Distribution of Boron in 9.5Cr–1.5MoCoVNbNB Martensitic Heat-Resistant Steel Studied by Secondary Ion Mass Spectroscopy and atom Probe Tomography

9.5Cr–1.5MoCoVNbNB heat-resistant steel has been designed for use at 620 ℃ in ultra-supercritical power plants and has been acknowledged as the most promising martensitic heat-resistant steel for turbine rotors. With the addition of 100 ppm B, the resulting precipitates and inclusions endow the steel with improved properties. However, the direct observation and quantitative analysis of B distribution in 9.5Cr–1.5MoCoVNbNB heat-resistant steel are lacking. Herein, the distribution of B in 9.5Cr–1.5MoCoVNbNB heat-resistant steel was analyzed. The results of secondary ion mass spectroscopy (SIMS) revealed that B segregated at the boundaries after tempering, and those of atom probe tomography (APT) revealed that B atoms were evenly distributed in M 23 C 6 carbide particles during aging at 620 ℃. The coarsening of M 23 C 6 carbides was found to be a process of alloy element redistribution. The BN inclusions might be detrimental during the tensile rupture fracture because the fish-eye fracture mode was observed. Cavity coalescence mainly occurs around type-B dimples (without BN particles). Graphical Abstract