Investigation of Boron Distribution in Martensitic 9% Cr Creep Resistant Steel

Chemical compositions of ferrite matrix and various other phases in a Fe - 0.17 wt.% C - 9.3 wt. % Cr - 1.55 wt.% Mo - 0.27 wt.% V - 0.015 wt.% N - 0.01 wt.% B creep resistant steel in as-received and crept conditions were analyzed with atom probe field ion microscopy. The results show the presence of some residual boron within the ferrite matrix. Analyses showed that boron was uniformly distributed within M23C6, M6C, MX, and Laves phases. Phosphor segregated to the M23C6 - ferrite matrix interface. The results are analyzed with thermodynamic calculations.