When you embark on your next metal manufacturing project, it is important to consider which type of steel to use. Choosing the right type of steel for a metalworking project is a crucial and rarely mentioned decision. There are many different types of steel, the two most common are stainless steel and carbon steel. Although these two types look the same, they differ in some key nuances. To help you make a decision, here is a further introduction to the difference in characteristics between carbon steel and stainless steel.
Basic knowledge of carbon steel and stainless steel materials
Steel is mainly composed of iron and about 2% carbon. If the carbon content exceeds 2%, it is called cast iron. Although cast iron does have useful applications, we usually don’t use it in metal manufacturing. When the carbon content is less than 1%, the resulting metal is carbon steel. This type of steel usually contains trace amounts of manganese, phosphorus, sulfur, silicon and phosphorus. The lower carbon content makes the steel easier to machine, has better ductility and is easier to weld.
Stainless steel is mainly carbon steel with a large amount of chromium. The chromium content is usually about 10.5%. Chromium has a strong affinity for oxygen, which makes stainless steel have ideal corrosion resistance. Ordinary carbon steel combines with oxygen, causing rust. On the other hand, in stainless steel, chromium oxide compounds are bonded to the surface, thereby preventing rust. In addition, when you scratch its surface, the newly exposed chromium will create more rust-proof oxygen bonds.
Factors to consider when choosing stainless steel and carbon steel
Perhaps this is obvious, but the start point is, what does the application need? Strength? Attractive appearance? Or just the lowest cost? Depending on what you want to achieve, there are some key factors to consider here.
- Finishing/appearance/corrosion resistance
Next, let’s compare carbon and stainless steel one by one.
Even for casual observers, carbon steel and stainless steel have some distinctive characteristics. Normally, carbon steel appears dull and dull. On the other hand, stainless steel seems to be more shiny and comes in various grades, which can increase the chromium in the alloy until the surface of the steel reflects like a mirror.
Although both can be sanded and polished to have a bright, shiny appearance, carbon steel needs to be coated with a coat of varnish quite quickly after the polishing process to avoid tarnishing and eventually rusting.
In the metal manufacturing process, carbon steel usually requires coating to prevent rust. Powder coatings and paints are both popular choices. Both require surface treatment, especially the paint may need regular finishing.
Unless used in a strong chlorine atmosphere, stainless steel does not require this protection. Swimming pools and sea water are environments that can cause chlorine corrosion. If this happens to a product, it is best to choose a stainless steel with higher chlorine resistance, such as 316.
Ductility essentially refers to how easily a metal can stretch or bend without breaking. Bending operations (such as press brakes) usually require metal with great ductility. We usually bend ductile metals with small radii, although they may crack when bent into sharp angles.
Low carbon steel has excellent ductility. In stainless steel, ductility largely depends on the composition. In addition to chromium, austenitic stainless steel also contains a large amount of nickel and has good ductility. The most common of these is level 304.
Stainless steels with higher carbon content (such as 420 and 440 grades) have very low ductility. As a result, they are rarely used in manufacturing.
As a rule, strength is inversely proportional to ductility. Thus stronger metals are harder to form. Any grade of stainless steel is stronger than plain low carbon steels.
As one of the most widely used steel metals, carbon steel is highly malleable and comes in a range of carbon content levels. Low-carbon steel is popular for its strength and low-cost, while high-carbon steel finds more niche opportunities in due to lighter weight and ability to hold a finely sharpened edge.
As the carbon content increases, the welding of ordinary carbon steel becomes more and more difficult. When the carbon content exceeds 1%, preheating is usually required to ensure a good welding effect.
Stainless steel is difficult to weld because its thermal conductivity is lower than that of ordinary carbon steel. In other words, considering the difference in electrical conductivity, the welding effect of austenitic stainless steel is very good. A particularly useful feature of austenitic stainless steel is that it does not harden when heated. This means that during welding, the heat-affected zone will not harden. However, welding increases the susceptibility to corrosion.
Cost is an important consideration for any project. Although the cost of different grades varies, stainless steel is generally more expensive than carbon steel. However, you should consider some mitigating factors. Because stainless steel is stronger, you can use less. In addition, because it is relatively more corrosion resistant, you do not need to pay for painting. As a result, considering the manufacturing time you may use, the cost difference will be significantly reduced.
In short, what is the difference between stainless steel and carbon steel?
Stainless steel has a high chromium content and can be used as a protective layer against corrosion and rust.
Carbon steel has a high carbon content and will corrode and rust quickly when exposed to moisture.
Stainless steel is more attractive to the eyes and can be used to decorate products.
Carbon steel is stronger and more durable than stainless steel.
What we can offer stainless steel and carbon steel in metal fabrication
While stainless steel and carbon steel are different, one is not necessarily superior to the other as context matters. Each type of steel has its advantages and disadvantages which should help you match the steel to the job requirement. Furthermore, we also can offer you these secondary finishing services such as black oxide, powder coating, plating chrome, nickel finishing, and more processes. At SANS Machining, we are ready to simplify this decision making so contact us now with any inquiry on your next metal fabrication project.