Evolution of the tempered lath structure of the 12% Cr steels with low N and high B contents during creep

Abstract

9-12% Cr martensitic steels are promising materials for elements of boilers, tubes, pipes, heaters and steam blades for fossil power plants, which are able to operate at ultrasupercritical parameters of steam. Creep tests were carried out for two 12% Cr and 9% Cr steels at 650°C. After tempering at 750-770°C, a tempered lath structure was revealed in all the steels studied. The 12% Cr-Ta steel had the smallest lath width among the steels studied that provided the longest creep rupture time after creep test at 650°C/120 MPa. During creep, the applied stress causes the lath growth and the formation of subgrains instead of martensitic laths