Achieving unprecedented yield strength of 2.2 GPa with high ductility in formed parts using strain-aging

Abstract

Ultra-high yield strength is important in extreme service conditions, but it severely deteriorates the ductility and also brings significant challenges for material forming. Here, we successfully developed a strategy involving the compositionally lean alloy design and strain-aging processing route to endow medium Mn steels with unprecedented ‘part performance’ of 2.0–2.3 GPa yield strengths and 8–14% uniform elongations. The significant bake hardening response with the maximum of 465 MPa higher than the most of existing researches is reported, which leads to the ultra-high yield strength above 2 GPa. By applying pre-strains, the morphology and volume fraction of retained austenite can be tailored, which affects the Lüders bands and the transformation-induced-plasticity (TRIP) effect. In the suitable pre-strain range, the film-like retained austenite with high stability can provide sustained TRIP effect, thus ensuring high uniform elongations in the strain-aged samples.