Alloy steel (part 3)

Function

Niobium (Nb)

Niobium can refine the grains and reduce the overheating sensitivity and temper brittleness of steel, and increase strength, but the plasticity and toughness are reduced. Adding niobium to ordinary low-alloy steel can improve the resistance to atmospheric corrosion and corrosion resistance of hydrogen, nitrogen and ammonia at high temperatures. Niobium can improve welding performance. Adding niobium to austenitic stainless steel can prevent intergranular corrosion.

Cobalt (Co)     

Cobalt is a kind of rare precious metals and is mostly used in special steels and alloys, such as heat-strength steel and magnetic materials.

Copper (Cu)  

Copper can improve strength and toughness, especially atmospheric corrosion performance. This advantage is that it is prone to hot brittleness during hot working, and the plasticity is significantly reduced when the copper content exceeds 0.5%. When the copper content is less than 0.50%, it has no effect on weldability.

Aluminum (Al)

Aluminum is a commonly used deoxidizer in steel. Adding a small amount of aluminum to the steel can refine grains and improve impact toughness. Aluminum also has oxidation resistance and corrosion resistance. The combination of aluminum, chromium and silicon can significantly improve the high temperature and no peeling performance and high temperature corrosion resistance of steel. The shortcoming of aluminum is that it affects the hot working, welding and cutting properties of steel.

Boron (B)  

Adding a small amount of boron to the steel can improve the compactness, hot rolling properties and strength of the steel.    

Nitrogen (N)

Nitrogen can improve the strength, low temperature toughness, weldability and aging sensitivity of steel.

Rare earth  

Adding rare earths to steel can change the composition, shape, distribution and properties of inclusions in steel, thereby improving various properties of steel, such as toughness, weldability and cold workability. For example, adding rare earth to ploughshare steel can improve wear resistance.     

Note: 

1. The prefix "G" means carbon steel and alloy steel, and "H" means steel with hardenability requirements.

2. a≤0.10%, b＝0.10%～0.20%, c＝0.15%～0.30%, d＝0.20%～0.40%, e＝0.30%～0.60%

3. AISI grades with the prefix E are electric furnace steels.

4. The chemical composition of H steel with hardenability requirements is basically taken from ASTM A304, and the chemical composition of carbon steel and alloy steel with prefix G is basically taken from ASTM A29. The chemical composition specified in A29. The chemical composition specified in A29 is used for the following technical conditions: 

Hot rolled alloy steel: ASTM A322-2007, A434-2006, A739-2006

Cold finished alloy steel: A331-2000, A434-2006, A696-2006

5. The chemical composition is only applicable to structural profiles, plates, strips and welded pipes.

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