Method for eliminating large particle inclusions in x55sirc a spring steel continuous cast billet

Abstract

The application discloses a method for eliminating large-particle inclusions in continuous casting billets of X55SiCrA spring steel, and belongs to the technical field of steelmaking. The method comprises the following steps: pouring molten steel in a ladle to obtain continuous casting billets; automatically guiding the molten steel in the ladle by using a guiding sand to complete a pouring process; the mass fraction of Cr2O3 in the guiding sand is 20-25%; the insertion depth of a long nozzle in the pouring process is more than 340 mm; and a flow stabilizer is arranged in a molten steel receiving area of a tundish. When the continuous casting billets obtained by the method are directly rolled without repair grinding, the surface quality of the wire rod is good, so that the rolling wire rod quality is improved, and the production cost is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metallurgy, and relates to a method for eliminating large-particle inclusions in continuous casting billets of X55SiCrA spring steel. BACKGROUND

[0002] When the deoxidation process of X55SiCrA spring steel smelting adopts silicon deoxidation, a large-particle inclusion containing Si, Cr, Mn and other elements and having a size range of 20-100 microns is usually formed under the skin of the continuous casting billet. If the continuous casting billet is directly rolled without grinding, a large number of fine cracks are formed on the surface of the wire rod, causing the rejection rate to increase sharply. In order to ensure the quality of the rolled wire rod of X55SiCrA spring steel, the surface of the continuous casting billet is usually fully ground, which causes great waste, and the quality of the grinding directly affects the generation of defects such as ears and scabs on the surface of the rolled wire rod. SUMMARY

[0003] The present application aims to provide a method for eliminating large-particle inclusions in continuous casting billets of X55SiCrA spring steel, so as to solve at least one aspect of the problems and defects in the background art.

[0004] Specifically, the present application provides a method for eliminating large-particle inclusions in continuous casting billets of X55SiCrA spring steel, comprising the following steps:

[0005] Pouring the molten steel in the ladle to obtain the continuous casting billet;

[0006] The molten steel in the ladle is automatically drained by the drainage sand to complete the casting process;

[0007] The mass fraction of Cr2O3 in the drainage sand is 20-25%;

[0008] The depth of the nozzle insertion is more than 340 mm during the pouring process;

[0009] A flow stabilizer is arranged in the steel receiving area of the tundish during the pouring process.

[0010] According to one of the technical solutions of the preparation method of the present application, at least the following beneficial effects exist:

[0011] By optimizing the composition of the drainage sand and the continuous casting process, the large-particle inclusions containing Si, Cr, Mn and other elements and having a size range of 20-100 microns under the skin of the continuous casting billet are eliminated, and the physical quality of the continuous casting billet and the quality of the rolled wire rod are improved.

[0012] By reducing the content of Cr2O3 in the drainage sand, the reaction among Si, Cr and Mn elements is weakened, and the generation of inclusions containing Si, Cr and Mn elements is reduced.

[0013] By adjusting the long nozzle insertion depth, the slag entrapment behavior of Si, Cr and Mn element inclusions in the tundish is inhibited.

[0014] According to some embodiments of the present application, a flow stabilizer is arranged in the tundish in the pouring process.

[0015] By arranging the flow stabilizer, the turbulent kinetic energy of the molten steel in the tundish is reduced, and the average residence time of the molten steel is increased, which is beneficial to the floating removal of large particle inclusions.

[0016] According to some embodiments of the present application, the continuous casting billet is rolled into a wire rod.

[0017] According to some embodiments of the present application, the mass fraction of SiO2 in the drainage sand is less than 25.0%.

[0018] According to some embodiments of the present application, the refractoriness of the drainage sand is above 1700℃.

[0019] According to some embodiments of the present application, the moisture content of the drainage sand is less than 0.5%.

[0020] According to some embodiments of the present application, the volume fraction of the drainage sand with a particle size of 0.1mm to 1.5mm is above 90.0%.

[0021] According to some embodiments of the present application, the casting machine section in the continuous casting process is 150 square.

[0022] According to some embodiments of the present application, the arc radius in the continuous casting process is 9m.

[0023] According to some embodiments of the present application, the immersion depth of the submerged nozzle in the continuous casting process is 90mm to 140mm.

[0024] According to some embodiments of the present application, the crystallizer water quantity in the continuous casting process is 2000L / min to 2050L / min.

[0025] According to some embodiments of the present application, the secondary cooling specific water quantity in the continuous casting process is 1.2L / kg to 1.5L / kg.

[0026] According to some embodiments of the present application, the casting speed in the continuous casting process is 2.4m / min to 2.5m / min.

