1. Comparison of the mineralogy and microstructure of EAF stainless steel slags with reference to the cooling treatmentMojca Loncnar, Ana Mladenovič, Marija Zupančič, Peter Bukovec, 2017, original scientific article Abstract: 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.
Keywords: electric arc furnace stainless steel slag, cooling path, microstructure, mineralogy
Published in DiRROS: 14.08.2024; Views: 257; Downloads: 148
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2. Influence of isothermal annealing in the 600 to 750 °C range on the degradation of SAF 2205 duplex stainless steelJaka Burja, Borut Žužek, Barbara Šetina, 2024, original scientific article Abstract: We studied the effect of isothermal annealing (600–750 °C, 1 to 1000 min) on the microstructure
and mechanical properties of SAF 2205 duplex stainless steel. Impact toughness was found
to be significantly more affected than hardness by annealing. Annealing at 750 °C for 1000 min
resulted in a more than 90% decrease in impact toughness, while hardness only increased by 25%.
Tensile strength increased up to 100 MPa, but elongation decreased by more than 50% under the
same conditions. Sigma phase formation was minimal at lower temperatures (650 °C and below)
but increased significantly at higher temperatures. At 750 °C and 1000 min of annealing, the ferrite
content dropped from 50% to 16%. These findings suggest that annealing temperature and time need
to be carefully controlled to avoid a reduction in impact toughness and ductility caused by sigma
phase precipitation. The harmful effect of sigma phase precipitation on mechanical properties was
directly shown.
Keywords: duplex stainless steel, sigma phase, precipitation kinetics, mechanical properties, isothermal annealing
Published in DiRROS: 24.07.2024; Views: 189; Downloads: 159
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3. Susceptibility of X17CrNi16-2 martensitic stainless steel to hydrogen embrittlement after conventional and deep cryogenic heat treatmentMirjam Bajt Leban, Bojan Zajec, Bojan Podgornik, Črtomir Donik, Patricia Jovičević Klug, Miha Hren, Andraž Legat, 2024, original scientific article Abstract: 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.
Keywords: martensitic stainless steel, deep cryogenic treatment, hydrogen embrittlement, slow strain rate tensile test
Published in DiRROS: 23.05.2024; Views: 351; Downloads: 334
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4. The effect of heat treatment on the interface of 155 PH martensitic stainless steel and SAF 2507 duplex steel in functionally graded AM componentsMartina Koukolíková, Pavel Podaný, Sylwia Rzepa, Michal Brázda, Aleksandra Kocijan, 2023, original scientific article Abstract: Multi-material components, also known as functionally graded materials (FGMs), are innovative materials that possess unique properties due to their composition and have many potential applications in engineering and science. The effect of the heat treatment (HT) of functionally graded materials 15–5 precipitation-hardened (PH) martensitic steel and SAF 2507 duplex stainless steel (and the opposite order of deposition, i.e. SAF 2507 first followed by 15–5 PH stainless steel) on the interface microstructures was systematically investigated in the presented research. The choice of HT followed the trend of optimum post-processing for the individual alloys. A significant modification in the interface microstructure, characterized in the microstructural transition zone (MTZ) formed above the fusion line. Mechanical properties by miniaturized testing method including hardness measurement characterized both types of interfaces. The sequence of the materials’ application did not have a significant effect on their final mechanical tensile properties in the heat-treated states. Nevertheless, the microstructural change at the MTZ led to drop in the hardness at the interface. The research presents heat-treated FGMs in a horizontal configuration to form a high-quality metallurgical joint between heterogeneous materials manufactured by powder-based directed energy deposition method.
