In order to explore the influence of niobium, tantalum and titanium modification on grain growth in high-thermal-conductive hot-work tool steel during austenitisation at high temperatures, three ...types of modified steels (sample HTCS-130 + 0.06 w/% Nb, sample HTCS-130 + 0.03 w/% Ta, sample HTCS-130 + 0.006 w/% Ti) based on reference (sample HTCS-130 – 0) were prepared. The effect of different austenitisation temperatures (1030, 1060, 1080 and 1100) °C on hardness after quenching and grain size were investigated. The results show that there is a positive effect on the mechanical properties and a decreased grain-growth effect in the modified steel samples. The precipitation behaviour of the carbides was also investigated with electron microscopy. The Mo-W carbides were relatively weak at retaining grain size, but their pinning effect was increased with the incorporation of other carbide-forming elements like Nb and Ta. MC-type carbides on the grain boundary were effective at grain-boundary pinning. Nb even further increased the resistance by forming NbC carbides. The addition of Ti, on the other hand, proved to be ineffective due to the intergranular precipitation of the formed carbonitrides.
Sodobno slovensko zgodovinopisje pri opazovanju preteklosti ozemlja današnje Slovenije v vedno večji meri opušča nacionalistično perspektivo, ki je prevladovala vse od 19. st. Avtor poskuša orisati ...pomen in utemeljenost uporabe tega pristopa v slovenskem glasbenem zgodovinopisju.
Standard heat treatment of martensitic stainless steel consists of quenching and tempering. However, this results in high strength and hardness, while Charpy impact toughness shows lower values and a ...large deviation in its values. Therefore, a modified heat treatment of 0.1C-13Cr-3Ni martensitic stainless steel (PK993/1CH13N3) with intercritical annealing between Ac1 and Ac3 was introduced before tempering to study its effect on the microstructure and mechanical properties (yield strength, tensile strength, hardness and Charpy impact toughness). The temperatures of intercritical annealing were 740, 760, 780 and 800 °C. ThermoCalc was used for thermodynamic calculations. Microstructure characterization was performed on an optical and scanning electron microscope, while XRD was used for the determination of retained austenite. Results show that intercritical annealing improves impact toughness and lowers deviation of its values. This can be attributed to the dissolution of the thin carbide film along prior austenite grain boundaries and prevention of its re-occurrence during tempering. On the other hand, lower carbon concentration in martensite that was quenching from the intercritical region resulted in lower strength and hardness. Intercritical annealing refines the martensitic microstructure creating a lamellar morphology.
The corrosion properties of an EN AC AlSi9Cu3(Fe) alloy (reference sample (RS)) and samples produced by recycling chips of RS by direct hot extrusion (DHES) and subsequent thixoforming (TFS) were ...tested in 0.5 M NaCl solution. The plastic deformation changes the microstructure of RS, and brittle, coarse Si particles and intermetallic compounds (IMCs) were effectively broken into ultrafine-grained particles and redistributed homogeneously into the α-Al matrix in DHES. TFS exhibits a globular structure, and polyhedral clusters rich in Si and IMCs were observed along the grain boundary. Electrochemical measurements combined with surface characterisation show that the microstructure significantly influences the tested samples’ corrosive properties. It was confirmed that corrosion resistance increased in the following order: RS < TFS < DHES. Similarly, the corrosion potential becomes nobler, the corrosion current decreases, the passive area increases, and the oxide layer becomes more stable (higher resistance and thickness). Also, the percentage of the surface affected by corrosion and the volume of pits reduce. The effect of microstructure is particularly pronounced in the level of the corrosion current and the volume of pits formed. The corrosion current of DHES and TFS decreases by 4–5 times, while the pit volume of DHES and TFS decreases by several orders of magnitude compared to RS. The corrosion stability of DHES and TFS in relation to RS is a consequence of the comminution of the Si particles and the IMC. The refined and homogeneous microstructure contributes positively to forming a stable oxide film on DHES and TFS and increases their corrosion resistance in an aggressive environment. The applied recycling method represents an innovative and sustainable process for the recycling of semisolid materials, with lower energy consumption and less greenhouse gas emissions compared to conventional recycling. The fact that the products obtained through recycling have a significantly higher corrosion resistance further increases the economic and environmental impact of the process.
