Morphology and distribution of martensite in 301L alloy induced by different subsequent processes after prior deformation

Abstract

The influence of different processing routes: either isothermally holding at 77 K for 72 h or deforming 10% at 77 K after prior deformation to a strain level of 20% on the increment, morphology and distribution of a9 martensites has been investigated in 301L austenitic steel. The results show that the degree of stimulation of the a9 martensite transformation depends on total strain path. A detailed microstructural study by transmission electron microscopy indicates that different morphology and distribution of a9 martensites are formed as a function of strain path which reflect the effect of stress and/or strain induced a9 martensite formation.On a examiné l'influence de diffé rentes voies de traitement -soit maintien isotherme à 77 K pendant 72 heures ou dé formation de 10% à 77 K aprè s dé formation pré alable à un niveau de dé formation de 20% -sur l'incré ment, la morphologie et la distribution de la martensite-a9 de l'acier austé nitique 301 L. Les ré sultats montrent que le degré de stimulation de la transformation de martensite-a9 dé pend du parcours de dé formation totale. Une é tude dé taillé e de la microstructure par microscopie é lectronique en transmission indique que diffé rentes morphologies et distributions de martensite-a9 sont formé es en fonction du parcours de dé formation, ce qui reflè te l'effet de la formation de martensite-a9 induite par contrainte ou par dé formation.

The mechanism of bcc α′ nucleation in single hcp ε laths in the fcc γ → hcp ε → bcc α′ martensitic phase transformation

“…In face-centered cubic (fcc)-c austenitic steels with low stacking fault energy (SFE), the formation of hexagonal closed packed (hcp)-e martensitic laths is resulted from gliding Shockley partial dislocations of Burgers vector a f 6 h1 1 2i on every second f1 1 1gc plane [11,12], where a f is the lattice constant of c austenite. Tremendous experimental and theoretical investigations [13][14][15][16][17][18][19][20][21][22][23] show that the hcp-e martensite is an intermediate phase in the formation of body-centered cubic (bcc)-a 0 martensite from the austenitic parent phase, proving the c (fcc) ? e (hcp) ?…”

Power-law description of martensite transformation curves

“…In this regard, Figure 8 compares the stress–strain curves typical of deformation of the 18/8 stainless steel at 273 and 203 K with the respective transformation curves [47]. As one can see, the maximum work-hardening rate correlates with the acceleration of the transformation at a shorter true plastic strain, which is larger at 203 K. It is apparent that the results of this formal analysis of the mechanical transformation in the 18/8 stainless steel are compatible with the relevance of the strain path [48] as well as with the thermodynamic effect of the acting stress [49].

Figure 8 Transformation and stress–strain curves of the 18/8 stainless steel [47].

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