THE EFFECT OF NIOBIUM ON THE MICROSTRUCTURE OF FERRITIC STAINLESS-STEEL

The effect of different amounts of Nb and of homogenization on the fer ritic stainless steels containing 17-18 wt.% Cr was investigated with scanning electron microscopy (SEM), optical microscopy, energy-dispers ive spectrometry (EDS), X-ray diffraction (XRD) and differential therm al analysis (DTA). It was observed that M23C6, NbC and sigma phase for med in these steels. In addition, the formation of Nb2C was observed i n the sample containing 3.0 wt.% Nb. While the amount of Nb increased from 0.5 to 3.0 wt.% Nb, the microhardness of the matrix and the amoun t of M23C6 decreased and the toughness of the samples increased. After homogenization, the increase in the toughness of the samples containi ng 1.5-3.0 wt.%Nb was considerable and impressive. (C) 1997 Elsevier S cience S.A.