Comparative analysis between quenching and partitioning versus quenching and tempering for SAE 4340

ABSTRACT A new heat treatment has been recently researched, whose denomination is quenching and partitioning (Q&P), in order to stabilize the retained austenite in the microstructure of steels. Initially, this treatment was carried out on high-silicon-steels, although, its potential reaches other materials with low alloys containing nickel or manganese. The same is done to perform a quenching between the initial (Ms) and final (Mf) temperatures of martensitic transformation, followed by a reheating to a isothermal stage over a period of time. In this work, the Q&P was conducted on SAE 4340 steel, austenitized at 870 ° C for 30 min, then quenching in polymer up to 240 ° C and partitioned into three different times: 10 s, 30 s, and 90 s. Also, a quenching and tempering (TR) treatment was conduct on the same material to evaluate and compare the microstructures and mechanical properties obtained in both processes, through optical microscopy, scanning electron microscopy, x-ray diffraction (XRD), as well as Vickers microhardness tests. A complex microstructure was observed in the samples from Q&P, unlike TR specimens. From the XRD, indications was obtained that the time of 30 s for the partitioning process was the most effective in stabilizing the retained austenite. Added to this, the high hardness reached, 696HV1.