High Quality Spring Steel Inclusion In The Low Melting Point Control Research

The spring steel is a very important part of the machinery and equipment manufactuiing of raw materials, parts made of spring steel needs to withand the alternating stress, so its performance requirements are very strict. In order to ensure the performance of spring steel, it is necessary to strictly control of its metallurgical and surface quality, requirements to minimize the oxygen content of molten steel in the smelting process, to reduce the content of nonmetallic inclusions, to improve the distribution of inclusions, to remove of harmful elements, to further improve the cleanliness of the spring steel. That is low oxygen, sulfur, phosphorus and nonmetallic inclusions in control of the smelting process of behavioral change and the source of large inclusions. Improve the cleanliness of the spring steel, thus improving its performance.The topics to60Si2MnA and the60Si2CrVA two spring steel for the study object, produced by Shijiazhuang Iron and Steel Company by " converter→LF+VD→CC (150×150mm2)". Analysis the change of steel T[O] in the smelting process, slag basicity and composition change, inclusion compositions and melting point change in various stages of the smelting(position in the phase diagram), Verify that the test results by thermodynamic calculation, analysis of main types of inclusions caused the rotating bending fatigue fracture, test each sample in a large inclusion content by large sample electrolysis experiments. The results show that:(1) the oxygen content at VD refining after, the oxygen content of the1402323furnaces times60Si2MnA is16ppm, the oxygen content of0412303furnaces times60Si2CrVA is12ppm. Oxygen content in the steel has reached a very low level, O content of the final roll are9ppm and5ppm. So continuous casting process played an important role in reduction of the total oxygen.(2) Large sample electrolysis results show that:Total inclusion level is1.59mg/10kg of the No.1402323furnaces times60Si2MnA billet, total inclusion level is0.44mg/10kg of the No.1402446furnaces times60Si2MnA billet. Isolated inclusions types have Silicate, Aluminosilicate, Sulfide, little iron and slag, and other complex compounds, and did not find the large inclusions which sizes larger than80μm. (3) The composition of inclusions change from A12O3→>Al2O3·MgO→MgO-Al2O3-CaO and MgO-Al2O3-CaO-SiO2and MgO-Al2O3-CaO-SiO2-sulfide, etc. Inclusions on the billet are in the low melting region in the phase diagram, exception of individual.(4)Most of inclusions of Fatigue specimen fracture are complex oxides, and most of which contains Calcium Sulfide. the Aluminum content in inclusions of60Si2MnA is higher than it in60Si2CrVA.