Calorizing
Calorizing is a surface modification process to diffuse aluminum into steel pipes. The purpose of calorizing process is to protect the base metal against severe oxidation and corrosion caused by the high temperature in the furnace or harsh environment.
When being heated up to 1,000oC, a heat resistant aluminum-iron alloy (known as a calorized layer) will be formed over the surface of the base metal (for the case of Calorized Lance Pipe product in Daiwa Lance, mild steel is used as the base metal).
At high temperature, calorized layer continues to change its properties and forms an aluminum oxide film over its original surface with a melting point at 2,050 oC. As can be seen from the diagram below, the aluminum oxide film here is the key to building a much stronger protection against the fiercely burning flame than the mere mild steel structure commonly used in the steel mills.
Nowadays, calorizing process is not only applied in the steel pipes, but it is also applied in other steel products such as steel plates, stainless steels, carbon steels, cast irons, rollers, etc.