[0027] According to some embodiments of the present application, high-carbon steel protective slag is added in the continuous casting process.

[0028] According to some embodiments of the present application, the molten steel is composed of the following mass fractions of elements:

[0029] C: 0.54% to 0.57%; Si: 1.40% to 1.50%; Mn: 0.65% to 0.75%; P ≤ 0.015%;

[0030] S ≤ 0.012%; Cr: 0.65% to 0.80%; N ≤ 0.0050%; H ≤ 0.0006%; O ≤ 0.0020%; the balance being Fe and inevitable impurity elements. BRIEF DESCRIPTION OF DRAWINGS

[0031] For the convenience of those skilled in the art to understand, the present application will be further described below in conjunction with the drawings.

[0032] Figure 1 The morphology diagram of the corner subsurface area of the continuous casting billet prepared in Example 1 of the present application.

[0033] Figure 2 The morphology diagram of the surface subsurface area of the continuous casting billet prepared in Example 1 of the present application.

[0034] Figure 3 The morphology diagram of the corner subsurface area of the continuous casting billet prepared in Example 2 of the present application.

[0035] Figure 4 The morphology diagram of the surface subsurface area of the continuous casting billet prepared in Example 2 of the present application.

[0036] Figure 5 The morphology diagram of the corner subsurface area of the continuous casting billet prepared in Example 3 of the present application.

[0037] Figure 6 The morphology diagram of the surface subsurface area of the continuous casting billet prepared in Example 3 of the present application.

[0038] Figure 7 The inclusion morphology diagram of the surface subsurface area of the comparative example of the present application.

[0039] Figure 8 The inclusion morphology diagram of the surface subsurface area of the comparative example of the present application and the composition analysis results. DETAILED DESCRIPTION

[0040] The concept and technical effects of the present application will be described clearly and completely in conjunction with the embodiments below, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0041] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in one or more embodiments or examples.

[0042] Unless otherwise specified, the embodiments are carried out under conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are conventional products that can be obtained by commercial purchase, unless otherwise specified.

[0043] Example 1

[0044] The present embodiment is a method for eliminating large particle inclusions in continuous casting billets of X55SiCrA spring steel, which comprises the following steps:

[0045] An industrial test was carried out on the 4-machine 4-flow continuous casting machine of Xiangtan Steel Plant, and the test steel grade was X55SiCrA. The composition of the molten steel in the ladle was as follows:

[0046] C: 0.56%; Si: 1.45%; Mn: 0.72%; P: 0.01%; S: 0.008%; Cr: 0.70%; N: 0.0040%; H: 0.0003%; O: 0.0018%; the balance being Fe and unavoidable impurity elements.

[0047] The continuous casting process is as follows:

[0048] The molten steel in the ladle is automatically guided through the inner guide sand of the upper water inlet, flows into the tundish steel receiving area (the long nozzle insertion depth of the pouring molten steel large tank is 346 mm), and flows into the crystallizer through the immersion nozzle in the tundish (with an internal flow stabilizer).

[0049] The molten steel crystallizes and solidifies in the crystallizer, and the billet is cast out through the dummy bar.

[0050] The continuous casting process parameters are as follows:

[0051] The casting machine section is 150 square, the arc radius is 9 m, the tundish capacity is 45 t, the immersion depth of the immersion nozzle is 95 mm, the high carbon steel protective slag is used, the crystallizer water quantity is 2050 L / min, the secondary cooling specific water quantity is 1.5 L / kg, and the withdrawal speed is 2.5 m / min.

[0052] The results show that:

[0053] When the mass content of Cr2O3 is 23.59%, the mass content of SiO2 is 23.9%, the mass content of H2O is 0.21%, the refractoriness is 1720°C, the particle size is 0.1mm-1.5mm, the volume ratio is 91.2%, the long nozzle insertion depth of the ladle is 346mm, and the built-in flow stabilizer is used in the tundish, no large particle inclusions are found in the corner and surface of the continuous casting billet (see Figures 1-2 ).

[0054] Example 2

[0055] The present embodiment is a method for eliminating large particle inclusions in X55SiCrA spring steel continuous casting billet, which comprises the following steps:

[0056] The 4-machine 4-flow continuous casting machine of Xiangtan Steel Plant is used for industrial test, and the test steel grade is X55SiCrA. The composition of the molten steel in the ladle is as follows:

[0057] C: 0.54%; Si: 1.42%; Mn: 0.73%; P: 0.013%; S: 0.012%; Cr: 0.73%; N: 0.0038%; H: 0.0004%; O: 0.0015%; the balance is Fe and unavoidable impurity elements.

