Search Results (9)

Among the materials used for components subjected to abrasive wear, chromium cast iron, hardfaced layers, martensitic steels and Hadfield steel should be singled out. Each of these types of materials exhibits a different morphology of structure and strength properties. Hadfield steel, characterized by an austenitic microstructure, shows the ability to strengthen the subsurface layers by cold work, while maintaining a ductile core. Hardox steels belong to the group of low-alloy martensitic boron steels. However, it should be noted that increasing hardness does not always translate into low wear values due to a change in the nature of wear. In view of the above, the authors decided to subject selected Hardox steels and Hadfield cast steels in the post-operational condition to abrasive wear tests in the presence of loose abrasive. The study showed that Hardox Extreme steel exhibits the highest resistance to abrasive wear (value of the coefficient k_b is equal to 1.39). In the case of Hadfield steel, the recorded values are slightly lower (k_b = 1.32 and 1.33), while the above ratios remain higher compared to Hardox 600 and Hardox 500 steels. The main wear mechanism of high-manganese steels is microploughing, plastic deformation and breakouts of larger fragments of material. In the case of Hardox 450 and Hardox 500 steels, the predominant wear mechanisms are microploughing and breaking out of material fragments. As the hardness of the steel increases, the proportion of wear by microcutting and scratching predominates. Full article

A study of the utilization of WC-Co tool tip scraps as reinforcement in MMC with a Hadfield austenitic manganese steel matrix was conducted using an in situ metal casting technique. This study concerns the effect of the heat-treatment process on the cast sample of MMC. The results show that the heating temperature affects the grain size of the austenite around the interface between Hadfield austenitic manganese steel and WC-Co tool tip scraps. Heating at high temperatures leads to an increase in the austenite grain size. Microstructure analysis also shows that the heat-treatment process does not affect the bond between WC-Co tool tip scraps and Hadfield austenitic manganese steel. However, mechanical property testing reveals that higher heat-treatment temperatures result in a decrease in the hardness of the MMC. Full article

Hadfield steel, under unit pressure conditions, strengthens itself by forming a high density dislocation structure, which results in increased resistance to dynamic impact wear. However, under abrasion conditions, the homogeneous microstructure of the cast steel is insufficient to achieve the expected service life. The aim of the research is to conduct a comparative analysis of the material in its as-delivered state and after two-stage heat treatment (isothermal annealing followed by re-austenitisation). It was found that after isothermal annealing of X120Mn12 grade steel at a temperature of 510 °C, a microstructure with a complex morphology consisting of colonies of fine-grained pearlite, (Fe,Mn)₃C carbides distributed along the grain boundaries of the former austenite and needle-like (Fe,Mn)₃C carbides was obtained in the austenite matrix. The subsequent thermal treatment of the steel with the use of supersaturating annealing at 900 °C resulted in a heterogeneous microstructure consisting of evenly distributed globular carbide precipitations in a matrix of considerably finer austenite grains in comparison with the as-delivered original state. As a result of the final microstructural changes achieved, a 16.4% increase in abrasion resistance was obtained compared to the delivered condition. Full article

Hadfield cast steel is characterized by high wear resistance, but this is only when it is subjected to the effect of dynamic loads. During unloaded abrasion, e.g., sand abrasion, its wear resistance is very low and comparable to the wear of carbon cast steel. To increase the wear resistance of this alloy for operation under the conditions of low pressure or low stress, primary vanadium carbides were produced by the metallurgical process to obtain a two-phase structure after alloy solidification. Compared to samples made of Hadfield cast steel, the primary, very hard carbides, evenly distributed in an austenitic or austenitic-martensitic matrix, increase (at least three times) the wear resistance of samples tested in an abrasive mixture of silicon carbide and water. The changes in microstructure and hardness obtained in alloys after heat treatment (quenching at 1000–1150 °C in water and tempering at 600 °C) are presented. The bulk hardness of the matrix ranged from 370 HV to 660 HV. After heat treatment, the secondary, dispersed vanadium carbides, precipitated in the alloy matrix. Full article

