Effect of stress on microstructural evolution and mechanical properties of 12Cr3W3Co steel during aging and short-term creep

The dual-phase (martensite and delta ferrite) microstructure in 12Cr3W3Co steel was obtained by the method of reheat treatment in the duplex phase (δ+γ) region. The coarsening process of martensite lath and precipitation behavior of M23C6 and Laves phase particles in this steel were investigated during aging and short-term creep under different stresses at 600°C for 1100h. The results showed that large numbers of Cr-rich M23C6 carbides formed in martensite matrix and Laves phase prefered to precipitate inside delta ferrite at the early stage of creep. The number of Laves phase precipitates inside delta ferrite in crept specimens was larger than that in aged specimen and the size increases with the stress increase in crept specimens. Martensite lath structure tended to grow and the recombination of lath boundaries under stress caused the disappearance of some lath boundaries leaving a row of M23C6 carbides in the martensite matrix. The short-term creep mechanical behavior was studied by analyzing steady-state creep rate and stress exponent. Reletively low steady-state creep rate and high stress exponent were found and these were attributed to the solid solution strengthening and precipitation strengthening.