Free Machining - Steels

Steels

The carbon content of steel greatly affects its machinability. High-carbon steels are difficult to machine because they are strong and because they may contain carbides that abrade the cutting tool. On the other end of the spectrum, low-carbon steels are troublesome because they are too soft. Low-carbon steels are "gummy" and stick to the cutting tool, resulting in a built up edge that shortens tool life. Therefore, steel has the best machinability with medium amounts of carbon, about 0.20%.

Chromium, molybdenum and other alloying metals are often added to steel to improve its strength. However, most of these metals also decrease machinability.

Inclusions in steel, especially oxides, may abrade the cutting tool. Machinable steel should be free of these oxides.