PRECIPITATION OF [[sigma]]-PHASE IN DUPLEX STAINLESS STEEL ZERON-100 Ping Liu Dept. of Physical Metallurgy, Research and Development Centre, AB Sandvik Steel S-811 81 Sandviken Sweden.
Precipitation of [[sigma]]-phase (FeCr, P42/mnm, a=8.790 Å and C=4.545 Å) was observed in welded metal of duplex stainless steel Zeron-100. Fig.1 shows a scanning electron microscope(SEM) micrograph of welded metal of Zeron-100(0.04 C-0.33 Si-0.87 Mn-24.49 Cr-8.93 Ni-0.67 Cu- 0.74 W). Transmission electron microscope(TEM) micrograph in Fig.2 shows that precipitation of [[sigma]]-phase took place at the grain boundaries and [[alpha]]-ferrite and [[gamma]]-austenite boundaries. Fig.3 shows a convergent beam electron diffraction pattern (CBED) from [001] zone axis of [[sigma]]-phase. Note that the presence of the M-G lines in the odd h00 and 0k0 reflections is dynamic absences due both to glide planes parallel to the zone axis and screw axes perpendicular to it. The composite electron diffraction patterns of [ll0][[gamma]]//[lll][[sigma]] in Fig.4 reveals that precipitation of [[sigma]]-phase obeys the following orientation relationship (O.R.) to [[gamma]]-austenite (Fm3m, a=3.585 Å): [110][[gamma]],//[111][[sigma]]; (111)[[gamma]]//(011)[[sigma]], (111)[[gamma]]//(110)[[sigma]] , which differs from the previously reported ones (1-2). The smaller lattice misfit in the present case provides an explanation for the occurrence of this O.R.
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