After more than 50 years of development, China’s spring steel production has grown from scratch and has made great progress. In recent years, Shanghai No. 5 Iron and Steel, Taiyuan Iron and Steel, Xingcheng Special Steel, Northeast Special Steel and other companies have built or renovated several advanced spring steel production lines, adopting “electric furnace primary refining→LF refining furnace→VD vacuum degassing→continuous casting→ The “continuous rolling” process produces various grades of alloy spring steel, which has greatly advanced the production technology of spring steel. Other companies have also shown strong development momentum, such as Jiangsu Shagang Huaigang Special Steel, Laiwu Special Steel, and Shigang. In particular, the market share of spring steel for railway compression springs and fasteners of Huaigang Special Steel Company is 80%. However, there are also some spring steel manufacturers whose steel output is gradually shrinking and their competitiveness is getting weaker and weaker. The main reasons are as follows:
(1) The quality and price of spring steel products lack market competitiveness
(2) The degree of product specialization is low, and the variety structure is unreasonable.
(3) The production technology and technical equipment of spring steel are backward.
(4) The research and development of advanced spring steel technology is weak
Foreign spring steel production started earlier, and it is more advanced than domestic in terms of production equipment, new technology, new technology research, product quality control, etc. For example, the supply of crude steel adopts large electric furnace or blast furnace-converter process, and electric furnace is used as primary furnace At the same time, the used scrap steel is selected to ensure that the participating elements in the crude steel are at a low level; the electric furnace adopts the slag-free tapping technology of powder spraying and dephosphorization; the converter steel is vacuum slag removal to reduce the phosphorus content and prevent Oxidized slag enters the refining furnace; RH vacuum degassing process is adopted on the basis of LF refining; the cross-section size of continuous casting billet is generally larger than that of domestic special steel plants. A large compression ratio is used to improve or eliminate some defects caused by casting. Electromagnetic stirring reduces continuity segregation and forging defects; adopts liquid phase cavitation reduction techniques such as light reduction, large diameter roll pressure and continuous forging to reduce segregation; in terms of finishing heat treatment, it has a perfect finishing heat treatment rotor and quality Assurance system.
Japan’s Datong Special Steel uses the production process shown in Figure 1 to produce ULO’s SUP6, SUP7 and SUP120. The specific steps of ULO treatment (Ultral Low Oxygen) are as follows: After melting molten steel in an alkaline electric arc furnace with excess power and blowing argon, add Fe-Si or Al to the molten steel for pre-deoxidation treatment to obtain high alkalinity Reduction slag. Then pour the molten steel into the ladle, insert the legs of the RH cycle degassing device into the molten steel, and draw the molten steel into the vacuum chamber of the degassing device. With the help of a large-capacity jet pump, the vacuum degree is kept less than 13.3 Pa, and a small flow of argon is introduced into the molten steel. The molten steel foams into the vacuum chamber, and the carbon deoxidation reaction in the molten steel proceeds rapidly to deoxidize the molten steel. When the carbon-oxygen reaction reaches equilibrium, an Al deoxidizer is added. In order to promote the floating separation and removal of deoxygenated products, and to maintain the stability of the deoxygenation state, continue the deoxygenation operation, and finally adjust the amount of Al added. After RH cycle degassing, the oxygen content dropped to about 15 mg/L. For example, to keep the oxygen content not greater than 15 mg/L, the molten steel should be kept free of oxidation during pouring and solidification to avoid contamination and promote the removal of deoxidized products.