Application of Quenching and Partitioning Treatment and Its Effect on Initiation Fracture Toughness in AISI 4140 Steel

Feasibility of Quenching and Partitioning on 4140 steel (42CrMo4) was investigated through the design and application of multiple heat treatments: different single step treatments were tested. The treated material was characterized both regarding the microstructure (SEM), and the mechanical properties, through tensile tests. XRD and EBSD analyses were conducted to evaluate the presence and the amount of retained austenite obtained. The designed treatments were reported to effectively introduce a fraction of retained austenite in the final microstructure, increasing the tensile properties with respect to a conventional quenching and tempering treatment, but maintaining good values for the elongation at break. In addition, fracture mechanics tests were performed, in order to investigate the effect of presence and amount of RA on the toughness of the material.