A smelting method for controlling oxygen content in high-sulfur high-oxygen free-cutting steel at low cost

Abstract

The application discloses a smelting method for controlling oxygen content in low-cost high-sulfur high-oxygen free-cutting steel, which comprises the following steps: converter or electric furnace smelting-LF refining-continuous casting; in the converter or electric furnace smelting step, silicon carbide and lime are added for pre-deoxidization and slag washing during tapping; in the LF refining step, after the molten steel enters a station and oxygen is determined, silicon carbide and lime, or silicon carbide, lime and fluorite are added for slagging and diffusion deoxidization; soft argon blowing is performed at the end of the LF refining; the smelting method is low in cost, avoids the intensified wear of tools in the cutting process caused by hard Al2O3 inclusions in aluminum deoxidization, and avoids the intensified wear of tools in the cutting process caused by silicate inclusions in silicon-manganese and silicon-iron precipitation deoxidization; according to the smelting method, the MnS inclusions in the cast blank are all in a spindle shape, the spindle shape is helpful to improve the free-cutting performance of the steel, and no oxide inclusions exist in the steel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, specifically relating to a low-cost smelting method for controlling the oxygen content in high-sulfur, high-oxygen free-cutting steel. Background Technology

[0002] Free-cutting steels are widely used in the automotive industry, home appliances, office and electronic equipment sectors due to their excellent machinability, which can reduce machining costs by 20%-40%. MnS inclusions in free-cutting steels have a significant impact on their machinability, and it is believed that controlling the oxygen content in the steel is beneficial for the formation of spindle-shaped MnS, thus improving machinability. However, under high oxygen content conditions, inappropriate deoxidation methods, while promoting the formation of favorable MnS morphology, may also promote the formation of oxide inclusions in the steel.

[0003] Chinese patent document CN107299271A discloses a smelting process for low-carbon, high-sulfur free-cutting steel. The process is characterized by: adding 1.2-2.0 kg / t of aluminum blocks to the converter for deoxidation based on the endpoint oxygen level; using 0-50 m of aluminum wire and 100-200 m of calcium wire for precipitation deoxidation during the refining process; bottom stirring at 100-200 L / min; and adding 10-20 kg of aluminum wire, 80-100 kg of barium-silicon calcium, and 0.3-0.7 kg / t of ferrosilicon for diffusion deoxidation. This process, using aluminum for deoxidation, not only has high smelting costs but also easily degrades the active oxygen in the steel to an excessively low level, forming a large amount of Al2O3 inclusions, which exacerbates tool wear during the cutting process of free-cutting steel.

[0004] Chinese patent document CN114752854A discloses a deoxidation and alloying method for smelting free-cutting steel. The method is characterized by: no deoxidizer being added during the converter tapping process; the addition of ferrosilicon manganese when the steel is 1 / 4 full; the addition of low-carbon ferromanganese at the end of tapping; and the addition of lime as slag. In the LF refining process, calcium carbide is used for slag surface deoxidation based on the oxygen content. This method, by not adding a deoxidizer during tapping, results in high oxygen content in the molten steel, which to some extent reduces the yield of ferrosilicon manganese and low-carbon ferromanganese alloys, increasing alloying costs. Furthermore, the excessive addition of ferrosilicon manganese alloys leads to an increase in silicon content in the steel, increasing its hardness but reducing the machinability of the free-cutting steel. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost smelting method for controlling the oxygen content in high-sulfur, high-oxygen free-machining steel. This smelting method is low-cost and avoids the accelerated wear of cutting tools caused by hard Al2O3 inclusions resulting from aluminum deoxidation, as well as the accelerated wear of cutting tools caused by silicate inclusions resulting from silicon manganese and silicon ferrosilicon precipitation deoxidation. In the slab obtained by the smelting method provided by this invention, the MnS inclusions are all in a spindle-shaped morphology. This morphology helps to improve the machinability of the steel, and the inclusion level in the steel is controlled at 0-0.5.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A low-cost smelting method for controlling the oxygen content in high-sulfur, high-oxygen free-cutting steel, the smelting method comprising the following steps: converter or electric furnace smelting—LF refining—continuous casting;

[0008] In the converter or electric furnace smelting process, silicon carbide and quicklime are added during the tapping process for pre-deoxidation and slag washing.

