ANS:A - carbon and silicon should be low.

In a good rimming steel, carbon should be low but silicon should be high. Rimming steel, also known as capped steel, is a type of steel commonly used for making high-quality, defect-free products through processes like hot rolling and cold forming. One of the distinctive characteristics of rimming steel is its ability to form a layer of gas bubbles (usually carbon dioxide) on its surface during solidification. This layer helps prevent the steel from reacting with atmospheric oxygen, reducing the risk of surface defects such as rimming. Here's why low carbon and high silicon content are desirable in rimming steel:

1. Low Carbon: Low carbon content helps ensure that rimming steel does not form excessive amounts of carbon monoxide gas during solidification. This gas evolution contributes to the formation of the gas layer on the surface of the steel, which helps prevent surface defects. Excessively high carbon content can lead to the formation of trapped gases, resulting in defects like blowholes or piping.
2. High Silicon: High silicon content aids in deoxidizing the steel and promoting the formation of a stable layer of silica (SiO2) on the surface during solidification. This silica layer acts as a protective barrier against further oxidation and gas evolution, contributing to the rimming behavior of the steel. Additionally, silicon helps improve the fluidity and castability of the steel during processing.