Microstructural Changes and Impact Toughness of Fill Pass in X80 Steel Weld Metal
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials and Welding Parameters
2.2. Experimental Method
3. Results and Discussion
3.1. Measurement of Welding Thermal Cycles
3.2. Tensile Test and Hardness Test
3.3. Toughness Impact Test
3.4. Hardness Test
3.5. Microstructure
3.6. Grain Size
3.7. M–A Constituents
3.8. Analysis
4. Conclusions
- (1)
- Yield and tensile strength showed an approximate linear relationship with the Vickers hardness in the FP2 in each cascade specimen, and the original FP2 and FP2 after double thermal cycles (JT-2 and JT-4) had the worse deformation ability.
- (2)
- The toughness of FP2 after a single thermal cycle improved, decreased after double thermal cycles, and improved again after triple thermal cycles. Weld metal toughness did not improve further after quadruple thermal cycles. Therefore, on the basis of the total number of weld layers, the number of thermal cycles each weld layer experienced and the toughness of each weld layer could be obtained.
- (3)
- The FP2 microstructure was not uniform after a single thermal cycle. The WM-CG, WM-CFG, and WM-FG regions were formed when FP2 underwent the single thermal cycle. However, microstructural uniformity increased along with the increase in the number of thermal cycles.
- (4)
- The content of each phase in the microstructure of FP2 changed under different thermal cycles. Granular bainite (GB) and Bainitic ferrite (BF) were the main phases in FP2 during the entire welding process. However, the content of the M–A constituents and the toughness of FP2 revealed a certain relationship, that is, the content of the M–A constituents was inversely proportional to FP2 toughness. Average grain size and toughness of FP2 also had the same relationship.
- (5)
- In the samples with low impact toughness, stress concentration was observed around the M–A constituents in the FP2 microstructure. Large massive M–A constituents and necklace-type M–A constituents were harmful to the toughness. The total content of M–A constituents was inversely proportional to the weld metal toughness.
- (6)
- The weld layer that did not undergo any welding thermal cycle and the weld layer that underwent two welding thermal cycles had the worst toughness. These weld layers were more affected by residual stress compared with other weld layers.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Material | Yield Strength Rt0.5 (MPa) | Tensile Strength Rm (MPa) | YS (Rt0.5)/TS (Rm) | Elongation (%) |
---|---|---|---|---|
X80 | 605 | 700 | 0.86 | 20.5 |
Parameters | Interpass Temperature (°C) | Arc Voltage (V) | Welding Current (A) | Welding Speed (cm/min) | Weld Heat Input (kJ/cm) |
---|---|---|---|---|---|
Root weld | 100 | 19–20 | 87–92 | 5.38 | 20.5 |
Fill pass 1 (FP1) | 100 | 20 | 200–210 | 18.7 | 13.6 |
Fill pass 2 (FP2) | 95 | 20 | 220–230 | 16.1 | 17.1 |
Fill pass 3 (FP3) | 103 | 19 | 210–230 | 10.9 | 24.1 |
Fill pass 4 (FP4) | 97 | 20 | 210–220 | 9.34 | 28.2 |
Fill pass 5 (FP5) | 101 | 20 | 210–220 | 12.05 | 21.9 |
Cap weld | 104 | 20 | 210–220 | 7.9 | 33.4 |
Content | C | Si | Mn | P | S | Nb | Cr | Ni | Mo | Ti | Al |
---|---|---|---|---|---|---|---|---|---|---|---|
wt.% | 0.074 | 0.184 | 1.839 | 0.015 | 0.008 | 0.097 | 0.099 | 0.223 | 0.264 | 0.011 | 0.035 |
Content | C | Si | Mn | P | S | Nb | Cr | Ni | Mo | Ti | Al |
---|---|---|---|---|---|---|---|---|---|---|---|
wt.% | 0.033 | 0.184 | 1.440 | 0.009 | 0.003 | 0.005 | 0.025 | 1.660 | 0.006 | 0.004 | 1.090 |
Content | C | Si | Mn | P | S | Nb | Cr | Ni | Mo | Ti | Al |
---|---|---|---|---|---|---|---|---|---|---|---|
wt.% | 0.044 | 0.197 | 1.530 | 0.008 | 0.004 | 0.010 | 0.070 | 1.480 | 0.033 | 0.007 | 0.815 |
Sample | JT-2 | JT-3 | JT-4 | JT-5 | JT-6 |
---|---|---|---|---|---|
Cycles | None | Single | Double | Triple | Quadruple |
Welding thermal cycles process | None |
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Bai, F.; Ding, H.; Tong, L.; Pan, L.; Wang, L. Microstructural Changes and Impact Toughness of Fill Pass in X80 Steel Weld Metal. Metals 2019, 9, 898. https://doi.org/10.3390/met9080898
Bai F, Ding H, Tong L, Pan L, Wang L. Microstructural Changes and Impact Toughness of Fill Pass in X80 Steel Weld Metal. Metals. 2019; 9(8):898. https://doi.org/10.3390/met9080898
Chicago/Turabian StyleBai, Fang, Hongsheng Ding, Lige Tong, Liqing Pan, and Li Wang. 2019. "Microstructural Changes and Impact Toughness of Fill Pass in X80 Steel Weld Metal" Metals 9, no. 8: 898. https://doi.org/10.3390/met9080898