Influence of grain boundary structure on discontinuous precipitation in austenitic steel

The Structure Of Interphase Boundaries In Solids

“…C < 50, and the plane of the boundary coincides with a plane of the CSL having a high density of coincident atoms (a simple boundary) then the discontinuous precipitation results in long thin fibres of VC behind the advancing grain boundary. While these observations are an up-to-date restatement of similar observations made by Aaronson (1956) and Clark (1967) on different systems, Ainsley et al (1979) have observed a still more interesting development, as follows. In situations where the orientation relationship between the austenite grains is of low multiplicity, but the boundary is complex, particulate VC are formed initially, but parts of the migrating boundary reorient until the boundary segments coincide with a plane of the CSL which contains a high density of coincident atoms.…”

“…10. A particularly interesting study has just been made by Ainsley et al (1979), who observed the discontinuous precipitation of VC in austenite Fe-13Mn-2V-0.8C alloys. For matrix grain boundaries which migrate during the reaction and which separate grains where the coincident site lattice (CSL) is of high multiplicity, e.g.…”

Transitions in carbide morphology in a ternary Fe-C-W steel

“…[6] However, in that case, the M 23 C 6 carbides form during a eutectoid reaction as pearlite (that is, they grow in association with ferrite), while in the present study, the M 6 C carbides precipitate in association with austenite. This distinction is of some importance: the threephase eutectoid reaction (␥ → ␣ ϩ carbide) observed by Mannerkoski [6] and others [15,22] is fundamentally different from the two-phase precipitation reaction (␥ ss → ␥ ϩ carbide) observed here and in austenitic steels, [25][26][27][28] in spite of their morphological similarities. The question of the reaction mechanism that is most likely to give rise to the precipitation of M 6 C in austenite will now be addressed.…”

“…[30] As well, fibrous and interphase vanadium carbide form simultaneously during discontinuous precipitation in Fe-C-V-Mn alloys. [26][27][28] It might be expected that Fe-C-W alloys would show transitions in carbide morphology similar to those observed in Fe-C-Cr and Fe-C-Mo alloys. To the authors' best knowledge, however, no studies of this type have been published since the initial work done on Fe-0.23C-6.30W (wt pct), as reported by Davenport and Honeycombe (DH) over 25 years ago.…”

“…[25] More recently, both interphase and fibrous vanadium carbide were observed during discontinuous precipitation from austenite retained in a high-manganese steel, and evidence for a ledge growth mechanism of such cellular colonies was presented. [26][27][28] Thus, these new carbide morphologies are not restricted to the eutectoid ␥ → ␣ ϩ carbide reaction but rather are seen to be of a more general nature.…”