Aim of this research work was to correlate different microstructures obtained by various heat treatments with hardness and anti-wear properties of hot work tool steel. Martensitic matrix was obtained after quenching, with two different austenitizing temperatures showing considerable difference in volume fraction of undissolved carbides (carbo-nitrides), being mainly vanadium rich MC type. Wear performance was influenced by austenitizing and tempering temperature. Lower wear rate at similar hardness over 50 HRc was observed in favour to specimens austenitized at higher temperatures. Similar results were observed for adhesive and abrasive wear components.
COBISS.SI-ID: 1476522
The aim of this study was to investigate the effect of a coating's crack density and a post-polishing process on the friction and wear performance of hard-chrome coatings. Three different crack densities combined with a post-polishing process were tested using the ball-on-disc configuration in a poly-alpha-olefin oil (PAO) lubricated point contact. The results clearly show that for hard-chrome coatings and random, non-uniform crack-type textures the size and density of the crack pattern determine the friction and wear performance of the contact. For the investigated contact conditions the best performance, i.e., low friction, fast running-in and minimum wear, was obtained when combining medium-density cracks of ~3% and the post-polishing.
COBISS.SI-ID: 1387434
The aim of the present work was to experimentally examine the effect of modifying the chemical composition on the properties of Si-Cr-V spring steel. The investigation was based on a commercial 51CrV4 spring steel, with its composition modified in terms of Si, Cr, and V contents, targeting a yield strength of over 2000 MPa in the tempered condition. The results show that the simulation software gave greatly exaggerated values when it comes to the yield-strength prediction and the influence of the steel’s composition. In terms of experimental results, the most influential element in terms of improving the decarburization resistance, the yield and tensile strengths, the fracture toughness, and most importantly the fatigue limit and the fatigue life is Si, followed by Cr, while increasing the amount of V has a mainly negative effect. However, when the Si content exceeds 1.6 pct, this leads to an increased decarburization depth and a drop in the tensile properties.
COBISS.SI-ID: 1402538
The aim of this study was to investigate the feasibility and possibilities of introducing nanosized particles into a steel matrix through a conventional casting process and to determine the effect of different nanoparticles and methods of incorporation on the strength, toughness and high-temperature wear resistance of martensitic steel. The results show that also in the case of a conventional casting process it is possible to obtain a homogeneous distribution of nanoparticles in the metal matrix, resulting in improved strength, maintained toughness and up to five times better high-temperature wear resistance of the Mn-Cr steel. However, the rate of improvement greatly depends on the method and type of nanoparticles incorporation. The most promising results were observed for the combination of carbon nanotubes, oxide nanoparticles and dispersant, sealed in a steel tube, with the dispersant providing the uniform distribution, the carbon nanotubes delivering the good toughness and the adhesive wear properties, and the oxide nanoparticles ensuring oxidation and abrasive-wear resistance.
COBISS.SI-ID: 1414570
Mathematical descriptions of true stress/true strain curves, experimentally obtained on cylindrical specimens under hot compressive conditions, are of great importance and are widely investigated. An additional black-box modelling approach using transfer functions (TF) is tested. For tested 51CrV4 steel, a TF of third order is employed for description of true stress (output) depending on the strain rate (input). Sets of TF coefficients are determined using numerical optimization techniques for each testing temperature and strain rate. To avoid scattering of TF parameters, time in Laplacian transformation is replaced with strain, while TF input is the strain rate. Obtained models cover deformations starting practically from zero to 0.7. Average absolute relative error for models based on TF of the third order and of the second order are 0.93% and 3.64%.
COBISS.SI-ID: 1514666