2025 Volume 65 Issue 1 Pages 20-25
From the viewpoint of expanding the allowable P limit, the effect of warm tempforming on delayed fracture resistance was evaluated for 0.09% P-doped 0.4%C–1%Cr–0.7%Mn–0.2%Mo steel (mass%). The P-doped steel was warm tempformed at 500°C with a caliber-rolling reduction of 78% and annealed at 550°C for 1 h. This thermomechanical treatment created an ultrafine elongated grain structure with a strong <110>//rolling direction fiber texture, in which P definitely cosegregated with Mn and Mo at grain boundaries. The slow-strain-rate-test and immersion test demonstrated that warm tempforming markedly enhanced the delayed fracture resistance of the P-doped steel at a tensile strength of 1100 MPa level, in contrast to conventional quenching and tempering treatment.
