Magnetic and metallographic investigation of phase transformations in duplex stainless steels

Heat treatment and cold working -induced microstructural processes were studied by metallography and different non-destructive magnetic in commercial lean, duplex and superduplex stainless steels. In DSS and SDSS the metastable ferrite can decompose to a sigma phase and secondary austenite due to heat treatment. All the mechanical, corrosion resistance and magnetic properties are strongly influenced by this microstructural changes. The capabilities of magnetic measurements allow a quantitative correlation between measured harmonics and mechanical properties obtained from destructive tests. In lean duplex the substitution of Ni by N and Mn in lean grades may result in austenite phase instability, and this phase tends to transform to metastable martensite. The cold rolled samples were examined with OM, SEM, XRD and Magnetic measures. Three different magnetic tests were applied for determining the magnetic behaviour of DSS samples. The effect of cold rolling is on grains size and shape and the magnetic tests suggest the martensite presence in 2101.