Effect of Carbon Content on the Creep Rupture Properties and Microstructure of 316H Weld Metals

doi:10.1007/s40195-020-01180-3

Acta Metallurgica Sinica (English Letters) ›› 2021, Vol. 34 ›› Issue (7): 986-996.DOI: 10.1007/s40195-020-01180-3

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Effect of Carbon Content on the Creep Rupture Properties and Microstructure of 316H Weld Metals

Langlang Zhao¹^,²^,³, Shitong Wei¹, Dianbao Gao⁴, Shanping Lu³()

¹Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China
²School of Materials Science and Engineering, University of Science and Technology of China, 72 Wenhua Road, Shenyang 110016, China
³Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China
⁴Nuclear Power and Petro-Chemical Business Group, China; First Heavy Industries, 1 Miangang Road, Dalian 116113, China

Received:2020-08-25 Revised:2020-10-08 Accepted:2020-10-11 Online:2021-02-05 Published:2021-02-05
Contact: Shanping Lu
About author:Shanping Lu, shplu@imr.ac.cn; IMRshplu@126.com

Abstract

Abstract:

Two types of 316 butt welds with carbon contents of 0.016% and 0.062% have been produced using the gas tungsten arc welding process. The δ-ferrite content decreased from 7.2 to 2.8% in volume as the carbon content increased. The creep-rupture strength and creep ductility of the two types of weld metals have been measured at 550 ℃ over the stress range of 290-316 MPa and at 600 ℃ over 230-265 MPa. The microstructure change and precipitation behavior of the weld metals were observed and related to the creep rupture properties. The creep rupture strength of the C2 (0.062% C) weld metal was higher than that of the C1 (0.016% C) weld metal at both 550 ℃ and 600 ℃. At 550 ℃, as the decrease in the applied stress, the difference of the creep-rupture life between the two weld metals diminished due to the higher depletion rate of carbon by precipitation of M₂₃C₆in the C2 weld metal, while at 600 ℃, the difference enlarged due to the massive precipitation of σ phase and extensive crack formation and propagation along σ/austenite boundaries in the C1 weld metal. For both the C1 and C2 weld metal, the decrease in ductility was adverse with the transformation percentage and related to products of the δ-ferrite transformation.

Key words: 316 stainless steel weld metal, Creep rupture properties, δ-ferrite;, M₂₃C₆, σ phase;

Langlang Zhao, Shitong Wei, Dianbao Gao, Shanping Lu. Effect of Carbon Content on the Creep Rupture Properties and Microstructure of 316H Weld Metals[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(7): 986-996.

Figures/Tables 19

Fig. 1 Photographs of the butt-type joint a and the weld metal welding sample b

Table 1 Chemical composition of the stainless steel weld metal(wt%)

	C	Cr	Ni	Mo	Mn	Si	N	P	S	δ-ferrite (vol.%)
C1	0.016	19.10	12.5	2.48	1.54	0.41	0.056	0.005	0.0029	7.2
C2	0.062	18.92	12.4	2.49	1.55	0.43	0.046	0.005	0.0009	2.8

Fig. 2 Configuration of the creep rupture specimen

Fig. 3 Stress-rupture properties of C1 and C2 weld metals at a 550 ℃, b 600 ℃. The dash line for the C2 weld and dot line for the C1 weld were obtained by fitting the power law relation

Fig. 4 Creep ductility of the C1 and C2 weld metals at a 550 ℃, b 600 ℃

Fig. 5 Decrease in the δ-ferrite content with the creep rupture time at a 550 ℃, b 600 ℃3.3 Precipitates X-ray Diffraction (XRD) Analysis

Fig. 6 Effect of creep duration time on precipitation phase type and content of bulk extracted residues of C1 and C2 weld metal at a 550 ℃; b 600 ℃

Fig. 7 Microstructures of the as-welded weld metal: a C1 as-welded weld metal; b C2 as-welded weld metal

Fig. 8 C1 weld metal; creep ruptured in 534 h at 550 ℃

Fig. 9 C1 weld metal; creep ruptured in 1736 h at 550 ℃

Fig. 10 C1 weld metal; creep ruptured in 223 h at 600 ℃

Fig. 11 C1 weld metal; creep ruptured in 892 h at 600 ℃

Table 2 EDS analysis results of the M23C6 carbide and σ phase (wt%)

	C	Cr	Fe	Mo	Mn	Ni	Si
M₂₃C₆	6.83	33.08	45.16	6.50	1.30	5.43	1.70
σ	-	36.07	56.05	4.09	1.05	2.35	0.39

Fig. 12 C2 weld metal; creep ruptured in 682 h at 550 ℃

Fig. 13 C2 weld metal; creep ruptured in 2565 h at 550 ℃

Fig. 14 C2 weld metal; creep ruptured in 1816 h at 600 ℃

Fig. 15 Specimen sections of ruptured a C1 weld metal in 534 h at 550 ℃; b C1 weld metal in 2069 h at 550 ℃; c C2 weld metal in 682 h at 550 ℃, dC2 weld metal in 2565 h at 550 ℃. Main fracture surfaces were located at the bottom of each micrograph

Fig. 16 Specimen sections of ruptured a C1 weld metal in 188 h at 600 ℃; b C1 weld metal in 896 h at 600 ℃; c C2 weld metal in 198 h at 600 ℃, dC2 weld metal in 1505 h at 600 ℃. Main fracture surfaces were located at the bottom of each micrograph

Fig. 17 SEM images showing fracture surfaces of a C1 weld metal creep ruptured in 534 h at 550 ℃; b C1 weld metal in 896 h at 600 ℃; c C2 weld metal in 682 h at 550 ℃; d C2 weld metal in 1505 h at 600 ℃

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Effect of Carbon Content on the Creep Rupture Properties and Microstructure of 316H Weld Metals

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