Chemical composition of seamless carbon steel pipe

Posted by zora li on October 12th, 2022

Seamless carbon steel pipes can be divided into low carbon steel, medium carbon steel and high carbon steel according to their chemical composition (ie carbon content). Mild steel, also known as mild steel, contains 0.10% to 0.30% carbon. Mild steel is acceptable in various processes such as forging, welding and cutting. Commonly used in the manufacture of chains, rivets, bolts, shafts, etc.

Medium carbon steel refers to carbon steel with a carbon content of 0.25% to 0.60%. There are killed steel, semi-killed steel, boiling steel and other products. In addition to carbon, it may also contain a small amount of manganese (0.70% to 1.20%). In addition to being used as a building material, it is also widely used in the manufacture of various mechanical parts. High carbon steels are commonly referred to as tool steels and contain 0.60% to 1.70% carbon. Such as drills, taps, reamers, etc. are all made of steel with a carbon content of 0.90% to 1.00%.

The role and element introduction of various components of steel:
1. Carbon, silicon, manganese, sulfur and phosphorus are the main impurity elements in pig iron and carbon steel, commonly known as "five elements". Because they have a great influence on the properties of the steel, their determination is required for general analysis.

2. Chromium (Cr): In structural steel and chromium, chromium can significantly improve strength, hardness and wear resistance, but at the same time reduce plasticity and toughness. Chromium can improve the oxidation resistance and corrosion resistance of steel, so it is an important alloying element of stainless steel and heat-resistant steel.

3. (Ni): Nickel can increase the strength of steel while maintaining good ductility and toughness. Nickel has high corrosion resistance to acids and bases, rust and heat resistance at high temperatures. However, since nickel is a scarce resource, other alloying elements should be used instead of nickel-chromium steel.

4. Molybdenum (Mo): Molybdenum can refine the grains of steel, improve hardenability and thermal strength, and maintain sufficient strength and creep resistance at high temperatures (long-term stress at high temperature, deformation, weighing creep) . The addition of molybdenum to structural steel improves mechanical properties. It can also suppress the brittleness of alloy steel caused by fire. The redness of tool steel can be improved.

5. Titanium (Ti): Titanium is a strong deoxidizer in steel. It can make the internal structure of the steel dense, refine the grain force; reduce the aging sensitivity and cold brittleness. Improve welding performance. Intergranular corrosion can be avoided by adding appropriate titanium to Cr 18 Ni 9 austenitic stainless steels.

6. Vanadium (V): Vanadium is an excellent deoxidizer for steel. Adding 0.5% vanadium to steel can refine the grains of the structure and improve the strength and toughness. Carbides formed from vanadium and carbon improve hydrogen corrosion resistance at high temperature and pressure.

7. Tungsten (W): Tungsten has a high melting point and a large specific gravity. It is an alloying element of noble earth. Tungsten and carbon form tungsten carbide with high hardness and wear resistance. The addition of tungsten to tool steel can significantly improve the red hardness and hot strength of cutting tools and forging dies.

8. Niobium (Nb): Niobium can refine grains, reduce overheating sensitivity and temper brittleness of steel, and increase strength, but reduce plasticity and toughness. Adding bismuth to ordinary low-alloy steel can improve the corrosion resistance of atmospheric corrosion and hydrogen, nitrogen and ammonia at high temperature. Niobium improves weldability. Twisting in austenitic stainless steel prevents intergranular corrosion.

9. (Cobalt): Cobalt is rare and precious and is used in special steels and alloys, such as heat-resistant steels and magnetic materials.

10. (Cu): Copper can improve strength and toughness, especially atmospheric corrosion. The disadvantage is that it is easy to produce hot brittleness during hot working, and the copper content is significantly reduced by more than 0.5%. When the copper content is less than 0.50%, there is no effect on the weldability.

11. (Al): Aluminum is a deoxidizer commonly used in steel. A small amount of aluminum is added to the steel to refine the grains and improve the impact toughness, such as 08Al steel for deep drawing sheets. Aluminum is also resistant to oxidation and corrosion. Aluminum combines with chromium and silicon to significantly improve the high temperature and corrosion resistance of steel. The disadvantage of aluminum is that it affects the hot workability, weldability and machinability of steel.

12. Boron (B): Adding a trace amount of boron to steel can improve the compactness and hot rolling properties of steel and increase the strength.

13. Nitrogen (N): Nitrogen can increase the strength, low temperature toughness and weldability of steel, and increase aging sensitivity.

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