DESIGN METHOD FOR HIGH-PERFORMANCE LF DESULFURIZATION REFINING SLAG

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 202411950157.0, filed on Dec. 27, 2024, the contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The disclosure belongs to the technical field of iron and steel metallurgy and steelmaking, and in particular relates to a design method for high-performance ladle furnace (LF) desulfurization refining slag.

BACKGROUND

Sulfur is one of the important factors affecting various properties of iron and steel materials. An excessively high sulfur content in steel may cause hot brittleness of steel, and simultaneously lead to the precipitation of a large number of large-sized manganese sulfide (MnS) inclusions during the solidification of molten steel, seriously affecting the mechanical properties of steel. Except for a few steel grades, most steel grades require desulfurization treatment. The sulfur content in molten steel needs be controlled at a relatively low level, and secondary refining is the final and main desulfurization process before casting. Ladle furnace (LF) refining is a widely used refining process, which may theoretically desulfurize to below 20 parts per million (ppm).

Desulfurization by refining slag is an important part of molten steel desulfurization in the LF refining process, and its composition has a significant impact on steel cleanliness. High-performance refining slag needs to have the characteristics of good fluidity, high inclusion adsorption capacity, and strong desulfurization ability. However, in the actual production process of steel products, the adjustment of refining slag composition is often carried out on-site through continuous trials to test the actual desulfurization effect. This method has a long test cycle, and the process may cause slag viscosity, affecting production and causing economic losses.

SUMMARY

To solve the above problems, the disclosure provides a design method for high-performance ladle furnace (LF) desulfurization refining slag, including:

• • step S1: extracting a refining slag composition of LF desulfurization refining slag, and calculating a complete melting temperature and a viscosity of the refining slag composition;
  • step S2: based on the refining slag composition and corresponding complete melting temperature and viscosity of the refining slag composition, calculating a desulfurization capacity of each of the refining slag composition, and determining a desulfurization range of the refining slag composition based on desulfurization capacity results; and
  • step S3: selecting a high-performance LF desulfurization refining slag composition based on a desulfurization capacity range of the refining slag composition, then analyzing a sulfur content in steel, and completing a design of the high-performance LF desulfurization refining slag.

Optionally, in the step S1, a process of extracting the refining slag composition of the LF desulfurization refining slag and calculating the complete melting temperature and the viscosity of the refining slag composition includes:

in a calcium oxide (CaO)-aluminum oxide (Al₂O₃)-silicon dioxide (SiO₂)-magnesium oxide (MgO)-based refining slag, a main body is a CaO—Al₂O₃—SiO₂ ternary system; and using a Phase Diagram module in FactSage 8.2 software to calculate a complete melting range and a viscosity of the refining slag at 1400-1600 degrees Celsius (° C.) with MgO contents of 4 percent (%), 6%, 8%, and 10%.

Optionally, an LF refining temperature of the CaO—Al₂O₃—SiO₂—MgO-based refining slag is 1600° C., and a refining slag composition lower than 1600° C. is selected.

Optionally, a MgO content of the CaO—Al₂O₃—SiO₂—MgO-based refining slag does not exceed 6%.

Optionally, the process of calculating the viscosity of the refining slag composition is:

Viscosity_{(solid+liquid)}=Viscosity_(liquid)·(1−solid fraction)^−2.5

• • where Viscosity_{(solid+liquid)} is a viscosity of a solid-liquid mixed slag, Viscosity_(liquid) is a viscosity of a liquid part of the slag, and solid fraction is a viscosity of a solid part of the slag.

Optionally, the desulfurization capacity range of the refining slag composition is calculated using an Equilib balance module for multi-component and multi-phase equilibrium of FactSage 8.2 software.

Optionally, in the step S3, a process of selecting a high-performance LF desulfurization refining slag composition based on a desulfurization capacity range of the refining slag composition, and analyzing a sulfur content in steel includes:

• • preparing a refining slag based on a selected high-performance LF desulfurization refining slag composition and performing pretreatment;
  • using an X-ray fluorescence (XRF) device to detect a composition of a pretreated refining slag; and
  • based on composition detection results, calculating a sulfur content in molten steel using a spark discharge analyzer.

Optionally, the method for the pretreatment includes:

• • respectively at an initial stage of LF, an slag adjustment stage of the LF, and an end stage of the LF during an LF refining process, inserting a steel rod into a slag layer to obtain corresponding refining slag, cooling it and putting it into a bag for testing; inserting a steel rod with an iron-adding bucket into the molten steel to obtain the corresponding molten steel, taking it out and rapidly placing it into water to cool to room temperature for testing; and grinding the obtained refining slag into fine powder and pressing it into a cake for sample preparation.

