Effect of cooling rate after solution treatment on subsequent phase separation during aging of Fe-Cr alloys: A small-angle neutron scattering study

Abstract

The effect of cooling rate after solution treatment on the initial structure of concentrated binary Fe-Cr alloys and the effect of the initial structure on phase separation during subsequent aging has been investigated. The nano-scale compositional fluctuations in the bulk of the alloys are studied using small-angle neutron scattering and the results are compared with simulations using the Cahn-Hilliard-Cook (CHC) model. The alloys investigated represent different mechanisms of phase separation and at higher Cr content, when spinodal decomposition (SD) is favored, the initial Cr compositional fluctuations due to slow cooling after solution treatment reduce the kinetics of phase decomposition, whereas, at lower Cr composition when nucleation and growth is favored, the kinetics of phase decomposition is more rapid. Regardless of the nominal Cr composition of the alloy, the phase decomposition after extended aging up to 300 h at 748 K is always larger for the more non-random initial structure. The CHC modeling of the cooling process and subsequent initial aging (below 10 h) is in reasonable qualitative agreement with the experimental results for the Fe-40 wt.% Cr alloy decomposing via SD. However, the modeling approach must be refined for accurate quantitative modeling of the full SD process, including coarsening.

Quantitative Nanostructure and Hardness Evolution in Duplex Stainless Steels: Under Real Low-Temperature Service Conditions

“…[22,27,56,57] The degree of phase separation would then primarily depend on the time spent within the miscibility gap, i.e., the cooling rate achieved. [49,58,59] Second, a positive short-range order (SRO) factor for Cr compositions above 10 at. pct may result in some Cr clustering above the miscibility gap.…”

“…In both cases, the mirror sectors were included. separation were then obtained by removing the contribution of the background and normalizing it with respect to B fit i.e., SðQÞ [36] The wavelength of the a and a¢ phase separation i.e., distance between the two a¢ domains was obtained as follows [23,26,27,44,49,50] :…”

Nanoscale phase separations in as-fabricated thick super duplex stainless steels

“…Zhou et al [11] showed that Cr atoms clustered in the solutionized condition of a Fe-46.6%Cr alloy, where this clustering decreased with increasing solutionizing temperature. Xu et al [12] also studied binary Fe-(20-40)% Cr alloys in furnacecooled and brine-quenched conditions and showed that the initial state of phase separation may have a significant effect on the outcome of subsequent aging. Lemoine et al [13] also mentioned the progression of spinodal decomposition during quenching of a cast DSS alloy.…”

Molecular‐Scale Modeling and Multiscale Experiments on the Elastic Properties of HR‐2 Steel Affected by Hydrogen

“…Experimental, nondestructive techniques have been developed to measure some key information needed for multiscale models at the macro‐ and micro‐scales. Small‐angle neutron diffraction can be used to nondestructively measure statistical information of micro‐defects . A neutron stress spectrometer can be used to measure the stress in situ and nondestructively …”