Effect of retained austenite on the fatigue performance of novel high carbon quenching-partitioning-tempering steel

The effect of retained austenite on the fatigue property of a novel Fe-0.65C-1.5Mn-1.5Si-0.6Cr-0.05Nb (wt.%) quenching-partitioning-tempering (Q-P-T) steel was investigated. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were performed to characterize the evolution of microstructure including retained austenite fraction and average dislocation densities in both martensite and retained austenite. Compared with traditional quenching and tempering (Q&T) steel, Q-P-T steel contains much more retained austenite by partitioning of carbon from supersaturated martensite to retained austenite. After Q-P-T, the tensile strength decreases slightly, while the elongation and the product of strength and elongation (PSE) improved 287% and 234%, respectively. The fatigue limit of Q-P-T steel (650 MPa) is increased by 100 MPa (18.2%) compared with Q&T steel (550 MPa). The mechanism of high fatigue performance for high-carbon Q-P-T steel is mainly stemmed from two aspects: one is the dislocation absorption of the retained austenite (DARA) effect existing in the fatigue test, which significantly enhances the deformation ability of martensite matrix; the other is the deformation-induced martensitic transformation effect which can effectively arrest crack to against fatigue. This work verifies the existence of DARA effect in high carbon Q-P-T steel under cyclic tension and compression loading and makes the third-generation advanced high-strength steels extend to the field of cyclic variable loads from static loads.