A method for smelting ultra-high clean sulfur-containing aluminum steel

Abstract

The invention relates to the technical field of steelmaking, and in particular to a smelting method of ultra-high clean sulfur-containing aluminum-containing steel. The sulfur-containing aluminum-containing steel is smelted by a BOF-LF-RH-CC process, comprising the following steps: (1) a converter adopts a blowing method, aluminum is first added to the converter for deoxidation, and then an alloy is added for alloying, and then slag is made; (2) a deoxidizer is added in the LF process for deoxidation, and the sulfur content of the molten steel is reduced to ≤40ppm after refining; sulfur iron or sulfur iron wire is used to control the sulfur content to 60-150ppm before RH refining ladle; (3) no alloy and slag are added in the RH vacuum process; after RH, the sulfur content is controlled to a target S content according to the S content requirement of the steel grade; and (4) a continuous casting process adopts full-process protective casting, and the sulfur content in the molten steel is controlled before the refining ladle, thereby controlling the generation of inclusions, so that the removal of molten steel circulation inclusions can be promoted, and the generation of CaS inclusions in the steel will not be excessively increased.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking, and in particular to a method for smelting ultra-high clean sulfur-containing and aluminum-containing steel. Background Art

[0002] The cleanliness of sulfur-containing and aluminum-containing steel, represented by gear steel, has a great influence on the fatigue life of the product. The control of large-sized inclusions is particularly important. The smaller the size of the inclusions in the steel, the easier it is to obtain a gear steel with a long life. Therefore, how to achieve the smelting of ultra-high cleanliness sulfur-containing and aluminum-containing steel has become a key issue in the smelting industry. After searching, many people at home and abroad have conducted many studies on the size of sulfur-containing and aluminum-containing inclusions, but there are many differences with this patent.

[0003] The document "Practical Discussion on Improving the Cleanliness of Liquid Steel Containing Sulfur and Aluminum Gear Steel" points out that in steel production, the cleanliness of liquid steel containing sulfur and aluminum gear steel is a key topic of concern. Based on this, the existing gear steel production process was studied, and improved technologies such as electric furnace endpoint control, steel tapping deoxidation, and variable flow bottom argon blowing were proposed and applied, which effectively improved the cleanliness of liquid steel for gear steel. The focus is on controlling the CO accumulation of converter steel tapping to reduce the overall number of oxide inclusions, and on the other hand, on controlling the refining operation to improve the cleanliness.

[0004] The document "Mechanism and Control of CA and CaS in Sulfur-Containing Gear Steel" points out that CaS inclusions in sulfur-containing steel are prone to cause nozzle blockage. The formation conditions of calcium aluminate inclusions and CaS in 20CrMnTiS steel were analyzed by thermodynamics and kinetics. The results show that when calcium treatment is carried out at 1600℃, when [Al]s in steel is 0.02%, Ca needs to be controlled at 0.003 9%~0.010%; in view of the kinetic analysis of the degeneration of Al2O3 inclusions, the Al2O3 inclusions in steel before calcium treatment should not be too large, and the optimal particle size is ≤1μm. In addition, sufficient calcium treatment time should be given before sulfur feeding to completely degenerate Al2O3 inclusions into calcium aluminate inclusions (12CaO·7Al2O3). The reasonable refining process of sulfur-containing gear steel is: hot metal pretreatment → converter → LF refining (calcium treatment) → RH vacuum degassing → soft blowing (soft blowing mid-to-late sulfur feeding line) → billet continuous casting. Emphasis is placed on the control of inclusions by calcium treatment. Summary of the invention

[0005] The technical problem to be solved by the present invention is: in order to overcome the problem of how to reduce inclusions in sulfur-containing and aluminum-containing steel in the prior art, a method for smelting ultra-high clean sulfur-containing and aluminum-containing steel is provided.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a method for smelting ultra-high clean sulfur-containing aluminum-containing steel, wherein the sulfur-containing aluminum-containing steel is smelted by a BOF-LF-RH-CC process, comprising the following steps:

[0007] (1) The converter adopts the blowing method. Aluminum is first added to the converter steel for deoxidation, and then alloy is added for alloying. After the alloy is added, lime and refined slag are added for slagging;

[0008] (2) Deoxidizer is added during the LF process for deoxidation, and the S content of the molten steel is reduced to ≤40ppm after refining;

[0009] Before hanging the RH refining bag, sulfur iron or sulfur iron wire is used to control S to 60-150ppm;

[0010] (3) No alloy or slag is added during the RH vacuum process, the RH vacuum degree is ≤67pa, and the RH high vacuum time is ≥20min; after the RH is completed, the S content is controlled to the target S content according to the S content requirements of the steel grade;

[0011] (4) The continuous casting process adopts full-process protective casting.