The main task for a ballast bed is to transmit the sleeper pressure in a form of stress cone to the subsoil, provide proper drainage and resist the sleeper displacement. Poorly maintained ballast could severely limit the maximum speed capacity and create further problems with the structural integrity, possibly leading to a complete failure of a given rail line. To prevent the unwanted corollaries, the ballast bed has to be periodically cleaned with an appropriate machinery. In this paper the authors investigated the effect of the chemical composition on the physical properties of the ballast excavating chains made of high-manganese steels. The authors focused on the wear mechanism, work hardening ability and hardness in the cross-sections areas. A microstructure analysis was performed as well, and observations revealed divergent morphology of precipitations at the grain boundaries, which influenced the size of austenite grains. The deformation twins formed as a result of operation were noticed in the samples. Research has shown that less carbon and chromium reduces the hardness of cast steel, and it specifically affects the ability to strain hardening. The authors explained the role of adjustments in chemical composition in the operational properties of high-manganese cast steels. It has been shown in the paper that different chemical compositions affect the properties of the alloys, and this causes different types of wear. The high content of chromium increases the hardness of materials before and after plastic deformation hardening, which in the conditions of selector chains results in greater dimensional stability during wear of holes in pin joints and will be more susceptible to abrasive wear in the presence of dusts from the ballast than creep. Full article

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. Full article

High-manganese Hadfield cast steel is commonly used for machine components operating under dynamic load conditions. The high fracture toughness and abrasive wear resistance of this steel are the result of an austenitic structure, which—while being ductile—at the same time tends to surface harden under the effect of cold work. Absence of dynamic loads (e.g., in the case of sand abrasion) causes rapid and premature wear of parts. To improve the abrasive wear resistance of high-manganese cast steel for operation under the conditions free from dynamic loads, primary niobium carbides are produced in this cast steel during the melting process to obtain in castings, after melt solidification, the microstructure consisting of an austenitic matrix and primary niobium carbides uniformly distributed in this matrix. The measured hardness of the tested samples as cast and after solution heat treatment is 260–290 HV and is about 30–60 HV higher than the hardness of common Hadfield cast steel, which is 230 HV. Compared to common Hadfield cast steel, the abrasive wear resistance of the tested high-manganese cast steel measured in the Miller test is at least three times higher at the niobium content of 3.5 wt%. Increasing the niobium content to 4.5 wt%. in the tested samples increases this wear resistance even more. Full article

This paper examines possible industrial applications of high manganese steel and the feasibility of its inoculation with a new ferroalloy, vanadium nitride. The abrasive and impact-abrasion surface wear experienced by castings has a classical pattern: microcutting—i.e., the deformation twinning of surface layers. Ferrovanadium nitride enhances the surface resistance of castings both as a cast and as thermally treated. A fine grain structure is formed in the surface layers, specifically layers in direct contact with abrasive particles. The deformation twins that are present at the solid solution grain boundaries tend to change their orientation and characteristics. The impact-abrasion wear also leads to hardened layer formation at the working surface due to deformation twinning. The carbides (nitrides) present in the surface wear do not produce any significant impact on the process of deformation twinning. As the wear line extends deeper into the casting surface, the carbides and nitrides are ripped out and cavities occur in the wearing zone. The wear is controlled by the solidification rate. Thus, at lower rates a hardened layer is formed, which accommodates adjacent areas with differing twin characteristics, such as orientation and spacing. Full article

The effect of in-situ precipitating particles on the grain size of Al-Ti-treated and untreated Hadfield steel cast in a pilot scale environment was studied. Hadfield steel was melted in an induction furnace and cast in Y-Block samples. Light Optical Microscopy (LOM) and the intercept method were utilized for the grain size measurements. Additionally, Thermo-Calc Software TCFE7 Steels/Fe-alloys database version 7 was used for thermodynamic equilibrium calculations of the mole fraction of particles. The planar disregistry values between the austenite and the precipitating particles were calculated. It was observed that increasing oxide content in samples with low Ti(CN) content resulted in a finer microstructure, while increasing the Ti(CN) content under similar oxide content levels led to a coarser microstructure. The potency of each type of particle to nucleate austenitic grains was determined. Spinel (MnAl₂O₄, MgAl₂O₄) particles were characterized as the most potent, followed by olivine (Mn₂SiO₄), corundum (Al₂O₃, TiO₂), and finally Ti(CN), the least potent particle. Full article