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Abstract
A quenching–partitioning–tempering (QPT) precipitation process is proposed to further increase the strength of ultra-high strength steels containing the carbide forming element Nb and/or Mo. Based on the recently developed QP treatment, the QPT process involves an additional tempering step to precipitate complex carbides from the martensite matrix. A designed QPT steel with nominal composition Fe–0·485C–1·195Mn–1·185Si–0·98Ni–0·21Nb has achieved ultimate tensile strengths >2000 MPa along with total elongation >10%. This superior ultra-high strength steel is believed to possess the best combination of properties among those containing <0·5%C developed to date.