Comparative Analysis of the Effects of Microstructures Formed After Hardening Heat Treatment on the Mechanical Properties of AISI 4140 and AISI 4340 Grade Steels

Vollständiger Abstract

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This study presents an experimental investigation into the mechanical and microstructural properties of AISI 4140 and AISI 4340 grade steels, which are widely used in the automotive industry, following hardening heat treatment. These medium-carbon alloy steels are critical for components that require high strength and wear resistance. The materials were subjected to austenitizing at 870 °C followed by water quenching and tempering at 550 °C. Mechanical performance was evaluated using tensile tests and Vickers hardness measurements, while microstructural changes were examined through optical microscopy after metallographic preparation. The results indicate that hardening heat treatment significantly improves the tensile strength and hardness of both steels; however, this enhancement comes with a reduction in ductility. Microstructural analysis revealed the formation of martensite and grain refinement, both contributing to the mechanical improvements. Notably, AISI 4340 steel, which contains additional nickel, exhibited superior tensile strength and hardness compared to AISI 4140 under identical heat treatment conditions. Overall, the findings suggest that the mechanical performance of AISI 4140 and AISI 4340 steels can be optimized through controlled heat treatment parameters, making them suitable for safety-critical and high-performance automotive applications. This comparative analysis provides valuable insights for materials selection and process optimization in the manufacturing of durable automotive components.