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- Qin, Xiao, 1993, et al.
(författare)
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Effect of low temperature carburizing on the corrosion and mechanical behavior of AISI 304 austenitic stainless steel after hydrogen charging
- 2023
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Ingår i: Conference Proceedings of ECHT 2023.
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Konferensbidrag (refereegranskat)abstract
- Hydrogen is a clean and renewable energy that could replace fossil fuels, being beneficial to sustainability. Many metallic components in hydrogen energy systems are made from austenitic stainless steels. This research evaluates the effect of hydrogen uptake on the mechanical and corrosion properties of AISI 304 commercial austenitic stainless steel with and without low temperature carburising (LTC) process S³P feat. Kolsterising®. Both solution annealed (SA) and cold worked (CW) conditions were included. Hydrogen was introduced into the steel by the cathodic electrochemical hydrogen charging method. Open circuit potential (OCP) test and potentiodynamic polarisation were employed to evaluate the corrosion resistance in 3.5 wt.% NaCl solution. Specific tensile tests were performed to evaluate susceptibility to hydrogen embrittlement (HE). It has been found that hydrogen uptake causes surface cracking, reduces OCP, corrosion potential, and breakdown potential considerably, accelerating corrosion. LTC samples showed increased OCP and corrosion potential compared to untreated samples after hydrogen uptake. For cold worked 304, LTC treatment improves the resistance to HE significantly due to stabilized austenite and consequently reduced deformation-induced martensite. In solution annealed condition, HE susceptibility was improved slightly by LTC treatment. The results from the current study demonstrated the beneficial effect of this surface engineering approach, i.e., LTC treatment on achieving an improved material performance when exposed to hydrogen.
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| 2. |
- Qin, Xiao, 1993
(författare)
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Hydrogen embrittlement and corrosion behavior of low-temperature carburized austenitic stainless steel
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For metallic components used in hydrogen environments, hydrogen embrittlement and corrosion have always been important considering potential failure risks. Among many metallic materials, austenitic stainless steel has found broad application because of its excellent corrosion and hydrogen embrittlement resistance. Type AISI304 austenitic stainless steel is promising due to its low cost compared to high alloyed ones, such as 316 and 904 etc. However, 304 is a metastable austenite stainless steel, which is susceptible to strain-induced martensitic transformation. This may reduce corrosion and hydrogen embrittlement resistance in hydrogen-containing environments. Moreover, low hardness and poor fatigue properties also limit their application. It is therefore of great importance to improve hydrogen embrittlement and corrosion resistance of austenitic stainless steel 304. In recent years, extensive studies have been done to improve the hydrogen embrittlement and corrosion resistance of austenitic stainless steels, such as composition design, processing technology and surface engineering. Low-temperature carburizing (LTC), a surface engineering approach, has great potential because of its economic benefit and sustainability. This treatment can introduce interstitial carbon into the surface region of the steel and form precipitate-free supersaturated solid solution, greatly improving the surface hardness and fatigue properties without compromising the corrosion resistance. It is of great interest to evaluate the feasibility of LTC on the alleviation of hydrogen embrittlement and corrosion for commercial austenitic stainless steel 304 after hydrogen uptake. In the present study, industrial low-temperature carburizing was performed on commercial AISI304 stainless steel in two conditions (cold worked and solution annealed). Mechanical properties, corrosion behavior, and microstructure of the S phase after hydrogen uptake have been studied and linked. It was found that low-temperature carburizing introduced ~ 22 μm thick S-phase with ultra-high hardness (775 HV) and high surface carbon concentration (2.2 wt.% in solution condition). Hydrogen uptake caused reduced corrosion resistance and hydrogen embrittlement due to hydrogen-induced cracking and hydrogen-induced martensite. For cold-worked 304, hydrogen-induced cracking and martensitic transformation resulted in high susceptibility to hydrogen embrittlement. Solution-annealed 304 showed low hydrogen embrittlement susceptibility due to the austenitic phase with less defects. Low-temperature carburizing improved the hydrogen embrittlement resistance due to the carbon-stabilized austenite. However, the high carbon concentration on the surface of the solution annealed 304 with LTC treatment led to hydrogen-induced cracking and reduced ductility. Potentiodynamic polarization curves and corrosion morphology/chemical analysis revealed that low-temperature carburizing improved corrosion resistance due to high carbon content and stabilized austenite.
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| 3. |
- Qin, Xiao, 1993, et al.
(författare)
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Microstructure and texture evolutions in FeCrAl cladding tube during pilger processing
- 2023
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Ingår i: Journal of Materials Research and Technology. - 2238-7854. ; 25, s. 5506-5519
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of FeCrAl cladding tubes depends on the fabricating process history. In this study, the microstructural characteristics of wrought FeCrAl alloys during industrial pilger processing into thin-walled tubes were investigated. The hot extruded tube showed ∼100 μm equiaxed grains with weak α∗-fiber in {h11}<1/h12> texture, while pilger rolling process change the microstructure to fragmented and elongated grains along the rolling direction. The pilgered textures could be predicted with the VPSC model. The inter-pass annealing at 800–850 °C for 1 h results in recovery and recrystallization of the ferric matrix and restoration of ductility. The final finished tube shows fine recrystallized grains (∼11 μm) with dominant γ-fiber in three dimensions. Pilger rolling enhanced α-fiber while annealing reduced α-fiber and enhanced γ-fiber. Microstructural evolution in the Laves precipitates followed the sequence of faceted needle-like → spherical → faceted ellipsoidal. Thermomechanical processing resulted in cladding tubes with an area fraction of ∼5% and a number density of 5 × 10−11 m−2 in Laves precipitates, which is half that of the first-pilgered tube. Laves precipitates pin the grain boundaries to control the microstructure and prevent grain coarsening.
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| 4. |
- Qin, Xiao, 1993, et al.
(författare)
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Recrystallization and texture evolution of cold pilgered FeCrAl cladding tube during annealing at 700 °C∼1000 °C
- 2023
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 577
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Tidskriftsartikel (refereegranskat)abstract
- FeCrAl alloys are being developed as potential accident-tolerant fuel cladding materials for the light water reactors due to significantly improved steam oxidation and good mechanical properties at high temperatures. In this study, the recrystallization and texture evolution of the cold pilgered FeCrAl cladding tube was investigated by means of hardness measurements and electron backscatter diffraction (EBSD) during annealing at 700∼1000 °C. The partially recrystallized maps were deconstructed into deformed, recovered, and recrystallized grain fractions based on the critical internal misorientation angle. In the early stages of recrystallization, cold pilgered cladding tubes contained a mixture of discontinuously recrystallized {111}<110> newly nucleated grains and heterogeneous deformed 〈110〉 orientation grains. The deformed microstructural inhomogeneity state could be explained based on the Taylor factor. The rate of recrystallization increased with increasing annealing temperature, which was described by the Johnson-Mehl-Avrami-Kolmogorov equation. The cladding tube showed slow recrystallization kinetics and thermally stable grains due to the pinning of the grain boundaries by the Laves precipitates. The dominant α-fiber decreased and γ-fiber increased with increasing recrystallization fraction in the cold pilgered tubes. The high area fraction and stable γ-fiber would be beneficial to the processability of the cladding tube.
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