What Does Killed Steel Mean?
When steel has been fully deoxidized before casting and no gas was evolved during solidification, the resultant steel is known as killed steel. This steel is characterized by a high degree of chemical homogeneity. It is free from gas porosity, which makes these steels more suitable for critical components and for applications involving heat treatment. It is combined with an agent like casting before use.
This steel is called "killed" because it quietly solidifies in the mold and no gas evolves. The identification mark of this steel is "K".
Corrosionpedia Explains Killed Steel
Killed steel is steel treated with a strong deoxidizing agent. This treatment is necessary to reduce the oxygen content so that no reaction occurs between carbon and oxygen during solidification. This steel has more uniform chemical composition and properties than other steel.
Aluminum, ferrosilicon and manganese are common deoxidizing agents used in solidification. Aluminums form aluminum oxide when reacting with the dissolved gases. It helps to form pin grain boundaries. These boundaries prevent grain growth during heat treatments. Killed steel is harder than rimmed steel for steels of the similar grade. Killed steels also suffer from deep pipe shrinkage defects.
Killed steels are used in many steel treatments, such as:
- Alloy steels
- Forging steels
- Carburizing steels
A variety of killed steel is known as semi-killed steel. Semi-killed steel is an intermediate steelbetween killed and rimmed steels. It also has variable degrees of uniformity in composition. In this steel more gas is evolved than killed steel, but lower than rimmed or capped steel.
All alloy steels are typically killed steels and this steel contains carbon equal or greater than 0.30 percent weight.