The martensite phases in 304 stainless steel

Abstract

A detailed analysis of martensite transformations in 18/8 (3b4) stainless steel,.utilizing transmission electron microscopy and diffraction in conjunction with X-ray and magnetization techniques, has established that the sequence of transformation is y ~ E ~ a. E is a thermodynamically stable hcp phase whose formation is greatly enhanced as a result of plastic deformation. Comparison with the E ~a transformation in pure Fe-Mn alloys lends further support to the above sequence and suggests that a transforma-.tion line between E and a in Fe-Cr:-Ni alloys can be expected. In the 304 stainless steel used in this investigation, formation of a was induced only by plastic deformation and subsequent to formation of E. Nucleation of. a occurs heterogeneously at intersections of E-bands or where E-bands abutt twin or grain boundari~s (which represent unilaterally compressed regions) .. From electron diffraction, the Nishiyama relationship between y and a phases appears to predominate at the start of the transformation, but then changes ·to that of Kurdjumov-Sachs. Based on these observations, a sequence of atom· movements from the hcp structure to the bee structure is proposed which has the basic geometric features of the martensitic transformation.

Correlation Between Microstructure and Mechanical Properties Before and After Reversion of Metastable Austenitic Stainless Steels

“…292 Significant discrepancy still exists in explaining the 293 strengthening mechanisms of metastable austenitic stain-294 less steels and, in concrete, the effect of the strain-in-295 duced a¢-martensite phase. Since the highly dislocated 296 a¢-phase is much harder than the austenite, some 297 authors [40,41] consider austenite-martensite mixtures as 298 composites of soft austenitic matrix with hard martensite 299 dispersion. Spencer et al [42] demonstrated that marten-300 site sustains a clearly higher stress than austenite, 301 concluding that a¢-martensite acts as the reinforcing 302 phase.…”

Effects of high magnetic fields on the flow stress of 18-8 stainless steels

“…This is attributable to an increased rate of martensite formation in conjunction with a mechanical effect of this martensite tenned the "window mechanism" (l6). Bee martensite is frequendy observed at intersections of two shear bands in 18-8 stainless steel (16)(17)(18)(19). It has been previously noted that the bee structure can be constructed from the fcc structure by two independent shears (20), for example at the intersection of an hcp shear band with a second shear band of highly faulted fcc or hcp crystal (21).…”

Influence of Microstructure on the Corrosion Resistance of AISI 317L (UNS S31703)

“…It has been observed that ε-martensite is formed at low strains in some low-SFE metastable steels, such as AISI 304 and 316 [15][16] . Generally, reaction (4) takes place for metastable austenitic steels with SFE < 20 mJ/m 2 17 .…”

“…Many authors studied the deformation induced martensites in austenitic [15][16][17][18][19][20][21][22] , duplex and lean duplex stainless steels [23][24] . Both ε-and α'-martensites can be observed by transmission electron microcopy (TEM) and quantified by X-ray diffraction (XRD).…”

“…It is worth noting that the Cr-rich precipitate produced by spinodal decomposition and the magnetic martensite produced by cold working are usually cited with the same symbol (α') [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] , but these are phases completely distinct. For this reason, in this paper, the Cr-rich precipitate produced by spinodal decomposition was called α 1 .…”