Abstract
Heat treatment is a metallurgical process for removing residual stresses in metals, improving their mechanical properties, reducing surface hardness, and preventing the formation of brittle fractures or cracks. The tempering (age hardening) process, which is a type of heat treatment in tempered steels, affects the mechanical and microstructural properties of the steel more than the other steel types. In this study, the base material test specimens with 13 HRC hardness and 12.5 mm diameter were heat-treated and tempered, and the effect of the heat treatment process on the mechanical and microstructural properties was investigated. AISI 4140 tempered steel was tempered at 600°C for 3 hours after 3 hours of heat treatment at 880°C, 850°C and 820°C and cooled in oil. While the base material has a tensile strength of 654.16 ± 12 MPa, the maximum tensile strengths were determined as 1022.44 ± 10 MPa, 1006.24 ± 9 MPa and 987.454 ± 11 MPa, respectively, after heat treatment at 880°C, 850°C and 820°C. The strength of the material increased by 56.29% by applying heat treatment at 880°C temperature. This increase in strength is associated with the transformation of the existing microstructure from ferritic to martensitic structure. The needle-like structure in the martensitic structure increased and lath martensite structure was formed with the combination of grain boundaries with increasing heat treatment temperature. Strength and hardness increased while the heat treatment temperature is increasing. It was observed that ductility decreased. Hereby, the temperature parameter in the heat treatment process is effective on the strength and the heat treatment has high advantages in terms of material saving in machine designs
Published Version
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