Boiling steel, killed steel and semi-killed steel
Boiling steel, killed steel and semi-killed steel
Steel ingots can be divided into 3 types, namely boiling steel, killed steel and semi-killed steel according to the degree of deoxidation of molten steel.
Boiling steel is steel that has not been deoxidized or is not sufficiently deoxidized. After the molten steel is injected into the ingot mold, as the temperature decreases, the carbon and oxygen in the molten steel react, and a large amount of carbon monoxide gas is discharged, resulting in a boiling phenomenon, so it is called boiling steel. The rimmed steel ingot does not produce concentrated shrinkage cavities, so the cutting rate of the steel ingot is about 5% to 8% lower than that of killed steel, but the segregation of rimmed steel is large and the composition is uneven.
Deoxidation is sufficient before pouring, the molten steel is calm during pouring, and the steel without boiling is called killed steel. Its structure is dense, high strength, less segregation and uniform composition. Due to the formation of central shrinkage cavity and increase the cutting rate, the cost of killed steel is higher than that of boiling steel. Steels with higher requirements for various indexes such as mechanical properties and special requirements are cast into killed steel ingots.
The degree of deoxidation is between killed steel and boiling steel. Due to incomplete deoxidation, there is still slightly boiling steel during the casting process, which is called semi-killed steel. It has smaller shrinkage in the center than killed steel and lower head cutting rate; it has less segregation than boiling steel and has better mechanical properties.
