Electrochemical Corrosion Behaviour of Different Grades of WC-Co, High-Cr White Cast Irons and Hadfield Steel in 1 M Sulphuric Acid

Electrochemical polarisation tests were carried out on three grades of WC-Co cemented carbides to investigate the corrosive behaviour of the hardmetals and rank them as viable protective liners for chutes and skips in the mining industry. The cobalt binder content and WC particle size varied. The binder content ranged from 6–12 wt%, and the grain size of the WC particles ranged from 0.4–2.3 µm. The performance of the WC-Co hardmetal was compared to three different grades of high chromium white cast irons and Hadfield steel. The cast irons varied in both their chromium content and the morphology of the Cr-rich primary carbides. Potentiodynamic polarisation and linear polarization resistance scans were used to determine the corrosion current density and other electrochemical parameters. The microstructural characteristics of the samples were analysed using Scanning Electron Microscope(SEM) with Energy Dispersive Spectroscopy (EDS), and optical microscopy. The potentiodynamic scans revealed that, although the WC-Co alloys were found to have generally improved corrosion resistance, it was the high-Cr white cast iron (22 wt% Cr) that recorded the lowest corrosion current density and therefore displayed the best resistance against corrosive attack in 1 M H2SO4. The Hadfield steel exhibited the poorest resistance to corrosion and therefore, suffered the most degradation to its exposed surface.

Predicting the composition of primary carbides of the multicomponent system Ni-5Cr-9Co-6Al-8.3W-4Re-4Ta-1Mo-1.5Nb-0.15C

Problem. Development of new and optimization of existing casting alloys for the manufacture of blades of gas turbine engines for various purposes is an important scientific and technical problem. Given the sensitivity of the structural components to the concentration of alloying elements, there are difficulties in assessing the expected set of properties of the blades from the optimization of the chemical composition or structural state of alloys. Goal. The aim of this work is to study the specifics of the influence of alloying elements on the distribution of primary carbides in the structure, their topology, morphology and their composition for a multicomponent system such as Ni-5Cr-9Co-6Al-8,3W-4Re-4Ta -1Mo-1 , 5Nb-0.15C using the calculation method of CALPHAD prediction (passive experiment) in comparison with the data obtained by electron microscopy (active experiment). Methodology. Modeling of thermodynamic processes occurring during crystallization (cooling) or heating in the structure of alloys was carried out by the CALPHAD method. Results. The results of thermodynamic calculations of the chemical composition of carbides are presented in comparison with experimental data obtained by electron microscopy on a microscope REM-106I with a system of energy-dispersion X-ray spectral microanalysis. Originality. It is shown that when the total concentration of carbide-forming elements increases, the chemical composition of carbides also becomes more complicated. At a concentration of more than 2% of the mass. But in the alloy, in the carbide of MS, the content of tantalum prevails over the content of niobium, it also leads to a decrease in the concentration of tungsten and molybdenum in the carbide. It was found that when the concentration of niobium is more than 3 wt%. in the alloy, its content in the primary carbide exceeds the content of tantalum and the carbide becomes based on Ta. Practical value. On the basis of an integrated approach, computational and experimental, for multicomponent heat-resistant alloys, new regression models are obtained that allow to adequately predict the chemical composition of carbides by the chemical composition of the alloy. which is confirmed by the obtained experimental data.

Influencing Microstructure of Vanadium Carbide Reinforced FeCrVC Hardfacing during Gas Metal Arc Welding

Vanadium carbide (VC) reinforced FeCrVC hardfacings have become important to improve the lifetime of tools suffering abrasive and impact loads. This is because the microstructural properties of such hardfacings enable the primary VCs to act as obstacles against the penetrating abrasive. Because dilution is supposed to be the key issue influencing the precipitation behaviour of primary carbides during surfacing, the development of deposit welding processes exhibiting a reduced thermal impact, and hence lower dilution to the base material, is the primary focus of the current research. By inserting an additional hot wire in the melt, an approach was developed to separate the material and energy input during gas metal arc welding (GMAW), and hence realised low dilution claddings. The carbide content could be increased, and a grain refinement was observed compared with conventional GMAW. These effects could be attributed to both the reduced dilution and heterogeneous nucleation.

Effects of Cryogenic Treatment on the Microstructure and Mechanical Properties of High-alloyed Tool Steels

In this work, the influence of a cryogenic treatment on the microstructure, mechanical properties and wear resistance of the high-alloyed tool steels X38CrMoV5-3, X153CrMoV12 and ~X190CrVMo20-4 were investigated. Based on tempering curves of the steels, the heat treatment parameters were determined for the mechanical and wear specimens so that the conventionally heat-treated steels and the cryogenically treated steels featured similar hardness. The investigations showed that an almost complete transformation of retained austenite and a more homogeneous distribution of secondary carbides in the microstructure could be achieved by incorporating a cryogenic treatment. However, the cryogenic treatment does not show significantly positive effects on the investigated mechanical properties and wear resistance of the tool steels. The wear resistance of the samples was dominated by primary carbides. The cryogenic treatment would have a positive effect on large tool components with large wall thicknesses in terms of uniform and complete transformation of retained austenite throughout the entire components.