Investigation of the effects of heat treatments on the mechanical properties of 51B60H and 51CRV4 steels

In today's automotive and heavy industry applications, the demand for steel materials exhibiting high strength and superior performance characteristics has been increasing in parallel with technological advancements in the industrial sector. In this context, 51CrV4 and 51B60H grade steels are widely preferred in the automotive industry, particularly due to their excellent mechanical strength properties. This thesis study aims to investigate the effects of heat treatment processes applied to 51CrMoV4 and 51B60H grade steels on their mechanical and metallographic properties. For this purpose, parabolically rolled 51CrV4 and 51B60H grade leaf spring specimens were used in the study. The materials were subjected to a heat treatment process consisting of austenitizing at 980°C for 44 minutes, quenching in oil, and subsequent tempering at 446°C for 104 minutes. The effects of these heat treatment processes on the hardness, strength, and metallographic characteristics of the materials were thoroughly examined. In this context, samples were cut from three designated regions of the heat-treated 51CrV4 and 51B60H leaf springs—namely, the front arm, center, and rear arm. Mechanical and metallographic test specimens were then prepared from the extracted samples. As part of the mechanical tests, Brinell hardness and tensile tests were conducted. Brinell hardness tests were used to measure the surface and core (bakla) hardness of the materials. Tensile tests were performed in accordance with the DIN 50125 standard, through which the yield strength, ultimate tensile strength, and percentage elongation values were determined. Additionally, metallographic analyses, including optical microscopy and SEM-EDX analysis, were performed to examine the phase distributions within the materials. According to the obtained results, a significant improvement in mechanical properties was observed for both steel grades following heat treatment. Furthermore, it was determined that the microstructure transformed predominantly into a martensitic phase.