Relative effect of B and N concentrations on the microstructural stability and mechanical properties of modified 9Cr-1Mo steel

The present study systematically varied the concentrations of B (0-100 ppm) and N (20-500 ppm) in modified 9Cr-1Mo steel to understand the combined effect of B and N addition on the microstructural stability and the creep resistance (650 degrees C, 120 MPa). The Auger Electron Spectroscopic analysis reveals the enrichment of B within the M23C6 precipitates at the vicinity of prior-austenite grain boundaries in B added steels both in normalized and tempered specimens and also in creep tested specimens. The 70 ppm B steel with 108 ppm N showed the best creep resistance (rupture time as high as 1536 h and minimum creep-rate as low as 1 x 10(-5)/h), followed by 90 ppm B, 90 ppm N steel. Too low B content (25 ppm or less) or too high N content (500 ppm) affected precipitate stability and consequently the creep resistance of the steel. Finally, it can be recommended that it is necessary to maintain optimum concentrations of B (70-100 ppm) and N (90-110 ppm) to improve the creep resistance of modified 9Cr-1Mo steel. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The systematic study on modified 9Cr-1Mo steel revealed the combined effect of B and N addition on microstructural stability and creep resistance. The best creep resistance was observed in the steel with 70 ppm B and 108 ppm N, while either too low B content or too high N content affected the precipitate stability and creep resistance of the steel.