Study on the Change Law of Microstructure of T91 Steel During Aging at 750℃

摘要

The microstructures of T91 steel specimens during long-term aging (up to 1700 hours)rnat 750℃ were investigated by SEM, EDS and TEM. The count, average size andrnamount of precipitates were measured, and the change discipline of the microstructurernwas analyzed. The size of grains increased continuously with the increase of agingrntime. The precipitates mainly consisted of M_(23)C_6 carbides and MX carbonitrides,rnwithout any Laves phase and Z phase. The relationship between the count (N),rndiameter (D) and area fraction (S) of the precipitate and the aging time (t) in this studyrncould be summarized respectively as follows: N=4776.80+22.30t?0.01t~2 , D= 0.46t~(0.20) andrnS=2.14+5.00×10~(?3)t+2.73×10~(?6)t~2. The content of Cr and Mo in the matrix tended torndecrease and that in the precipitates tended to increase. It is suggested that Cr and Mornmigrated from matrix to precipitate during the aging procedure, and that thernredistribution of Cr and Mo occurred.