Compared with the prior art, the beneficial effects of the disclosure are as follows.

The method of the disclosure uses FactSage thermodynamic software to calculate the complete melting temperature and viscosity range of the refining slag. The method of the disclosure uses FactSage thermodynamic software to calculate the theoretical desulfurization capacity of the refining slag. The method of the disclosure obtains the refining slag composition with strong desulfurization capacity conductive to production through theoretical calculation, and verifies it through industrial tests to obtain the refining slag composition conductive to actual production.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings forming a part of the present disclosure are used to provide a further understanding of the present disclosure. The schematic embodiment and descriptions of the present disclosure are used to explain the present disclosure and do not constitute an improper limitation of the present disclosure. In the accompanying drawings:

FIG. 1A, FIG. 1B, FIG. 1C, and FIG. 1D are diagrams of the complete melting range of a series of refining slags designed in an embodiment of the disclosure; where FIG. 1A is the complete melting range of the aluminum oxide (Al₂O₃)-calcium oxide (CaO)-silicon dioxide (SiO₂)-based refining slag with 4 percent (%) magnesium oxide (MgO) content, FIG. 1B is the complete melting range of the Al₂O₃—CaO—SiO₂-based refining slag with 6% MgO content, FIG. 1C is the complete melting range of the Al₂O₃—CaO—SiO₂-based refining slag with 8% MgO content, and FIG. 1D is the complete melting range of the Al₂O₃—CaO—SiO₂-based refining slag with 10% MgO content.

FIG. 2A and FIG. 2B are diagrams of the complete melting temperature and viscosity of a series of refining slags designed in an embodiment of the disclosure; where FIG. 2A is an effect diagram of different CaO contents on the complete melting temperature of the refining slag, and FIG. 2B is an effect diagram of CaO contents on the viscosity of the refining slag.

FIG. 3 is a diagram of the theoretical desulfurization capacity of a series of refining slags designed in an embodiment of the disclosure.

FIG. 4 is a flow chart of the steps of a design method for high-performance LF desulfurization refining slag in an embodiment of the disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to better understand the technical scheme of the disclosure, the embodiment of the disclosure will be described in detail below with reference to the accompanying drawings. It needs be clear that the described embodiment is only a part of the embodiments of the disclosure, not all of them. Based on the embodiment in the disclosure, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the disclosure. The terms used in the embodiment of the disclosure are only for the purpose of describing specific embodiments and are not intended to limit the disclosure. The singular forms “a”, “said” and “the” used in the embodiment of the disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

Embodiment

A design method for high-performance ladle furnace (LF) desulfurization refining slag, as shown in FIG. 4, includes:

• • step S1: extracting a refining slag composition of LF desulfurization refining slag, and calculating a complete melting temperature and a viscosity of the refining slag composition.

In a calcium oxide (CaO)-aluminum oxide (Al₂O₃)-silicon dioxide (SiO₂)-magnesium oxide (MgO)-based refining slag, a main body is a CaO—Al₂O₃—SiO₂ ternary system, and MgO is mainly derived from the erosion of refractory materials, etc. Firstly, using the Phase Diagram module in FactSage 8.2 thermodynamic software to calculate the complete melting range of the refining slag at 1400-1600 degrees Celsius (° C.) with MgO content of 4 percent (%), 6%, 8%, and 10%, as shown in FIG. 1A, FIG. 1B, FIG. 1C, and FIG. 1D, where FIG. 1A is the complete melting range of the Al₂O₃—CaO—SiO₂-based refining slag with 4% MgO content, FIG. 1B is the complete melting range of the Al₂O₃—CaO—SiO₂-based refining slag with 6% MgO content, FIG. 1C is the complete melting range of the Al₂O₃—CaO—SiO₂-based refining slag with 8% MgO content, and FIG. 1D is the complete melting range of the Al₂O₃—CaO—SiO₂-based refining slag with 10% MgO content. The complete melting ranges of the refining slag corresponding to different MgO contents are quite different. The complete melting range under the MgO content of the refining slag corresponding to the smelted steel grade is observed. The LF refining temperature of this industrial test reaches 1600° C., and the refining slag composition with a temperature lower than 1600° C. is selected. The melting temperature of the refining slag with more than 6% MgO is extremely high, and the slag is in a solid state at 1600° C., affecting actual production. It is necessary to strictly avoid the MgO content of the refining slag exceeding 6% during the production process.

