There is no uniform definition and concept for special steel. It is generally considered that special steel refers to mold steel with special chemical composition (alloying), special process, special organization and performance, and special needs. Special steels have higher strength and toughness, physical properties, chemical properties, biocompatibility and process properties than ordinary steels.

     China and Japan, the European Union's definition of special steel is relatively close, the skd61 special steel is divided into three categories of high-quality carbon steel, alloy steel, high alloy steel (alloying elements greater than 10%), of which alloy steel and high alloy steel account for special steel 70% of production. Main steel grades, special carbon structural steel, carbon tool steel, skh-9 carbon spring steel, alloy spring steel, alloy structural steel, ball bearing steel, alloy tool steel, high alloy tool steel, high speed tool steel, stainless steel, Heat resistant steel, as well as high temperature alloys, precision alloys, electrothermal alloys, etc. At present, there are nearly 2,000 special steel grades and about 50,000 varieties in the world. In addition to a wide variety of skh-59 special steels, the specifications also show different characteristics from ordinary steel. In addition to plates, tubes, wires, belts, rods and profiles, there are composites, surface alloys, surface treatments, precision forgings, precision castings, powder metallurgy products, etc.