The machinability of steel differs depending on alloying elements, heat treatments and manufacturing processes (forged, cast etc.)
Steels can be categorized as unalloyed, low alloyed steel and high alloyed steel, all of which affect the machining recommendations for turning.
Unalloyed steel
Material Classification: P1.1
ap > re
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).
The machining properties for unalloyed steels with a higher carbon content
are similar to those for low alloyed steels.
Chip control:
To control the chip flow, use a cutting depth greater than the size of the nose
radius. Choose an entering angle as close to 90° as possible. Radial
back-turning should be avoided.
Aim for the highest feed possible; the use of Wiper inserts is highly recommended. The –LC and –WL geometries are optimized for low carbon steels.
Cutting data:
Application area for CNMG: 120408 in –LC and –WL geometries
Use high cutting speeds to avoid built-up edge on the insert, which can
negatively influence both surface finish and tool life. Sharp edges and
geometries, together with thin coated grades, e.g. GC2025 or GC1515, will
decrease the smearing tendencies and prevent edge detoriation.
At low cutting depths or feed, ground inserts with positive geometries and
small nose radii should always be used for best cutting action.
Low alloyed steel
Material Classification: P2.x
F = Finishing
M = Medium
R = Roughing
Low alloyed steels are the most common material for metal cutting on the market. The group includes both soft and hardened materials (below 50 HRc).
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 low alloyed steels in a non-hardened condition, the first choice is the GC4200 series of grades and the wiper geometries.
Because hardened materials produce higher heat in the cutting zone, plastic deformation is a common wear mechanism.
Thus, extra heat and flank wear resistance are required; cast iron grades are recommended for these operations.
High alloyed steel
Material Classification: P3.x
High alloy steels include carbon steels with a total alloy content over 5%. The group includes both soft and hardened materials (below 50 HRc). Machinability decreases at higher alloy contents and hardnesses.
As for the low alloyed steels, the first choice is the GC4200 series of grades and the wiper geometries. Steels with more than 5% alloying elements, and with hardness up to 450 HB, impose extra demands on plastic deformation resistance and edge strength, which is why cast iron grades are often a good choice.
CoroTurn® HP coolant supply
CoroTurn HP can be applied to increase cutting data and improve chip control, especially for steels with a low carbon content. It can also be applied in harder steels to decrease crater wear and plastic deformation.
First choice geometry and grade recommendations