Study on Oxygenation of Molten Steel to Liner Material in Vacuum Induction Melting Process

Experimental Research on Special Steels* Study on Oxygen Supply of Molten Steel from Lining Materials in Vacuum Induction Melting Process Xue Zhengliang, Gao Junbo, Qi Jianghua, Li Zhengbang, Zhang Jiawen (School of Materials and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081) (Institute of Iron and Steel Research, Beijing 100081) The calcium oxide sand crucible vacuum induction furnace was used to perform the oxygen supply test of lining refractories to the molten steel during the vacuum melting process. The basic rules of the oxygen supply to the molten steel from the lining refractories of the lining and the main factors influencing the oxygen supply from the lining to the molten steel were studied. The test results show that when deep deoxidation of molten steel is performed in the ultra-low oxygen range, avoiding lining decomposition is the key to further deoxidation of the molten steel; at a vacuum of 0.5 to 10 Pa, the degree of vacuum and molten bath temperature increase. Oxidation of furnace lining to the molten pool increases, and the final oxygen content in the steel increases with the increase of the amount of molten steel in the molten steel; the amount of oxygen supplied to the molten steel from the magnesium sand furnace is greater than the amount of oxygen supplied to the molten steel by the calcium oxide furnace.

The smelting process provides experimental evidence. The first test of ademic ElectrnicPublishil is also carried out in a 50kg vacuum induction furnace under vacuum metallurgy conditions. The supply of oxygen to the molten steel from the lining material means that the alloy elements in the molten steel are burned. In severe cases, carbon and active alloy elements are out of order. The burning of alloying elements in molten steel also causes the addition of oxide inclusions. In this case, even if the composition of the molten steel is qualified, the use performance of the steel will be affected due to the increased content of oxide inclusions. Especially in the smelting process of ultra-low oxygen steels, it is important to avoid the lining material supplying oxygen to the molten steel. As early as the 1960s, Mr. Shao Xianghua and other researchers discovered that an important source of oxygen for the crucible is that some of the metal that penetrates into the crucible is oxidized by air when it is broken at a high temperature after the steel is pulled out from the induction furnace, and re-enters the melt at the next melting. Pool.

This research mainly aims to investigate the basic law of the decomposition of the lining material to the molten steel by observing the state of the molten pool in the vacuum induction melting process and the analysis of the final molten steel chemical composition, and to study the conditions for oxygen supply from the lining to the molten pool. For the development of ultra-low oxygen steel vacuum 1 with magnesium slag lining melting helium oxygen phenomenon kg kiln lining in the vacuum induction furnace lining for the first test, the surface shot blasting of carbon steel rod Carbon is used to make the carbon content in the steel from the original 0.33% to 0.55%. The melting power is maintained at 70~80kW. Since the original oxygen content of the steel rod is not high (0.0013% TO), see the molten steel after the phenomenon of no splash, therefore, the steel During the melting process, the mechanical pump (ie, rotary vane vacuum pump) is always on and the vacuum degree is maintained at about 10 Pa. The molten steel temperature after thawing is high, and bright bubbles appear on the surface of the molten pool. When the input power is reduced to 30-40 kW, the steel surface no longer bubbling. The furnace is then filled with argon to about 60 kPa, carbon is added to the bath, and the carbon is fused to cool the steel. The carbon content of the ingot was analyzed to be 0.47%, the carbon loss during the melting process was 0.08%, and the oxygen content was also increased from 0.0013% to 0.001. The target content was the original content. The actual content of the first ninth was the original content. The new enamel fused magnesia. The purpose of the test was to remelt steel ingots containing 0.46% of carbon and 0.48% of c in order to reduce the carbon content in the steel to 0.44%. The diluent was a steel rod containing 0.2% of C and 0.002% of CT.0. Ingots and thinners are shot blasted. The smelting results are shown in Table 1. It can be seen from Table 1 that the carbon loss of the first furnace reaches 0.13%. This furnace steel is seriously blazed on the surface of the molten pool in the early stage of refining. The time is as long as 7 minutes. When the temperature of the bath is seen to be high, By reducing the input power from 60 kW to 30 kW, bubbling ceased immediately. In the smelting process of the 2nd and 3rd furnace steel, the steel material maintains a low input power after melting, basically no bubbling occurs, and the carbon loss of the steel is only 0.03%. kg Magnesium for vacuum induction furnace Changes in Carbon and Oxygen Content of Steel in Two Tests of Smelting in Sand-smelting.

