Effect of V and Nb on precipitation behavior and mechanical properties of high Cr steel

Onizawa, Takashi  ; Wakai, Takashi ; Ando, Masanori ; Aoto, Kazumi 

This paper studies the long term efficiency and stability of strengthening mechanisms provided by V and Nb in high chromium ferritic steels. These elements are believed to improve the high temperature strength of high Cr steels by precipitating as carbides and/or nitrides, namely fine MX particles. However, the long term efficiency and stability of such precipitation strengthening mechanisms provided by the fine MX particles have not been clarified yet. A series of trial products controlling V and Nb contents is produced and mechanical tests are conducted to investigate the effect of these elements on the mechanical properties and the long term stability of the MX strengthening mechanism. Before and after a long term aging process, metallurgical examinations and quantitative analyses are conducted to investigate the effect of these elements on the microstructure evolutions. Based on these results, the long term efficiency and stability of the strengthening mechanisms provided by the fine MX particles are discussed.