Buyers Guide To Carbon Steel

¬¬¬¬Six Questions when Buying Carbon Steel

Carbon steel is a widely used material, found in items from structural steel to kitchen knives. However, these industries do not necessarily use the same grade of steel. At its most basic, this metal group is made up of any steel alloy with added carbon. The carbon percentage will usually be somewhere between 0.05% to 2.0% of the metal’s overall weight.
In any chemical composition, a range of 0.05 to 2.0 is a significant margin. Steel is no different: when it comes to formulating steel alloys, the variance in carbon percentage has a transformational effect on the produced metal. Carbon strengthens and hardens the steel, but decreases its ductility. That means the higher the carbon percentage, the less flexible the steel becomes. A high-carbon steel grade put under high or repeated stress would be more brittle and liable to crack. A grade of steel with lower carbon content will be more ductile, but not nearly as strong.
So before starting a project with carbon steel, you should carefully consider the grade you select. It can make a big difference in the end result’s success. Reviewing these six questions beforehand can help in making your choice:

1. Will the carbon steel be machined?
Machining is a process where the parts and shapes are cut from the metal. Because lower carbon grades are relatively softer steel, they are more easily and efficiently machined. A high carbon grade can be used, provided the alloy’s chemical composition includes sulfur which improves the steel’s machinability. Without sulfur, the hardness of high carbon steel will result in major wear of the cutting tools.

2. Will the carbon steel be welded?
In general, the same grades of lower carbon steel more suited for machining can be more easily welded as well. High carbon steels can be used, but often require additional treatments before and after welding. And in contrast to machining, the steels grades containing sulfur are not recommended for use in welding. The sulfur in these alloys will have a higher risk of developing cracks at the weld join.

3. Does the carbon steel need to be heat-treatable?
When it comes to heat, a good rule of thumb is 0.3. Steels with a carbon content of 0.3% or higher can be heat treated easily. This is due to the carbon itself, which helps the formation of martensite crystallization within the steel, reinforcing its hardness and strength. Grades of lower carbon steels lack the carbon necessary for martensite formation, making heat treatments unsuccessful.

4. Does the carbon steel need good formability?
Due to the wide margin of carbon percentages across grades, it can be difficult to say which grades might be more formable than others. The selected grade is often dependent on the shape: rolled sheet requires a much more ductile type of steel, but forming pieces such as angle and beam can involve a wider grade range. Overall, the more ductile carbon steels – meaning, lower carbon grades – are much easier to form.

5. Does the carbon steel need high corrosion resistance?
Because steel’s main element is iron, it is vulnerable to oxidation leading to corrosion. This is an accepted fact that when using any grade of carbon steel, it will develop a certain amount of rust. In applications where corrosion resistance is a high priority, it may be better to consider using another material such as stainless steel instead. To minimize corrosion of carbon steels, they can be coated to create a barrier between the metal and its environment. This can go from involved processes such as galvanization or plating the metal to simply applying a coat of paint.

6. How strong a carbon steel is needed?
The steel’s application is crucial to deciding the strength needed for your metal. High carbon steel is incredibly strong, but if intended to be used for making small parts such as nuts and bolts, your needs would be better served by low carbon steel’s machinability. But while low carbon steel is more formable, it would be worth the greater effort when making tools to use high carbon steel for its hardness and durability. While it may be tempting to select the hardest and strongest material available, its actual use should be an important factor in selecting the right carbon steel.