Phase-Field Modeling of Sigma-Phase Precipitation in 25Cr7Ni4Mo Duplex Stainless Steel

Malik, Amer; Odqvist, Joakim; Höglund, Lars; Hertzman, Staffan; Ågren, John

doi:10.1007/s11661-017-4214-7

Cited by 30 publications

(14 citation statements)

References 47 publications

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“…Most recently, other aspects of σ such as the influence of surface finish on precipitation kinetics [19], the phase field modeling of precipitation [20], and the effect of σ on mechanical properties [21] have been studied. However, σ morphology and its influence on properties for different aging temperatures have not been well-studied.…”

Section: Introductionmentioning

confidence: 99%

Effect of Sigma Phase Morphology on the Degradation of Properties in a Super Duplex Stainless Steel

et al. 2018

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Sigma phase is commonly considered to be the most deleterious secondary phase precipitating in duplex stainless steels, as it results in an extreme reduction of corrosion resistance and toughness. Previous studies have mainly focused on the kinetics of sigma phase precipitation and influences on properties and only a few works have studied the morphology of sigma phase and its influences on material properties. Therefore, the influence of sigma phase morphology on the degradation of corrosion resistance and mechanical properties of 2507 super duplex stainless steel (SDSS) was studied after 10 h of arc heat treatment using optical and scanning electron microscopy, electron backscattered diffraction analysis, corrosion testing, and thermodynamic calculations. A stationary arc was applied on the 2507 SDSS disc mounted on a water-cooled chamber, producing a steady-state temperature gradient covering the entire temperature range from room temperature to the melting point. Sigma phase was the major intermetallic precipitating between 630 °C and 1010 °C and its morphology changed from blocky to fine coral-shaped with decreasing aging temperature. At the same time, the average thickness of the precipitates decreased from 2.9 µm to 0.5 µm. The chemical composition of sigma was similar to that predicted by thermodynamic calculations when formed at 800–900 °C, but deviated at higher and lower temperatures. The formation of blocky sigma phase introduced local strain in the bulk of the primary austenite grains. However, the local strain was most pronounced in the secondary austenite grains next to the coral-shaped sigma phase precipitating at lower temperatures. Microstructures with blocky and coral-shaped sigma phase particles were prone to develop microscale cracks and local corrosion, respectively. Local corrosion occurred primarily in ferrite and in secondary austenite, which was predicted by thermodynamic calculations to have a low pitting resistance equivalent. To conclude, the influence of sigma phase morphology on the degradation of properties was summarized in two diagrams as functions of the level of static load and the severity of the corrosive environment.

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Section: Introductionmentioning

confidence: 99%

Effect of Sigma Phase Morphology on the Degradation of Properties in a Super Duplex Stainless Steel

et al. 2018

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“…And these regions have more contribution from Ni in the passive film. When the sigma phase nucleates, Cr and Mo are concentrated in sigma while Ni is rejected, generating a high Ni region in sigma boundaries leading to secondary austenite formation [90,91,95,[100][101][102]. Peak 3 arises in specimens in the second stage of sigma precipitation, that is, in the moment of coarsening of sigma grains.…”

Section: Resultsmentioning

confidence: 99%

DL-EPR vs. LSV-KOH: from simple detection of deleterious phases to analysis of morphology and high accuracy on determination of sigma phase in UNS S32750 stainless steel

Sampaio

Furtado

Ignácio

et al. 2022

Corrosion Engineering, Science and Technology

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An optimised electrochemical technique, linear sweep voltammetry (LSV) in KOH solution (LSV-KOH) was confronted with the double loop electrochemical Potentiokinetic reactivation (DL-EPR) to verify which is the best technique to quantify deleterious phases (DP) in a UNS S32750 super duplex stainless steel. DL-EPR presented an error in determination of deleterious phases in the range of 6.9-100%. LSV-KOH show a better accuracy in quantification of deleterious phases volume fractions, the error range for LSV-KOH was 2.4-26.2%. When the morphology of sigma changes from lamellar to divorced, was observed modifications on LSV-KOH voltammograms. In specimens where lamellar morphology is present, the voltammograms show two peaks curve. Meanwhile, in specimens where occurred also divorced precipitation of sigma the voltammograms changes to a 3 peaks curve. This feature is due to the dissolution of sigma phase boundaries which has different compositions according to the form of sigma precipitation.

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“…[89,90] The complex behavior of TCP-phases in c=c 0 taking into account the microstructural evolution, diffusion processes, available nucleation sites, interface energies, and the interaction between TCP-phases is an ongoing research topic. All these aspects can be combined in phase-field simulations [82,91,92] and then applied to TCP-phase precipitation in Ni-base superalloys.…”

Section: Tcp-phase Simulationmentioning

confidence: 99%

Development of Single-Crystal Ni-Base Superalloys Based on Multi-criteria Numerical Optimization and Efficient Use of Refractory Elements

Markl

Müller

Ritter

et al. 2018

Metall Mater Trans A

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The development of new Ni-base superalloys with a complex composition consisting of eight or more alloying elements is a challenging task. The experimental state-of-the-art development cycle is based on the adaption of already existing compositions. Although new alloy compositions with potentially improved material properties are expected to be similar to already known superalloys, this procedure impedes efficiently finding these compositions in the large multi-dimensional design-space of all alloying elements. Modern alloy development combines numerical optimization methods with experimental validation to guide the development towards promising compositions. In this work, an improved numerical multi-criteria optimization tool using CALPHAD calculations and semi-empirical models for alloy development is presented. The model improvements to its predecessor are described and the successful application for the development of rhenium-free single-crystal Ni-base superalloys ERBO/13 and ERBO/15 is revisited. The optimization tool is described and the designed alloys are discussed regarding phase stability. Finally, a possible phase stability model extending the optimization tool and improving the alloy composition predictions is presented.

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Phase-Field Modeling of Sigma-Phase Precipitation in 25Cr7Ni4Mo Duplex Stainless Steel

Cited by 30 publications

References 47 publications

Effect of Sigma Phase Morphology on the Degradation of Properties in a Super Duplex Stainless Steel

Effect of Sigma Phase Morphology on the Degradation of Properties in a Super Duplex Stainless Steel

DL-EPR vs. LSV-KOH: from simple detection of deleterious phases to analysis of morphology and high accuracy on determination of sigma phase in UNS S32750 stainless steel

Development of Single-Crystal Ni-Base Superalloys Based on Multi-criteria Numerical Optimization and Efficient Use of Refractory Elements

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