Influence of carbon and silicon on the properties of seamless steel tubes

The effects of carbon and silicon in the chemical elements of seamless tubes on the properties of steel are as follows:

1. Carbon (C): Carbon is the main element next to iron in steel for seamless steel tubes. As the carbon content increases, the strength of the steel increases, while plasticity and toughness, especially low-temperature impact toughness, decrease, while weldability, Corrosion resistance and cold bending performance are significantly reduced.

Therefore, the carbon content of steel for seamless steel tube structure should generally not exceed 0.22%, and for welded structures should be less than 0.2%. High carbon content will also reduce the atmospheric corrosion resistance of steel, and the high carbon steel in the open stockyard is easy to rust; in addition, carbon can increase the cold brittleness and aging sensitivity of steel.

2. Silicon (Si): The raw material of seamless steel tube is added with silicon as a reducing agent and a strong 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 becomes an alloying element. An appropriate amount of silicon can improve the strength of steel without obvious adverse effects on plasticity, toughness, cold bending performance and weldability. Silicon can significantly improve the elastic limit, yield point and tensile strength of steel, so it is widely used to make 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, and is used in the electrical industry to make silicon steel sheets. When the silicon content is too large, the plasticity, toughness, corrosion resistance and weldability of the steel will be reduced.