Ferrite (phase)

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Ferrite is the metallographic name for the body-centered cubic modification ( phase ) of pure iron and its mixed crystals .

Different names of the ferritic phase

The ferritic phase (defined by the body-centered cubic lattice structure) occurs at the following temperatures under standard pressure:

  • between 1536 ° C and 1392 ° C as so-called δ-ferrite with a lattice constant a of 0.293 nm, measured at 1425 ° C. δ-ferrite is formed when the pure iron melt solidifies.
  • from 911 ° C to lower temperatures than α-ferrite, which is formed from γ-iron up to a pressure of about 11 GPa. α-ferrite is divided into
    • β-ferrite in the range from 911 ° C to 769 ° C with paramagnetic properties and a lattice constant of 0.290 nm at 800 ° C
    • α-Ferrite in particular as α-Ferrite below the Curie temperature T c = 769 ° C and ferromagnetic properties, with a lattice constant of 0.286 nm at 20 ° C.

The different names for one and the same phase (α-ferrite, β-ferrite, δ-ferrite have the same lattice structure) have historically emerged from the thermal analysis of iron based on different breakpoints . The 102-meter-high Atomium building in Brussels represents a 165 billion-fold enlargement of a ferritic phase.

Influences of alloying elements on the stability of ferrite

The formation of the ferritic phase is influenced by austenite or ferrite stabilizing elements.

Austenite formers are, for example, the elements nickel , manganese , nitrogen , carbon and cobalt . They inhibit the formation of α mixed crystals, while ferrite formers such as chromium , silicon , molybdenum , vanadium , titanium and aluminum promote their formation. This is done by directly influencing the size of the area of ​​γ mixed crystals in equilibrium diagrams , for example the iron-carbon diagram , which can indirectly influence the size of the area of ​​α mixed crystals. In graphs such as the Schaeffler diagram , especially when combining ferrite and austenite formers, the structural compositions resulting from the phases that are created can be read off.

Occurrence of the ferritic phase in structural components

The ferritic phase is contained in the following structural components:

See also

Individual evidence

  1. Bargel / Schulze (ed.): Material Science Springer, Berlin-Heidelberg 2008, ISBN 978-3816918394
  2. Oettel (Ed.), Schumann (Ed.): Metallographie Wiley-VCH, Weinheim 2011, ISBN 978-3527306794
  3. Weißbach: Material Science. Structures, properties, testing. Vieweg + Teubner, Wiesbaden 2010, ISBN 978-3834815873