Nanocrystalline materials demonstrate superior strength but usually lack any sufficient ductility. Here we show that a new nanocrystalline metastable stainless steel demonstrates yield strength of 1.5 GPa and strain to failure of 35% thanks to a development of martensitic transformation-governed Lüders deformation [1]. Samples with a composition Fe60Co15Ni15Cr10 (at. %) were produced by conventional vacuum arc-melting, homogenized at 1473 K, cold rolled and annealed at 1275 K for 10 min. After subsequent processing by high pressure torsion, a uniform fully FCC nanocrystalline microstructure with a mean grain size of 60 nm and a high density of lattice defects (mostly stacking faults) was obtained. Room temperature tensile test demonstrated peculiar deformation behavior with a pronounced yield point at 1600 MPa and extended stage of steady deformation for ~25% followed by a short strain hardening stage, necking and fracture. During visual monitoring of tensile test, a propagation of Lüders band across the whole specimen gauge was observed. Post-fracture TEM and synchrotron XRD investigations revealed almost complete FCC to BCC transformation. Coarse grained and cold rolled samples of the same composition showed typical for such states tensile behavior without any phase transformation. The obtained results indicated that the increase of the MD temperature in this novel steel is related to a presence of high density of lattice defects (grain boundaries and stacking faults) which allowed the Transformation Induced Plasticity (TRIP) effect at room temperature and achieving remarkable combination of high strength and high ductility. The strategy of improving the transformation kinetics by microstructure tailoring, would be also potentially feasible in other metastable alloys and austenitic steels with TRIP FCC→ BCC effect to enable them to demonstrate better mechanical performance at ambient temperatures. [1] Lu Y., Overcoming plasticity reduction in a severely deformed nano-grained metastable alloy, Materials Research Letters, Vol. 12(7), pp. 525-534, 2024.