The effect of cold rolling reduction on the high-temperature mechanical properties of 9Cr-3Co-3W martensite heat-resistant steel

To optimize the high-temperature mechanical properties of 9Cr-3Co-3W steel, cold rolling reductions of 0 %, 20 % and 40 % were applied, followed by tempering at 800°C for 30 min. The microstructure, precipitation behavior and fracture morphologies were then characterized to explain the mechanical properties. The results show that the steel with a 20 % cold rolling reduction exhibits the best mechanical performance (σ_b= 475 MPa, δ= 25 %), outperforming the 0 % and 40 % reduction. The high strength is primarily attributed to the dislocation strengthening and precipitation strengthening, as the 20 % reduction leads to the highest average dislocation density due to the lower recovery rate and fine precipitates. The good ductility is attributed to the lower recovery and precipitation nucleation driving force, which preserves microstructure homogeneity and maintains fine precipitate sizes, thus preventing high-temperature failure caused by large precipitates and deformation incompatibility, as observed in the fractured 40 % cold-rolled steel.