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32. Scanning electron microscope images of isolates of small cellular particles Phaeodactylum tricornutum grown in media supplemented with Guillard’s (F/2) marine : marine water enrichment solution, BG11 broth and Lennox LB brothApolonija Bedina Zavec, Darja Božič, Matej Hočevar, Aleš Iglič, Marko Jeran, Veronika Kralj-Iglič, Anna Romolo, 2024, objavljeni znanstveni prispevek na konferenci Objavljeno v DiRROS: 08.03.2024; Ogledov: 99; Prenosov: 49
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35. Understanding carbide evolution and surface chemistry during deep cryogenic treatment in high-alloyed ferrous alloyPatricia Jovičević Klug, Levi Tegg, Matic Klug Jovičević, Rahul Parmar, Matteo Amati, Luca Gregoratti, László Almásy, Julie M. Cairney, Bojan Podgornik, 2023, izvirni znanstveni članek Ključne besede: cryogenic temperature, surface chemistry, microstructure, atom probe tomography (APT), scanning photoelectron microscopy (SPEM), small angle neutron scattering (SANS)
Objavljeno v DiRROS: 08.03.2024; Ogledov: 98; Prenosov: 94
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36. In vitro and in vivo degradation behavior of Mg-0.45Zn-0.45Ca (ZX00) screws for orthopedic applicationsDiana C. Martinez, Anna Dobkowska, Romy Marek, Hanna Ćwieka, Jakub Jaroszewicz, T. Plociński, Črtomir Donik, Heike Helmholz, Bérengère Luthringer-Feyerabend, Berit Zeller-Plumhoff, Regine Willumeit-Römer, Wojciech Święszkowski, 2023, izvirni znanstveni članek Ključne besede: magnesium alloys, biodegradable implants, microstructure, electron microscopy, corrosion layers
Objavljeno v DiRROS: 08.03.2024; Ogledov: 103; Prenosov: 103
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37. Ladle melt treatment of high sulfur stainless steelsJaka Burja, 2024, objavljeni znanstveni prispevek na konferenci Povzetek: 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.
Ključne besede: desulfurization, sulfur, stainless steel, steelmaking
Objavljeno v DiRROS: 28.02.2024; Ogledov: 164; Prenosov: 64
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38. High temperature oxidation of EN AW 7075 aluminium alloyNejc Velikajne, Tilen Balaško, Jaka Burja, Matjaž Godec, Irena Paulin, 2024, objavljeni znanstveni prispevek na konferenci Povzetek: Aluminium alloys are highly valued for their exceptional strength-to-weight ratio, making them a preferred choice in structural applications. Among these alloys, EN AW 7075 stands out for its superior mechanical properties, finding widespread use in industries such as aerospace, mechanical engineering, and sports equipment. This study investigates the high-temperature oxidation behavior of EN AW 7075 alloy. The gathered results can provide valuable insights into the behavior of the mentioned alloy during the selective laser melting (SLM) process. These results can contribute to a better understanding of how the alloy responds to specific conditions and parameters. SLM is an additive manufacturing technique. The process involves the sequential steps of preheating, melting, and rapid cooling of metal powder. To minimize the influence of oxygen, the build chamber is filled with inert gas. A protective argon atmosphere is continuously maintained. However, despite these precautions, oxidation can still occur, leading to potential issues in the final product. Hence, we examined the oxidation kinetics of the EN AW 7075 alloy in an oxygen atmosphere in the temperature range of 300-500 °C. The findings of this investigation significantly contribute to an understanding of the behavior of the alloy during high-temperature oxidation, particularly for ongoing studies focused on processing Al-Zn-Mg-Cu alloys using the selective laser melting technique. Thermogravimetry was employed to analyze the oxidizing behavior, with three samples subjected to a 6-hour exposure in an oxidizing atmosphere at temperatures of 300, 400, and 500 °C. Surprisingly, no oxidation occurred, as indicated by the negligible and negative changes in mass observed across all samples.
