Ferrite is a magnetizable, body centered constituent with
various chemical composition. Ferrite is formed at the solidification of the steel
or through transformation out of austenite or sigma-phase. Alpha- and delta-iron
are both cubic body centered. In the microstructure of austenitic chromium-nickel
and chromium-nickel-molybdenum-steels is occasionally a little amount of ferrite
determineable. It is dependent from the chemical composition and from the heat
treatment. The partly transformation of the austenite in ferrite is proveable through
an occurence of magnetizability. At the molybdenum bearing steels a light magnetism
is frequently possible. The mechanical properties or the stability against corrosion
are not unfavorable influenced. If the steels get annealed and quenched (solution
annealing) the microstructure transformed completely in austenite and the magnetizability
disappears.
In austenitic welding materials a determined amount of delta-ferrite is aimed to
reduce the tendency of hot cracky. A material without delta-ferrite is bad for
hot forming at increased temperatures. Nitrogen in the steel suppresses the formation
of delta-ferrite.
The following examinations and the micrographs are realized
at following materials.
1.4307 ( X2CrNi18-9 )