What Does Rimmed Steel Mean?
Rimmed steel is a low-carbon steel. This steel contains an amount of iron oxide such that continuous generation of carbon monoxide during solidification is not inhibited. Rimmed steel is virtually free from voids, and is easily bendable and cleanable.
Most rimmed steels contain less than 0.1% carbon. Rimmed steel has an excellent, defect-free surface which gives it advantages over other types of steel.
Steel sheets and plates are produced from rimmed steel.
Corrosionpedia Explains Rimmed Steel
Rimmed steel is different from other steels in terms of chemical composition across the section and from top to bottom of an ingot. It requires partial deoxidization before casting. This deoxidization allows a rim, containing mostly iron, to form in the steel. The concentration of carbon, sulfur and phosphorus in rimmed steel is lower than average for an ingot in the outer rim and higher in the core of the rim. Fine gas bubbles form in the body of the ingot after solidification of the outer rim which help to protect solidification shrinkage. The rim's internal voids are removed during rolling and forging, but it remains in the clean outer rim. This clean surface enhances the quality of the steel surface.
Steels made with 0.15 percent carbon are rimmed steel. This steel is valued more for its easy workability than its strength and durability.
This steel is not as hard as other steels. Therefore, easily machinable or bendable products can be made of rimmed steel. Since it is easily rolled, cold-bent and cold-formed, it shows high aesthetic properties and low roughness. In hot-bending and other hot processes this steel can be problematic.