Solid State Phenomena Vol. 188

Abstract: After a number of experiments it was noticed that mechanical vibrations affect the process of austenite on cooling conversion. The behavior of 41Cr4 steel was studied during the hardening process in mechanical vibrations action environment. At low power of sinusoidal signal excitation, respectively at low amplitudes of test samples oscillations, a hardness increase can be observed, as well as on surface and in depth. By exciting the test samples on different resonance frequencies, when the oscillations amplitude is higher, it is obvious that the hardness of cooling surface remains high while the depth hardness decreases. This presumes a growth of resistance to abrasion and improvement of product toughness. By modifying the influences of the excitation system, the frequency and the power of the mechanical excitation generator can be achieved, both on test samples and different products, superior results about toughness, resistance to abrasion and endurance strength.

Abstract: Abstract. The paper presents some theoretical and experimental data regarding the directional solidification, revealing the main factors (especially those which are related to the heat transfer process) which have influence on the crystals size and morphology. The crystalline structure of alloys is determined by three important factors: chemical composition, thermal conditions, and characteristics of germination and growth from liquid of solid nuclei. The solidification structure can be influenced by acting on the mould properties or directly on the cast material, both of these actions being based upon the change of temperature distribution in the alloy-mould system. Experimental data demonstrated the major influence of the thermal regime on the crystallization-solidification process, on the transcrystallization zone and they pointed out the limits to direct the crystals formation (size and shape) by changing the cooling regime.

Abstract: The structural characteristics of electric melt, as-cast grey irons were studied in critical solidification conditions, such as very low sulphur content (< 0.025%) and a low (%Mn) x (%S) control parameter (< 0.015) with low Al residual (< 0.002%), without resulphurising or preconditioning. The efficiency of Ce-Ca-Al-FeSi alloy was tested at lower addition rates (0.15-0.25wt.%), as traditionally high inoculant addition rates have been employed in low sulphur grey cast irons. Ce bearing ferrosilicon with similar Ca and Al levels appears to be more efficient than a commercial Ba-Ca-Al-FeSi inoculant, especially at low addition rates (< 0.2wt.%) for the key structure parameters: fewer carbides and less undercooled graphite with small eutectic cells at a higher count.

Abstract: Ca, Ba and Ca-Ba bearing FeSi alloys were compared for their effectiveness in chill (carbide) control, using iron chemistries with critical element levels [< 0.035%S, (%Mn) x (%S) < 0.02, <0.003%Al]. Relative clear and total chill measurements were employed, for chill wedges with different cooling modulii (CM = 0.11 – 0.35 cm). Previous experiments illustrated that the eutectic undercooling of this type of base iron is excessively high, demonstrating a relatively high need for inoculation. Under these conditions, Ca inoculation had a significant effect compared to Ba inoculation, while a Ca-Ba combination improved most of the solidification parameters. The results also illustrate the importance of residual Al and confirm its key role in graphite nucleation in grey irons. The content of the active elements (Al, Ca, Ba) in FeSi based alloys appears to be more important if they inoculate low sulphur irons, more so than increasing the addition rate of an unsuitable inoculant composition.

Abstract: Efficient machining of advanced Ti- and Ni-based alloys, which are typically difficult-to-machine, is a challenge that needs to be addressed by the industry. During a typical machining operation of such alloys, high cutting forces imposed by a tool on the work-piece material lead to severe deformations in the process zone, along with high stresses, strains and temperatures in the material, eventually affecting the quality of finished work-piece. Conventional machining (CT) of Ti- and Ni-based alloys is typically characterized by low depths of cuts and relatively low feed rates, thus adversely affecting the material removal rates (MRR) in the machining process. In the present work, a novel machining technique, known as Ultrasonically Assisted Turning (UAT) is shown to dramatically improve machining of these intractable alloys. The developed machining process is capable of high MRR with an improved surface quality of the turned work-piece. Average cutting forces are significantly lower in UAT when compared to those in traditional turning techniques at the same machining parameters, demonstrating the capability of vibration-assisted machining as a viable machining method for the future.

