Efforts are being made worldwide to transform road transport to minimise its contribution to greenhouse gas emissions, with a focus on reducing vehicle mass. Lightweight manganese–aluminium steels ...have gained popularity for this purpose due to their low density and combination of strength and plasticity. In this particular study, the solidification process of five lightweight manganese–aluminium steels with different silicon content was investigated. The steels were fabricated by inductive melting in a vacuum and remelted during further thermal analysis. A reference steel composition (Fe-14Mn-10Al-0.2Si-0.8C) was used, and the remaining four steels contained different amounts of silicon (0.5, 1.0, 2.0 and 4.0 mass%). The impact of silicon on solidification was analysed by thermodynamic calculations (CALPHAD method), differential thermal analysis and optical microscopy. The thermodynamic calculations gave good estimates for the liquidus and austenite liquidus temperatures, but higher solidus temperatures than the experimental results. The presence of silicon decreases the density and lowers the solidus and liquidus temperatures, resulting in a prolonged solidification interval. In addition, the spacing of the secondary dendrite arms decreases, except at a silicon concentration of 0.5 mass%, where an increase was observed compared to the reference steel.
The high-temperature oxidation behaviour of three hot-work tool steels, Dievar, H11 and W600, was investigated by simultaneous thermal analysis (STA). Since the steels studied are usually used in the ...heat-treated condition, the high-temperature oxidation was studied in two conditions, the soft-annealed condition and the hardened and tempered condition. Simultaneous thermal analysis was used to study the effects of temperature, chemical composition and thermal condition of the steels on the high-temperature oxidation kinetics. The samples were oxidised for 100 h in air atmosphere in the STA instrument. The temperature range studied was between 400 and 700 °C. The equations describing the high-temperature oxidation kinetics were derived from the STA results. The kinetics can be described by three mathematical functions, namely exponential, parabolic and cubic. However, which function best describes the kinetics depends on the oxidation temperature, chemical composition and thermal state of the steel. Hardened and tempered samples have been shown to oxidise less, resulting in a slower oxidation rate. In addition, steels containing chromium (H11 and Dievar) generally oxidise less than a steel without chromium (W600).
Recently, low-density Fe–Mn–Al–C steels have attracted attention because of their low density with excellent combinations of strength and ductility. They can be divided into three categories: ...ferritic steels, duplex steels and austenitic steels, depending on the microstructure. The solidification of five duplex low-density steels was investigated. Five steels Fe–15Mn–10Al–0.8C, Fe–15Mn–10Al–1.7Ni–0.8C, Fe–15Mn–10Al–3.9Ni–0.8C, Fe–15Mn–10Al–5.6Ni–0.8C and Fe–15Mn–10Al–8.6Ni–0.8C were produced in a vacuum induction furnace under Ar atmosphere and remelted in a simultaneous thermal analyser (NETZSCH STA 449 C Jupiter). The influence of Ni on the solidification process was analysed using thermodynamic calculations and differential scanning calorimetry. The samples were analysed by light microscopy. The thermodynamic modelling was performed with commercial software Thermo-Calc using the CALPHAD method. The Thermo-Calc calculations show a better agreement for the liquidus temperatures at lower Ni additions, while the higher Ni additions show a better agreement for the solidus temperatures. The Ni additions slightly increase the density, reduce the distance of the secondary dendrite arms and lower both the solidus and liquidus temperatures, but do not influence the solidification interval.
During the die-casting process as well as the hot forming process, the tool is subjected to complex thermal, mechanical, and chemical stresses that can cause various types of damage to different ...parts of the tool. This study was carried out to determine the resistance of various tool steels, i.e., UTOPMO1, HTCS-130, and W600, in molten Al99.7 aluminum alloy at a temperature of 700 °C. The formation kinetics of the interaction layer between the molten aluminum and tool steels was studied using differential scanning calorimetry. Light and field-emission scanning electron microscopy were used to analyze the thickness and nature of the interaction layers, while thermodynamic calculations using the Thermo-Calc software were used to explain the results. The stability of the HTCS-130 and W600 tool steels is better than the stability of the UTOPMO1 tool steel in the molten Al99.7 aluminum. Two interaction layers were formed, which in all cases indicate an intermetallic Al
Fe
layer near the aluminum alloy and an intermetallic Al
Fe
layer near the tool steels, containing small round carbides. It was confirmed that Ni reduces the activity of aluminum in the ferrite matrix and causes a reduction in the thickness of the intermetallic layer.
The aim of our study was to investigate how different thermal conditions affect the transformation temperatures of two hot-work steels with high thermal conductivity. We focused on two conditions: ...soft annealing, and quenching and tempering. Soft annealing results in a ferritic steel matrix with spherical carbides, while quenching and tempering result in a fully hardened and tempered martensitic matrix with secondary and tempering carbides. We analysed samples using a simultaneous thermal analysis (STA) and differential scanning calorimetry (DSC) to determine the transformation temperatures. Controlled heating and cooling allowed us to observe the energy changes associated with the phase transformations. The equilibrium temperatures were calculated using the CALPHAD method. Our study investigated the influence of thermal conditions on different transformation temperatures, including solidus/liquidus temperatures, austenite solid transformation temperatures (A1 and A3), austenite solidification temperatures and bainite and/or martensite transformation temperatures. A DSC analysis was used to quantitatively measure the transformation temperatures and energy absorption during the endothermic processes (austenite solid transformation and melting) and to study the energy release during the exothermic processes (solidification and transformation). The results showed that soft annealing reduced the solidification interval and the solidus temperature, while energy absorption increased during melting. Conversely, quenching and tempering reduced the austenite solid transformation temperatures and energy release during solidification, including δ-ferrite solidification.
