Thermal Stability of Intermetallic Phases in Fe-rich Fe-Cr-Ni-Mo Alloys

Yang, Ying; Tan, Lizhen; Busby, Jeremy T.

doi:10.1007/s11661-015-2997-y

Cited by 11 publications

(9 citation statements)

References 23 publications

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“…To study the phase transformation between the χ and Laves phases, a high-Mo-content model alloy was designed to have a composition of Fe-13.2Cr-14.2Mo-12.9Ni in weight percentage (wt%), using computational thermodynamics with an optimized thermodynamic database [10]. The calculated phase amount in the alloy as a function of temperature is shown in Fig.…”

Section: Experimental Methodsmentioning

confidence: 99%

In situ phase transformation of Laves phase from Chi-phase in Mo-containing Fe–Cr–Ni alloys

Tan

Yang

2015

Materials Letters

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a b s t r a c tAn in situ phase transformation of the Chi (χ) phase to the Laves phase was observed in a Fe-Cr-Ni-Mo model alloy. The morphology, composition, and crystal structure of the χ and Laves phases, and their orientation relationship with the matrix austenite phase were investigated. The resulted Laves phase has larger lattice mismatch with the matrix phase than the χ phase, leading to the increase of local strain fields and the formation of dislocations. This finding is helpful to understand the precipitation behavior of the intermetallic phases in the Mo-containing austenitic stainless steels.

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Section: Experimental Methodsmentioning

confidence: 99%

In situ phase transformation of Laves phase from Chi-phase in Mo-containing Fe–Cr–Ni alloys

Tan

Yang

2015

Materials Letters

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“…Laves phase is also an intermetallic phase with hexagonal crystal structure and it usually consists of iron, molybdenum, titanium, niobium, silicon, chromium and nickel [26,27]. In niobium containing steels, Laves phase is detrimental for the creep properties because it promotes formation of M 6 C [17].…”

Section: Precipitationmentioning

confidence: 99%

“…But in high nickel austenitic stainless steels with tungsten, it is found that the formation of Laves phase in the grain boundaries may improve the creep strength [28]. Generally Laves phase is found dispersed inside the grains, but sometimes also at grain boundaries after long time high-temperature exposure between 600 • C and 1000 • C. In niobium and tungsten containing austenitic stainless steels it can form as Fe 2 Nb and/or Fe 2 W after ageing around 600 • C and 800 • C [21,26,27].…”

Section: Precipitationmentioning

confidence: 99%

High-Temperature Fatigue Behaviour of Austenitic Stainless Steel : Influence of Ageing on Thermomechanical Fatigue and Creep-Fatigue Interaction

Wärner

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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The global energy consumption is increasing and together with global warming from greenhouse gas emission, create the need for more environmental friendly energy production processes. Higher efficiency of biomass power plants can be achieved by increasing temperature and pressure in the boiler section and this would increase the generation of electricity along with the reduction in emission of greenhouse gases e.g. CO 2. The power generation must also be flexible to be able to follow the demands of the energy market, this results in a need for cyclic operating conditions with alternating output and multiple start-ups and shutdowns. Because of the demands of flexibility, higher temperature and higher pressure in the boiler section of future biomass power plants, the demands on improved mechanical properties of the materials of these components are also increased. Properties like creep strength, thermomechanical fatigue resistance and high temperature corrosion resistance are critical for materials used in the next generation biomass power plants. Austenitic stainless steels are known to possess such good high temperature properties and are relatively cheap compared to the nickel-base alloys, which are already operating at high temperature cyclic conditions in other applications. The behaviour of austenitic stainless steels during these widened operating conditions are not yet fully understood. The aim of this licentiate thesis is to increase the knowledge of the mechanical behaviour at high temperature cyclic conditions for austenitic stainless steels. This is done by the use of thermomechanical fatigue-and creepfatigue testing at elevated temperatures. For safety reasons, the effect of prolonged service degradation is investigated by pre-ageing before mechanical testing. Microscopy is used to investigate the microstructural development and resulting damage behaviour of the austenitic stainless steels after testing. The results show that creep-fatigue interaction damage, creep damage and oxidation assisted cracking are present at high temperature cyclic conditions. In addition, simulated service degradation resulted in a detrimental embrittling effect due to the deterioration by the microstructural evolution.

