Effect of Precipitation Behavior and Deformation Twinning Evolution on the Mechanical Properties of 16Cr-25.5Ni-4.2Mo Superaustenitic Stainless Steel Weld Metals

doi:10.1007/s40195-024-01787-w

Abstract

Abstract:

In the study, three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%, 0.075 wt%, and 0.045 wt%, were prepared to investigate the microstructural evolution and its effect on mechanical behavior. At a C content of 0.082 wt%, the microstructure of weld metal consisted of austenite, M₆C, and M₂₃C₆, where M₆C was the main carbide. The number and average size of the M₆C carbides significantly decreased as the C content decreased. At a C content of 0.045 wt%, only a very small number of M₆C carbides were observed in the weld metal. For the tensile process, the number of deformation twins increased as the C content decreased, which introduced a stronger dynamic Hall-Petch effect, resulting in only a small decrease in the ultimate tensile strength of the weld metal. Meanwhile, the increase in deformation twins significantly enhanced the elongation of the weld metals. For the impact process, the impact energy increased from 204 to 241 J as the C content decreased. The crack initiation resistance was improved due to the reduction in M₆C carbide, which inhibited cracking at the interface of M₆C/matrix. Additionally, the crack propagation resistance was enhanced due to the increase in deformation twins, which consumed more impact energy.

Key words: Superaustenitic stainless steel weld metal, Microstructural evolution, Carbides, Mechanical properties, Deformation twins

Chenghao Liu, Wenchao Dong, Jian Sun, Shanping Lu. Effect of Precipitation Behavior and Deformation Twinning Evolution on the Mechanical Properties of 16Cr-25.5Ni-4.2Mo Superaustenitic Stainless Steel Weld Metals[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(2): 338-352.

Figures/Tables 20

Table 1 Chemical composition of weld metals and base metal (wt%)

Materials	C	Cr	Ni	Mo	Mn	N	Fe
C1	0.082	16.0	25.2	4.26	1.43	0.086	Bal.
C2	0.075	15.9	25.5	4.38	1.48	0.085	Bal.
C3	0.047	15.8	25.6	4.40	1.51	0.092	Bal.
Base metal	0.097	15.89	25.6	6.22	1.42	0.12	Bal.

Fig. 1 Illustration of the sample preparation: a sampling locations, b the dimension of the tensile sample, c the dimension of the impact sample, d analysis diagram of both tensile and impact fractures

Fig. 2 Results of the solidification process for weld metals with various C contents

Table 2 K-factors of major elements under the L-γ condition

	Fe	Ni	Cr	Mo	Mn
C1	1.21	1.35	0.76	0.54	1.09
C2	1.21	1.33	0.77	0.57	1.07
C3	1.20	1.29	0.79	0.61	1.04

Fig. 3 SEM images of weld metals: a, d, g C1, b, e, h C2, c, f, i C3

Table 3 EDX results of the IDR, DCR and precipitated phase in Fig. 3 (wt%)

	Fe	Ni	Cr	Mo	Mn	C
IDR	46.44	24.06	18.68	8.83	1.99	-
DCR	53.11	25.55	15.98	3.81	1.55	-
Spot 1	29.91	14.23	18.56	24.59	1.50	11.20
Spot 2	29.80	12.93	18.33	24.90	1.29	12.74
Spot 3	30.90	14.51	19.70	21.20	1.48	12.21
Spot 4	41.37	17.87	22.81	13.68	2.02	2.25
Spot 5	41.85	20.65	21.87	12.04	2.05	1.54

Table 4 SR of major elements of C1-C3 weld metals

	Fe	Cr	Ni	Mo
C1	0.90 ± 0.02	1.17 ± 0.02	0.97 ± 0.02	1.86 ± 0.15
C2	0.91 ± 0.02	1.14 ± 0.05	0.99 ± 0.02	1.69 ± 0.10
C3	0.94 ± 0.01	1.09 ± 0.02	1.01 ± 0.01	1.45 ± 0.04

Fig. 4 TEM images of precipitated phases in the C1 weld metal: a STEM image, b STEM-EDS mappings of a, c BF image, d SAED pattern of M6C, e HRTEM and FFT images of M23C6

Fig. 5 Dislocation density analysis of the C1-C3 weld metals: a-c TEM images, d XRD patterns

Fig. 6 Tensile properties of the C1-C3 weld metals: a YS and UTS, b elongation

Fig. 7 Micrographs of fractured surfaces of tensile samples of the weld metals: a C1, b C2, c C3. d Local enlargement of a

Fig. 8 EBSD inverse pole figure (IPF) maps and corresponding average grain diameter of the weld metals: a C1, b C2, c C3

Fig. 9 a Engineering stress-strain curves and b-d SHR curves for tensile samples of C1-C3 weld metals

Fig. 10 EBSD characterization of the longitudinal section of tensile fracture

Fig. 11 Impact properties of the C1-C3 weld metals

Fig. 12 Micrographs of fractured surfaces of impact samples: a, d C1, b, e C2, c, f C3

Fig. 13 Microstructures of the longitudinal section of impact fracture: a, d, g C1, b, e, h C2, c, f, i C3. a-f SEM images and g-i ECCI images

Fig. 14 Statistical results of the M6C carbides: a statistical regions, b the number of M6C carbides, c the average size of M6C carbides

Fig. 15 EBSD characterization of the longitudinal section of impact fracture, and instrumented Charpy impact test: a-c and d-f the IPF, KAM, and load-displacement curves of C1 and C3, respectively

Fig. 16 Fracture mechanisms of the C1 and C3 weld metals: a, b tensile process, c, d impact process

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