Improving the Ductility of Quenching and Partitioning Steel by Cyclic Intercritical Annealing

The influences of cyclic intercritical annealing on the microstructure and mechanical properties of cold‐rolled and martensite‐based quenching and partitioning (CR/M‐QP) steels were studied. It was found that with increasing annealing cycles, the ductility of CR/M‐QP steel improved significantly without a notable decease in strength. During cyclic annealing, acicular and globular austenite nucleated dominantly at the interfaces between the preformed martensite and the matrix. Repeated austenite reversion and martensitic transformation promoted the formation of acicular austenite, refined both the reverted austenite and the matrix, and gradually enhanced the Mn enrichment. This increased the volume fraction of film‐like retained austenite (RA), raised its Mn content, and refined the RA itself, thereby improving the RA stability after QP treatment. The enhanced RA stability, combined with matrix refinement, improved ductility and achieved an excellent strength–ductility balance in both types of QP steels. This provides a novel approach to enhance the ductility of QP steel without an apparent loss of strength.