The mechanical properties test of carbon structural steel is carried out under natural cooling conditions after rolling.

Therefore, the actual grain size and structural state of the rolled steel have a direct impact on the mechanical performance indicators.

Taking Q235 steel bar as an example, the chemical composition stipulates that the carbon content is 0.14~0.22%. If it is slowly cooled to normal temperature after rolling, its structure is 16.8~26.4% pearlite and 83.2~73.2% ferrite.

If water is sprayed and cooled after rolling, the austenite will be supercooled to a low temperature of below 550°C, and its structure will be the product of continuous cooling - troostite (also called troostite) structure. Its strength and hardness are higher than troostite. Pearlite is higher, and the tensile strength can reach the level of Q275 steel.

Carbon structural steel uses water spray cooling to replace killed steel with boiling steel.