Abstract: Most often, product quality is based on purity and homogeneity. To meet these conditions secondary metallurgy was developed including different methods for steel refining, but more important is the choice method of casting and its components. Casting metal melts is one of the key points that can ensure the desired product quality. Depending on the castings complexity, to obtain a high quality material several methods of casting have been developed. One of the most common methods of pouring large ingots is vacuum casting because the metal bath is protected from reoxidation. Another advantage of vacuum casting of steel ingots is achieving wide stream by injecting inert gas (Ar), this stimulates the floating of inclusions and prevents convection currents forming in the metal bath. This wide jet creates particularly advantageous conditions in the degassing process by increasing surface contact between vacuum and molten metal, managing to achieve maximum efficiency of removing gas and lowering the inclusion content. Like other methods of casting metals, besides the benefits of obtaining a quality material some disadvantages may influence the future products. One of the great disadvantages that can lead to scrap is the formation of a crown on the spray limiter during casting. Crowns get formed from non-metallic inclusions obtained from the "washing" the spray limiter. During ingot vacuum pouring because of the contact between steel and spray limiter pieces fall from the formed crown representing a powerful source of exogenous inclusions which can reject the finished product in non-destructive checks. Experimental research presents interesting information on the causes of crown formation and the solutions applied to avoid its formation.

Abstract: A new low Ni maraging steel, based on 18Ni (300) type has been developed. The optimized chemical composition (complex alloyed with Al-Si-Ti or Si-Zr-Nb) in accordance with optimum heat treatment was found (solution: 970 °C/1h/air and ageing: 550 °C/3h/air), in order to obtain maximum service temperature of over 600 0C and ensured the good combination of strength and toughness properties. The precipitates, such as Ni3(Mo, Ti), were well controlled in lath martensite (R_m=2090N/mm2 and Rp_0,2=1930N/mm²)and the presence of Si, Zr and Nb enhance structure stability at high temperature (for example the ultimate tensile strength at 5500C is about 1440N/mm²). Therefore, this new type of maraging steel was the subject of a national patent: “Maraging steel for high temperature service and heat treatment technology” – PATENT No.120356/30.08.2010.

Abstract: Mechanical characteristics required for the manufacture of steel wheels piece of property gives it a combination of toughness with wear and fatigue resistance, so that rail movement to take place safely. Quality steels, physical-mechanical characteristics that are influenced by chemical composition, practical content elements influence positive and negative. This paper presents the correlations obtained by industrial processing in Excel and Matlab programs between chemical composition and physical-mechanical characteristics of steel components for the manufacture of rolling stock.

Abstract: This paper presents the preparation of magnetorheological fluids (MRF) starting from iron powder in size of 4-6 µm, silicone oil and a few commercial additives. The structure and magnetic properties of iron powder are evaluated by X-rays diffractions and hysteresis curves. The MRFs were selected through gamma radiation transmission, upon the determination of the sedimentation rate in the gravitational field. The dispersion of MRFs particles is presented using the electron transmission microscopy. The magnetorheological behavior in dynamic conditions was tested in a device specially designed for that purpose

Abstract: The paper presents the results of experimental researches on the formation of barium hexaferrite type M (BHFM) by microwave heating. The microwave heating process takes only a few minutes to obtain calcined barium ferrite powders. Micronic and nanometric powders of BaCO3 and α-Fe2O3 were used as raw materials. In order to obtain BHFM, the microwave heating process was used with following mixtures: stoichiometric homogeneous mixture of BaCO3 and α-Fe2O3 powders, mechanically alloyed mixtures of BaCO3 and α-Fe2O3 powders for 5 and 20 hours in wet medium using a high energy ball mill Pulverisette 4. Using high energy ball milling, the powder size was turned into nanoscale. After using the microwave heating process it was observed a significant reduction of temperature-time parameters to BHFM formation for mechanically alloyed mixtures compared to homogeneous mixture.