[0009] In the LF refining process, after the molten steel enters the station and the oxygen is determined, silicon carbide and quicklime, or silicon carbide, quicklime and fluorite are added to form slag and perform diffusion deoxidation. At the end of the LF refining process, soft argon blowing is performed.

[0010] In the converter or electric furnace smelting process, the tapping temperature is 1630-1660℃, and the tapping carbon is controlled within the range of 0.03≤[C]≤0.05%.

[0011] In the converter or electric furnace smelting process, when the tapped carbon is controlled at 0.03≤[C]≤0.04%, 0.8-1.0 kg / t silicon carbide and 2.5-3.5 kg / t quicklime are added during the tapping process for deoxidation and slag washing;

[0012] When the carbon content of the tapped steel is controlled at 0.04 < [C] ≤ 0.05%, 0.6-0.8 kg / t silicon carbide and 2.0-2.5 kg / t quicklime are added during the tapping process for deoxidation and slag washing.

[0013] In the LF refining process, after the molten steel enters the station, it is heated to above 1560℃ to determine its oxygen content. When the free oxygen content of the molten steel is 65ppm < [O] ≤ 85ppm, 0.3-0.4 kg / t silicon carbide, 2.0-3.0 kg / t quicklime, and 0.3-0.5 kg / t fluorite are added for slag formation and diffusion deoxidation. When the free oxygen content of the molten steel is 40ppm ≤ [O] ≤ 65ppm, 0.2-0.3 kg / t silicon carbide and 1.0-2.0 kg / t quicklime are added for slag formation and diffusion deoxidation.

[0014] At the end of LF refining, the molten steel is subjected to oxygen determination. When the free oxygen content of the molten steel is 60ppm < [O] ≤ 80ppm, the soft argon blowing time is 15-20min; when the free oxygen content of the molten steel is 40ppm ≤ [O] ≤ 60ppm, the soft argon blowing time is 10-15min.

[0015] The high-sulfur, high-oxygen free-cutting steel contains ≤0.01% silicon by mass, 0.30-0.40% sulfur by mass, ≤0.002% aluminum by mass, and 120ppm-160ppm total oxygen content.

[0016] The present invention also provides a high-sulfur, high-oxygen free-cutting steel obtained by the smelting method described in the present invention, wherein the MnS in the high-sulfur, high-oxygen free-cutting steel is spindle-shaped and there are no oxide inclusions in the steel.

[0017] The smelting method provided by this invention involves adding silicon carbide and quicklime for pre-deoxidation and slag washing during the tapping process in a converter or electric furnace. In the LF refining step, silicon carbide and quicklime, or silicon carbide, quicklime, and fluorite, are added for slag formation and diffusion deoxidation. At the end of LF refining, soft argon blowing is performed. This method has low smelting costs and avoids the increased wear on cutting tools caused by hard Al2O3 inclusions resulting from aluminum deoxidation, as well as the increased wear on cutting tools caused by silicate inclusions resulting from silicon manganese and silicon ferrosilicon precipitation deoxidation. Furthermore, this invention employs different oxygen control methods according to different steel conditions, ensuring that the oxygen content of the molten steel in different processes remains stable within the required range, guaranteeing product quality stability. At the end of LF refining, the soft argon blowing time is adjusted according to the different oxygen contents of the molten steel. This serves two purposes: firstly, to homogenize the composition and temperature of the molten steel and remove residual oxide-like non-metallic inclusions; and secondly, to facilitate the removal of gases from the molten steel in high-oxygen free-cutting steels, reducing the impact of CO gas on surface defects of the cast billet.

