Effects of Alloying Elements on Steel Properties

Various problems often occur in the metal cutting process, and the analysis of material composition is inevitable.

There are many elements contained in steel. In addition to the main components of iron and carbon, it also contains a small amount of silicon, manganese, sulfur, phosphorus, oxygen, nitrogen and some alloying elements. Although the content of these alloying elements is small, it determines the quality of the steel. Product performance and processing performance have a great influence.

The following introduces some knowledge about the influence of alloying elements in steel, which may be helpful for analyzing the cause of the problem.

1. Carbon (C)

Occurs in all steels and is the basic hardening element. Generally, as the carbon content increases, the hardness of steel increases correspondingly, but its plasticity and toughness become worse.
The carbon content of low carbon steel is less than 0.25%, the carbon content of medium carbon steel is 0.25%-0.6%; the carbon content of high carbon steel is more than 0.6%. High-carbon steel is harder and stronger than low-carbon steel, and is often used to manufacture tools and mechanical parts that require high strength and wear resistance.
Mild steel, on the other hand, is more malleable and malleable, making it easier to form. Generally, low carbon steel needs to be carburized before quenching.

2. Manganese (Mn)

As one of the five major alloying elements, it increases the strength and hardenability of steel and increases the carbon permeability during carburizing. General steel contains 0.30-0.50% manganese. When more than 0.70% is added to carbon steel, it is considered "manganese steel". Compared with ordinary steel, it not only has sufficient toughness, but also has higher strength and hardness, which improves the hardenability of steel and improves the hot workability of steel.
For example, the yield point of 16Mn steel is 40% higher than that of A3, and the spring steel, tool steel and bearing steel produced by adding manganese have good heat treatment performance. High alloy steel with high manganese content (high manganese steel, 11-14% manganese) has good wear resistance. However, due to the work hardening phenomenon of high manganese steel, the tool is easy to wear.

3. Phosphorus (P)

Increases strength and hardness, but also sacrifices the ductility of steel. In general, phosphorus is a harmful element in steel, which increases the cold brittleness of steel, deteriorates welding performance, reduces plasticity, and deteriorates cold bending performance.
Therefore, it is usually required that the phosphorus content in steel is less than 0.045%, and the requirement for high-quality steel is even lower. On the other hand, low carbon steel contains high sulfur and phosphorus, which can make it easy to cut and break, which is beneficial to improve the machinability of steel.

4. Sulfur (S)

Sulfur is also a harmful element under normal circumstances. It causes hot brittleness of steel, reduces the ductility and toughness of steel, and causes cracks during forging and rolling.
Sulfur is also detrimental to welding performance and reduces corrosion resistance. Therefore, the sulfur content is usually required to be less than 0.055%, and the high-quality steel requires less than 0.040%. Adding 0.08-0.20% sulfur to the steel can improve the machinability, usually called free-cutting steel.

5. Silicon (Si)

Silicon is added as a reducing agent and deoxidizer in the steelmaking process, so the killed steel contains 0.15-0.30% silicon. If the silicon content in steel exceeds 0.50-0.60%, silicon is considered an alloying element. Silicon can significantly improve the elastic limit, yield point and tensile strength of steel, so it is widely used as spring steel.
Adding 1.0-1.2% silicon to quenched and tempered structural steel can increase the strength by 15-20%. Combining silicon with molybdenum, tungsten, chromium, etc. can improve corrosion resistance and oxidation resistance, and can be used to manufacture heat-resistant steel. Low-carbon steel containing 1-4% silicon has extremely high magnetic permeability. It is used in the electrical industry to make silicon steel sheets. The increase in silicon content will reduce the welding performance of steel