Carbon steel is an iron-carbon alloy with a carbon content of 0.0218% to 2.11%. Generally also contains a small amount of silicon, manganese, sulfur, and phosphorus. The higher the carbon content, the greater the hardness and strength, but the lower the plasticity. According to the different carbon content, it can be divided into three types, namely low carbon steel（WC≤ 0.25%）, medium carbon steel（WC:0.25%—0.6%）, and high carbon steel（WC>0.6%）. The most commonly used in investment casting are low carbon steel and medium carbon steel. It is used to manufacture mechanical parts with complex shapes and high mechanical properties， which are difficult to be formed by forging and other methods.