Study on creep behavior and microstructure of a Fe–Cr–Al–Nb–W ferrtic heat-resistant steel based on C, N and Al element control

Abstract

In this work, the effects of C, N, and Al on the microstructures and creep properties of Fe-Cr-Al-Nb-W ferritic alloys were investigated through scanning electron microscopy, x-ray diffractometry, as well as uniaxial creep testing and hardness testing. The results demonstrated that the matrix of the Fe-Cr-Al-Nb-W heat-resistant steel was ferrite, while the precipitation phases were Laves phases, M 23 C 6 carbides and MX nitride phases. M 23 C 6 and MX precipitated at grain interior, Laves phases precipitated at grain interior, grain boundary and around MX phases. C, N and Al affected microstructure and creep of heat-resistant steel. As the Al content increased or as N content decreased along with the C increase, the average diameter of the Laves phases, along with M 23 C 6 and MX phase grain interior decrease. Moreover, the unit density increased and the phase spacing decreased, which led to the minimum creep rate decrease and creep rupture time increase. Compared to M 23 C 6 , Laves and MX phases mainly affected the alloy creep strength. The decrease of Laves phase continuity coefficient (ratio of Laves phase particle spacing and size) on the grain boundary was conducive to the plasticity improvement of heat-resistant steel.