[0058] The continuous casting process is as follows:

[0059] The molten steel in the ladle is automatically guided through the upper water inlet guide sand, flows into the tundish receiving area (the long nozzle insertion depth of the ladle is 359mm), and then flows into the crystallizer through the submerged nozzle.

[0060] The molten steel crystallizes and solidifies in the crystallizer, and the continuous casting billet is cast out through the dummy bar.

[0061] The continuous casting process parameters are as follows:

[0062] The casting machine section is 150 square, the arc radius is 9m, the tundish capacity is 45t, the submerged nozzle immersion depth is 115mm, the high carbon steel protective slag is used, the crystallizer water quantity is 2010L / min, the secondary cooling specific water quantity is 1.4L / kg, and the withdrawal speed is 2.4m / min.

[0063] The results show that:

[0064] When the mass content of Cr2O3 in the flow sand used for the ladle is 24.12%, the mass content of SiO2 is 25.0%, the mass content of H2O is 0.35%, the refractoriness is 1730°C, the volume ratio of the particle size in the range of 0.1mm to 1.5mm is 92.1%, the long nozzle of the ladle is inserted to a depth of 359mm, and the built-in flow stabilizer is used in the tundish, no large particle inclusions are found in the skin under the corner and surface of the continuous casting billet (see Figures 3-4 ).

[0065] Example 3

[0066] The present example is a method for eliminating large particle inclusions in the continuous casting billet of X55SiCrA spring steel, which comprises the following steps:

[0067] An industrial test is conducted on the 4-strand continuous caster in the steelmaking plant of Xiangtan Steel, and the steel grade is X55SiCrA. The composition of the molten steel in the ladle is as follows:

[0068] C: 0.57%; Si: 1.48%; Mn: 0.68%; P: 0.014%; S: 0.009%; Cr: 0.73%; N: 0.0045%; H: 0.0004%; O: 0.0017%; the balance is Fe and unavoidable impurity elements.

[0069] The continuous casting process is as follows:

[0070] The molten steel in the ladle is automatically guided through the flow sand in the upper nozzle, flows into the tundish through the long nozzle (the long nozzle of the ladle is inserted to a depth of 342mm), and then flows into the mold through the submerged nozzle.

[0071] The molten steel solidifies in the mold, and the continuous casting billet is cast out through the dummy bar.

[0072] The continuous casting process parameters are as follows:

[0073] The cross section of the caster is 150m2, the arc radius is 9m, the tundish capacity is 45t, the submerged nozzle immersion depth is 115mm, the high carbon steel powder is used as the protective slag, the mold water flow is 2010L / min, the secondary cooling water flow is 1.3L / kg, and the casting speed is 2.5m / min.

[0074] The results show that when the mass content of Cr2O3 in the flow sand used for the ladle is 21.98%, the mass content of SiO2 is 19.8%, the mass content of H2O is 0.44%, the refractoriness is 1710°C, the volume ratio of the particle size in the range of 0.1mm to 1.5mm is 91.2%, the long nozzle of the ladle is inserted to a depth of 342mm, and the built-in flow stabilizer is used in the tundish, no large particle inclusions are found in the skin under the corner and surface of the continuous casting billet (see Figures 5-6 ).

[0075] Comparative Example

[0076] The present comparative example is a method for eliminating large particle inclusions in a continuously cast billet of X55SiCrA spring steel, which comprises the following steps:

[0077] An industrial test was conducted on a 4-strand continuous caster in the Steelmaking Plant of Xiangtan Iron and Steel Co., Ltd. The steel grade was X55SiCrA, and the composition of the molten steel in the ladle was as follows:

[0078] C: 0.55%; Si: 1.40%; Mn: 0.74%; P: 0.013%; S: 0.012%; Cr: 0.78%; N: 0.0042%; H: 0.0004%; O: 0.0015%; and the balance being Fe and unavoidable impurities.

[0079] The continuous casting process was as follows:

[0080] The molten steel in the ladle was automatically drained through the drainage sand in the upper nozzle, flowed into the tundish through the long nozzle, and then flowed into the mold through the submerged nozzle. The molten steel crystallized and solidified in the mold, and the billet was cast by the dummy bar.

[0081] The continuous casting process parameters were as follows:

[0082] The casting machine had a cross section of 150 square meters and an arc radius of 9 meters, the tundish had a capacity of 45 tons, the submerged nozzle had an immersion depth of 95 mm, high-carbon steel protective slag was used, the mold had a water flow of 2050 L / min, the secondary cooling had a water flow of 1.5 L / kg, and the withdrawal speed was 2.5 m / min.

