Abstract
This paper reports on the precipitate evolution and its influence on the high temperature creep resistance of 9% Cr martensite ferritic steel FSW joint. The creep rupture time of the FSW joints welded by 400 rpm and 200 rpm are 859.29 h and 1173.8 h respectively, while that of BM is 3398 h. The creep fracture occurs in ICHAZ where a pronounced increase of coarse Laves phase is detected. Most of the Laves phase particles are large in size and mainly nucleate and grow rapidly at the micrograin boundaries adjoining the M23C6 particles where W, and other elements segregate. The large Laves phase particles will deteriorate the pinning effect of M23C6, weaken the solid solution strengthening effect and attribute to the increased cavity nucleation. In addition the size of Laves phase in ICHAZ is bigger than that in stir zone (SZ). These reasons explain why creep fracture occurs in the ICHAZ and the time to rupture will be shorter than base metal.
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