Study on the Formation and Mechanical Stability of Retained Austenite in Complex Phase Steel with High Formability

Herein, a 1300 MPa grade complex phase steel with high formability (CH) is developed, which is achieved through the formation of cementite during pretreatment and the control of austempering temperature to enhance the stability of retained austenite (RA). Due to the insufficient diffusion of Mn during cementite dissolution, Mn enrichment enhances the mechanical stability of austenite, thereby increasing austenite content at room temperature. As the austempering temperature increases from 340 °C to 400 °C, the RA content increases, but its stability decreases significantly. Compared with the content of RA, its stability is more critical for enhancing plasticity. RA formed at lower austempering temperatures is highly stable, enlarging the strain range of the transformation‐induced plasticity effect and improving material plasticity. The experimental steel achieves optimal plasticity while maintaining strength when overaged at 360 °C. Specifically, the yield strength is 963 MPa, the ultimate tensile strength is 1394 MPa, and the total elongation is 14.0%.