Comparative Analysis of the Effects of Microstructures Formed After Hardening Heat Treatment on the Mechanical Properties of AISI 4140 and AISI 4340 Grade Steels
Year: 2026
Type: article
Abstract: This study presents an experimental investigation into the mechanical and microstructural properties of AISI 4140 and AISI 4340 medium-carbon alloy steels following hardening heat treatment. The specimens were austenitized at 870 °C, quenched in water, and subsequently tempered at 550 °C. Mechanical performance was evaluated through tensile tests and Vickers hardness measurements, while microstructural evolution was analyzed via optical microscopy. The results showed that heat treatment significantly enhanced the mechanical properties of both steels. Following quenching, hardness values increased from 231.24 HV to 520.00 HV for AISI 4140 and from 283.20 HV to 610.00 HV for AISI 4340. After tempering, the hardness settled at 338.44 HV and 331.56 HV, while ultimate tensile strengths reached 1096.80 MPa and 1099.20 MPa for AISI 4140 and AISI 4340, respectively. Microstructural observations confirmed that mechanical improvements were primarily driven by martensitic transformation and grain refinement. Notably, nickel-bearing AISI 4340 steel exhibited higher quench hardness and superior ductility (14% elongation) owing to its finer, more homogeneous martensitic matrix compared to AISI 4140 (11% elongation). Overall, the findings demonstrate that controlled quenching and tempering optimize the mechanical performance of both steels, providing critical insights for material selection and cost-performance trade-offs in automotive applications.
Authors: Murat Ok, Bahadır Aydaş
Institution: Düzce Üniversitesi
Language: Turkish
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W7204849600