Nanocomposite coatings with metal phases provide generation of self-lubricating films at high temperatures. This provides exceptional tribological properties of metalic components. Within this interdisciplinary investigation of Cr and Ag containing nanocomposite coating deposited on Cr-V ledeburitic tool it was showed that the surface population density of silver agglomerates first increases with annealing time and after 2h it starts to decrease. The increase is more pronounced at lower annealing temperatures. This behaviour is due to the competition between three phenomena, namely the transport of detached Ag atoms to the free surface, formation of oxide layer on the surface and sublimation of silver from the surface. At lower temperatures and/or shorter annealing times, the Ag-transport to the free surface is prevalent, thus, an increase in population density of silver agglomerates takes place. On the other hand, for higher temperatures and/or longer annealing times the population density of Ag-agglomerates decreases due to retarding effect of thicker oxide layer and sublimation of silver.
COBISS.SI-ID: 1171114
The aim of our research work was to investigate the effect of deep cryogenic treatment on fracture toughness, wear resistance and load-carrying capacity of cold work tool steel and to determine the effectiveness of deep cryogenic treatment depending on the tool steel type and chemical composition. The type and chemical composition of the tool steel considerably affect the way how deep cryogenic treatment changes mechanical, tribological and load-carrying capacity of the tool steel. For lower carbon and higher W and Co containing cold work tool steel properties can be improved for up to 70%, but are very limited in the case of high-speed steel. At high carbon and vanadium contents properties of cold work tool steels can even be deteriorated after deep cryogenic treatment. In terms of abrasive wear resistance and load-carrying capacity increasing the hardness is the most decisive factor.
COBISS.SI-ID: 1171370
The main challenge in realizing the immense potential of nano-engineered steels is to manufacture large components and quantities at low costs, where homogeneous dispersion of ceramic nano-particles in molten metals is extremely hard to achieve. Investigation was performed on the conventional 51CrV4 spring steel, where different types of nano-particles were added into the melt. Effect of nanoparticles alloying was investigated after hot rolling, soft annealing and vacuum heat treatment using typical processing parameters. Research was focused on the yield and ultimate tensile strength, fracture toughness and fatigue properties. Results of this investigation indicate that nano-particles reinforcement of spring steel is feasible even by using simple liquid metal casting routes, with the nano-particles type and size having impact on ultimate tensile strength and fatigue limit. Finer and more uniform is the distribution of nano-particles better fracture toughness, fatigue properties and flexibility can be expected together with high hardness and improved tensile properties, which is between 10 and 20%.
COBISS.SI-ID: 1128874
Tools and dies used in hot metal forming are exposed to very demanding contact conditions, which lead to different types of tool damage. However, for forming of new light-weight high-strength materials the most critical ones are wear and fatigue fracture, requiring use of surface engineering techniques and proper balance between hardness and fracture toughness. This is greatly escalated when thinking about coated forming tools. The aim of this work was to investigate the effect of austenitizing and tempering temperature on properties of AISI H11 hot work tool steel, including fracture toughness, wear resistance and load-carrying capacity. Results show that optimal vacuum heat treatment mainly depends on the properties required. In terms of load-carrying capacity and coating support high core hardness is of primary importance followed by sufficient fracture toughness level. However, for tool steel wear resistance good fracture toughness prevails over the ultimate core hardness.
COBISS.SI-ID: 1102762
In this study we determine the optimal parameters for surface modification using the laser surface melting of powder-metallurgy processed, vanadium-rich, cold-work tool steel. A combination of steel pre-heating, laser surface melting and a subsequent heat treatment creates a hardened and morphologically modified surface of the selected high-alloy tool steel. The pre-heating of the steel prior to the laser surface melting ensures a crack- and pore-free modified surface. Using a pre-heating temperature of 350 °C, the extremely fine microstructure, which typically evolves during the laser-melting, became slightly coarser and the volume fraction of retained austenite was reduced. In the laser-melted layer the highest values of microhardness were achieved in the specimens where a subsequent heat treatment at 550 °C was applied. The performed thermodynamic calculations were able to provide a very valuable assessment of the liquidus temperature and, especially, a prediction of the chemical composition as well as the precipitation and dissolution sequence for the carbides.
COBISS.SI-ID: 13845275