[0012] Further, the composition requirements for sulfur-containing and aluminum-containing steel are: S: 0.010%~0.050%, Al: 0.010%~0.10%.

[0013] The method further comprises the step (2) of reducing the sulfur content of the molten steel to ≤40 ppm at the end of refining, ensuring that the content of (TFe+MnO+Cr2O3) in the slag is ≤1.50%, and the slag basicity is 3-8, and the argon flow rate during the refining process is 300-500 L / min.

[0014] The beneficial effects of the present invention are as follows: the present invention provides a method for smelting ultra-high clean sulfur-containing aluminum steel, which controls the sulfur content in the molten steel before the refining ladle to control the generation of inclusions, thereby promoting the removal of inclusions in the molten steel circulation without excessively increasing the generation of CaS inclusions in the steel. DETAILED DESCRIPTION

[0015] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0016] FIG1 is a schematic diagram of the structure of the present invention, a method for smelting ultra-high clean sulfur-containing aluminum steel, smelting the sulfur-containing aluminum steel using the BOF-LF-RH-CC process, comprising the following steps:

[0017] (1) The converter adopts the blowing method. Aluminum is first added to the converter steel for deoxidation, and then alloy is added for alloying. After the alloy is added, lime and refined slag are added for slagging;

[0018] (2) Deoxidizer is added in the LF process for deoxidation. After refining, the S content of the molten steel is reduced to ≤40ppm. During LF refining, the S content of the molten steel needs to be reduced to ≤40ppm, and the weak oxide content in the slag is ≤1.50% to achieve deep deoxidation and desulfurization. At the end of LF, ferrosulphide is added or ferrosulphide wire is fed according to the target sulfur content of 60-150ppm. Then, with the help of S as a surface active element, there is a concentration gradient at the interface, which improves the ability of the molten steel in the RH process to efficiently remove large-sized inclusions.

[0019] Before hanging the RH refining bag, sulfur iron or sulfur iron wire is used to control S to 60-150ppm;

[0020] (3) No alloy or slag is added during the RH vacuum process. No sulfur alloy is added during the RH process, which can effectively reduce the formation of calcium sulfide inclusions. After the RH is completed, the target S content is adjusted to meet the requirements, and the maximum DS inclusion in the sulfur-containing and aluminum-containing steel is finally achieved. The RH vacuum degree is ≤67pa, and the RH high vacuum time is ≥20min. After the RH is completed, the S content is controlled to the target S content according to the S content requirements of the steel grade;

[0021] (4) The continuous casting process adopts full-process protective casting.

[0022] The composition requirements for sulfur-containing and aluminum-containing steel are: S: 0.010%~0.050%, Al: 0.010%~0.10%.

[0023] The requirement for reducing the sulfur content of the molten steel to ≤40 ppm at the end of refining in step (2) is to ensure that the (TFe+MnO+Cr2O3) content in the slag is ≤1.50%, and the slag basicity is 3-8, and the argon flow rate during the refining process is 300-500 L / min.

[0024] Since it is usually not convenient to measure the total oxygen content of molten steel during the LF refining process, the thermodynamic condition for desulfurization of molten steel is that the molten steel must be deoxidized first. Therefore, the lower the sulfur content of the molten steel, the higher the total oxygen content in the steel. On the other hand, according to the slag-steel equilibrium, the lower the content of weak oxidation (TFe+MnO+ Cr2O3) in the slag, the lower the oxygen content in the corresponding equilibrium molten steel. Therefore, the present invention emphasizes that the molten steel must first undergo self-cleaning smelting during the LF process, and requires that the S content is ≤40ppm and the slag (TFe+MnO+ Cr2O3) is ≤1.50% at the end of LF. S is a surface active element, and its concentration is highest at the interface. Its concentration decreases as it goes deeper into the molten steel. Therefore, there is a concentration near the interface. Since the higher the S content in the molten steel, the smaller the interfacial tension of the molten steel. Therefore, the S content can be used as a favorable element to promote the removal of inclusions from the molten steel. However, too high an S content will lead to the formation of CaS inclusions in the steel. The wetting angle of CaS inclusions with the molten steel is less than 90°, and it is not easy to remove them during the RH cycle. Therefore, the present invention controls the S content to be about 100 ppm at the end of LF, which promotes the removal of inclusions in the molten steel cycle without excessively increasing the formation of CaS inclusions in the steel.

