A method for producing high-carbon steel continuous casting billets with large cross-sections at low cost and high efficiency

Abstract

A method for producing high-carbon steel continuous casting billets with large cross-sections at low cost and high efficiency belongs to the technical field of iron and steel metallurgy. During the continuous casting process, a casting speed of 0.75 - 0.79 m / min is adopted. The superheat of the tundish for the first furnace of each casting heat is controlled at ≥50°C, and for consecutive casting heats, it is controlled at ≥41°C. At the same time, the electromagnetic stirring in the mold is cancelled, and electromagnetic strong stirring is started at the end of solidification and the soft reduction process is adopted. By increasing the continuous casting speed and the superheat of the tundish, the present invention reduces the residence time of molten steel in the tundish, promotes the floating of non-metallic inclusions, and controls the segregation of elements and the quality problems of the continuous casting billets such as central porosity caused thereby by means of strong stirring at the end of solidification and the soft reduction process. For the large cross-section continuous casting billets produced by the present invention, after pickling and corrosion, the macrostructure ratings for central segregation and central porosity are both grade 0, and there is no central shrinkage cavity; the qualified rate of finished product non-metallic inclusion inspection is over 99.7%.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and particularly relates to a method for producing high-carbon steel continuous casting billets with large cross-sections at low cost and high efficiency. Background Art

[0002] In the production process of high-carbon steel continuous casting billets with large cross-sections, the continuous casting process, as the last and most important process, shoulders many missions such as the internal quality and external quality of the billets. Generally speaking, the quality of the continuous casting process control directly determines the final results of the internal and external quality of the billets.

[0003] In recent years, the production of high-end quality steel using continuous casting billets with large cross-sections has been gradually adopted by various steel mills. However, in the process of producing high-carbon steel with continuous casting billets having large cross-sections, due to characteristics such as high carbon content, large billet cross-section, poor thermal conductivity, long solidification time, and uneven cooling, billet defects such as center segregation, center porosity, center shrinkage cavity, and surface cracks are likely to occur. In order to avoid the occurrence of the above defects, generally, when producing high-carbon steel continuous casting billets with large cross-sections, the process control idea adopted in continuous casting is: low superheat, low casting speed, electromagnetic strong stirring in the mold, and reduction at the solidification end. By this means, quality problems such as element segregation and center porosity that are likely to occur during the solidification of continuous casting billets with large cross-sections can be avoided. However, precisely because of this, when producing continuous casting billets with large cross-sections, the casting speed of continuous casting is low, and the molten steel stays in the tundish for too long, which not only makes it difficult to control the superheat of the tundish, but also easily causes the non-metallic inclusions to exceed the standard. In addition, the power of the electromagnetic stirring in the mold is too large, and negative segregation is likely to occur under the skin of the billet, affecting the internal quality of the billet. The above problems result in low production efficiency and extremely high costs when producing high-carbon steel by continuous casting with large cross-sections, which are difficult problems that need to be solved urgently by technical personnel in the industry.

[0004] Application No. 202011122827.1 discloses that in the continuous casting process, crystallization electric stirring and end electric stirring are used for stirring and soft reduction is adopted to ensure the internal and surface quality of the continuous casting billets. However, the core control idea is still low superheat, and at the same time, by means of electromagnetic stirring in the mold, electromagnetic stirring at the solidification end of the billet, and dynamic soft reduction, etc., the production of continuous casting billets is realized. Therefore, there are still quality problems such as internal segregation and porosity in the billets.

[0005] Application No. 201810700010.4 discloses that by controlling the superheat of the molten steel for pouring, the pouring speed, the reduction process at the solidification end, etc., the compactness and homogeneity of the continuous casting billets of 42CrMoH steel for large billets are improved. In this application, strong stirring is adopted for electromagnetic stirring, electromagnetic stirring is added between the secondary cooling and the solidification end, and heavy reduction is adopted at the solidification end, with the reduction amount being 8-11 mm, to solve the compactness of the continuous casting billets of medium-carbon steel. However, for high-carbon steel, this process idea still cannot completely solve the quality problems such as internal segregation and porosity in the billets. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a method for producing high-carbon steel continuous casting billets with large cross-sections at low cost and high efficiency, ensuring the quality of the billets and improving the steelmaking control level.

