Precipitation behavior of (sigma) phase in 19Cr–9Ni–2Mn and 18Cr–0.75Si stainless steels hot-rolled at 800 °C with various reduction ratios

The effects of various reduction ratios on the precipitation behavior of the (sigma) phase in 19Cr-9Ni-2Mn and 18Cr-0.75Si stainless steels as hot-rolled at 800 °C have been investigated in this study. The morphology, quantity and chemical composition of the (sigma) phase were analyzed by using optical microscopy (OM), X-ray diffractometry (XRD), image analysis, scanning electron microscopy (SEM) and wavelength dispersive spectrometer (WDS), respectively. The (sigma) phase showed a dendrite-like morphology in the asreceived materials. A hot-rolling process changed the morphology of the (sigma) phase from dendrite-like to globular, especially at higher reduction ratio. The amounts of (sigma) phase in the stainless steels also increased gradually at 800 °C with increasing the reduction ratio from 0 to 75%. The XRD analyses showed that a higher reduction ratio enhanced the conversion of (delta)-ferrite (1 1 0) to (sigma) phase (5 4 2). The (sigma) phase was identified to be a Cr- and Mo-rich phase by WDS analysis, which indicated that although Cr and Mo elements are stabilizers of (delta)-ferrite in stainless steels as hot-rolled at 800 °C, these elements partition to the (sigma) phase at high temperature.