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Povzetek: This study explores the mechanical and corrosion properties of yttria-reinforced 316L stainless steel. Powder precursor materials were prepared using mechanical alloying. Varying yttria (Y2O3) contents (1, 3, and 5 wt%) were used to assess its impact on the steel’s properties. X-ray diffraction and scanning electron microscopy confirmed the successful dispersion of Y2O3 within the matrix, with the formation of chromium carbides during spark plasma sintering (SPS). The mechanical properties, including hardness and compressive yield strength, improved with increasing Y2O3 contents, with the highest strength observed in the 316L-5Y2O3 sample. However, corrosion resistance decreased with higher yttria concentrations. The 3 wt% Y2O3 sample exhibited the highest corrosion rate due to localized corrosion in areas enriched with oxide particles and chromium carbides. Electrochemical testing revealed that carbide formation and Cr-depleted regions from SPS processing contributed to the corrosion behaviour. These findings suggest that while yttria reinforcement enhances mechanical strength, optimizing the Y2O3 content and processing methods is crucial to balance both mechanical and corrosion performance in ODS 316L stainless steel.
Ključne besede: mechanical milling, SPS, 316L, austenitic stainless steel, yttria, ODS steel, corrosion, EPR-SL
Objavljeno v DiRROS: 31.01.2025; Ogledov: 125; Prenosov: 89
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Povzetek: Stainless steel production typically follows the duplex process, beginning with the electric arc furnace (EAF) and proceeding to the vacuum oxygen decarburizer (VOD) or argon oxygen decarburizer (AOD). The EAF's role is to melt the charge and heat it up for further processing, reducing tap-to-tap times through partial oxidation. However, this partial oxidation in the EAF leads to chromium losses as oxygen interacts with the high chromium steel melt. To address this issue, parameters affecting chromium burn-off have been identified and presented. A primary challenge in EAF steel production with elevated chromium content is to lower carbon levels while maximizing chromium yield in the melt. Unlike VOD and AOD processes, which permit low carbon and high chromium levels through vacuum or argon blowing, the EAF provides limited protection, mainly through silicon. At higher temperatures, carbon oxidation predominates, hence it is important to limit oxygen input into the system in the initial stages, while “protecting” the chromium with silicon. During the oxidation phase of the steel melt, carbon content decreases; however, attention must be paid to ensure that the concentration is not too low, as this increases chromium activity in the melt, leading to more intense oxidation. A practical model, derived from thermodynamic calculations, has been developed to guide carbon, chromium, and other element oxidation during scrap melting. This model, validated through industrial trials, aids in optimizing steel melt oxidation to minimize chromium losses effectively.
Ključne besede: EAF, stainless steel scrap, carbon oxidation, chromium oxidation, thermodynamics
Objavljeno v DiRROS: 16.01.2025; Ogledov: 136; Prenosov: 60
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Povzetek: TIn the present study the differences in the mineralogical composition and microstructure of various types of EAF stainless steel (EAF S) slag with regard to the cooling treatment, the operation practice in an EAF (electric arc furnace) and environmental ageing reactions were evaluated. It was shown that the mineralogy of the investigated EAF S slags varied from one slag to another, depending on the quality of the produced stainless steel. The production process of the treated steel also has a strong influence on the mineralogy of the slags. The conditions during water cooling treatment were not sufficient to prevent the crystallization of primary mineral phases, which occurs predominantly in air-cooled EAF S slags, probably due to the high basicity of the investigated slags. However, the water cooling treatment of hot slag leads to the absence of γ-CaSiO 4 and the formation of secondary mineral phases predominantly calcite, portlandite, ettringite, calcium aluminate hydrate and calcium silicate hydrate. It has been shown that during the environmental ageing test (down-flow column test) secondary mineral phases were formed, which were the same as those formed during the water cooling treatment.
Ključne besede: electric arc furnace stainless steel slag, cooling path, microstructure, mineralogy
Objavljeno v DiRROS: 14.08.2024; Ogledov: 490; Prenosov: 270
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Povzetek: A low carbon/ high chromium martensitic stainless steel, X17CrNi16-2, was heat treated using two different hardening and tempering regimes (1050 ◦ C/480 ◦ C or 980 ◦C/600 ◦C) — promoting either a high strength or high toughness state, respectively and further combined with deep cryogenic treatment (DCT) at 196 ◦C for 24 h. Over recent years DCT has been recognized as a promising technique to improve the properties of steel, predominantly with respect to its tensile strength, toughness and wear resistance. The influence of DCT on the hydrogen embrittlement resistance of martensitic stainless steel has not yet, however, been reported. A slow strain rate tensile test (SSRT) with simultaneous cathodic hydrogen charging was selected as the method to assess potential susceptibility to hydrogen embrittlement (HE). Relatively low-intensity hydrogen charging, utilizing a constant current density of 0.1 mA/cm2, in a non-corrosive, slightly alkaline buffer solution, led to a clear reduction in the ultimate tensile stress. This reduction, and therefore the HE susceptibility, was more pronounced in the steel with a higher strength (i.e. that subject to the 1050 ◦C/ 480 ◦C heat treatment condition). Furthermore, DCT did not appear to have any impact on the steel’s mechanical properties in the presence of hydrogen. Fractographic analysis showed clear evidence of HE in the hydrogen-charged specimens. This paper presents results of the SSRT tests and further fractography results, and discusses the impact of conventional and deep cryogenic treatment on HE susceptibility.
Ključne besede: martensitic stainless steel, deep cryogenic treatment, hydrogen embrittlement, slow strain rate tensile test
Objavljeno v DiRROS: 23.05.2024; Ogledov: 609; Prenosov: 469
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Ključne besede: austenitic stainless steel, powder bed fusion, low-temperature plasma nitriding, wear and corrosion behaviour, dislocation cell structure
Objavljeno v DiRROS: 25.03.2024; Ogledov: 584; Prenosov: 356
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