Combined with the MgO content of the refining slag in actual production, the MgO content is set at 5%. The test steel grade at this station is an aluminum-killed steel, the refining slag has a high basicity, and the SiO₂ content varies slightly, which is set at 10% and 8%. A series of CaO contents are designed. Using the Equilib balance module for multi-component and multi-phase equilibrium of FactSage 8.2 software, the complete melting temperature of the refining slag composition corresponding to the designed CaO content and the liquid and solid proportions of the refining slag at 1600° C. under the industrial conditions are calculated sequentially. Through the Viscosity module, the viscosity of the refining slag composition corresponding to the designed CaO content at 1600° C. is calculated in turn. The designed refining slag composition have a solid part, and the viscosity of the designed refining slag is obtained in turn through the formula Viscosity_{(solid+liquid)}=Viscosity_(liquid)·(1−solid fraction)^−2.5. The calculated complete melting temperature and viscosity of the refining slag are shown in FIG. 2A and FIG. 2B, where FIG. 2A is an effect diagram of different CaO contents on the complete melting temperature of the refining slag, and FIG. 2B is an effect diagram of CaO contents on the viscosity of the refining slag. Through calculation, the change of SiO₂ content has little effect on the refining slag. The refining temperature of this industrial test is 1600° C. Among the refining slag compositions with a complete melting temperature lower than 1600° C., the CaO content is less than 58%, and among the refining slag compositions with a viscosity lower than 0.1, the CaO content is 52%-61%. Under this industrial test, to ensure good fluidity of the refining slag, the CaO content in the refining slag needs to be 52-58%, with an optimal value is about 56%.

The process of calculating the viscosity of the refining slag composition is.

Viscosity ( solid + liquid ) = Viscosity ( liquid ) · ( 1 - solid ⁢ fraction ) - 2.5 ,

• • where Viscosity_{(solid+liquid)} is a viscosity of a solid-liquid mixed slag, Viscosity_(liquid) is a viscosity of a liquid part of the slag, and solid fraction is a viscosity of a solid part of the slag.

Step S2: based on the refining slag composition and corresponding complete melting temperature and viscosity of the refining slag composition, calculating a desulfurization capacity of each of the refining slag composition, and determining a desulfurization range of the refining slag composition based on desulfurization capacity results.

Using the Equilib balance module for multi-component and multi-phase equilibrium of FactSage 8.2 software, the calculation is carried out at a ratio of 1 ton of slag to 100 tons of steel. With the MgO content in the refining slag set at 5%, the corresponding theoretical desulfurization capacity of the refining slag of different CaO and Al₂O₃ contents is calculated under the conditions of 10% and 8% SiO₂ content, and the results are as shown in FIG. 3. The calculation shows that the theoretical desulfurization capacity increases with the continuous increase of CaO content. When the CaO content reaches 60%, the theoretical desulfurization capacity of the refining slag reaches the limit, with the desulfurization rate reaches over 90%. Theoretically, the higher the CaO content, the stronger the desulfurization capacity of the refining slag. When the CaO content in the refining slag exceeds 60%, the refining slag may no longer desulfurize.

Step S3: selecting a high-performance LF desulfurization refining slag composition based on a desulfurization capacity range of the refining slag composition, then analyzing a sulfur content in steel, and completing a design of the high-performance LF desulfurization refining slag.

Based on the theoretical results of Step S1 and Step S2, five refining slag compositions with CaO content of 50-60% are designed to verify the calculation results. Actual operations are carried out on the industrial site. At three moments during the LF refining process: the initial stage, after slag adjustment, and before tapping, a steel rod is inserted into the slag layer to obtain the corresponding refining slag, which is then cooled and put into a bag for testing; a steel rod with an iron-adding bucket is inserted into the molten steel to obtain the corresponding molten steel, which is taken out and rapidly placed into water to cool to room temperature for testing.

The refining slag is crushed into powder and pressed into a cake sample, and detected by an X-ray fluorescence (XRF) device to obtain the composition of the taken refining slag. The steel sample in the bucket sample is taken out, cut at a position 10 millimeters (mm) from the bottom, and the oxide layer on the upper surface is ground off, and the sulfur content in the steel is detected by a spark discharge analyzer. In this way, the sulfur content of the molten steel at the beginning and end of refining is obtained, and the desulfurization rate is obtained to verify the theoretical calculation results. The test results show that the desulfurization effect is the best when the CaO content is 55-57%, reaching over 80%. Too low or too high CaO content leads to the slag to become viscous, affecting actual production and further affecting the desulfurization effect. It is necessary to strictly control the refining slag within the range of complete melting temperature and good fluidity.

The embodiment of the present disclosure is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiment of the present disclosure is required to be included in the protection scope of the present disclosure.