Free cutting steel
A free- cutting steel is a steel that is optimized for the machining processes of turning and drilling (uninterrupted cut) on automated machine tools . By alloying with phosphorus or sulfur is brittle inclusions, to which the forming chips can break.
- Alloying with lead results in finely distributed heterogeneous lead inclusions in the steel, on which the chips can break. Free- cutting steels for very high cutting speeds are alloyed with lead. Since toxic lead vapors are released from the melt during alloying , special equipment in the steelworks must be used to extract and separate the vapors. This is why lead-alloyed free cutting steels are no longer produced in large quantities.
- By alloying with sulfur (0.08% –0.4%) and manganese (0.7% –1.7%), similar properties can be set as with the lead alloy. The addition of sulfur creates soft, line-shaped manganese sulfide inclusions in the steel, on which the chips break.
Free-cutting steels are mainly used in series production on automatic lathes and combined machining centers .
The most important free cutting steels are listed in DIN 1651 / EN 10087 and EN 10277-3.
Some of the most famous representatives of free cutting steel are listed in the table.
| Steel grade | Material number.: | Chem. Composition % | properties |
|---|---|---|---|
| 9 S20 | 1.0711 | C ≤0.13%, Si ≤0.05% Mn 0.9%, P ≤0.1%, S 0.2% | For parts with low stress. |
| 11SMn30 | 1.0715 | C ≤0.11%, Si ≤0.05% Mn 1.1%, P ≤0.11%, S 0.3% | For parts with low stress. |
| 9 SMnPb 28 | 1.0718 | C ≤0.14%, Si ≤0.05% Mn 1.1%, P ≤0.11%, S 0.3%, Pb 0.28% | For parts with low stress. Pb addition to achieve smooth working surfaces. |
| 11 SMn 37/9 SMn 36 | 1.0736 | C ≤0.14%, Si ≤0.05% Mn 1.3%, P ≤0.11%, S 0.37% | For parts with low stress. |
| 11 SMnPb 37/9 SMnPb 36 | 1.0737 | C ≤0.14%, Si ≤0.05% Mn 1.3%, P ≤0.11%, S 0.37%, Pb 0.28% | For parts with low stress. Pb addition to achieve smooth working surfaces. |
| 11 SMnPbTe 37 | 1.0738 | C ≤0.14%, Si ≤0.05% Mn 1.3%, P ≤0.11%, S 0.37%, Pb 0.28%, Te 0.04% | Variant of the 1.0737. Pb addition to achieve smooth working surfaces. Tellurium improves machinability when turning. |
| 11 SMnPbBiTe 37 | 1.0739 | C ≤0.14%, Si ≤0.05% Mn 1.3%, P ≤0.11%, S 0.37%, Pb 0.28%, Bi 0.065%, Te 0.015% | For parts with low stress. Pb addition to achieve smooth working surfaces. Bismuth , like tellurium, improves machinability when turning. |
| 10 S 20 | 1.0721 | C 0.1%, Si ≤0.4% Mn 0.9%, P ≤0.06%, S 0.2% | Case hardenable free cutting steel for e.g. B. Bolts or tapered pins. |
| 10 SPb 20 | 1.0722 | C 0.1%, Si ≤0.4% Mn 0.9%, P ≤0.06%, S 0.2%, Pb 0.28% | Case hardenable free cutting steel for e.g. B. Bolts or tapered pins. |
The chemical analysis / the determination of the alloy components of the free-cutting steel is usually carried out with a spark emission spectrometer .
Machinability
The machinability of free-cutting steel can be classified as good with regard to all criteria: low cutting forces, low wear, good chip breaking, good surface quality and long service life. These are achieved through the protective and lubricating effect of lead and manganese sulfide.
literature
- Europe teaching material: Metal table book. 30th edition. Pforzheim 1978, ISBN 3-8085-1060-9
- Verlag Stahlkey Wegst GmbH: Steel key . Edition 2001. Verlag Stahlkey Wegst GmbH, Marbach 2001, ISBN 3-922599-17-6
