After more than two years of practical application, it is evident that the 3,1 electric arc furnace and its auxiliary system transformation at our factory have proven to be both reasonable and reliable. These modifications fully meet the production requirements under current conditions, ensuring smooth operations and efficiency.
The 81 tapping process was implemented as a cost-effective and efficient way to upgrade the existing electric arc furnace. As an intermediate step between the electric arc furnace and the refining furnace, this transformation has enhanced the overall process technology of our plant, improving coordination with the original refining system.
However, after over a year of operation, some issues have emerged with the 81 electric arc furnace. One major challenge is the limited availability of scrap steel. The types of scrap steel used are inconsistent, leading to significant fluctuations in composition. This instability affects the yield and makes smelting operations more difficult, increasing melting time and complicating slag control, which in turn impacts the performance of the refining furnace.
Another issue is the low refractory grade used in our furnace linings. This leads to rapid erosion, increased nozzle diameter, and frequent lining replacements, which hinder the optimization and improvement of key electric arc furnace performance indicators.
Additionally, since our factory operates three large electric arc furnaces and one smaller one equipped with a continuous casting machine, the smaller furnace not only serves a refining function but also needs to align with the casting rhythm. This dual role has somewhat negatively affected the furnace's performance metrics.
**Acknowledgements**
Recent developments in welding materials for high-tensile-strength steels have been highlighted by the National Institute of Metals in Japan. They are currently working on new welding materials designed to address preheating challenges during the welding process. These materials incorporate nickel and chromium, enabling a martensitic transformation at lower temperatures. Under normal conditions, the combination of these elements results in a wider martensitic transformation zone, enhancing material properties.
Cracking in the weld or connection areas of high-tensile-strength steel can occur at low temperatures. This is due to hydrogen accumulation during welding, which causes shrinkage and residual stress. With the new materials, however, tensile or expansion-induced residual stresses are converted into compressive ones, significantly reducing the risk of cracking.
If these new welding materials become commercially available, they could be used in electric arc welding to join structural steels for applications such as ship bridges, container construction, and machinery manufacturing. This development supports the growing demand for ultra-high-tensile-strength steels, such as those with a tensile strength of 800 MPa. In fact, high-tensile-strength steel with a strength of 784 MPa has already been successfully used in the construction of the Akashi Strait Bridge in Japan, where ultra-low hydrogen welding rods were employed.
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