Production method for tube blank steel for -195 DEG C ultra-low temperature seamless steel tube

The invention belongs to the field of metallurgy and particularly relates to a production method for tube blank steel Gr.8 for a -195 DEG C ultra-low temperature seamless steel tube. The production method for the tube blank steel for the ultra-low temperature seamless steel tube includes the technological processes of smelting of a high-impedance ultra-high power electric arc furnace, LF refining and VD vacuum treatment. In the process of smelting of the electric arc furnace, the percent of C of smelting end-point molten steel is controlled to be smaller than or equal to 0.02%, and the percent of P of the smelting end-point molten steel is controlled to be smaller than or equal to 0.002%. During steel tapping of the electric furnace, pre-deoxygenation is conducted, and the content of Al of the molten steel is controlled to range from 0.09% to 1.4%. The steel tapping temperature of the electric arc furnace ranges from 1,650 DEG C to 1,670 DEG C. In the process of LF refining, lime and synthetic slag are adopted for slag making, and the total mass of the lime and the synthetic slag accounts for 1.4% to 2.0% of the mass of the molten steel. The mass percent of the lime ranges from 70% to 80%, the mass percent of the synthetic slag ranges from 20% to 30%, and the synthetic slag is prepared from 60%-68% of CaO, 15%-20% of Al2O3, 10%-15% of CaF2, 5% or less of SiO2, 3% or less of MgO and 0.1% or less of S. The tube blank steel, for the ultra-low temperature seamless steel tube, produced through the method is high in purity and can be directly used for rolling the seamless steel tube, and therefore volume production is achieved.