Uniaxial Low-Cycle Fatigue Study of Alloy 800H Weldments at 700 °C
Abstract
:1. Introduction
2. Materials and Methods
2.1. Alloy 800H and Welding Procedures
2.2. Test Methods
3. Results and Discussion
3.1. Initial Microstructure and Microhardness
3.2. Low-Cycle Fatigue Properties
3.3. Influence of Hold-Time
3.4. Fracture Micrographs
4. Conclusions
- (1)
- The LCF life of the BM and weldments was found to be comparable, indicating a good welding technique, and the increase of total strain range reduced the LCF life both materials. The fatigue life was strongly reduced by means of additional HT.
- (2)
- Cyclic stress response behavior varied between both materials. The BM showed an initial cyclic hardening for the first 100 cycles, followed by saturation phase just prior to failure, whereas the weldments were cyclically softened with cycles for the whole life.
- (3)
- The serrated yielding was observed in the cyclic stress–strain curves for both materials in all tests. These serrations occurred predominantly for BM specimens and disappeared after some cycles. This type of serrated flow stress belongs to Type C according to their characteristic of the dropped stress below the general level of the stress–strain curve.
- (4)
- LCF tests with HT induced an unequal cyclic stress response, and thus a visible lower peak tensile stress rather than the compressive stress. During the HT, the effective inelastic strain was promoted by the SRB, which suggests the creep recovery process of dislocation.
- (5)
- The fracture mechanism depended on the type of material and waveform. The fracture analysis show that both materials display mixed ductile/brittle fracture, although the presence of more brittle fracture can be observed for weldments. In LCF tests, the crack initiation and propagation for both materials occurred in a classical transgranular fracture mode. The introduction of HT caused a transition to intergranular cracks (mixed-mode fracture mode). The fatigue life and fracture mechanisms were severely influenced by the fatigue, oxidation, and M23C6 precipitates. In LCF tests, the oxide-enhanced transgranular fracture dominated crack growth. The damage between the time-dependent creep, fatigue, and oxidation occurred synergistically in LCF tests with HT.
Author Contributions
Funding
Conflicts of Interest
References
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Material | C | Ni | Fe | Si | Mn | Cr | Ti | P | S | Al | Cu |
---|---|---|---|---|---|---|---|---|---|---|---|
A800H | 0.07 | 30.18 | Bal | 0.42 | 0.98 | 20.43 | 0.54 | 0.022 | - | 0.49 | 0.45 |
KW-T82 | 0.07 | 30.18 | Bal | 0.42 | 0.98 | 20.43 | 0.54 | 0.022 | - | 0.49 | 0.45 |
Test Conditions | LCF Test | LCF Test with Hold Time | |
---|---|---|---|
700 °C | 700 °C | ||
No. of specimen | BM | 5 | 1 |
Weldments | 4 | 1 |
Specimen/Cinstants | εf’ | c | σf’ (MPa) | b |
---|---|---|---|---|
BM | 2.967 | −1.017 | 1047.0 | −0.193 |
Weldments | 1.393 | −0.902 | 1100.5 | −0.182 |
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Dewa, R.T.; Kim, S.-J.; Kim, W.-G.; Kim, E.-S. Uniaxial Low-Cycle Fatigue Study of Alloy 800H Weldments at 700 °C. Metals 2018, 8, 918. https://doi.org/10.3390/met8110918
Dewa RT, Kim S-J, Kim W-G, Kim E-S. Uniaxial Low-Cycle Fatigue Study of Alloy 800H Weldments at 700 °C. Metals. 2018; 8(11):918. https://doi.org/10.3390/met8110918
Chicago/Turabian StyleDewa, Rando Tungga, Seon-Jin Kim, Woo-Gon Kim, and Eung-Seon Kim. 2018. "Uniaxial Low-Cycle Fatigue Study of Alloy 800H Weldments at 700 °C" Metals 8, no. 11: 918. https://doi.org/10.3390/met8110918