Alloy steel pipe with different diameter (reducer) characteristics of pipe material and the pipe fittings for this kind of steel is a kind of low carbon steel structure, alloy element content is less, generally below 3%, which is significantly higher than the same amount of carbon steel strength, good toughness and ductility, weldability and corrosion resistance good. In order to improve and improve the properties of steel, other alloy elements such as silicon, manganese, chromium, nickel, tungsten, vanadium and titanium are added on the basis of carbon steel. This kind of steel is called alloy steel (Alloy steel). Alloy steel has different properties according to different alloy elements, such as high wear resistance, corrosion resistance, low temperature resistance, high magnetic properties and other special properties. Alloy steel is divided into alloy structural steel, alloy tool steel and special performance steel by use.