Carbon Element in Machining
Carbon is a chemical element designated by the symbol C; moreover, carbon is a critical factor in several machining topics.
Although it is added in small doses of 0.03% up to 3% (Usually between 0.1 -1%) to metals, it is the most influential element in many materials used in machine shops.
The machinability is very sensitive to the amount of carbon since carbon directly influences the hardness and ductility of steel. The “Sweet Spot” that yields the highest machinability rating is around 0.2%. Steel with less than 0.15% Carbon is very soft; thus, it is almost impossible to break the chips, and BUE is easily formed on the cutting edge. Above 0.3%, the material becomes harder, and therefore wear is formed faster on the cutting edge.
When the carbon content is increased to 2-4%, cast iron is formed. This small increase in carbon amount creates a material with completely different properties. The material is brittle at room temperature but has a low melting point and thus has excellent castability. Most cast Iron materials are very brittle, lack the steel’s ductility, and therefore have a lower quality of mechanical properties. On the other hand, small chips form very easily, making them behave like free-cut steel with excellent machinability.
The carbon content must be kept at around 0.03% to form stainless steel with excellent corrosion resistance (Like the 300 series); because of this, most austenitic stainless steel alloys are very soft (Learn more about the implications). Martensitic stainless steel can contain up to 1% carbon, making it stronger at the expense of corrosion resistance.
PCD stands for “Poly Crystalline Diamond,” the hardest available cutting material. PCD is a synthetic diamond produced by sintering diamond particles and a metal binder at a high temperature and pressure.
The diamond is a structure of Carbon atoms; thus, carbon is the primary material in a PCD cutting tool.