Effect of niobium on microstructure and precipitation in As-annealed Sanicro 25 steel

Abstract

The chemical compositions of Sanicro 25 stainless steel added with different concentrations of niobium (Nb) (0, 0.29, 0.58, and 0.86 wt-%) were investigated. X-ray diffraction analysis showed that the matrix of all the prepared materials was austenite. The average grain size decreased from 426 to 90 µm with the increase in Nb content. Electron backscatter diffraction and energy dispersive Xray spectroscopy analyses showed that Cr 23 C 6 was the main precipitate in the Nb-free steel, whereas Nb(C, N) were the main precipitates in Nb-containing steel. The increase in Nb content also increased the volume fraction and average particle size of the precipitates.

Effect of Niobium Addition on the High-Temperature Oxidation Behavior of 22Cr25NiWCoCu Stainless Steel in Air

“…These results show that when the Nb addition increases in 22Cr25NiWCoCu stainless steels, the average grain size decreases, and the precipitates of Nb (C, N) tend to cluster. These phenomena were also observed in our previous study [13], in which the fine and coarse precipitates of Nb (C, N) simultaneously appeared. The hardness values of the four steels were~210 HV, as shown in Table 2.…”

“…This finding indicates that the grain size did not affect the oxidation rate. According to a previous study [13], the volume fractions of Nb (C, N) precipitates for 0-Nb, 0.29-Nb, 0.58-Nb, and 0.86-Nb were 0, 3.1, 5.2, and 3.5 wt.%, respectively.…”

“…In our previous study, the microstructure of 22Cr25NiWCoCu-xNb stainless steel with a modified Nb content from 0-0.86 wt.% was investigated. The results showed that the average grain size was reduced with increasing Nb content, and the volume fraction and particle size of the precipitates were also changed [13]. A reduction in grain size is beneficial in oxidation resistance because the grain boundaries act as fast diffusion paths for Cr to form a protective Cr 2 O 3 layer [14][15][16][17][18].…”