Study on the deformation mechanism of a high-nitrogen duplex stainless steel with excellent mechanical properties originated from bimodal grain design

The alloy design for high-nitrogen duplex stainless steels (DSSs) has been received ascendant attentions due to their excellent strength, ductility and anticorrosion. However, the yield ratios of these steels are usually low and cannot meet the requirement of structural parts. In this work, a DSS 2202 with fine austenite grains and bimodal ferrite structure was obtained through ingenious heat treatment and rolling process and the yield strength (YS) increased from 416.5 to 716.4 MPa while the total elongation still maintained at high level of 45.8%. Furthermore, the transformation-induced plasticity (TRIP) effect was suppressed during the whole tensile test. Based on the detailed microstructure characterization, the deformation mechanism of this DSS was discussed and a novel strengthening method was proposed, that is, the unusually rapid dislocation proliferation mechanism in coarse ferrite was triggered and its dislocation density reaches to 1.3326 × 10 ¹⁴ m ⁻² after deformation which is equivalent to that of austenite (1.5229 × 10 ¹⁴ m ⁻² ). This work provides a new way for the material selection of some structural components with the demands of high yield ratio and high corrosion resistance.