A Novel Nano-Structured Die Steel with High Strength and High Thermal Stability

A novel oxide-dispersion-strengthened (ODS) die steel was fabricated by mechanical alloying and hot consolidation. Annealing and quench-tempering treatments both obtained an ultra-fine grain structure (mean size: 310–330 nm) with an ultra-high density of ultra-fine Y-Al-O nano-oxides (number density: ~ (1–1.5) × 10²³ m⁻³, mean size: 5.1–7.2 nm). Prolonged thermal exposure further induced the new, highly dense precipitation of ultra-fine Y-Zr-O nano-oxides. Both nano-oxides tended to be wrapped up with a B2-NiAl nano-shells. Although the quench-tempered sample showed much higher room-temperature strength (yield strength = 1393 ± 40 MPa and ultimate tensile strength = 1774 ± 11 MPa) and slightly lower elongation (elongation = 13.6% ± 0.6%) than the annealed sample (YS = 988 ± 7 MPa, UTS = 1490 ± 12 MPa, and EL = 15.2% ± 1.1%), both samples exhibited better strength-ductility synergy at room temperature and much higher thermal stabilities at high temperatures (600–700 °C) than all those conventional hot-work die steels, which makes the new ODS steel highly promising for advanced hot-work mold and die applications at high temperatures above 600 °C.