Is 1018 Steel?
The SAE/AISI designation 1018 represents the chemical composition of plain carbon steel with around 0.18% carbon. The first two numbers in the SAE system stand for the type of steel, while the last two digits stand for the amount of carbon in hundredths. While sometimes listed as AISI (American Iron and Steel Institute), the material specifications are actually established by the Society of Automotive Engineers (SAE) (Bringas, 2004, p. 14).
Chemically, 1018 is very similar to A36 but with a little less carbon, less manganese, and fewer impurities. The actual chemical composition of 1018 steel is 98.81-99.26% iron, 0.18% carbon, 0.6-0.9% manganese with traces of phosphorus and sulfur (Capital Steel & Wire Inc., 2015).
Low carbon 1018 steel comes in a variety of forms, shapes, and sizes. 1018 is available in round bar, square bar, rectangular bar, hexagonal bar, plate, and sheet. Standard steel bar measurements can range in thickness from 1.25 inches to 6 inches. You can choose 1018 in either hot-rolled or cold-rolled form. Remember, what you might gain in terms of price and material size, you will lose in strength and finish. A hot-rolled version of the 1018 sheet is available as thin as 1.25 inches (metalsupermarkets.com).
What Is 1018 Steel Used For (Advantages)
The toughness, ductility, and surface hardening characteristics of 1018 steel make it well-suited for machining purposes, especially when cold rolled. Its ductility and yield strength are good for cold forming techniques like crimping, swaging or bending. Machine parts like spindles, shafts, pins, and rods are often made of 1018 steel (Capital Steel & Wire Inc., 2015).
Whether in hot-rolled or cold-rolled form, 1018 has better mechanical properties than A36 with higher yield strength, tensile strength, and Brinell hardness. Cold-rolled 1018 has a yield strength of around 54,000 PSI, a tensile strength of 63,000-64,000 PSI, and a Brinell hardness of 126. The cold-rolled 1018 will be better suited to precision applications than hot-rolled 1018 or A36.
There is a greater degree of variation with hot-rolled 1018. When Hot-rolled, 1018 has a lower yield strength ranging from 40,000 to 45,000 PSI, a tensile strength ranging from 60,000 to 67,000 PSI, and a Brinell hardness ranging from 116 to 137 (Capital Steel & Wire Inc., 2015; metalsupermarkets.com).
Another advantage of 1018 steel is that it can be case hardened through processes like carbonitriding or carburizing (metalsupermarkets.com). Carbonitriding is a method of surface hardening used frequently on cheaper low carbon steels to grant them some of the qualities of more expensive steels. This process is used for things like gear teeth, bearings, and shafts. Carburizing does essentially the same thing but has a greater tendency to change the dimensions of the metal.
Both 1018 and A36 are popular for blacksmithing. However, since 1018 is measured specifically by its carbon content, it is easier for blacksmiths to forge. The higher carbon content, the inconsistency of that content, and the higher difficulty in forging A36 steel are relegated to cheaper applications (Stanaitis, 2010).
Disadvantages Of 1018
One of the chief disadvantages of 1018 steel is that it costs nearly twice as much as A36, especially in cold-rolled form. 1018 steel’s superior machinability, strength, precision, and finish all come with a higher price tag. The increased production costs of processing mean that it comes in smaller bars or sheets (Capital Steel & Wire Inc., 2015).
The other disadvantage of 1018 is that its higher yield strength and lower ductility mean that it does not bend as easily as A36. While A36 has an elongation at 50mm of 20%, a measure of ductility, that of 1018 is only 15% (Capital Steel & Wire Inc., 2015).
What Is A36 Steel?
In contrast to 1018, A36 is designated by its mechanical properties instead of its chemical properties. In the American Society for Testing Materials (ASTM) system, the A stands for ferrous metal while the 36 refers to its minimum yield strength of 36,000 PSI (Bringas, 2004; Metal Supermarkets, 2017).
A36 steel is low carbon steel with less than 0.3% carbon. 1.03% manganese, 0.28% silicon, 0.2% copper, 0.04% phosphorus, 0.05% sulfur. A quick comparison reveals that it has a little more carbon and manganese in it than 1018. A36 is most commonly found as hot-rolled steel that is allowed to cool after the hot-rolling process (Capital Steel & Wire Inc., 2015; Metal Supermarkets, 2017).
