The chemical composition of steel is important. The higher the alloy composition of the steel, the more difficult it is to machine. When the carbon content increases, the metal cutting performance decreases.
The structure of the steel is also very important to the metal cutting performance. Different structures include: forged, cast, extruded, rolled and machined. Forgings and castings have surfaces that are very difficult to machine.
Hardness is an important factor affecting metal cutting performance. The general rule is that the harder the steel, the harder it is to machine. High-speed steel (HSS) can be used to machine materials with a hardness of up to 330-400 HB; high-speed steel + titanium nitride (TiN) coating can be used to machine materials with a hardness of up to 45 HRC; and for materials with a hardness of 65-70 HRC , cemented carbide, ceramics, cermets and cubic boron nitride (CBN) must be used.
Non-metallic inclusions generally have an adverse effect on tool life. For example, Al2O3 (alumina), which is a pure ceramic, is highly abrasive.
The last one is residual stress, which can cause metal cutting performance problems. A stress relief operation is often recommended after rough machining.