[0007] To achieve the above invention object, the technical solution adopted by the present invention is as follows:

[0008] A method for producing high-carbon steel continuous casting billets with large cross-sections at low cost and high efficiency, in which a casting speed of 0.75 - 0.79 m / min is adopted during the continuous casting process, the superheat degree of the tundish for the first furnace of each casting heat is controlled at ≥50°C, and for continuous casting heats it is controlled at ≥41°C, reducing the residence time of the molten steel in the tundish and promoting the full floating of inclusions;

[0009] Meanwhile, in order to avoid problems such as negative segregation and porosity in the billets, the mold electromagnetic stirring is cancelled, electromagnetic strong stirring is started at the solidification end, and the heavy reduction process is adopted to eliminate the quality defects of the billets caused by element segregation inside the billets at the solidification end of the billets, realizing the production of high-quality billets.

[0010] In the present invention, the superheat degree of the tundish for the first furnace of each casting heat is controlled at 50 - 55°C, and for continuous casting heats it is controlled at 41 - 50°C.

[0011] In the present invention, the current intensity of the electromagnetic strong stirring at the solidification end is 450 - 500 A, and the frequency is 5.5 - 6.5 Hz.

[0012] In the present invention, the reduction amount of the heavy reduction process is 15 - 20 mm.

[0013] The cross-section specifications of the large cross-section continuous casting billets in the present invention are 280 mm × 32 mm and 280 mm × 380 mm.

[0014] Compared with the production of high-carbon steel with conventional large cross-section continuous casting billets, by adopting process controls such as low superheat degree and low casting speed, the present invention increases the continuous casting speed and the superheat degree of the tundish, reduces the residence time of the molten steel in the tundish, promotes the floating of non-metallic inclusions, avoids the problem of excessive non-metallic inclusions caused by refractory erosion and foreign object entrainment, etc., and with the help of processes such as strong stirring and heavy reduction at the solidification end, controls the element segregation and the billet quality problems such as center porosity caused thereby, while improving the production efficiency, achieving a substantial reduction in the smelting cost.

[0015] For the large cross-section continuous casting billets produced by the present invention, after pickling corrosion, the macrostructure rating of center segregation and center porosity are both grade 0, and there is no center shrinkage cavity; the qualified rate of finished product non-metallic inclusion inspection is above 99.7%. Compared with the conventional process, the continuous casting pouring time of the present invention is reduced by 10% - 20%, the number of continuous casting heats per tundish is increased by 3 - 5 heats, and the comprehensive cost is reduced by 12 - 22 yuan / ton.

[0016] This invention achieves the goal of low-cost, efficient production of large-section continuous casting slabs of high-carbon steel. It can be applied on a large scale in the steelmaking process, offering simple operation and stable results. Compared to traditional steelmaking processes, this invention can effectively improve continuous casting efficiency, reduce overall continuous casting costs, and enhance product quality. DETAILED DESCRIPTION

[0017] Example 1

[0018] In this example, a 120-ton ladle was used to continuously cast a slab with a cross-section of 280 mm x 380 mm. The steel grade used was U71Mn rail steel. The casting speed was 0.75 m / min, the continuous pouring heat was the second heat, the tundish superheat was 41°C, the mold electromagnetic stirring was disabled, and the electromagnetic stirring process parameters at the end of solidification were 500 A, 6.5 Hz, and a reduction of 15 mm.

[0019] After production was completed, the ingots were inspected for quality. The pickling and etching macro-ratings showed a grade of 0 for both central segregation and porosity, with no central shrinkage cavities. The non-metallic inclusion inspection pass rate was 99.75%, fully meeting rail standards. Continuous casting time was reduced by 10% compared to conventional processes, and the number of continuous casting furnaces increased by three, reducing overall costs by 12 yuan per ton.