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“…Laves phase has a hexagonal structure, it consists mostly of iron, molybdenum, an intermediate content of chromium and nickel [51,53,57] and a small amount of manganese, silicon, titanium and niobium [53]. It precipitates at intragranular sites and occasionally at GBs, often in small amounts, after 1000 hours ageing at temperatures between 600…”

Section: Carbides and Nitridesmentioning

confidence: 99%

“…X-phase has a body centred cubic (BCC) structure, it is rich in iron, chromium and molybdenum [13,57]. It forms at GBs and intragranularly, where it nucleate on dislocations, after 5000 hours at temperatures between 700…”

Section: Carbides and Nitridesmentioning

confidence: 99%

On High-Temperature Behaviours of Heat Resistant Austenitic Alloys

Calmunger¹

2015

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Advanced heat resistant materials are important to achieve the transition to long term sustainable power generation. The global increase in energy consumption and the global warming from greenhouse gas emissions create the need for more sustainable power generation processes. Biomass-fired power plants with higher efficiency could generate more power but also reduce the emission of greenhouse gases, e.g. CO 2 . Biomass is the largest global contributor to renewable energy and offers no net contribution of CO 2 to the atmosphere. To obtain greater efficiency of power plants, one option is to increase the temperature and the pressure in the boiler section of the power plant. Raised temperature and pressure increase the demands of the operating materials of the future high-efficient biomass-fired power plants. This requires improved properties, such as higher yield strength, creep strength and high-temperature corrosion resistance, as well as structural integrity and safety. Also, the number of start-and-stop cycles will increase, leading to demands on increased material performance under cyclic loading, both from thermal and mechanical loads.Heat resistant austenitic alloys, such as austenitic stainless steels and nickelbased alloys, possess excellent mechanical and chemical properties at the elevated temperatures and cyclic loading conditions of today's biomass-fired power plants. Today, some austenitic stainless steels are design to withstand temperatures up to 650• C in tough environments. Nickel-based alloys are designed to withstand even higher temperatures. Austenitic stainless steels are more cost effective than nickel-based alloys due to a lower amount of expensive alloying elements. However, the performance of austenitic stainless steels at the elevated temperatures of future operation conditions in biomassfired power plants is not yet fully understood.This thesis presents research on the influence of long term high-temperature ageing on mechanical properties, the influence of very slow deformation rates at high-temperature on deformation, damage and fracture, and the influence iii of high-temperature environment and cyclic operation conditions on the material behaviour. The research has been conducted on several commercial heat resistant austenitic alloys. Mechanical testing, such as impact toughness tests, uniaxial tensile tests at elevated temperatures using various strain rates and creep-fatigue interaction tests, has been performed. Also, thermal testing such as long term ageing and thermal cycling in a water vapour environment has been performed. The mechanical and thermal testing have been followed by subsequent studies of the microstructure, using scanning electron microscopy, to investigate the deformation, damage and fracture mechanisms as well as the precipitation and corrosion behaviours.Results shows that long term ageing (up to 10 000 hours) at high temperatures (up to 700• C) leads to the precipitation of intermetallic phases. These intermetallic phases are brittle at room temperatu...

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Thermal Stability of Intermetallic Phases in Fe-rich Fe-Cr-Ni-Mo Alloys

Cited by 11 publications

References 23 publications

In situ phase transformation of Laves phase from Chi-phase in Mo-containing Fe–Cr–Ni alloys

In situ phase transformation of Laves phase from Chi-phase in Mo-containing Fe–Cr–Ni alloys

High-Temperature Fatigue Behaviour of Austenitic Stainless Steel : Influence of Ageing on Thermomechanical Fatigue and Creep-Fatigue Interaction

On High-Temperature Behaviours of Heat Resistant Austenitic Alloys

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