What metal is used to make bicycle gear cogs?

Bicycle gear cogs are commonly made from steel due to its strength and durability, which can withstand the stress of shifting and pedaling. Some higher-end cogs may be made from aluminum for a lighter weight, while others may use materials like titanium for increased performance and corrosion resistance. Additionally, certain cogs may be coated with materials like nickel or chrome to enhance durability and reduce wear.