[0020] Example 2

[0021] In this example, a 120-ton ladle was used to continuously cast a slab with a cross-section of 280 mm x 380 mm. The steel grade used was U71Mn rail steel. The casting speed was 0.75 m / min, the continuous pouring heat was the 10th, the tundish superheat was 48°C, the mold electromagnetic stirring was disabled, and the electromagnetic stirring process parameters at the end of solidification were 450 A, 5.5 Hz, and 18 mm reduction.

[0022] After production was completed, the ingot quality was inspected and the pickling and etching macro-rating results showed that both central segregation and central porosity were graded 0, with no central shrinkage cavities. The non-metallic inclusion inspection pass rate was 100%, fully meeting rail standards. The continuous casting time was reduced by 12% compared to conventional processes, and the number of continuous casting furnaces increased by three, resulting in a reduction of 16 yuan per ton in overall costs.

[0023] Example 3

[0024] In this example, a 280 mm x 380 mm cross-section billet was continuously cast in a ladle with a nominal capacity of 120 tons. The steel grade used was U75V rail steel. The casting speed was 0.75 m / min, the first heat was poured, the tundish superheat was 50°C, the mold electromagnetic stirring was disabled, and the electromagnetic stirring process parameters at the end of solidification were 480 A, 6.0 Hz, and a reduction of 19 mm.

[0025] After production, the quality of the continuous casting billets was inspected. For the macrostructure rating after pickling and corrosion, both the central segregation and central porosity were rated as grade 0, and there was no central shrinkage cavity. The qualified rate of non-metallic inclusions inspection was 99.5%, fully meeting the requirements of the rail standard. The continuous casting pouring time was reduced by 15% compared with the conventional process, the number of consecutive casting furnaces per casting heat was increased by 4 furnaces, and the comprehensive cost was reduced by 18 yuan per ton.

[0026] Example 4

[0027] In this example, on a ladle with a nominal capacity of 120 tons, the continuous casting billet cross-section was 280mm×320mm, and the steel grade for smelting was 900A rail steel. The continuous casting speed was 0.79m / min. For the first furnace of the casting heat, the superheat in the tundish was 55°C, the electromagnetic stirring in the mold was turned off, and the process parameters of electromagnetic stirring at the solidification end were a current of 450A, a frequency of 6.5Hz, and a reduction amount of 20mm.

[0028] After production, the quality of the continuous casting billets was inspected. For the macrostructure rating after pickling and corrosion, both the central segregation and central porosity were rated as grade 0, and there was no central shrinkage cavity. The qualified rate of non-metallic inclusions inspection was 100%, fully meeting the requirements of the rail standard. The continuous casting pouring time was reduced by 16% compared with the conventional process, the number of consecutive casting furnaces per casting heat was increased by 4 furnaces, and the comprehensive cost was reduced by 19 yuan per ton.

[0029] Example 5

[0030] In this example, on a ladle with a nominal capacity of 120 tons, the continuous casting billet cross-section was 280mm×320mm, and the steel grade for smelting was GCr15 bearing steel. The continuous casting speed was 0.75m / min. For the 13th furnace of the continuous casting heat, the superheat in the tundish was 45°C, the electromagnetic stirring in the mold was turned off, and the process parameters of electromagnetic stirring at the solidification end were a current of 500A, a frequency of 5.5Hz, and a reduction amount of 17mm.

[0031] After production, the quality of the continuous casting billets was inspected. For the macrostructure rating after pickling and corrosion, both the central segregation and central porosity were rated as grade 0, and there was no central shrinkage cavity. The qualified rate of non-metallic inclusions inspection was 99.7%, fully meeting the requirements of the product standard. The continuous casting pouring time was reduced by 15% compared with the conventional process, the number of consecutive casting furnaces per casting heat was increased by 4 furnaces, and the comprehensive cost was reduced by 15 yuan per ton.