Co-Cr alloys have good mechanical properties such as high hardness, excellent magnetic properties and good corrosion resistance. For this reason, they are most commonly used as dental and orthopaedic ...implants. Generally, cast Co-Cr-Mo alloys and forged Co-Ni-Cr-Mo alloys are used for the production of implants. In this study, we investigated two dental alloys, namely, Co-Cr-Mo and Co-Cr-W-Mo alloys. The aim of this study was to determine the effect of heat treatment on the development of the microstructure and to evaluate its influence on the alloys’ mechanical and tribological properties. The samples were first solution-annealed at 1200 °C in an argon atmosphere for 2 h, then quenched in water and subsequently aged at 900 °C in an argon atmosphere for 1, 3 and 12 h. A microstructural analysis was performed using SEM, with EDS for microchemical analysis and EBSD for phase identification. In addition, the Vickers hardness and wear resistance of the two alloys were analysed before and after heat treatment. The Co-Cr-Mo alloy showed better wear resistance and also a generally higher hardness than the Co-Cr-W-Mo alloy. Both alloys showed signs of abrasive and adhesive wear, with carbide particles detaching from the Co-Cr-W-Mo alloy due to the lower hardness of the matrix. The Co-Cr-Mo alloy showed the best abrasion resistance after the longest aging time (12 h), while the Co-Cr-W-Mo alloy showed the best as-cast abrasion resistance. With ageing, the wear resistance of both alloys increased.
The constant need for the development of new alloys with an improved ratio between weight and strength is the driving force for the progress of the present work, which deals with the production of a ...new Al-cast alloy with the addition of lithium (Li). 0.8 wt% Li was added to the AlSi7Mg alloy. The solidification behaviour of such a new alloy was the focus of the work. The melt was produced in an inert gas atmosphere in an induction furnace. The solidification behaviour was described by CALPHAD simulations, optical microscopy, scanning electron microscopy (SEM) and simple thermal analysis. In addition, the Vickers hardness (HV) was measured 29 days after casting and compared with the results of the AlSi7Mg base alloy. Solidification proceeds somewhat differently from the base alloy, where the liquidus temperature is raised to 637 °C, where the primary AlLiSi phase forms, followed by αAl dendrites, eutectic βSi and other phases in the form of eutectics, which are known to occur during solidification of the AlSi7Mg alloy. The hardness of the new alloy is increased compared to the base alloy, especially at higher cooling rates, where the hardness gain is up to 36%.
An accurate prediction of the core losses is crucial for the optimal design and selection of the electrical steels used in electrical devices. The measured specific core losses are divided into three ...main parts, i.e., the eddy-current loss, the hysteresis loss, and the excess loss. In this paper, a simplified, predictive model for the core loss in a non-oriented electrical steel using fixed coefficients is proposed. The coefficients for a wide frequency spectrum up to 10 000 Hz of validity for the prediction of the eddy current, the hysteresis, and the excess components were calculated with respect to a sinusoidal voltage using the modified Steinmetz equation and a polynomial regression analysis.
In this paper thermal cycling of tungsten alloy WNi28Fe15 used as a filler material for cladding of the surfaces on the high pressure die casting tools is presented. Gas tungsten arc welding was used ...for deposition of the tungsten alloy in a form of a welding rod on the cylindrical specimens made of AISI H13 hot work tool steel. High frequency generator working with 20kHz was used for thermal cycling of the 40mm high specimens with the diameter of 30mm. Water with a temperature of 8°C was flowing through the internal hole of the specimen. Each thermal cycle consisted of 5s long heating section and 30s long cooling section. The temperature of the surface during thermal cycling was measured using infrared camera. The resulting clad was studied by means of microstructural analysis. The results have shown superior thermal fatigue resistance of cladded layer compared to reference heat treated hot work tool steel AISI H13. Surface hardness of the specimens cladded with tungsten alloy is approximately 100HV0.5 higher compared to heat treated AISI H13 steel at the end of thermal cycling. Additionally coefficient of the linear thermal expansion was measured for WNi28Fe15 alloy in the range from room temperature to 1100°C. An average value of the coefficient of the linear thermal expansion in the range between 25°C and 700°C is 12.3·10−6K−1.
•Thermal fatigue resistance of WNi28Fe15 alloy was studied.•WNi28Fe15 alloy in combination with GTAW results in prolonged lifetime of cladded specimens.•The tempering effect results in decrease of hardness of heat treated AISI H13 steel.•WNi28Fe15 alloy has lower coefficient of linear thermal expansion compared to AISI H13 hot work tool steel.
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