Table 1 Change of carbon and oxygen content of steel in 50kg vacuum induction furnace with magnesite smelting Target content Original content Actual content Target content 1st furnace original content 2nd furnace 3rd furnace 1st furnace actual content 2nd furnace 3rd furnace 2 Oxygen supply during smelting with calcium oxide lining The smelting of molten steel with calcium oxide sand is performed on a 25 kg vacuum induction furnace. The purpose of smelting with calcium oxide barium is to further reduce the oxygen content in the steel, and at the same time to recharge the molten steel during the refining process. Three steel ingots to be melted were surface shot blasted to remove rust, and the carbon content was 0 31%, 041%, and 041%, respectively (Table 2). After seeing the molten steel, the argon is filled to about 60 kPa, the bar is melted and then the carbon is added to 0.42%, and then the open Roots pump is used to increase the vacuum to 0.5 Pa. After 3 to 10 minutes of refining, all 3 steels appear to varying degrees. Bright bubble phenomenon. Analysis of the carbon content of ingots, carbon practical barium oxide barium for the second test of the original bar containing 0.37% C, 0.003% T.0. Taking into account the possibility of carbon loss during the smelting process, when the total carbon amount to 0 47%. Maintain a low bath temperature by controlling the input power during the refining process. The carbon content of the 4 furnace steel is basically no burning phenomenon, and the oxygen content in the steel is also very low.

Changes of Carbon and Oxygen Content in Steel for Two Tests of Calcium Oxide Tantalum Melting in a Kilogram Vacuum Induction Furnace .

Table 2 Variation of carbon and oxygen content of steel in smelting with calcium oxide sand for 25kg vacuum induction furnace Test item Item (7 3 Discussion 3.1 Carbon and oxygen reaction in liquid steel Carbon and oxygen dissolved in molten steel Press under vacuum Reaction (1) The reaction produces CO gas: the oxygen in the molten steel comes from the oxygen in the raw material on the one hand, and the thermal decomposition reaction of the lining material under vacuum on the other hand: when the molten steel contains a relatively high content of carbon, it is under vacuum. The thermal decomposition of the lining material will become more easily: 20 "refining time of the city steel sloppy phenomenon. Sub-Pub points. And because the furnace, lining material oxygen steel liquid may reach the most. netbookmark3 When the lining material is certain, the lining The high theoretical oxygen content (furnace lining) of the material decomposing into the bath is actually determined by the bath temperature and the smelting vacuum degree. The higher the temperature and vacuum, the higher the theoretical oxygen content (furnace lining) reached by the lining oxygen supply to the bath. When the actual oxygen content in the molten steel is higher than the highest theoretical oxygen content (furnace lining) of the lining oxygen supply, the lining material does not thermally decompose, and the carbon-oxygen reaction in the molten steel is performed according to (1); when the actual oxygen in the molten steel Less than When the maximum theoretical oxygen content (lining) of oxygen lining, thermal decomposition will lining material molten steel oxygen. In this case the CO bubbles emerge from the primary reaction bath surface (7) and (9).

3.2 Relationship between bubbling phenomenon in the molten pool and the loss of molten steel carbon and oxygen content in the steel Two different bubbling phenomena can be observed during the melting of the carbon-containing alloy in the vacuum induction furnace: The first bubbling phenomenon usually occurs in the melt. After clearing and initial refining, the bubbles appear black, indicating that the bath temperature is not high. This is the carbon deoxidation reaction according to reaction (1) when the dissolved oxygen content in the molten steel is high. At this time, the carbon loss amount can pass through the chemical reaction. The reaction equation is accurately calculated. The second kind of bubbling phenomenon often occurs in the refining stage, sometimes bubbling in the middle of refining, and the bubbles appear bright white, indicating that the temperature of the bath is high. At this time, the dissolved oxygen content in the molten steel has been lower than the maximum theoretical oxygen content (furnace lining) of the furnace lining oxygen supply under the corresponding molten bath temperature and melting vacuum degree. The oxygen source for decarburization of the molten steel comes from thermal decomposition of the lining, and the burning loss of carbon Increase with bubbling time.

At 600*C, the lining of magnesia at a vacuum of 10 Pa = 0.0127%, the lining of calcium oxide at a vacuum of 0 5 Pa = higher (1) 18% lining). When the actual oxygen content in the bath is lower than the lining, the lining begins to supply oxygen to the molten steel.

Oxygen from the lining to the molten steel usually manifests itself in the brightening of white bubbles on the surface of the bath during the refining stage, resulting in the burning of carbon. The greater the amount of carbon burned, the higher the oxygen content in the final molten steel.

This subject is the National Natural Science Foundation and Shanghai Baosteel Group Corporation

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