Alloy steel pipes are mainly made by selecting high-quality carbon steel, alloy structural steel and stainless heat-resistant steel as materials, and are manufactured by hot rolling, including extrusion and expansion, or cold rolling. Alloy steel pipes are mainly used for power generation in power plants, nuclear power generation, and high-pressure boiler transportation. The alloy steel pipes used in boilers mainly include seamless steel pipes and welded steel pipes. Seamless steel pipes are divided into hot-rolled seamless steel pipes and cold-rolled seamless steel pipes according to their manufacturing methods. Usually we can see different types of alloy steel, and the elements and symbols in them all have certain meanings.

(1) The first two digits of the steel number refer to the carbon content of the steel, and the method of expression is to say how many parts of the average carbon content is, such as 20Cr.

(2) Except for individual microalloying elements in steel, the main alloying elements are generally expressed in a few percent. When the average alloy content is less than 1.5%, the content is generally not indicated in the steel number, and only the element symbol is used to indicate it. Sometimes in order to prevent confusion, the number "1" can also be marked after the element symbol, such as steel grades "12CMoV" and "12Cr1MoV". The first steel number represents 0.4%-0.6% chromium content, and the second represents 0.9%~ 1.2%, the rest of the ingredients are the same.