Keywords: heat treatment, additive manufacturing, martensitic stainless steel, duplex steel, microstructure, mechanical properties
Published in DiRROS: 04.04.2024; Views: 409; Downloads: 126
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5. Effect of post-treated low-temperature plasma nitriding on the wear and corrosion resistance of 316L stainless steel manufactured by laser powder-bed fusionMatjaž Godec, Črtomir Donik, Aleksandra Kocijan, Bojan Podgornik, Danijela Anica Skobir Balantič, 2020, original scientific article Keywords: austenitic stainless steel, powder bed fusion, low-temperature plasma nitriding, wear and corrosion behaviour, dislocation cell structure
Published in DiRROS: 25.03.2024; Views: 389; Downloads: 245
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6. A comparative analysis among quenched, tempered, and stepped cooled TIG welded SS-304 plates based on tensile strength, hardness, and microstructural appearanceSaurabh Dewangan, Saksham Saksham, Adhir Chandra Paul, Jaka Burja, 2023, original scientific article Keywords: welding, austenitic stainless steel, heat affected zone, mechanical properties
Published in DiRROS: 15.03.2024; Views: 400; Downloads: 182
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7. Ladle melt treatment of high sulfur stainless steelsJaka Burja, 2024, published scientific conference contribution Abstract: The influence of sulfur on both slag and melt is very important in steelmaking. This is especially true for highsulfur machining steels. Machinability is achieved by alloying high sulfur contents, above 300 ppm. These are steels that form small chips and shavings during mechanical processing by cutting, which is more appropriate and favorable for both the workpiece and the processing tool and machine. However, the secondary steelmaking slag is typically designed for desulfurization. This means that the sulfur content rapidly falls after sulfur additions. This is especially true for high machinability stainless steel grades where S contents can exceed 1000 ppm. This causes the sulfur wire yield to vary greatly in each charge, making the process unreliable. Some aspects of understanding the interaction between the steel melt and slag and the effect on casting are presented in this work. Based on industrial charges, we analyzed the yield of sulfur additions and the influencing factors on the efficiency of the sulfur addition. The lower slag basicity was linked to lover sulfur distribution rations, and lover sulfur distribution rations were linked to higher sulfur yields. Melt and slag samples were analyzed. Slag entrapment during ingot casting was linked to the high sulfur contents.
Keywords: desulfurization, sulfur, stainless steel, steelmaking
Published in DiRROS: 28.02.2024; Views: 421; Downloads: 180
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8. Austenite reversion suppression with deep cryogenic treatment : a novel pathway towards 3rd generation advanced high-strength steelsPatricia Jovičević Klug, Matic Klug Jovičević, Lars Thormählen, Jeffrey McCord, Michael Rohwerder, Matjaž Godec, Bojan Podgornik, 2023, original scientific article Keywords: Martensitic stainless steel, deep cryogenic treatment, microstructure, mechanical properties, microstructural transformations, phase transformation
Published in DiRROS: 02.02.2024; Views: 487; Downloads: 228
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9. Complex interdependency of microstructure, mechanical properties, fatigue resistance, and residual stress of austenitic stainless steels AISI 304LPatricia Jovičević Klug, Matic Klug Jovičević, Michael Rohwerder, Matjaž Godec, Bojan Podgornik, 2023, original scientific article Keywords: stainless steel, AISI 304L, deep cryogenic treatment (DCT), microstructure, mechanical properties, fatigue, residual stress
Published in DiRROS: 02.02.2024; Views: 549; Downloads: 256
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10. Tribological evaluation of vegetable ▫$oil/MoS_2$▫ nanotube-based lubrication of laser-textured stainless steelMarjetka Conradi, Bojan Podgornik, Maja Remškar, Damjan Klobčar, Aleksandra Kocijan, 2023, original scientific article Abstract: In the present work, the functionalisation of austenitic stainless steel, AISI 316L surfaces via nanosecond Nd:YAG laser texturing in order to modify the surface morphology with crosshatch and dimple patterns is presented. A tribological analysis under lubrication with sunflower and jojoba oil with and without the addition of a solid lubricant, MoS2 nanotubes, was performed. In conjunction with friction/wear response laser-textured surface wettability, oil spreadability and oil retention capacity were also analysed. It was shown that the crosshatch pattern generally exhibited lower friction than the dimple pattern, with the addition of MoS2 nanotubes not having any significant effect on the coefficient of friction under the investigated contact conditions. This was found in addition to the better oil spreadability and oil retention capacity results of the crosshatch-textured surface. Furthermore, texturing reduced the wear of the stainless-steel surfaces but led to an approximately one order of magnitude larger wear rate of the steel counter-body, primarily due to the presence of hard bulges around the textured patterns. Overall, the crosshatch pattern showed better oil retention capacity and lower friction in combination with different vegetable oils, thus making it a promising choice for improving tribological performance in various environmentally friendly applications.
Keywords: tribology, stainless steel, vegetable oil lubrication, MoS2 nanotubes
Published in DiRROS: 02.02.2024; Views: 1630; Downloads: 189
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