Ključne besede: EN AW 7075, high-temperature oxidation, oxide film, selective laser melting
Objavljeno v DiRROS: 28.02.2024; Ogledov: 169; Prenosov: 70
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39. Enhancing ductility of hot-work tool steel through isothermal bainitic transformationAnže Bajželj, Aleš Nagode, Tilen Balaško, Barbara Šetina, Jaka Burja, 2024, objavljeni znanstveni prispevek na konferenci Povzetek: Hot-work tool steels are extensively used in industrial applications that require high resistance to mechanical and chemical degradation at elevated temperatures. To meet these requirements, hot-work tool steels must exhibit good mechanical properties, including high tensile strength, hardness, wear resistance, and tempering resistance, as well as high thermal conductivity and ductility. This study investigates the ductility of the hot-work tool steel HTCS-130, which suffers from low ductility due to the presence of stable molybdenum-tungsten carbides (M6C) on the prior austenite crystal grain boundaries. Increasing austenitisation temperatures or prolonging the dwelling time at temperature can promote intensive migration of grain boundaries, leading to negative effects on the mechanical properties of the steel. To address this issue, isothermal transformation in the bainitic area between 350 and 500 °C was performed. Isothermal transformation at around 350 °C leads to the formation of lower bainite, which has similar hardness to tempered martensite. As the temperature of isothermal transformation increases, the hardness of the material decreases, due to the formation of upper bainite. The hardness analysis was measured using the Vickers method, the impact toughness of the steel samples was measured using a Charpy test with V-notched samples. The microstructure characterization was performed using optical and scanning electron microscopy. The improvement of ductility can be achieved by controlling the isothermal transformation of bainite and adjusting the heat treatment conHot-work tool steels are extensively used in industrial applications that require high resistance to mechanical and chemical degradation at elevated temperatures. To meet these requirements, hot-work tool steels must exhibit good mechanical properties, including high tensile strength, hardness, wear resistance, and tempering resistance, as well as high thermal conductivity and ductility. This study investigates the ductility of the hot-work tool steel HTCS-130, which suffers from low ductility due to the presence of stable molybdenum-tungsten carbides (M6C) on the prior austenite crystal grain boundaries. Increasing austenitisation temperatures or prolonging the dwelling time at temperature can promote intensive migration of grain boundaries, leading to negative effects on the mechanical properties of the steel. To address this issue, isothermal transformation in the bainitic area between 350 and 500 °C was performed. Isothermal transformation at around 350 °C leads to the formation of lower bainite, which has similar hardness to tempered martensite. As the temperature of isothermal transformation increases, the hardness of the material decreases, due to the formation of upper bainite. The hardness analysis was measured using the Vickers method, the impact toughness of the steel samples was measured using a Charpy test with V-notched samples. The microstructure characterization was performed using optical and scanning electron microscopy. The improvement of ductility can be achieved by controlling the isothermal transformation of bainite and adjusting the heat treatment conditions. These findings provide useful insights into the design and optimization of heat treatment processes for hot-work tool steels.ditions. These findings provide useful insights into the design and optimization of heat treatment processes for hot-work tool steels.
Ključne besede: hot-work tool steel, austempering, bainitic transformation, ductility, dilatometry
Objavljeno v DiRROS: 28.02.2024; Ogledov: 157; Prenosov: 69
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40. Effect of heat treatment on thermal conductivity of additively manufactured AISI H13 tool steelSamo Tome, Blaž Karpe, Irena Paulin, Matjaž Godec, 2024, objavljeni znanstveni prispevek na konferenci Povzetek: AISI H13 is commonly used for tooling, where higher wear resistance, thermal fatigue resistance, or hot toughness is required. Such examples include forging dies, plastic molds, hot shear blades, high-pressure die casting, and extrusion dies. Thus, thermal conductivity is one of the most important factors for hot work tools. Typically, the work cycle of a hot work tool designed for forging consists of four main phases: the forging stroke, with which the die imparts its shape onto the part, a brief pause while the die is reset to its original position, a lubrication phase, and a post lubrication dwell phase. During the forging phase, a significant amount of heat is transferred to the die while it is in contact with the part. This heat must then be dispelled for the part to return to a working temperature. While somewhat different, other hot work processes mentioned above are similar in that the hot work tool gets heated to a high temperature due to the contact with the object of deformation. The process of additive manufacturing (AM) promises better, more efficient tool production with features like conforming cooling channels, which would reduce the thermal fatigue of tools, prolonging tool life. However, the powder bed fusion (PBF) method creates a columnar microstructure, which has a detrimental effect on the thermal conductivity of H13 tool steel. Our investigation focused on the beneficial effect of heat treatment, specifically annealing at different temperatures, on the thermal conductivity of AM-produced H13 parts.
Ključne besede: SLM, thermal conductivity, tool steel, heat treatment
Objavljeno v DiRROS: 28.02.2024; Ogledov: 129; Prenosov: 73
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