Production method of small square billet 70kg-grade welding wire steel

The invention relates to a production method of small square billet 70kg-grade welding wire steel. The steel comprises the following chemical components in percentage by weight: 0.03-0.08% of C, 0.70-0.85% of Si, 1.45-1.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.23-0.25% of Ti, less than or equal to 0.010% of Al, less than or equal to 10ppm of Ca and the balance of Fe and inevitable impurities. According to the invention, a BOF + LF + CC smelting technology is adopted; c at the end point of the converter is smaller than or equal to 0.05%, a converter sliding plate stops slag, silicon and manganese alloys are added in the tapping process, Al and Ti alloys and a deoxidizing agent are not added, and lime slag is added behind the converter for washing; high-alkalinity white slag is manufactured through an LF, SiFe powder is thrown on the slag surface for deoxidation in the smelting process, and Al particles are strictly prohibited from being thrown or a Ca line and an Al li