| Abstract |
| Cold cracking is one of the most common catastrophic defects in welds. In this study, we investigated the effect of the shield gas composition (specifically Ar+5 ~ 20% CO2) on the cold-crack ratio on the preheating temperature of 20℃~100℃ in flux-cored arc welds. Critical assessment of the cold-crack ratio was achieved by observing the weld cross-section, appearance of surface cracks, and fractography. The cold-crack ratio decreased as the preheating temperature increased from 20 to 100℃. For the preheating temperature of 50℃, the shield gas (containing 20% CO2) provided higher oxygen content in the weld metal and increased the number of nucleant inclusions for acicular ferrite; thereby eliminating cold cracks. The shield gas with 15% CO2 produced welds that had nearly the same amount of acicular ferrite as compared with the 5% and 10% CO2 cases. However, the 15% CO2 shield gas produced the greatest hardness and largest amount of non-nucleant inclusions in the weld metal, therefore exhibiting the largest cold-crack ratio. If the volume fraction of acicular ferrite remains unchanged, hardness and non-nucleant inclusions should be considered roughly for assessment of the cold-crack ratio. |
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| Key Words |
| metals, welding, microstructure, transmission electron microscopy, TEM, cold crack |
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