| 2Crl3 is a martensitic stainless steel which has a good corrosion resistance and mechanical properties. So it is widely used in aerospace, marine environment, machinery parts and medical equipment and other fields. And with the decline of domestic nickel reserves and improve of nickel dependence on external resources, 2Crl3 stainless steel without nickel will have a low production cost advantage. The domestic research on stainless steel is focused on heat treatment, quality control of slab and the effect of alloying elements on the properties of 2Crl3. The clean steel production of 2Crl3 stainless steel is less concerned about. To meet the requirements of high-end products on the performance of stainless steel, the study of 2Crl3 is needed from the perspective of clean steel production. And then the purpose of producing high quality 2Crl3 stainless steel is achieved.In this paper, the study is carried out on the background of EF+VOD process in a domestic factory. Through the investigation and analysis of the process the main problems found in the production of stainless steel are as follows:high total oxygen content after deoxidation, poor control of inclusions modification, reoxidation in refining process and the production of chromium-containing solid waste in stainless steel production process. Therefore, the key metallurgical technology of stainless clean steel will be studied by stainless steel vacuum aluminum deoxidation equilibrium, reaction equilibrium between refining slag 'and steel, argon bottom blowing, stainless steel calcium treatment and decarburization reaction with oxidation slag through thermodynamic analysis and industrial trail.First, in order to decrease the total oxygen content of stainless steel after deoxidation and the reoxidation in refining process, stainless steel aluminum deoxidation equilibrium, control of acid-dissolved aluminum after refining and effect of refining slag composition on reoxidation were discussed, the oxygen activity in the bulk steel is controlled by the slag composition and Al content. The results are shown as follows. A basicity of 3-5 and an Al content greater than 0.015wt% in the melt resulted in an oxygen content less than 0.0006wt%. Because of the equilibrium of the Si-O reaction between the slag and steel, the activity of SiO2 will increase while the Si content increases; thus, the Si content should be lowered to enable the formation of a high-basicity slag. A high-basicity, low-Al2O3 slag and an increased Si content will reduce the Al consumption caused by SiO2 reduction. To improve the stirring condition, the ladle with soft blowing plug located in central will be replaced by plug located at 1/2R. Argon stirring rate will be controlled between 2.1 m3/h and 3.6 m3/h and argon stirring rate under vacuum will be controlled at 7.2 m3/h. The soft blowing will be lasted more than 15 minutes.To reduce hard inclusions proportion after deoxidation and melting point of inclusion, calcium treatment was discussed. The results are shown as follows. To prevent the reoxidation and the loss of calcium wire feeding caused by slag, the mole fraction of FeO in slag should be controlled to less than 0.0012, and the content of acid soluble aluminum in molten steel should be more than 0.01wt%. When the calcium content in liquid steel can be controlled in 0.0019wt%-0.0035wt%, Al2O3 and spinel inclusions in steel will be modified to calcium aluminate. In additions the activities of CaO, Al2O3 and CaS in ternary diagram were employed in order to show the relationship between CaS precipitation with various calcium aluminates. And it provides a basis for the control of high melting point CaS inclusion formation.In order to reduce Cr-bearing solid waste emissions in stainless steel production and improve the utilization rate of chromium in steel works, the study on the use of stainless steel oxidation slag in vacuum decarburization was carried out in paper. The results are shown as follows. The stainless steel slag is composed of molten slag phase and FeCr2O4 phase. The carbon content in molten was calculated by the thermodynamic equilibrium between steel and different composition of the slag. And decarburization capacity is determined as follows: ?Fe2O3?> ?FeO?>Cr2O3 ?s?>FeCr2O4 ?s?> ?Cr2O3?. The influence of vacuum pressure is obviously in decarburization reaction.Finally, in order to verify the feasibility of vacuum oxidation slag decarburization reaction, the decarburization experiment with oxidation slag was carried out. The results are shown as follows. After decarburization the contents of Cr2O3 and Fe2O3 in slag were 5.7wt% and 3.9wt%, respectively which is obviously lower than Cr2O3 and Fe2O3 content in EF and VOD process. Then Cr-bearing solid waste emissions are reduced. And compared to VOD process, it can effectively reduce the amount of deoxidizer used in refining process. Finally the cleanliness of stainless steel improves. In the establishment of oxidation slag decarburization reaction kinetic equation based on the double film theory, the decarburization rate constants and mass transfer coefficient are calculated. The rate constants of decarburization reaction is between 0.00087 and 0.0022 s-1 and overall mass transfer coefficient of carbon is between 8.8 ×10-6 and 2.1×10-5 cm/s. But the final carbon content was significantly affected by mass transfer. And it is advantageous for the production of ultra-low carbon steel to increase the mass transfer of carbon in steel by means of bottom blowing and so on. |
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