Low Cycle Fatigue Behavior of Laser Welded DP980 Steel Joints

Zhanjiang Zhai; Lin Zhao; Yun Peng; Jiao Zhu; Yang Cao

doi:10.3788/CJL202148.1802003

Journals >Chinese Journal of Lasers >Volume 48 >Issue 18 >Page 1802003 > Article

Chinese Journal of Lasers
Vol. 48, Issue 18, 1802003 (2021)

Low Cycle Fatigue Behavior of Laser Welded DP980 Steel Joints

Zhanjiang Zhai^1、2, Lin Zhao^1、**, Yun Peng^1、*, Jiao Zhu², and Yang Cao¹

Author Affiliations

¹Institute of Welding, Central Iron & Steel Research Institute, Beijing 100081, China;

²NCS Testing Technology Co., Ltd., Beijing 100081, China

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DOI: 10.3788/CJL202148.1802003 Cite this Article Set citation alerts

Zhanjiang Zhai, Lin Zhao, Yun Peng, Jiao Zhu, Yang Cao. Low Cycle Fatigue Behavior of Laser Welded DP980 Steel Joints[J]. Chinese Journal of Lasers, 2021, 48(18): 1802003 Copy Citation Text

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Fig. 1. Dimensions of fatigue specimen

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Fig. 2. Microstructure of DP980 steel

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Fig. 3. Morphologies of welding joints under different heat inputs. (a) 80 J·mm^-1; (b) 100 J·mm^-1; (c) 133 J·mm^-1

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Fig. 4. Microhardness profiles of DP980 welding joints under different heat inputs

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Fig. 5. Typical tensile failure locations of DP980 welding joints and base material. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample

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Fig. 6. Relationship between total strain amplitude and 2N_f for base material and DP980 welding joints

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Fig. 7. Microstructures of L2 sample. (a) Weld zone, supercritical HAZ, and intercritical HAZ; (b) subcritical HAZ

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Fig. 8. Microstructures of subcritical HAZ under different heat inputs. (a) 80 J·mm^-1; (b) 100 J·mm^-1; (c) 133 J·mm^-1

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Fig. 9. Variation of stress amplitudes of base material and DP980 welding joints under different strain amplitudes with numbers of cycles. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample

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Fig. 10. Stabilized hysteresis loops at half fatigue life

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Fig. 11. Low-cycle fatigue specimens of base material and joints

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$Fatigue fracture domains of L2 and L3 samples. (a) Subcritical HAZ near L2 fracture; (b) subcritical HAZ near L3 fracture$

Fig. 12. Fatigue fracture domains of L2 and L3 samples. (a) Subcritical HAZ near L2 fracture; (b) subcritical HAZ near L3 fracture

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$Macroscopic fatigue fracture morphologies of base material and welding joints when Δεt/2=0.3%. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample$

Fig. 13. Macroscopic fatigue fracture morphologies of base material and welding joints when Δε_t/2=0.3%. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample

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$Microscopic fatigue fracture morphologies of base material and welding joints when Δεt/2=0.3%. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample$

Fig. 14. Microscopic fatigue fracture morphologies of base material and welding joints when Δε_t/2=0.3%. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample

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$Macroscopic fatigue fracture morphologies of welding joints of L3 sample under different strain amplitudes. (a) Δεt/2=0.25%; (b) Δεt/2=0.3%; (c) Δεt/2=0.4%; (d) Δεt/2=0.5%$

Fig. 15. Macroscopic fatigue fracture morphologies of welding joints of L3 sample under different strain amplitudes. (a) Δε_t/2=0.25%; (b) Δε_t/2=0.3%; (c) Δε_t/2=0.4%; (d) Δε_t/2=0.5%

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$Microscopic fatigue fracture morphologies of welding joints of L3 sample under different strain amplitudes. (a) Δεt/2=0.25%; (b) Δεt/2=0.3%; (c) Δεt/2=0.4%; (d) Δεt/2=0.5%$

Fig. 16. Microscopic fatigue fracture morphologies of welding joints of L3 sample under different strain amplitudes. (a) Δε_t/2=0.25%; (b) Δε_t/2=0.3%; (c) Δε_t/2=0.4%; (d) Δε_t/2=0.5%

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Sample No.	Heat input /( J·mm^-1)	Laser power /W	Welding speed /( m·min^-1)	Focal length /mm	Flow rate /( L·min^-1)
L1	80	2000	1.5	300	15
L2	100	2000	1.2	300	15
L3	133	2000	0.9	300	15

Table 1. Welding parameters

Sample No.	Yield strength /MPa	Tensile strength /MPa	Elongation /%	Product of strength and elongation /( GPa ·%)
DP980	706	1071	14.0	15.0
L1	704	1026	12.0	12.3
L2	737	1028	10.5	10.8
L3	727	1010	10.5	10.6

Table 2. Mechanical properties of DP980 steel and welding joints

Sample No.	σ_f /MPa	b	ε_f	c	N_t /cycle
DP980	1860	-0.1136	0.7407	-0.6429	2536
L1	1776	-0.1200	1.1537	-0.7561	1148
L2	1625	-0.1158	1.2824	-0.7771	1122
L3	1521	-0.1127	0.2765	-0.5862	957

Table 3. Low cycle fatigue parameters of DP980 steel and welding joints

Zhanjiang Zhai, Lin Zhao, Yun Peng, Jiao Zhu, Yang Cao. Low Cycle Fatigue Behavior of Laser Welded DP980 Steel Joints[J]. Chinese Journal of Lasers, 2021, 48(18): 1802003

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