[0083] The drainage sand used in the molten steel pouring pot had a mass content of Cr2O3 of 45.23%, a mass content of SiO2 of 23.6%, and a mass content of H2O of 0.43%, a refractoriness of 1740°C, a particle size of 0.1 mm to 1.5 mm with a volume ratio of 92.9%, a long nozzle insertion depth of 275 mm, and no internal flow stabilizer in the tundish.

[0084] When the long nozzle insertion depth of the molten steel pouring pot was 275 mm and the tundish had no internal flow stabilizer, large particle inclusions were found under the surface of the continuously cast billet (see Figures 7-8 ). The composition of the large particle inclusions was as follows (mass fraction): O 41.55%, Si 22.09%, Mn 9.94%, Cr 21.23%, and Fe 2.19%.

[0085] In the present application, when the silicon deoxidation process is used in the X55SiCrA spring steel smelting and deoxidation process, a large particle inclusion with Si, Cr, Mn and other elements, with a size range of 20-100 microns, is usually formed under the surface of the continuous casting billet. If the continuous casting billet is directly rolled without grinding, a large number of fine cracks are formed on the surface of the wire rod, causing the rejection rate to increase sharply. In order to ensure the quality of the X55SiCrA spring steel wire rod, the surface of the continuous casting billet is usually fully ground, which causes great cost waste, and the quality of the grinding directly affects the generation of defects such as surface ears and scarring of the rolled wire rod.

[0086] In the present application, by optimizing the composition of the drainage sand, the continuous casting process parameters and the flow field of the tundish, the large particle inclusions under the surface of the continuous casting billet are eliminated.

[0087] In the present application, when the mass content of Cr2O3 in the drainage sand used for pouring the steel ladle is 20-25%, the long nozzle insertion depth of the pouring steel ladle is greater than or equal to 340 mm, and the built-in flow stabilizer is used in the steel receiving area of the tundish, the large particle inclusions under the surface of the continuous casting billet are completely eliminated, and the quality of the wire rod directly rolled from the continuous casting billet without grinding is good.

[0088] In the present application, the continuous casting billet is directly rolled into a wire rod with a high qualification rate without grinding, the physical quality of the continuous casting billet and the rolled wire rod is improved, the production cost of the X55SiCrA spring steel is reduced, and a new process for producing the X55SiCrA spring steel product is developed.

[0089] In summary, in the present application, the mass content of Cr2O3 in the drainage sand used for pouring the steel ladle is reduced from more than 45% to 20-25%, the long nozzle insertion depth of the pouring steel ladle is increased from less than 280 mm to 340 mm or more, and the built-in flow stabilizer is used in the steel receiving area of the tundish. This method eliminates the large particle inclusions with Si, Cr, Mn and other elements, with a size range of 20-100 microns, under the surface of the X55SiCrA spring steel continuous casting billet, realizes the direct rolling of the continuous casting billet without grinding, improves the quality of the rolled wire rod, and reduces the production cost.

[0090] The above specific embodiments further illustrate the purpose, technical solutions and advantages of the present application, and it should be understood that the above description is only for specific embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for eliminating large particle inclusions in X55SiCrA spring steel continuous casting billets, characterized in that, Includes the following steps: molten steel is poured from a ladle to produce a continuously cast billet. The molten steel in the ladle is automatically diverted by diversion sand to complete the pouring process. The mass fraction of Cr2O3 in the diversion sand is 20%~25%; During the pouring process, the insertion depth of the long sprue should be more than 340mm; A flow stabilizer is installed in the steel-receiving zone of the tundish during the casting process; The mass fraction of SiO2 in the diverting sand is below 25.0%.

2. The method according to claim 1, characterized in that, The continuously cast billet is rolled into wire rod.

3. The method according to claim 1, characterized in that, The refractoriness of the diversion sand is above 1700℃.

4. The method according to claim 1, characterized in that, The immersion depth of the submerged nozzle during the continuous casting process is 90mm~140mm.

5. The method according to claim 1, characterized in that, The water flow rate in the crystallizer during the continuous casting process is 2000L / min to 2050L / min.

6. The method according to claim 1, characterized in that, The secondary cooling water volume during the continuous casting process is 1.2L / kg to 1.5L / kg.

7. The method according to claim 1, characterized in that, The casting speed during the continuous casting process is 2.4 m / min to 2.5 m / min.

8. The method according to claim 1, characterized in that, High-carbon steel protective slag is added during the continuous casting process.

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