Improved creep strength of 10% Cr steels with low N and high B content via increasing quenching temperature

Abstract

An increase in quenching temperature from 1050 °C to 1100 °C is found to be an effective approach to improving the creep strength at 650 °C in two Re-containing 10% Cr martensitic steels with low N and high B contents. Creep time at creep tests of 650 °C/120 MPa increases at the expense of the appearance of the steady-state creep stage in both steels. Moreover, the room yield strength and ultimate tensile strength are also increased by 10% with increasing quenching temperature in the steel with 0.8% Cu, whereas tensile tests at 650 °C do not reveal the increment in strength in both steels. Improvement in creep and tensile properties is caused by an increase in particle strengthening due to M23C6 carbides, mainly in both steels. The NbX, VX, and “Cu”-clusters/precipitates make minor contributions to the change in particle strengthening. Refinement of M23C6 carbides in both steels is accompanied by an increase in particle number density along the martensitic laths and an increase in the fraction of fine particles with sizes below 50 nm. Such changes in M23C6 carbide dispersions are caused by an increase in the lath area per unit volume and the enrichment of the solid solution with boron because of the dissolution of W2B particles with increasing quenching temperatures.