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

Abstract 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, (Nb 0.7 V 0.2 Cr 0.1 )(C,N) and (Nb 0.55 V 0.35 Cr 0.1 )(C,N), vanadium–niobium-rich carbonitride (V 0.45 Nb 0.45 Cr 0.1 )(C,N), chromium-rich carbonitride (Cr 0.83 V 0.12 W 0.05 ) 2 (C,N) and chromium-rich carbide (Cr 0.7 Fe 0.25 W 0.05 ) 23 -C 6 , whilst the precipitations of vanadium-rich carbonitrides, (V 0.65 Nb 0.2 Cr 0.15 )(C,N) and (V 0.55 Nb 0.25 Cr 0.2 )(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.