23Mn (Q345B) steel pipe is a low-alloy high-strength structural steel with carbon content of 0.1%-0.25%, and main alloying elements such as manganese, silicon, vanadium, niobium and titanium are added. Its total alloy content is less than 3%. Grade A and B steels are usually called 16Mn16mn steel pipes.

Chemical composition of 23Mn steel pipe:
C：0.12~0.20; Mn:1.20~1.60; Si:0.20~0.88; Tensile strength: 486~660 N/mm2; Yield strength: 275~345 N/mm2; Elongation: 21%. The specific value should be based on the thickness or diameter of steel, and the thickness or diameter of steel corresponding to the above data is 16~100mm.

According to the strength, it can be divided into four levels: 300, 350, 400 and 450MPa. There are mainly Q295, Q345, Q390, Q420 and Q460. : "Q" is the Chinese phonetic alphabet of the yielding "Qu" character. The following number is the minimum yield point (σs) value of the grade, and the following symbols are divided into A, B, C, D, etc. according to the content of impurity elements (sulfur and phosphorus) in the steel from high to low with the change of carbon and manganese elements.

Usage of 23Mn steel pipe:
The special steel grade for bridges is 16Mnq, for automobile girders 23MnL and for pressure vessels 23MnR. The formula for calculating the weight of 23Mn steel pipe is [(outer diameter-wall thickness) * wall thickness ]*0.04066=kg/ m (weight per meter).
This kind of steel depends on adjusting the carbon (C) content to improve the mechanical properties of steel. Therefore, according to the carbon content, this kind of steel can be divided into:
High carbon steel—carbon content is generally greater than 0.60%. This kind of steel is generally not used to make steel pipes.
Low carbon steel—carbon content is generally less than 0.69%, such as 10, 20 steel, etc.
Medium carbon steel—carbon content is generally between 0.25 ~ 0.98%.

Before spraying (castwing) treatment, the grease and scale on the surface of steel pipe are removed by cleaning, and the pipe body is preheated to 40-60℃ by heating furnace to keep the pipe surface dry. During spraying (casting) treatment, because the steel pipe surface does not contain grease and other dirt, the derusting effect can be enhanced, and the dry steel pipe surface is also beneficial to the separation of steel shot, steel sand, rust and scale, which makes the derusted steel pipe surface cleaner.