Predicting microstructure and strength of maraging steels: Elemental optimisation

Kinetics analysis of two-stage austenitization in supermartensitic stainless steel

“…As part of a physics-based modeling framework Galindo-Nava et al modelled diffusion controlled reversion of austenite from lath martensite during isothermal holding based on transformation of a single lath [29]. The model describes the grain boundary kinetics dependent on the geometrical constraints of the lath, the equilibrium phase fraction of austenite and an effective diffusivity parameter.…”

Development of Ni-free Mn-stabilised maraging steels using Fe2SiTi precipitates

“…Previous work showed that grain-boundary embrittlement due to Mn segregation to the prior-austenite boundaries can in principle be avoided if the volume fraction of reverted austenite, f γ , is high enough to allow Mn redistribution [4]. It was found that at least 25 % austenite is required in order to avoid grain-boundary embrittlement and the Mn content is tailored such that f γ ≥ 30% is formed at equilibrium at the ageing temperature.…”

“…However, their widespread use has been limited by their high cost (>£1,600-7,200 per tonne, Table 1). A large portion of this cost is due to alloying with the austenite stabilisers Ni and Co, which control the (lath) martensite start temperature (M s ) and promote the formation of reverted face-centredcubic (fcc) austenite for improved ductility [3,4]. The strength of these steels is based on the precipitation during ageing of nm-scale intermetallics, a variety of which are employed, such as D0 24 Ni 3 (Ti,Mo), ordered body-centred-cubic (bcc) intermetallic precipitates such as B2 NiAl and NiMn, or L2 1 Heusler structured intermetallics, e.g.…”

“…The strength of these steels is based on the precipitation during ageing of nm-scale intermetallics, a variety of which are employed, such as D0 24 Ni 3 (Ti,Mo), ordered body-centred-cubic (bcc) intermetallic precipitates such as B2 NiAl and NiMn, or L2 1 Heusler structured intermetallics, e.g. Ni 2 TiAl and Ni 2 AlMn, as well as G phase Ni 16 Si 7 Ti 6 [5,4,6,7]. Ordered bcc precipitates are of particular interest since they can be coherent with the martensitic ferrite matrix, providing hard particle strengthening as well as misfit strain strengthening of the surrounding matrix.…”

“…Fe 2 TiSi (a = 5.72 Å [11]) has a larger misfit (calculated as per [12]) of ∼ 2.5% than NiAl (NiAl a = 2.89Å [13]) ∼ 1.6%, which could be anticipated to increase the misfit strain strengthening contribution. Recent lean maraging steels and advanced high strength steels (AHSS) with transformation induced plasticity (TRIP) have been successful in utilising Mn as the austenite stabiliser, greatly reducing Ni contents [14,4].…”