carbon tool steel
1. The steel number is prefixed with "t" to avoid mixing with other steel types.
2. The number in the steel number indicates the carbon content, expressed in thousandths of the average carbon content. For example, "t8" means the average carbon content is 0.8%.
3. For those with higher manganese content, "mn" is marked at the end of the steel number, such as "t8mn".
4. The phosphorus and sulfur content of advanced high-quality carbon tool steel is lower than that of general high-quality carbon tool steel. The letter "a" is added at the end of the steel number to show the difference, such as "t8mna".
Free cutting steel
1. The steel number is prefixed with "y" to distinguish it from high-quality carbon structural steel.
2. The number after the letter "y" indicates the carbon content, expressed in ten-thousandths of the average carbon content. For example, the free-cutting steel with an average carbon content of 0.3% has a steel grade of "y30".
3. For those with higher manganese content, "mn" is also marked after the steel number, such as "y40mn".