While in most cases, A36 steel will have been hot-rolled, it is also available in a cold-rolled form, which gives it a better finish as well as more precise dimensions. It is less common, and the tradeoff here will, again, be price.
What Is A36 Steel Used For (Advantages)
The greatest advantage of hot-rolled A36 steel is that it costs about half as much as cold-rolled 1018 steel. Because of its low cost and weldability, A36 is widely used for structural purposes. This includes the frames of bridges, buildings, automobiles, and general fabrication. The railroad track is made from A36, and it is used in the oil and gas industries. In addition to coming in round, square, and rectangular form, it can be made into I-beams, H-beams, simple angle, or channels (Capital Steel & Wire Inc., 2015; Metal Supermarkets, 2017).
Due to its low yield strength of 36,000 PSI, Brinell hardness of 112, and higher ductility, A36 will bend much easier than 1018 (Capital Steel & Wire Inc., 2015). Hot-rolled A26 is more readily available in larger sections than steel plate 1018 which is more common in the flat bar. Standard sizes include a tread plate around 0.074-0.25 inch and steel plate around 0.188-1 inch, while the square bar is available in similar sizes to 1018 bar (metalsupermarkets.com).
Unlike 1018 steel, case hardening processes like carburizing or carbonitriding are not recommended for A36. On its own, A36 does not have very good resistance to corrosion. However, you can get a galvanized A36 steel which is very common in construction. This is A36 steel that has been hot dipped into a zinc mixture to increase the metal’s strength and corrosion resistance.
Disadvantages of a36 Steel
While A36 is the more cost-effective of the two metals, 1018 wins out in most other categories for quality. With a minimum yield strength of 36,000 PSI and tensile strength of 58,000 PSI, A36 is not as strong as either hot-rolled or cold-rolled 1018 (Capital Steel & Wire Inc., 2015). Measurements for hot-rolled A36 are also not as precise as cold-rolled steels since they warp and bend slightly during the cooling process.
The decreased hardness, strength, and measurement consistency means that A36 is not well-suited to precision work, finishing, or machining. While A36 can still be machined, it is much more difficult to do so than with 1018 because of higher levels of carbon and silicon. Hot-rolled A36 steel in particular also develops mill scale on the surface during the hot rolling process. Mill scale makes it harder for the paint to adhere to the surface (Capital Steel & Wire Inc., 2015; Metal Supermarkets, 2017).
Another downside to A36 is the difficulty in predicting the level of carbon in the steel since it is primarily measured by its mechanical properties, not its chemical ones. The carbon level can vary from 0.25% to 0.29%. A36 may also contain more impurities than in 1018 (Stanaitis, 2010).
Can you weld 1018 to a36?
Welding uncoated 1018 to A36 poses no real barriers since both are low carbon or mild steels. Low carbon steels, defined as having less than 0.3% carbon, are well-suited to most welding types such as stick welding (SMAW), MIG welding (GMAW), TIG welding (GTAW), flux-cored welding (FCAW), and submerged arc welding (SAW).
Cheaper welding methods like stick welding, oxyacetylene welding, or MIG welding are commonly used on A36 in construction. Whenever MIG welding mild steel, you will need to carefully choose your shielding gas. Make sure you choose a mixture that contains less than 100 percent argon with a small percentage of carbon dioxide (10-25%) or oxygen (1-5%) mixed in.
Complications are more likely to arise if the metal is coated. If 1018 steel is case hardened by carbonitriding or carburizing, you will need to grind away the surface to get a quality weld. The decision of whether or not to do that will be affected by the thickness of the material you’re working with. The same thing goes for galvanized A36, you will need to grind away the zinc coating to get a proper weld if possible.
Both A36 and 1018 steel are highly sought after in the market for their specific applications. The main advantage of A36 is that it costs less than 1018, making it better suited for high-volume structural work. While costing more, 1018’s better finish, precise measurements, and toughness make it the better option for precision work and machining. Both are available in a hot-rolled or cold-rolled form, which affects the finishing, cost, and strength for each.
When making your decision on which to use for your particular application, think carefully about what it is you’re looking to achieve. While A36 has a rough look and finish, some prefer that finish as an artistic touch. If you’re looking for a finer finish or need consistent, precise measurements, you can go with a cold-rolled 1018. In the end, it will come down to your needs, preferences, and budget.
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