[0032] Example 6

[0033] In this example, on a ladle with a nominal capacity of 120 tons, the continuous casting billet cross-section was 280mm×320mm, and the steel grade for smelting was 82B steel for steel strand. The continuous casting speed was 0.79m / min. For the 20th furnace of the continuous casting heat, the superheat in the tundish was 47°C, the electromagnetic stirring in the mold was turned off, and the process parameters of electromagnetic stirring at the solidification end were a current of 480A, a frequency of 6.0Hz, and a reduction amount of 16mm.

[0034] After production, the quality of the continuous casting billets was inspected. For the macrostructure rating of the pickled and etched billets, the central segregation and central porosity were both grade 0, there was no central shrinkage cavity, and the qualified rate of non-metallic inclusions inspection was 99.7%, fully meeting the requirements of the product standard. The continuous casting pouring time was reduced by 18% compared with the conventional process, the number of consecutive casting heats in a casting campaign was increased by 3 heats, and the comprehensive cost was reduced by 14 yuan per ton.

[0035] Example 7

[0036] In this example, a ladle with a nominal capacity of 120 tons was used. The cross-section of the continuous casting billet was 280 mm × 380 mm, and the steel grade for smelting was Z15 bearing steel. The continuous casting speed was 0.75 m / min, the 12th heat in a casting campaign, the superheat of the tundish was 50 °C, the electromagnetic stirring in the mold was turned off, and the process parameters of the electromagnetic stirring at the solidification end were a current of 500 A, a frequency of 5.5 Hz, and a reduction amount of 19 mm.

[0037] After production, the quality of the continuous casting billets was inspected. For the macrostructure rating of the pickled and etched billets, the central segregation and central porosity were both grade 0, there was no central shrinkage cavity, and the qualified rate of non-metallic inclusions inspection was 100%, fully meeting the requirements of the product standard. The continuous casting pouring time was reduced by 20% compared with the conventional process, the number of consecutive casting heats in a casting campaign was increased by 5 heats, and the comprehensive cost was reduced by 22 yuan per ton.

[0038] Example 8

[0039] In this example, a ladle with a nominal capacity of 120 tons was used. The cross-section of the continuous casting billet was 280 mm × 380 mm, and the steel grade for smelting was 72A wire rod steel. The continuous casting speed was 0.70 m / min, the 16th heat in a casting campaign, the superheat of the tundish was 45 °C, the electromagnetic stirring in the mold was turned off, and the process parameters of the electromagnetic stirring at the solidification end were a current of 450 A, a frequency of 5.5 Hz, and a reduction amount of 20 mm.

[0040] After production, the quality of the continuous casting billets was inspected. For the macrostructure rating of the pickled and etched billets, the central segregation and central porosity were both grade 0, there was no central shrinkage cavity, and the qualified rate of non-metallic inclusions inspection was 100%, fully meeting the requirements of the product standard. The continuous casting pouring time was reduced by 15% compared with the conventional process, the number of consecutive casting heats in a casting campaign was increased by 4 heats, and the comprehensive cost was reduced by 17 yuan per ton.

Claims

1. A method for producing high-carbon steel continuous casting billets with large cross-sections at low cost and high efficiency, characterized in that, During continuous casting, the casting speed is 0.75 - 0.79 m / min; at the same time, the electromagnetic stirring in the mold is cancelled, and electromagnetic strong stirring is started at the end of solidification and the soft reduction process is adopted; For the first ladle of the ladle superheat casting campaign, it is controlled at 50 - 55 °C, and for the continuous casting ladles, it is controlled at 41 - 50 °C; The cross-sectional specifications of the large-section continuous casting billet are 280×320 mm or 280 mm×380 mm; The current intensity of the electromagnetic strong stirring at the end of solidification is 450 - 500 A, and the frequency is 5.5 - 6.5 Hz; The reduction amount of the soft reduction process is 15 - 20 mm.