Fig. 1 ESR macrostructure of the Plate III, which was the No. 3 slice cut from the ingot’s longitudinal central section and was sampled at the center, the mid-radius and the edge

Fig. 2 SEM observations on S-nitrides (a) at the ingot’s mid-radius before exposure, and (b) at the center, (c) the mid-radius, (d) the edge after being exposed at 1200 °C for 60 min, respectively

Fig. 3 Dark-field OM observations on S-nitrides in the specimens thermally exposed at 1100 °C for (a, b) 30 min, and (c) 240 min. b is an enlarged image of the area framed in a

Fig. 4 TEM characterizations of S-nitrides: a the morphology, b selected area diffraction pattern and c EDS

Fig. 5 SEM observations on S-nitrides in the mid-radius specimens thermally exposed at a-d 1100 °C, e-h 1200 °C, i-l 1300 °C for 30, 60, 120 and 240 min, respectively

Fig. 6 Statistical analysis on the a average particle radius, b average particle quantity of S-nitrides

Fig. 7 SEM observations on S-nitrides in the specimens thermally exposed for 60 min at a 1200 °C, b 1350 °C, respectively

Fig. 8 Qualitative elemental mapping images of Ti, N, Cr and Ni at the center, the mid-radius and the edge of the ingot

Fig. 9 Concentration profiles of a Cr, b Ti, c Ni obtained across dendritic arms at the center, the mid-radius and the edge of the ingot

Fig. 10 Quantitative analysis on the growth of S-nitrides including the a linear relationships between \(\bar{r}^{3}\) and t at various exposing temperatures, b the temperature dependence of ln k

Fig. 11 Schematic illustration of the growing mechanism of S-nitride particles. a S-nitride particles have formed between dendritic arms; b nitrogen diffuses to the interdendritic region for sustaining the growth of S-nitride particles. The brightness of red color and intensity of greenish color represent the concentration of titanium and nitrogen, respectively