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The purpose of this study is to develop a lower bainite structure consists of a dispersion of fine carbide inside plates of bainitic ferrite from chemical composition unmodified conventional pearlitic steel under bainitic transformation and to investigate its effect on tensile properties and wear resistance.

A commercial hypereutectoid pearlitic rail steel was subjected to three different bainitic transformation treatments followed by tempering to develop a desirable microstructure with a DIL805 BÄHR dilatometer. A comprehensive microstructural study was performed by scanning electron microscopy and energy dispersive x-ray spectroscopy. Finally, the mechanical properties and wear resistance were evaluated by tensile, microhardness, and pin-on-disc tests.

The results showed that the best combination of mechanical properties and sliding wear resistance was obtained in the sample subjected to bainitic transformation at 300°C for 600 s followed by tempering at 400°C for 300 s. This sample, which contained a bainitic ferrite structure, exhibited approximately 20% higher hardness and approximately 53% less mass loss than the as-received pearlitic sample due to the mechanically induced transformation in the contact surface.

Although pearlitic steel is widely used in the construction of railways, recent studies have revealed that bainitic transformation at the same rail steels exhibited higher wear resistance and fatigue strengths than conventional pearlitic rail at the same hardness values. Such a bainitic microstructure can improve the mechanical properties and wear resistance, which is a great interest in the railway industry.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2019-0282/

Given the current challenges for improving the tribological behavior in automotive engines, which require lubricants that adapt to different operating conditions through replacement mechanisms to reduce friction and wear, this study aims to analyze the use of hexagonal boron nitride nanoparticles blended in the lubricating oil of a diesel engine. The target was to minimize frictional power losses and wear of cylinder liner surfaces to validate what was observed in laboratory and to confirm improvements in thermal efficiency.

Before the definition of the concentration to be used in a real engine environment, tests of sample dispersion were conducted using an ultrasound bath. The mixtures were added to storage bottles in concentrations of 0.1% and 0.5%, as observed in Figure 1. The samples were subsequently analyzed using the dynamic light scattering (DLS) technique. There was a reduction in the hydrodynamic size for the sample with 0.5% of hexagonal boron nitride (hBN), possibly due to sedimentation of the powder during the analysis, which supported this work to continue with the use of 0.1% concentration.

The behavior of hBN as nano additive in a real diesel engine was problematic when compared with laboratory environment, leading to impact in oil temperature. In addition, it was noticed a high amount of deposit formation at the top dead center (TDC) and mid-stroke (MC) and nonsignificative wear at MC and bottom dead center (BDC) of the cylinder, with unusual formation of products from antiwear additives known as zinc dialkyl-dithiophosphate at MC position with the use of hBN. For this reason, this work provides insights into how hBN nanoparticles may not contribute toward the improvement of tribological performance.

The findings of this work aimed to provide a better understanding of the impact of hBN nanoparticles used as additives in real engine environment in terms of performance and tribological impacts. The results of this work indicated that hBN as additive gave poor results in terms of performance and wear prevention.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2024-0047/

This paper aims to understand the effect of steadite in gray cast iron (GCI) cylinder liners performance (friction and wear) when lubricated with new lube oil formulations to verify if steadite can be reduced or suppressed from cylinder liners composition.

The paper presents an experimental approach to quantify the separated effect of lube additives and steadite content on GCI performance. Friction and wear of GCI samples with and without steadite were analyzed under lubricated conditions with a 5W30 lubricant and a base oil of similar viscosity under operating conditions similar to the ones observed at the top dead center of Otto engines. Scanning electron microscopy (SEM)-EDS analysis was used to evaluate wear and tribofilm formation.

The paper shows that steadite stabilizes friction coefficient and slightly reduces wear in the tests performed with base oil. However, its advantages are marginal in comparison to the ones provided by the fully formulated oil. Furthermore, SEM-EDS analyses of the wear track showed that steadite does not chemically react with zinc and sulfur compounds, reducing the tribofilm formation on the real area of contact and consequently changing the tribosystem behavior.

This paper covers an identified need to study the effect of lube additives and GCI composition using actual piston ring and cylinder liners under operating conditions similar to the ones observed at the top dead center of Otto engines.