1 Introduction
2 The Trans-Varestraint Test
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Lack of an optimal apparatus setup to conduct the experiments with
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Lack of a specific way to apply the augmented strain during the experiment
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Lack of an optimal strain rate that should be used for the experiment
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Lack of specimen specifications
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Lack of specification of welding time.
3 Method
3.1 The Basis of a Standardized Testing Methodology
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Every test shall be carried out using a standard setup that ensures repeatability and comparison of results. The primary parameter that affects solidification cracking in these tests is the strain applied on the weld, which is determined by the radius of the formers used according to Eq. [1]. By defining standard discrete former radii, a selection table (e.g., Figure 6) could be used to ensure the desired strain, according to the thickness of the specimen.[30]×
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An appropriate measurable parameter for crack length, from which hot cracking susceptibility can be reliably determined, should be identified and defined.
3.2 Experiment Design
Grade and Class | C (Pct Wt.) | Mn (Pct Wt.) | Si (Pct Wt.) | P (Pct Wt.) | S (Pct Wt.) | Nb (Pct Wt.) | V (Pct Wt.) | Ti (Pct Wt.) |
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X65 PSL 1 | 0.26 (max) | 1.40 (max) | — | 0.030 (max) | 0.030 (max) | the sum must not exceed 0.15 pct | ||
EN3B | 0.16 to 0.24 | 0.50 to 0.90 | 0.35 (max) | 0.05 (max) | 0.05 (max) |
Augmented Strain (Pct) | Former Radius (mm) | Stroke Length (mm) | Specimens |
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2 | 600 | 14 | TVA 2.1, TVA 2.2, TVA 2.3 |
3 | 400 | 20 | TVA 3.1, TVA 3.2 |
4 | 300 | 27 | TVA 4.1, TVA 4.2, TVA 4.3 |
6 | 200 | 40 | TVA 6.1, TVA 6.2, TVA 6.3 |
8 | 150 | 54 | TVA 8.1, TVA 8.2, TVA 8.3 |
9 | 133 | 61 | TVA 9.1, TVA 9.2 |
10 | 120 | 69 | TVA 10.1, TVA 10.2, TVA 10.3 |
11 | 109 | 76 | TVA 11.1, TVA 11.2 |
3.3 Post-Experimental Process
4 Results
5 Discussion
5.1 Ensuring Test Repeatability
5.2 Reliable Application of Augmented Strain
5.3 Measurement of Hot Crack Susceptibility
5.4 Evolution of Hot Cracks
5.5 Significance of Findings
5.6 Limitations
6 Conclusions
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The augmented strain applied during the Trans-Varestraint tests can be controlled accurately and reliably, using the experimental methodology applied in the present study. This will allow tests that are conducted using experimental setups similar to the one described to be comparable.
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The effect of the strain rate can now be studied as the experimental methodology in the present study allows for accurate control of the augmented strain.
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It can be confirmed that EN3B is significantly more susceptible to hot cracking than X65 since it constantly presents a MCL higher than that for X65 at lower augmented strains, 0.5 mm MCL at 1 pct augmented strain vs 0.25 mm MCL at 3 pct strain, respectively.
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Examination of the hot cracks under SEM revealed that the orientation of dendrites that originate from the crack initiation points has a 45 deg angle with the surface of the weld.
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This observation of dendrite orientation at the crack initiation points, in combination with an analytical model, may allow for initiation sites of hot cracks during welding to be predicted as the point where the solidifying material experiences the maximum shear.