Fig. 1 Schematic diagram of the weldment and samples: a butt weld joint design, b tensile sample, c impact sample

Fig. 2 Detailed post-weld heat treatment (PWHT) procedure

Fig. 3 Calculated precipitation sequence of the weld metal during the solidification

Fig. 4 Microstructure characterization of as-welded weld metal: OM images of a fully austenitic microstructure and b precipitate distribution, c SEM micrograph of interdendritic precipitates, d corresponding EDS semiquantitative result

Fig. 5 EPMA mappings: a backscattered electron image, elements distribution of b C, c N, d Cr, e Mo, f Fe

Fig. 6 TEM characterization of primary precipitates in as-welded weld metal: a HAADF-STEM micrograph of M6C carbide and b corresponding SAED pattern, c HAADF-STEM micrograph of M23C6 carbide, d corresponding SAED pattern, e STEM-EDS mappings of M23C6 carbide

Fig. 7 SEM micrographs of the weld metal after PWHT: a 690 °C/4 h, b 690 °C/8 h, c 690 °C/12 h

Fig. 8 XRD patterns of the precipitates in the weld metal after PWHT

Fig. 9 TEM characterization of needlelike precipitates (confirmed as M2X carbonitrides): a BF micrograph, b DF micrograph, c SAED pattern of M2X, d corresponding EDS result (elemental carbon and nitrogen were detected in the spectrum but not listed in the chart because the content of light elements were not accurate)

Fig. 10 TEM characterization of secondary M23C6 carbides in the grain boundary: a HAADF-STEM micrograph, b STEM-EDS mapping of Cr-rich M23C6, c STEM-EDS mapping of Cr-rich M23C6, d, e: the corresponding SAED patterns of (b) and (c), respectively

Fig. 11 Secondary M23C6 carbides in the interdendritic region: a BF micrograph, b local amplification of (a), c SAED pattern of M23C6

Fig. 12 Room temperature tensile property of SASS weld metal: a comparison (as-welded) with typical base metal of DMW [9, 46,47,48], b evolution among different conditions (as-welded and PWHT)

Fig. 13 SEM micrographs of tensile specimens after fracture: a as-welded, b 690 °C/4 h, c 690 °C/8 h, d 690 °C/12 h

Fig. 14 Impact toughness of the weld metal (room temperature)

Fig. 15 SEM fractography and dimple patterns of the weld metal after impact fracture: a, e as-welded, b, f 690 °C/4 h, c, g 690 °C/8 h, d, h 690 °C/12 h

Fig. 16 SEM micrographs of the weld metal after impact toughness test (longitudinal section): a as-welded, b 690 °C/4 h