Austenite (structural component)
The structural component of austenite is the main structural component of many stainless steels and the most important structural component of the so-called austenitic alloys and steels . It is usually in a metastable state. It mainly consists of the face-centered cubic austenitic phase . In the reflected light microscope it can be recognized by its characteristic twin boundaries because of the low stacking fault energy . If the alloy composition favors the formation of non-metallic inclusions ( carbides , nitrides , etc.), these can be embedded in the austenitic matrix.
properties
The following properties are ascribed to the austenitic structural component in steel:
- lower strength values (at room temperature the values of the 0.2% yield strength of austenitic standard steels are around 200–205 N / mm² and the tensile strength values are around 600 N / mm²)
- high toughness values (typical elongation at break values (A5) are around 40-50% and thus twice as high as with ferritic steels )
- low thermal conductivity
- relatively high coefficient of thermal expansion
- An influence of the lattice structure on the specific electrical resistance was not observed.
- The strength can be increased enormously by cold forming ; therefore austenitic steels are generally difficult to machine .
- high temperature resistance due to the low stacking fault energy
Machinability
The machinability of austenite, i.e. its machinability through milling, drilling, turning, etc., is considered to be mediocre to poor. Austenitic steel causes major problems when machining. Austenite is distinguished from other structural components of steel by a high deformability (elongation at break 50%) and medium tensile strength and hardness (180 HV, 530–750 N / mm²).
Austenite tends to form built- up edges and to stick to the edge. The tendency to adhesion is particularly pronounced with austenite. In addition, long ribbon or tangled chips are formed. Because of the high plastic deformation during processing, work hardening of the newly created surface occurs during processing. This leads to increased cutting forces during further processing. In addition, the thermal conductivity of austenite is a third lower, which hinders the dissipation of the heat generated in the chip. The cutting edge is therefore subject to higher thermal loads. (See energy conversion and heat during machining )
Processing in welding technology
The austenitic stainless steels are very suitable for welding. There is neither the risk of coarse grain formation nor the tendency to cold cracks. However, the action of the welding heat can lead to carbide precipitations, which are present as chromium carbides. In non-stabilized steels with a C content of over 0.07%, these carbides can lead to intergranular corrosion. Welding consumables with low carbon contents or Nb-stabilized types can help.
See also
Individual evidence
- ↑ a b Edelstahl-Vereinigung e. V. with Association of German Ironworkers (VDEh) (Ed.): Stainless steels. 2nd, revised edition, Verlag Stahleisen mbH, Düsseldorf 1989, ISBN 3-514-00333-5 , p. 29.
- ↑ a b c Edelstahl-Vereinigung e. V. with Association of German Ironworkers (VDEh) (Ed.): Stainless steels. 2nd, revised edition, Verlag Stahleisen mbH, Düsseldorf 1989, ISBN 3-514-00333-5 , p. 39.
- ↑ Wolfgang Bergmann: Werkstofftechnik , 7/1, revised edition, Carl Hanser Verlag, Munich 2013, ISBN 978-3-446-43581-0 , p. 111.
- ↑ Fritz Klocke, Wilfried König: Production Process Volume 1: Turning, Milling, Drilling , Springer, 8th edition, 2008, p. 274 f.
- ↑ ESAB OK manual welding stainless steels , ESAB online manual , 2020, http://www.esab-okhandbuch.de/index