What’s different killed steel and Rimmed steel!!!

Killed steel is steel that has been completely deoxidized by the addition of an agent before casting such that there is practically no evolution of gas during solidification. It is characterized by a high degree of chemical homogeneity and freedom from gas porosities.

Semi-killed steel is mostly deoxidized steel, but the carbon monoxide leaves blowhole type porosity distributed throughout the ingot. The porosity eliminates the pipe found in killed steel and increases the yield to approximately 90% by weight. Semi-killed steel is commonly used for structural steel with a carbon content between 0.15 and 0.25% carbon, because it is rolled, which closes the porosity.

Rimmed steel, also known as drawing quality steel, has little to no deoxidizing agent added to it during casting which causes carbon monoxide to evolve rapidly from the ingot. This causes small blow holes in the surface that are later closed up in the hot rolling process. Most rimmed steel has a carbon content below 0.25%, a manganese content below 0.6%, and is not alloyed with aluminum, silicon, and titanium.Due to the non-uniformity of alloying elements it is not recommended for hot-working applications.