Effect of precipitation under long-term aging at 650 °c on the tensile strength of advanced 10%Cr heat-resistant steel

Abstract

The effect of long-term aging for 103 to 3.9•104 h at 650 °C on the microstructure, dispersion of secondary phases, and tensile strength properties was studied in a low-nitrogen 10%Cr martensitic steel with 3%Co and 0.008%B additives. Tensile tests of small specimens cut from grip portions of creep tested specimens were carried out at ambient and elevated (650 °C) temperatures. An increase in the yield stress and ultimate tensile strength after 10,000 h of aging was revealed to be associated with the precipitation of V-rich MX carbonitrides, which compensated for the coarsening of the boundary particles and depletion of W and Mo solutes from the ferritic matrix. The effect of changes of the microstructure and dispersion of secondary phases on strengthening of the steel is discussed.