Steels can be categorized as unalloyed, low-alloyed and high-alloyed, all of which affect the machining recommendations for turning.
Turning unalloyed steel
Material Classification: P1.1
Unalloyed steel has a carbon content of up to 0.55%. Low-carbon steels (carbon content < 0.25%) require special attention, due to the difficult chip breaking and the tendency to smear (built-up edge).
In order to break and steer the chip, aim for the highest feed possible. A wiper insert is highly recommended.
Use high cutting speeds to avoid built-up edge on the insert, which can negatively influence the surface. Sharp edges and light cutting geometries will decrease the smearing tendencies and prevent edge deterioration.
Turning low-alloyed steel
Material Classification: P2.x
The machinability for low-alloyed steels is dependent on alloy content and the heat treatment (hardness). For all materials in this group, the most common wear mechanisms are crater and flank wear. For hardened materials, plastic deformation is also a common wear mechanism due to higher heat in the cutting zone.
For low-alloyed steels in a non-hardened condition, the first choice is the steel series of grades and geometries. In hardened materials, it is beneficial to use a harder grade (cast iron grades, ceramics and CBN).
Turning high-alloyed steel
Material Classification: P3.x
High-alloyed steels include carbon steels with a total alloy content over 5%. The group includes both soft and hardened materials. Machinability decreases at higher alloy contents and hardness.
As for the low-alloyed steels, the first choice is the steel grades and geometries.
Steels with more than 5% alloying elements, and with hardness over 450 HB, require extra demands on plastic deformation resistance and edge strength. Consider using a harder grade (cast iron grades, ceramics and CBN).
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