In order to realize the stable batch production of ultra-low P welding wire EF3 for high-grade pipelines， the conditions of dephosphorization were determined by studying the thermodynamic and dynamic conditions of dephosphorization. Through the process of molten iron dephosphorization，100 t converter dephosphorization， ladle dephosphorization， slagging， secondary LF refining and anti-return P process， combined with low P alloy， stable production of ultra-low P welding wire EF3 is realized. By controlling molten iron

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［Si］≤0.15% and making high basicity slag with R = 6， it can remove P and S at the same time，

achieve molten iron

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［P］≤ 0.020%， iron

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［S］ ≤0.005%； The end temperature of converter is from 1 595 ℃ to 1 610 ℃， the basicity of the final slag is about 4.0， the content of FeO in the final slag is 23.0%-26.0% ， the tapping

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［P］ of the converter is less than 0.008% ；The molten steel

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［P］ is less than 0.004% by ladle dephosphorization； After dephosphorization with slag removal process， slag removal before and after the basic does not return P， Secondary LF is used to prevent P increase . P increase is very little with low P alloy .The slag removal process is adopted， the P content of molten steel

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［P］≤0.005% in tundish can be achieved