MATERIALS ENGINEERING, Vol. 20 (2013), No. 3


Jesperson, H. (pp. 94-101)
Gross cracking of die-casting dies with inferior toughness sometimes occurs through too low preheating temperature and/or too slow cooling during quenching. This study aimed to clarify the influence of cooling rate on the toughness of the hot-work tool steel grade Uddeholm Vidar Superior at ambient temperature and at 200 °C, a typical preheating temperature for aluminium die-casting dies. Toughness was measured through instrumented Charpy V-notch impact testing. The decrease in energy absorption with increasing cooling time between 800 °C and 500 °C at both ambient temperature and 200 °C was pronounced. At ambient temperature, the decrease in total energy was a consequence of a decrease in initiation energy whereas, at 200 °C, the decrease in total energy was due to a decrease in propagation energy. The present investigation does not explain the decrease in toughness with increasing cooling time between 800 °C and 500 °C. This can only be revealed by studying the metallographic structure by light microscope, scanning electron microscope, and transmission electron microscope.

Handa, A., Chawla, V. (pp. 102-111)
Joining of dissimilar metals is one of the most essential needs of industries. There are various welding methods that have been developed to obtain suitable joints in various applications. However, friction welding is a joining process that allows more materials and material combinations to be joined than with any other welding process. Continuous drive friction welding studies on austenitic stainless steel and ferritic steel combinations has been attempted in this investigation. Friction welding process parameter optimization, mechanical characterization and fracture behavior is the major contribution of the study. The microhardness across the weld interface was measured and the strength of the joint was determined with tensile tests and impact tests. Also the tensile fractured specimens were examined by scanning electron microscopy so as to study its fracture behavior. The experimental results indicate that axial pressure has a significant effect on the mechanical properties of the joint and it is possible to increase the quality of the welded joint by selecting the optimum axial pressures.

Voděrová, M.. Novák, P. (pp. 112-118)
PROTECTIVE LAYERS OF IRON AND NICKEL ALUMINIDES ON STEEL Full text (PDF 623 kB) - Available online 28 July 2013
Intermediary phases Ni-Al and Fe-Al are promising materials due to their superior properties such as hardness and good resistance against oxidation at high temperatures. Moreover, Fe-Al phases are resistant in sulphur - containing atmospheres. Because of these characteristics, the above mentioned intermetallic phases seem to be prospective for the use in many technical applications such as energetics, chemical or automotive industry in a form of a bulk material or coatings. Presently, the protective aluminide layer is usually prepared by thermal spraying. Nevertheless, this method is not suitable for complex-shaped components. Therefore, the aim of this work was to find an alternative way to prepare layers consisting of nickel or iron aluminides by other technique than thermal spraying. At first, carbon steel samples were coated using galvanic or electroless nickel plating. Coated samples were subsequently submerged into molten aluminium at various temperatures and process durations. The influence of the temperature and duration on the intermetallic phase growth was studied by scanning electron and light microscopy. Thickness and microhardness of the intermetallic layer was also measured.

Kumar, S., Ratol, J.S. (pp. 119-131)
Effects of Tribological Parameters on Slurry Erosion Behaviour of Uncoated and Coated Materials: A Review Full text (PDF 405 kB) - Available online 10 September 2013
This paper describes the pioneering work of various researchers in the field of slurry erosion behaviour of uncoated and coated materials in various industrial applications. The present study is focused on the slurry erosion behaviour of ash slurry disposal system of thermal power plants. The key components such as impeller and casing of ash slurry disposal pumps in thermal power plants experience this phenomenon of wear. Tribological parameters such as solid particle concentration, impact velocity of erodent on the target surface, impact angle, erodent particle size and shape, hardness of the striking particles and target material, etc. are responsible for slurry erosion. The research results show that the influence of tribological parameters on the slurry erosion is found to be significant and need to be evaluated and analyzed properly. The slurry erosion can be minimized by proper selection of materials and/or by providing the suitable protective coating on the material which can enhance the surface properties.

Benešová, S., Kříž, A. (pp. 132-137)
Optimization of heating of gear wheel using numerical modeling Full text (PDF 486 kB) - Available online 29 September 2013
Successful heat treating and carburizing of gear wheels for wind turbine gear boxes requires that plastic deformation in the wheel is minimized. Numerical modeling using the DEFORM software was aimed at exploring the effects of the base, on which the gear wheel rests during heating, on the heating process. Homogeneous heating was assumed. It was found that the base heats up more quickly than the workpiece. It is the consequence of the base's shape and volume. As a result, the base expands and slides against the wheel, predominantly at the first heating stage. Later on, it prevents the gear wheel from expanding, causing plastic deformation in the wheel. The findings were used for designing new heating schedules to minimize these undesirable interactions and to reduce the plastic deformation to a negligible magnitude. In addition, this paper presents an example of a practical use of numerical modeling in the DEFORM software.

Jurči, P., Sobotová, J., Salabová, P., Prikner, O., Suštaršič, B., Jenko, D. (pp. 138-146)
Sub-zero Treatment of P/M Vanadis 6 Ledeburitic Tool Steel Full text (PDF 737 kB) - Available online 29 September 2013
The Cr-V ledeburitic steel Vanadis 6 was vacuum austenitized at different temperatures, nitrogen gas quenched and double tempered at 530 °C for 2 h. For the selected samples, a sub-zero period was inserted between quenching and tempering. The obtained results infer that: I) as-quenched microstructure consisted of martensite, retained austenite and undissolved carbides, II) sub-zero processing reduced the amount of the retained austenite and increased the tetragonality of the martensitic lattice, III) as-quenched hardness of the steel was higher by 2 – 3 HRC due to sub-zero processing, IV) as-tempered hardness increased with increasing austenitizing temperature but it decreased slightly with the sub-zero period, V) no negative impact of sub-zero processing on toughness was recorded, VI) wear resistance increased with sub-zero period when 100Cr6 steel has been used as a counterpart.

Djordjević, M., Aleksandrović, S., Lazić, V., Stefanović, M., Nikolić, R.R., Arsić, D. (pp. 147-152)
Experimental analysis of influence of different lubricants types on the multi-phase ironing process Full text (PDF 663 kB) - Available online 29 September 2013
This paper is aimed at presenting results of an experimental analysis of the different types of lubricants influence on the multi-phase ironing process. Based on sliding of the metal strip between the two contact elements a special tribological model was adopted. The subject of experimental investigations was variations of the drawing force, contact pressure and the friction coefficient for each type of the applied lubricants. The ironing process was conducted in three-phases at the constant sliding velocity. The objective of this analysis was to compare all the applied lubricants in order to estimate their quality from the point of view of their applicability in the multi-phase ironing process.

© University of Žilina, Faculty of Mechanical Engineering, ISSN 1335-0803