The terms "rimmed", "semi-killed" and "killed" steel refer to the degree of what?

The terms "rimmed", "semi-killed", and "killed" steel specifically refer to the degree of deoxidation that the steel undergoes during the molten phase before it is solidified. These processes significantly influence the characteristics and quality of the steel produced.

Rimmed steel has not been fully deoxidized, allowing some gas pockets to form during solidification, which can affect the mechanical properties and appearance of the steel. Semi-killed steel has some degree of deoxidation, improving the quality and homogeneity of the steel compared to rimmed steel. Killed steel is fully deoxidized, which eliminates gas bubbles and results in a more uniform structure, enhancing the steel's overall mechanical properties and reliability.

Understanding these terms is important as they relate to the manufacturing process and impact the final properties of the steel, including its machinability, toughness, and weldability, but they primarily arise from differences in deoxidation practices.