DEFORMATION INDUCED MARTENSITIC PHASE TRANSFORMATION IN STAINLESS STEEL TYPE OF 304L Ping Liu*, Laizhu Jiang** & Åke Roos**, *Dept. of Physical Metallurgy, **Dept.of Wire Research & Development, Research and Development Centre, AB Sandvik Steel S-811 81 Sandviken Sweden.

Deformation induced [[epsilon]]-martensitic phase transformation was observed in stainless steel type of 304L. Fig.1 shows a transmission electron microscope(TEM) micrograph of thin foil from a deformed stainless steel type 304L (0.03 C-1.0 Si-2.0 Mn-18.0-20.0 Cr-8-12 Ni ). Note that there are two sets of twins, between which there is an interaction zone as indicated by the arrow. Electron diffraction pattern from the twins is shown in Fig.2. More importantly, [[epsilon]]-martensite was observed as shown in Fig. 3. The thickness of [[epsilon]]-martensite is about 20 nm. Fig.4 show composite electron diffraction patterns of {111} [[gamma]]-austenite and <0001> [[epsilon]]-martensite, which reveals the orientation relationship: {0001} _[[epsilon]] // {111} _[[gamma]] and <1120>_[[epsilon]]// <110>_[[gamma]]. Hence, the formation of [[epsilon]]-martensite attributed to low stacking fault energy in 304L stainless steel. The elements of Cr, Mn, Co, Si, C, N tend to lower stacking fault energy in [[gamma]]-austenite and hence, promote the formation of twin and the transformation of [[gamma]]-austenite to smartensite during deformation because an extrinsic stacking fault is a twin embryo and intrinsic is an hcp embryo(1).

1.G.B. Olson and M. Cohen, Metall. Trans.7A. 1976(1897-1904).