Tribological Performance of Pack Boronized AISI 4140 Steel via Waste‐Derived Green Lubricants at Elevated Temperatures

Enhancing the tribological performance of alloy steels under eco‐friendly lubrication and high‐temperature conditions has gained importance for sustainable engineering applications. In this regard, the current study investigates the impact of biolubricants and high temperatures on the tribological properties of AISI 4140 steel, with a specific focus on the effects of pack boronizing. The formation of an outer FeB layer and an inner Fe 2 B layer led to a surface hardness approximately seven times greater than that of the untreated steel, indicating enhanced boron diffusion promoted by the high B 4 C content. Tribological tests were conducted on both as‐received and boronized samples using a ball‐on‐flat configuration at temperatures of 25°C, 75°C, and 125°C. Hemp oil, frying oil, and onion oil were employed as biolubricants. The findings indicate that elevated temperatures decreased lubricant viscosity, resulting in reduced oil layer thickness and consequent increases in friction and wear. Due to its consistently steady flow properties and relatively high viscosity, onion oil experienced superior tribological performance across all temperatures compared to the other lubricants. Under all conditions, wear severity increased with temperature; however, the boronized samples exhibited much less wear than the untreated specimens due to their substantially improved hardness.