Fig. 1 a-c IPF (inverse pole figure) and d-f grain size distribution images showing the microstructure evolution during the solution treating for 15 min at a, d 1100 °C, b, e 1150 °C, c, f 1200 °C

Fig. 2 a-c BSE images and d-f EDS spectra showing the representative second phase particles in specimens after annealing for 15 min at a 1100 °C, b 1150 °C, (c) 1200 °C: d EDS spectrum of matrix, e EDS spectrum of TiN, f EDS spectrum of Nb (CN)

Fig. 3 a XRD, b EBSD, and c, d TEM results identifying the representative precipitation phases in the aged specimens: a detected on the specimens after solution treating at 1100 °C and ageing for 32 h at 800 °C, b observed on the specimens after solution treating at 1200 °C and ageing for 16 h at 800 °C, c, d observed on the specimens after solution treating at 1100 °C and ageing for 0.5 h at 800 °C

Fig. 4 a BSE image and b-d EDS spectra showing the representative precipitation phases in specimens after annealing for 15 min at 1150 °C and ageing for 16 h at 800 °C: b EDS spectrum of χ-phase, c EDS spectrum of Laves phase, d EDS spectrum of σ-phase

Fig. 5 BSE images showing the typical precipitation after solution treating at 1200 °C and ageing at 800 °C for: a 0.5 h, b 1 h, c 4 h, d, 8 h, e 300 h, f 400 h

Fig. 6 Schematic diagram illustrating the precipitation evolution during ageing at 800 °C

Fig. 7 Volume fraction of σ-phase in the ST specimens after 800 °C ageing treating

Fig. 8 a, c and e Linearized σ-phase volume fraction as a function of time assuming JMA kinetic model for σ-phase formation in tested steel and b, d and f the JMA curves at different solution treating temperatures: a and b for 1100 °C solution treating, c and d for 1150 °C solution treating, e and f for 1120 °C solution treating condition

Fig. 9 Laves phase morphology in the specimens after solution treating at 1100 °C and ageing for 1 h at 800 °C