Influence of tempering temperature upon precipitate phases in a 11%Cr ferritic/martensitic steel

The effect of tempering temperature on the precipitate phases in a 11%Cr ferritic/martensitic steel normalized at 1050 °C for 1 h and tempered for 2 h at temperatures ranging from 600 to 780 °C has been investigated using transmission electron microscope and energy-dispersive X-ray spectroscopy. The results show that tempering temperature does not affect the existences of niobium-rich carbonitrides, (Nb0.7V0.2Cr0.1)(C,N) and (Nb0.55V0.35Cr0.1)(C,N), vanadium–niobium-rich carbonitride (V0.45Nb0.45Cr0.1)(C,N), chromium-rich carbonitride (Cr0.83V0.12W0.05)2(C,N) and chromium-rich carbide (Cr0.7Fe0.25W0.05)23-C6, whilst the precipitations of vanadium-rich carbonitrides, (V0.65Nb0.2Cr0.15)(C,N) and (V0.55Nb0.25Cr0.2)(C,N) are dependent on tempering temperature, which were detected only at the higher tempering temperatures of 750 and 780 °C. No coarsening was occurred during the temperings for the niobium-rich and spherical vanadium-rich carbonitrides. There was a low coarsening rate for the chromium-rich carbonitrides and chromium-rich carbides with increasing the tempering temperature from 600 to 700 °C and 650 to 780 °C, respectively, and a high coarsening rate for the chromium-rich carbonitrides and chromium-rich carbides at the tempering temperatures 750 through 780 °C and 650 °C, respectively. The compositions show an increase in vanadium and a decrease in niobium and chromium contents for the niobium-rich carbonitrides, and a decrease in niobium and an increase in vanadium and chromium contents for the vanadium–niobium-rich carbonitrides, and an increase in vanadium and a decrease in tungsten contents for the chromium-rich carbonitrides. The chromium-rich carbides show an increase and a decrease in their iron and chromium contents, respectively, with increasing the tempering temperature from 650 to 780 °C.