Mild steel: Definitions, characteristics and application cases

Mild steel is steel made from the combination of iron and carbon. Due to the presence of iron, it has good magnetic properties. Mild steel is not alloy steel. Due to the presence of more carbon, its chemical composition is very different from other elements or other steels, and because mild steel has a good surface quality, you can increase its surface hardness in different ways. Let's learn more about this material.

What is mild steel?

The main component of steel is iron. Depending on the carbon content, there are low carbon steel (also called low carbon steel or ordinary carbon steel), medium carbon steel and high carbon steel.

Mild steel is a type of steel containing 0.05% to 0.25% carbon. Due to its plasticity and malleability, the material is easy to form and process. Low carbon steel parts are generally very suitable for stamping and forging. Mild steel is widely used in tools, auto body parts, construction and infrastructure.

How is mild steel made?

The manufacturing process of mild steel is similar to that of other carbon steels. These processes have been changing over time and are currently more efficient and cheaper than before. In modern manufacturing processes, there are three main steps involved in producing mild steel from pure iron or iron ore.

1. Primary steelmaking

In this process, iron is mixed with coal and lime and heated in a blast furnace. Modern primary steelmaking uses modern furnaces, such as basic oxygen furnaces or electric arc furnaces. Generally, the steel parts that come out of EAF are of high quality.

2. Secondary steelmaking

The purpose of secondary steelmaking is mainly to reduce the carbon content to the desired degree and to add other alloying elements to improve the properties of the steel. This step is mainly to control and monitor the heat treatment and cooling of the furnace.

3. Casting and primary molding

As soon as the steel in the furnace reaches the specified carbon content and the mechanical properties are improved to a certain extent, the steel is poured into the mold, which is called casting, and some people say cast iron, which is not right. During this process, the liquid steel will cure and form various geometries. The cast steel of these crystal structures will then be cut into smaller parts.

Cast steel has many defects. A primary forming process called hot rolling is used. After hot rolling, the steel gains more strength, ductility, weldability, etc.

4. Secondary molding

In general, there is a secondary forming process, such as CNC machining, cold rolling, powder coating, surface hardening or electroplating, to further improve the mechanical and chemical properties or aesthetic effects of low carbon steel parts. In these processes, metallic coatings such as zinc coatings or any other type of carbon steel are applied appropriately.

Mechanical properties of mild steel

Mild steel has a lower carbon content than other carbon steels. Mild steel has a carbon content of only 0.25%.

Low carbon steel has good impact strength, good ductility and weldability, and the possibility of cold forming. With these properties, CNC machining of mild steel is easier than CNC machining of other types of steel.

The main disadvantage of mild steel is its relatively low tensile strength, which means it is more likely to break than other types of steel.

Fortunately, a heat treatment process called carburizing can be used to improve the tensile strength. Carburizing is the surface hardening process of heating mild steel to a certain temperature and then cooling the steel so that the steel is hardened on the surface while keeping the core soft and malleable.

Application of low carbon steel

Mild steel is widely used. Typical applications include common hardware tools, cookware, medical devices, machinery, construction, infrastructure, etc.

1. Buildings and infrastructure

The low carbon steel building frame in the construction project has good tensile strength. It meets the requirements of earthquake resistance and wind resistance, can not be destroyed by bugs, and low carbon steel has corrosion resistance and flame retardant, which is very suitable for use in construction.

2. Machinery

Low carbon steel's high strength, ductility and hardness make it the first choice for machine parts manufacturing. Due to its low carbon content, this steel can be processed, cut, pressed, and formed without breaking.

3. Cooking utensils

Due to its very low carbon content, mild steel does not rust, keeping cookware clean and sharp for a long time. Low carbon steel is more heat resistant than other materials, can be used as a non-stick material, and is healthier than aluminum cookware.

4. Plumbing

Because low carbon steel is extremely malleable, pipes made of low carbon steel are very popular when people make various pipes and poles. Mild steel can be used as a food safety material, so it is ideal for transporting water, beverages and natural gas in steel pipes. In addition, due to its low carbon content, pipes used outdoors will not rust in harsh environments and cold weather. Compared with plastic pipes, low-carbon steel pipes are more environmentally friendly and have a longer service life. It can also be cut into rectangles.

Mild steel use cases

AISI 316L has a very low carbon content, only 0.03%, and is a typical mild steel that is very commonly used. In the course of dealing with various companies over the years, we have found that medical instrument companies love to use this material. To prototype or customize small batch steel parts, CNC machining is usually the first choice. CNC machined 316L steel parts usually do not require surface treatment or any heat treatment process. CNC mild steel parts can be used as final products, not just prototypes. Other common products such as fishing tools are also heavily used in AISI 316L.

Low carbon steel CNC machining and small batch production

Why do people often complain that steel is difficult to CNC machining? The machinability of steel is mainly determined by its carbon content. High carbon steels are difficult to process mainly because of their unyielding properties coupled with internal stresses.

However, mild steels are also difficult to process because they are too soft. Chips that appear during CNC machining tend to stick and build up, which can lead to longer cleanup times and potentially damage to the tool. The ideal carbon content for easy processing is about 0.20%.

For example, some mild carbon steels are too soft and can cause chip accumulation problems. One method we sometimes use is to first surface harden the mild steel. The low carbon steel is hardened on the outside, the inside of the steel remains soft, thus solving the chip accumulation problem, and because the core of the steel is still soft, when the external stress generated during the processing process is applied to the material, the softness or ductility of the low carbon steel will still absorb the stress, so that the part cannot break.

For the short-term production of mild steel parts, CNC machining is the only way. The low carbon steel material used in CNC machining is what we call "block material", which is of good quality and reasonable price. Compared to casting and molding, CNC machining is very fast. For casting and molding, the time and cost of making molds are very large. For short production or low volume production of mild steel parts, the total cost is usually much cheaper than casting and molding, because you do not need to make a mold.

Low carbon steel long-term production: casting and molding

If you want to produce large quantities of mild steel parts, the common method is called casting. Metal injection molding (MIM) is similar to plastic injection molding in that liquid metal is injected into a mold, and the liquid metal will cure in the mold. After the steel parts are removed from the mold, they are roughly formed. There are some post-processing processes that can further improve the beauty of the molded part.

As with plastic injection molding, when designing MMI molds and parts, designers must consider issues such as die Angle, release, shrinkage, tolerance, and so on.

conclusion

Mild steel has a carbon content of less than 0.25. Due to its properties, mild steel is widely used in almost all industries. The common method of making prototype or small batch production grade parts of low carbon steel is through CNC machining. For high volume products, metal injection molding and casting is a more feasible way.