Study of Cooling Medium Variables during Quenching in SAE 4340 Steel Using Statistical and Modeling Tools

Abstract

Although quenching is one of the most widely used heat treatments in the metal-mechanical industry to improve the mechanical properties of steels, it is also responsible for the generation of residual stress, distortion, and fractures in the treated parts. The high-temperature gradients present during quenching and martensitic transformation are the main failure mechanisms. Cooling is the critical quenching stage where several variables that need to be controlled are involved in reducing these problems. The objective of this research was to evaluate the main variables in the quenching process in SAE 4340 steels, which promote distortion, residual stress accumulation, and fracture failures. A 2ᴷ factorial experiment was designed, samples with C-ring geometry susceptible to changes in quenching variables were used, and the variables studied were the agitation and temperature of the quenching medium. Experimental measurements, statistical tools and modeling were used to evaluate and predict the distortion generated in quenched samples. Such tools include Minitab 21® software and its statistics utilities. Furthermore, a finite element method model was carried out using STFC Deform®. The results suggest that there are optimal conditions in the quenching process to minimize distortion and residual stresses and to improve mechanical properties of quenched parts; therefore, the methods used in this work could be useful to detect and control the appearance of defects in an industrial environment.