There is no unified definition and concept for special steel, and it is generally believed that special steel refers to steel with special chemical composition (alloying), produced using special processes, possessing special structures and properties, and being able to meet special needs. Common special steels include carbon steel, high-quality structural steel, alloy steel, etc.

There is no unified concept and definition of special steel in various countries around the world, making it more difficult to draw a clear boundary between special steel and ordinary steel. It is generally believed that special steel is a type of steel with special composition, special production process, special structure and properties that can meet special needs, that is, all steel types except ordinary steel belong to special steel. Compared with ordinary steel, special steel has better strength and toughness, physical properties, chemical properties, biocompatibility, and process performance.

The concept of special steel in Japan includes alloy steel, medium to high carbon steel, and high-strength steel with tensile strength greater than 590MPa. Germany and France are similar to Japan. Special steels in the United States include stainless steel plus alloy steel (including carbon steel, hollow steel, and high-strength low alloy steel), except for the carbon manganese series in alloy steel. The meaning of British special steel is alloy steel. The former Soviet Union did not have a clear division of the category of special steel. Chinese special steel includes high-quality carbon structural steel, alloy structural steel, carbon and alloy tool steel, spring steel, bearing steel, high-speed tool steel, heat-resistant steel and stainless steel, high-temperature alloy and precision alloy.