Microstructure formation in δ/γ duplex phase stainless steel during isothermal ageing and continuous heating

Phase transformations in the temperature range from 350 to 600 degrees C in a duplex stainless steel have been investigated by means of differential scanning calorimetry (DSC), electron resistivity measurement (ERM) and transmission electron microscopy (TEM). The solution treated specimens were either heated continuously at a constant rate or aged isothermally. During the continuous heating up to 650 degrees C, the compositional fluctuation, the homogeneous precipitation of fine plates and the dissolution of them occurred at temperatures around 400, 450 and 500 degrees C, respectively. In the isothermally aged samples, the compositional fluctuation, the formation of the plate-shaped precipitates and the precipitation of fine spherical Cu particles were observed at temperatures under 400, between 400 and 550, and between 550 and 600 degrees C, respectively. The precipitation of austenite plates was recognized above 600 degrees C.