[0025] The gear steel SCr420H steel is produced by using a 130-ton converter, a 130-ton refining furnace, a 130-ton RH furnace, and a continuous casting machine. The steel composition requirements are: C: 0.17-0.23%, Si: 0.15-0.35%, Mn: 0.55-0.95%, S: 0.01-0.03%, Cr: 0.85-1.25%, Al: ≥0.024%. Embodiment 1:

[0026] The top and bottom double-blown converter adopts conventional blowing method, and the end point C is controlled at 0.086%. When the converter is tapping steel, 130kg aluminum cake, 345kg low-aluminum and low-titanium ferrosilicon, etc. are first added, and then lime and refined slag are added.

[0027] LF uses Al particles and silicon carbide for deoxidation and adjusts the composition of molten steel. The S content of LF is controlled at 0.004% in the final sampling. Sulfur iron wire is added before the ladle is hoisted to RH. The S content of RH sampling is 0.009%. The RH vacuum is controlled at 35Pa, and the RH high vacuum time is 26min. After RH breaks through the air, the sulfur iron wire is fed to the molten steel until the sulfur content is 0.017%.

[0028] The weak oxide content and basicity in the LF end slag are shown in the following table (unit of each component: wt%):

[0029] MnO <![CDATA[Cr2O3]]> TFe R 0.06 0.08 0.72 4.8

[0030] For the inspection of finished rolled products, the number of samples taken is 6 and the maximum inclusion size detected is 15μm. Embodiment 2:

[0031] The top and bottom double-blown converter adopts conventional blowing method, and the end point C is controlled at 0.072%. When the converter is tapping steel, 130kg aluminum cake, 345kg low-aluminum and low-titanium ferrosilicon, etc. are first added, and then lime and refined slag are added.

[0032] LF uses Al particles and silicon carbide to deoxidize and adjust the composition of molten steel. The S content of LF is controlled at 0.003% in the final sampling. Sulfur iron wire is added before the bag is hoisted to RH. The S content of RH sampling is 0.01%. The RH vacuum is controlled at 28Pa, and the RH high vacuum time is 23min. After RH breaks through the air, the sulfur iron wire is fed to the molten steel until the sulfur content is 0.018%.

[0033] The weak oxide content and basicity in the LF end slag are shown in the following table (unit of each component: wt%):

[0034] MnO <![CDATA[Cr2O3]]> TFe R 0.04 0.06 0.39 5.8

[0035] For the inspection of finished rolled products, the number of samples taken was 6 and the maximum inclusion size detected was 17μm.

[0036] Comparative Example 1:

[0037] The top and bottom double-blown converter adopts conventional blowing method, and the end point C is controlled at 0.069%. When the converter is tapping steel, 130kg aluminum cake, 345kg low-aluminum and low-titanium ferrosilicon, etc. are first added, and then lime and refined slag are added.

[0038] LF uses Al particles and silicon carbide for deoxidation and adjusts the composition of the molten steel. The argon gas in the LF process is reduced and sulfur-retaining operations are adopted. The S content of the final LF sample is controlled at 0.013%. Sulfur wire is added before the bag is hoisted to the RH. The S content of the RH sample detected when entering the station is 0.021%. The RH vacuum degree is controlled at 34Pa, the RH high vacuum time is 26min, and the S content of the RH after breaking the air is 0.017, and there is no need to supplement the sulfur wire.

[0039] The weak oxide content and basicity in the LF end slag are shown in the following table (unit of each component: wt%):

[0040] MnO <![CDATA[Cr2O3]]> TFe R 0.14 0.09 0.89 4.3

[0041] For the inspection of finished rolled products, the number of samples taken was 6 and the maximum inclusion size detected was 92μm.

[0042] The top and bottom double-blown converter adopts conventional blowing method, and the end point C is controlled at 0.083%. When the converter is tapping steel, 130kg aluminum cake, 345kg low-aluminum and low-titanium ferrosilicon, etc. are first added, and then lime and refined slag are added.