[0018] The slab obtained by the smelting method provided by the present invention, after rolling, has MnS inclusions in the rolled material in a spindle shape. This shape helps to improve the machinability of the steel, and there are no oxide inclusions in the steel. Attached Figure Description

[0019] Figure 1 The image shows the microstructure of the high-sulfur, high-oxygen free-cutting steel in Example 1. The black part in the image represents MnS.

[0020] Figure 2 This is a microstructure diagram of the high-sulfur, high-oxygen free-cutting steel in Example 2;

[0021] Figure 3 This is a microstructure diagram of the high-sulfur, high-oxygen free-cutting steel in Example 3;

[0022] Figure 4The image shows the microstructure of the high-sulfur, high-oxygen free-cutting steel in Comparative Example 1.

[0023] Figure 5 The image shows the microstructure of the high-sulfur, high-oxygen free-cutting steel in Comparative Example 2.

[0024] Figure 6 This is a schematic diagram showing the "C" shaped chip morphology of the high-sulfur, high-oxygen free-cutting steel after turning in Example 1. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the embodiments.

[0026] Example 1

[0027] A low-cost smelting method for controlling the oxygen content in high-sulfur, high-oxygen free-machining steel includes the following steps:

[0028] (1) 120t converter smelting: the converter tapping temperature is 1660℃, the carbon content of the tapping steel is 0.035%, and 120kg silicon carbide and 360kg quicklime are added during the tapping process for pre-deoxidation and slag washing;

[0029] (2) 120t LF refining: After the molten steel enters the station, it is rapidly heated to 1580℃. The oxygen content of the molten steel is 60ppm. 24kg silicon carbide and 120kg quicklime are added for slag formation and diffusion deoxidation. The LF refining is completed. The oxygen content of the molten steel is 65ppm. The soft blowing argon time is 15min and the soft blowing flow rate is 150NL / min.

[0030] (3) 180×180mm continuous casting: tundish superheat 25℃, casting speed 1.5m / min.

[0031] Example 2

[0032] A low-cost smelting method for controlling the oxygen content in high-sulfur, high-oxygen free-machining steel includes the following steps:

[0033] (1) 120t converter smelting: the converter tapping temperature is 1655℃, the tapping carbon content is 0.048%, and 72kg silicon carbide and 240kg quicklime are added during the tapping process for pre-deoxidation and slag washing;

[0034] (2) 120t LF refining: After the molten steel enters the station, it is rapidly heated to 1585℃. The oxygen content of the molten steel is 66ppm. 36kg silicon carbide, 240kg quicklime and 36kg fluorite are added for slag formation and diffusion deoxidation. The LF refining is completed. The oxygen content of the molten steel is 55ppm. The soft blowing argon time is 12min and the soft blowing flow rate is 120NL / min.

[0035] (3) 180×180mm continuous casting: tundish superheat 30℃, casting speed 1.4m / min.

[0036] Example 3

[0037] A low-cost smelting method for controlling the oxygen content in high-sulfur, high-oxygen free-machining steel includes the following steps:

[0038] (1) 120t converter smelting: the converter tapping temperature is 1638℃, the carbon content of the tapping steel is 0.042%, and 72kg silicon carbide and 240kg quicklime are added during the tapping process for pre-deoxidation and slag washing;

[0039] (2) 120t LF refining: After the molten steel enters the station, it is rapidly heated to 1580℃. The oxygen content of the molten steel is 73ppm. 48kg silicon carbide, 360kg quicklime and 60kg fluorite are added for slag formation and diffusion deoxidation. The LF refining is completed. The oxygen content of the molten steel is 70ppm. The soft blowing argon time is 18min and the soft blowing flow rate is 180NL / min.

[0040] (3) 180×180mm continuous casting: tundish superheat 28℃, casting speed 1.4m / min.