The influence of the thermal condition of the steel on the transformation temperatures of two chromium hot-work tool steels was investigated. The steels studied were in two different thermal states: ...the soft -annealed state and the hardened-and-tempered state. The soft-annealed condition, i.e., the fully annealed condition, is a thermal state of steels in which the matrix is ferritic, and the carbon is chemically bonded in spherical carbides. The hardened-and-tempered condition, on the other hand, means a fully hardened-and-tempered martensitic matrix with uniformly distributed (primary and secondary) carbides. The samples were analysed in a simultaneous thermal analyser (STA) using the differential scanning calorimetry (DSC) method to determine the transformation temperatures. We also performed calculations based on the CALPHAD method to obtain the equilibrium temperatures of the transformations. The aim of the study was to determine the influence of different thermal conditions of chromium hot-work tool steels on the transformation temperatures such as solidus/liquidus temperatures, eutectoid transformation temperatures (A1 and A3), austenite solidification temperature and martensite transformation start temperatures. Since DSC analysis also measures thermal influence, we were able to determine the energies absorbed during eutectoid transformation and melting (endothermic processes) and the energies released during the solidification of δ-ferrite and γ-austenite (exothermic processes), as well as the energies released during martensite transformation. It was found that hardening and tempering reduce both eutectoid transformation temperatures and that the solidification intervals are closer to those calculated. From an energetic point of view, hardening and tempering reduce the energies absorbed during melting.
Hot-work tool steels play a crucial role in applications exposed to extreme thermal, mechanical, and chemical stresses and require exceptional properties such as high strength, hardness, wear ...resistance, and toughness. The latter is crucial to prevent an unexpected tool failure due to the formation and propagation of fatigue cracks in demanding environments. In addition, high thermal conductivity is crucial to prevent overheating of the tool and the resulting degradation of the material. This study focuses on a new generation hot-work tool steel with increased Mo and W contents, which has excellent thermal conductivity but limited toughness, as it contains stable Mo-W carbides that remain stable up to 1100 °C. To improve toughness, an alternative heat-treatment method involving austempering at different temperatures was applied. The investigation begins with the characterisation of the chemical composition of the steel, followed by the determination of the martensite-start (MS) and martensite-finish (Mf) temperatures. Based on the results, the researchers established a set of samples for austempering heat treatment. They investigated the effects of different isothermal holding temperatures on the microstructure of the steel and its subsequent mechanical properties. The results show that reduced bainite formation, achieved by austempering at certain temperatures, led to significantly improved impact toughness and moderate hardness. This study also showed a correlation between the isothermal holding temperature and the extent of martensitic transformation, which affected the microstructure and mechanical properties of the steel.
This study presents a comprehensive investigation of the formation, composition and behaviour of oxide layers during the high-temperature oxidation of four different steel alloys (16Mo3, 13Cr, T24 ...and P91) at a uniform temperature of 650 °C. The study is aimed at assessing the oxidation damage due to short-term overheating. The research combines CALPHAD (CALculation of PHAse Diagrams) calculations, thermogravimetric analysis (TGA) and advanced microscopy techniques, including scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), to elucidate the complex mechanisms controlling oxidation kinetics and oxide layer development. CALPHAD calculations were used to determine the thermodynamically stable phases for each steel type at 650 °C and different oxygen activities. The results showed different phase compositions, highlighting the importance of the chromium content in steel for the formation of oxide layers. The different oxidation kinetics and oxide layer compositions are presented and associated with the increased risk of material degradation due to overheating. These results have significant implications for industrial applications, mainly the susceptibility to oxidation of low-alloyed steels like 16Mo3 and 13 Cr and contribute to a deeper understanding of oxidation processes in steels.
Lightweight Fe-Mn-Al-Ni-C steels are an attractive material, due to the combination of low density, high elongation, and yield strength. However, the high Al content is also interesting from the ...point of view of high-temperature resistance. High-temperature resistance is important for high-temperature applications and oxidation during heat treatment. Oxidation tests at 700, 800 and 900 °C were carried out to investigate the oxidation rates. Oxidation at 700 °C resulted in slight decarburisation, which was reflected in a slight weight loss in the thermogravimetric analysis. In contrast, the weight in the thermogravimetric analysis increased at 800 and 900 °C and the kinetics followed a parabolic law. The higher the temperature, the more weight is gained and the thicker the oxide layer becomes. The oxidation layer at 800 and 900 °C consisted mainly of hematite and magnetite, with minor amounts of wüstite, alumina and hercynite. Preferential oxidation of austenite was also observed, as it has an increased Mn content. In addition, ferrite had an increased content of Al and Ni, which provide additional oxidation resistance.
The tool used in die casting or hot forming is subjected to thermal and mechanical stress, resulting in damage and cracking due to thermal fatigue and melt flow. This reduces the profitability and ...efficiency of production, as the products may not meet the required dimensions and mechanical properties. Understanding the interaction between tool steel and molten aluminium alloy is critical to extending tool life. AlCrN protective coatings on tool surfaces can improve corrosion resistance, thermal fatigue and wear resistance.
The present work was carried out to predict the effect of the AlCrN protective coating on the interaction kinetics between H11 tool steel and molten aluminium alloy Al99.7. The AlCrN protective coating on the H11 tool steel sample served its purpose and slowed down the interaction between the aluminium melt from Al99.7 and the H11 tool steel, as the DSC curve of the sample that had the AlCrN protective coating applied flattened out faster, indicating the cessation of dissolution in the material at all investigated temperatures. Measurements of the thicknesses of the interaction layers also confirmed these results, whereas the thickness of the composite layer was almost the same at both experimental temperatures, 670°C and 700°C, respectively, without an AlCrN protective coating; the temperature has no effect on this layer and the types of interaction layers did not differ from each other.
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