[0043] LF uses Al particles and silicon carbide for deoxidation and adjusts the composition of molten steel. The S content of the final LF sample is controlled at 0.004%. Sulfur iron wire is added before the bag is hoisted to RH. The S content of RH sampling at the station is 0.022%. The RH vacuum degree is controlled at 38Pa, the RH high vacuum time is 21min, and the S content of RH after breaking the air is 0.017%, and no sulfur iron wire needs to be fed.

[0044] The weak oxide content and basicity in the LF end slag are shown in the following table (unit of each component: wt%):

[0045] MnO <![CDATA[Cr2O3]]> TFe R 0.06 0.04 0.41 4.9

[0046] For the inspection of finished rolled products, the number of samples taken was 6 and the maximum inclusion size detected was 101μm.

[0047] Comparative Example 3:

[0048] The top and bottom double-blown converter adopts conventional blowing method, and the end point C is controlled at 0.049%. When the converter is tapping steel, 130kg aluminum cake, 345kg low-aluminum and low-titanium ferrosilicon, etc. are first added, and then lime and refined slag are added.

[0049] LF uses Al particles and silicon carbide for deoxidation and adjusts the composition of the molten steel. The S content of the final sample of LF is controlled at 0.004%. Sulfur iron wire is added before the bag is hoisted to RH. The S content of the RH sample taken when entering the station is 0.009%. The RH vacuum degree is controlled at 28Pa, the RH high vacuum time is 5min, and after the RH breaks through the air, the sulfur iron wire is fed until the sulfur content of the molten steel is 0.016%.

[0050] The weak oxide content and basicity in the LF end slag are shown in the following table (unit of each component: wt%):

[0051] MnO <![CDATA[Cr2O3]]> TFe R 0.05 0.06 0.36 6.1

[0052] For the inspection of finished rolled products, the number of samples taken was 6 and the maximum inclusion size detected was 67μm.

[0053] The top and bottom double-blown converter adopts conventional blowing method, and the end point C is controlled at 0.063%. When the converter is tapping steel, 130kg aluminum cake, 345kg low-aluminum and low-titanium ferrosilicon, etc. are first added, and then lime and refined slag are added.

[0054] LF uses Al particles and silicon carbide for deoxidation and adjusts the composition of molten steel. The S content of the final LF sample is controlled at 0.003%. No sulfur alloy is added before the bag is hoisted to RH. The S content of RH sampling is 0.003%. The RH vacuum degree is controlled at 39Pa, the RH high vacuum time is 28min, and the sulfur iron wire is fed after RH breaks the air until the sulfur content of the molten steel is 0.014%.

[0055] The weak oxide content and basicity in the LF end slag are shown in the following table (unit of each component: wt%):

[0056] MnO <![CDATA[Cr2O3]]> TFe R 0.05 0.06 0.42 6.0

[0057] For the inspection of finished rolled products, 6 samples were taken and the maximum inclusion size detected was 49μm.

[0058] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for smelting ultra-high clean sulfur-containing aluminum steel, characterized in that: The sulfur-containing aluminum-containing steel is smelted by the BOF-LF-RH-CC process, which includes the following steps: (1) The converter adopts the blowing method. Aluminum is first added to the converter steel for deoxidation, and then alloy is added for alloying. After the alloy is added, lime and refined slag are added for slag making. The alloy is low-aluminum and low-titanium ferrosilicon; (2) Deoxidizer is added in the LF process for deoxidation. After refining, the S content of the molten steel is reduced to ≤40ppm. The deoxidizer is Al particles and silicon carbide. Before hanging the RH refining bag, sulfur iron wire is used to control S to 60-150ppm; (3) No alloy or slag is added during the RH vacuum process, the RH vacuum degree is ≤67pa, and the RH high vacuum time is ≥20min; after the RH is completed, the S content is controlled to the target S content according to the S content requirements of the steel grade; (4) The continuous casting process adopts full-process protective casting.

2. A method for smelting ultra-high clean sulfur-containing aluminum-containing steel as claimed in claim 1, characterized in that: The composition requirements of the sulfur-containing and aluminum-containing steel are: S: 0.010% to 0.050%, Al: 0.010% to 0.10%.

3. The method for smelting ultra-high clean sulfur-containing and aluminum-containing steel according to claim 1, characterized in that: The requirement for reducing the S content of the molten steel to ≤40 ppm at the end of refining in step (2) is to ensure that the (TFe+MnO+Cr2O3) content in the slag is ≤1.50%, the slag basicity is 3-8, and the argon flow rate during the refining process is 300-500 L / min.