A 2.6 GPa Ultra-Strong Steel with Ultrafine Lamellar Structure Produced by Heavy Warm Rolling

Abstract

An ultra-strong steel with enhanced ductility and ultrafine lamellar structure was produced by heavy warm rolling (HWR) of metastable austenite and subsequent quenching. The HWR steel exhibited an ultrahigh yield strength of 1.09 GPa and an ultimate tensile strength of 2.6 GPa, with a total elongation of 6.7% at room temperature. The high yield strength was primarily attributed to the synergistic strengthening of high-density dislocations, nanotwins, and ultrafine martensite grains with an average effective grain size of 1.02 μm. The enhanced ductility is attributed to the parallel lamellar structure, which increased the work-hardening capacity and resulted in delamination toughening. Compared to the heavy multistage rolling (HMR) process, which starts rolling at higher temperatures, the HWR method employed in this study demonstrates significant enhancements in both strength and ductility. Following a 150 °C low-temperature tempering for 1 h, the yield strength of HWR steel was further increased to 2.2 GPa, and the total elongation improved to 10.1%.