Examinations to the delta-ferrite

 

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 )          

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