Abstract
AISI 4340 is a high-strength, medium-carbon low-alloy steel used extensively in the quenched and tempered condition. Its chemical composition places it in a domain where both plate and lath martensites may occur. Our observations show that the lath packet is the fundamental transformation unit rather than individual laths. Thus, the packet can be considered as a low aspect ratio plate formed at the highest of martensite transformation temperatures. An observed degeneracy in the plate tip is thought to be attributable to the need to minimise the high interface curvature associated with a singularly tipped plate.
Phase Transformations, York Conference, April 1979
The Institution of Metallurgists, Series 3, No. 11, Vol. 2, pp. IV-9 to IV-13
Recent Observations: Carbon in Solid Solution
Modern atom probe tomography data continue to emerge, showing that even in low-carbon (0.16 wt%), low-alloy, fully bainitic steels, the majority of carbon remains in solid solution within αb (bainitic ferrite).
When some of this dissolved carbon in a mildly plasticised (εp = 0.008) sample is allowed to segregate to dislocations by annealing at 50°C for just one minute, the steel effectively resists deformation when reloaded [Gao:2025b]. This suggests that the presence of mobile dislocations, rather than a lack of carbon, is responsible for the unique yielding behaviour of fresh bainite.
Martensitic Phase Transformations
- Short review of martensite crystallography and nucleation
- Comprehensive book on martensite crystallography
- Elementary undergraduate lecture on martensite
- Tempered martensite
- Crystallography of austenite, ferrite and interstices
- Bain correspondence and Bain strain
- Deformation due to martensitic transformation
