I found many publications, which suggest that the "delta ferrite↔sigma phase + austenite" transformation in duplex stainless steels is eutectoid. According to well known definition the eutectoid transformation is three-phase reaction by which, on cooling, a solid transforms into two other solid phases at the same time. This transformation might be expected during slow cooling. However many authors showed that in the case of duplex stainless steels, "delta ferrite↔sigma phase + austenite" transformation occurs also during heating from the (metastable) as-cast state and/or ageing at elevated temperatures. Can we therefore define this transformation as eutectoid?
In many aspects sigma phase formation is different from an eutectoid reaction. For example you cant assigned a eutectoid temperature to the reaction. Normally its formation is a diffusion control in situ transformation and you can not change the microstructure by heating it above the transformation temperature.
Thank you Ms Attrian for your answer. I agree with you and I am of an opinion that the transformation, which was described in my question, should not be called as an eutectoid.
Our calculations with our newest Matcalc database for Hyperduplex suggests non-eutectoid transformations.
Thank you Erwin, for sharing your results. My calculations with TCFE7 database for austenitic and duplex stainless steels suggest the same.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Thermodynamics