On the nucleation and dissolution process of Z-phase Cr(V,Nb)N in martensitic 12%Cr steels

Kinetics of Z-Phase Precipitation in 9 to 12 pct Cr Steels

“…crystallographically into Z-phase. [5,8,9] This results in Z-phase having two different crystal structures, which can coexist in a single precipitate particle. [10] The primary Z-phase crystal structure is tetragonal with lattice parameters of a = 0.286 nm and c = 0.739 nm, and it is likely the most thermodynamically stable.…”

“…[4] Investigations by electron microscopy have revealed the nucleation of Z-phase to be a diffusion of Cr atoms from the matrix into existing MX particles, physically transforming them into Z-phase. [5] The effects of Z-phase on the creep strength of 12 pct Cr steels has been well described because of the relatively fast precipitation, but recent investigations of commercial 9 pct Cr steel grades have indicated that the Z-phase might also affect these steels within their expected service life. [6] As these steels already are extensively used around the world, this could affect the lifetime of existing power plants.…”

Physical Metallurgy of Modern Creep-Resistant Steel for Steam Power Plants: Microstructure and Phase Transformations

“…Therefore, Z-phase directly contributes to a reduction in the creep rupture strength of the observed 12CrMoVNb steel. Precipitation of large Z-phase particles, Cr(V, Nb)N, which depletes the matrix of fine MX nitrides, (V, Nb)N, was observed to be the major cause of early breakdown in long-term creep strength of a number of new 9-12%Cr martensitic steels [50]. Study shows that large concentration of niobium (0.9 wt%) enhances the precipitation of -phase.…”

“…In general, the precipitation of Z-phase, M 6 X, and Fe 2 (W, Mo) Laves phase during creep causes a loss of creep strength at long times, because they consume existing fine M 2 X and MX and or M 23 C 6 precipitates [42,50]. Retardation of the Z-phase formation is necessary to improve strength of creep-resistant steels [49].…”

Thermomechanical controlled processing to achieve very fine grains in the ISO 5832-9 austenitic stainless steel biomaterial

“…When the particles are small, they tend to decrease the mobility of grain boundaries formed upon straining by dynamic recrystallization and during the interpass time by static and metadynamic recrystallization. In turn, when precipitates coalesce, a degradation of fatigue properties and corrosion resistance of the material is noticed [11][12][13][14][15][16]. The formation of Z-phase is unclear at present and not well established whether it is formed from prior nitride precipitates as proposed by some authors [13,[17][18][19] or directly nucleated as suggested by others [8,20,21].…”