The effects on the mechanical properties of AISI 4140 and AISI 4340 steels of the tempering temperature

Hardenable steels are alloyed and unalloyed machine manufacturing steels, which are particularly suitable for hardening especially in terms of carbon content in their chemical compositions and which exhibit high toughness at a certain tensile strength at the end of the process.They contain these properties as a result of the quenching of Cr and Mo elements with high martensite structure. Because of the superior mechanical properties of corrosion steels, which are needed industry, they are used in almost all machine parts (gear, shaft, coupling, and so on). In this study, the effects of tempering temperature on the mechanical properties of AISI 4140 and AISI 4340 treatment steels applied after quenching, which have wide usage area in industry, were investigated. Samples were first prepared by machining and then oil quenching at room temperature at 850 °C was applied, and then samples were cooled to room temperature for 1 hour at 4 different temperatures, 300, 450, 550 and 650 °C. For the determination of mechanical properties, the hardness measurements of the samples were made. Samples were also subjected to tensile and impact tests. The relation of the mechanical values with the microstructure was investigated by the metallographic examination method. As a result, the yield, tensile strength and hardness values of the materials at 300 °C were better than the tempered samples at high temperature while the best impact resistance was observed in the samples tempered at 650 °C with the increase of tempering temperature.