Low carbon steel is steel with low carbon. High carbon steel is steel with high carbon

MS stands for mild steel. This is steel than only has a small about of carbon. It's strong, but not easily tempered. CS stands for carbon steel. In carbon steel, the main alloying element is carbon.

Carbon steel is an iron alloy with less than 2% carbon, no chromium, and contains copper and magnesium not more than 0.6%

Stainless steel is an iron alloy with less than 2% carbon and it contains chromium and it's resistive to corrosion

Yes, D-2 is a high carbon tool steel. D-2 tool steel has about 1.55% carbon in its chemical composition.

Any grade of tool steel with more than 0.5% carbon is generally considered to be a high carbon tool steel. Tool steel needs to have a minimum of .4% carbon to harden properly.

For more information on tool steels, their properties and alloying element, please see the related link.

High carbon steel is a metal.The addition of carbon makes the steel harder after heat treatment.