[0041] Comparative Example 1

[0042] A method for smelting high-sulfur, high-oxygen free-machining steel includes the following steps:

[0043] (1) 120t converter smelting: converter tapping temperature 1650℃, tapping carbon content 0.040%, and additives during tapping process. 300 kg of quicklime and 200 kg of aluminum ferrophosphate were used for pre-deoxidation and slag washing;

[0044] (2) 120t LF refining: After the molten steel enters the station, it is energized for 10 minutes, and the oxygen content of the molten steel is 53ppm. Then, [the following steps are added] 40kg silicon Iron powder and 30kg aluminum granules Diffusion deoxidation was carried out on the slag surface. After LF refining, the oxygen content of the molten steel was 48 ppm. The soft blowing argon time was 10 min and the soft blowing flow rate was 150 NL / min.

[0045] (3) 180×180mm continuous casting: tundish superheat 23℃, casting speed 1.5m / min.

[0046] Comparative Example 2

[0047] A method for smelting high-sulfur, high-oxygen free-machining steel includes the following steps:

[0048] (1) 120t converter smelting: converter tapping temperature 1630℃, tapping carbon content 0.048%, 240kg of quicklime and... 500kg silicon manganese Pre-deoxidation and slag washing are performed;

[0049] (2) 120t LF refining: After the molten steel enters the station, it is energized for 12 minutes, and the oxygen content of the molten steel is 63ppm. Then, [the following steps are added] 50kg silicon Iron powder Diffusion deoxidation was carried out on the slag surface with 150 kg of quicklime. LF refining was completed, and the oxygen content of the molten steel was 62 ppm. Soft blowing argon time... 12 min, soft blow flow rate 160NL / min.

[0050] (3) 180×180mm continuous casting: tundish superheat 27℃, casting speed 1.4m / min.

[0051] The weight percentages of some components in the high-sulfur, high-oxygen free-cutting steels obtained by smelting in the above embodiments and comparative examples are shown in Table 1.

[0052] Table 1

[0053] Si (%) S(％) Al(％) C(％) Total oxygen (ppm) Example 1 0.001 0.36 0.001 0.062 130 Example 2 0.002 0.35 0.001 0.058 140 Example 3 0.001 0.36 0.001 0.055 138 Comparative Example 1 0.012 0.34 0.005 0.060 98 Comparative Example 2 0.031 0.36 0.002 0.053 105

[0054] The oxide inclusion levels in the high-sulfur, high-oxygen free-cutting steels obtained from the above embodiments and comparative examples are shown in Table 2.

[0055] Table 2

[0056]

[0057]

[0058] As can be seen from Table 2, the sulfides obtained by the smelting in the example have a grade of 0-0.5 for coarse B, fine B, coarse C, fine C and impurities; while the sulfides obtained by the smelting in the comparative example have a grade of 0.5-1.0 for coarse B, fine B, coarse C, fine C and impurities.

[0059] The morphology of MnS in the high-sulfur, high-oxygen free-cutting steels obtained from Examples 1-3 and Comparative Examples 1-2 is shown in the appendix. Figure 1-5 As shown.

[0060] As can be seen from the figure, the sulfides obtained by rolling after smelting in the example are all spindle-shaped, which helps to improve the machinability of steel; the sulfides obtained by rolling after smelting in the comparative example are mostly long and thin strips, which is not conducive to the machinability of steel.

[0061] The above detailed description of a low-cost smelting method for controlling oxygen content in high-sulfur, high-oxygen, free-cutting steel, with reference to the embodiments, is illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A low-cost smelting method for controlling the oxygen content in high-sulfur, high-oxygen free-machining steel, characterized in that, The smelting method includes the following steps: converter or electric furnace smelting—LF refining—continuous casting; In the converter or electric furnace smelting process, silicon carbide and quicklime are added during the tapping process for pre-deoxidation and slag washing. In the LF refining process, after the molten steel enters the station and the oxygen is determined, silicon carbide and quicklime, or silicon carbide, quicklime and fluorite are added for slag formation and diffusion deoxidation. At the end of the LF refining process, soft argon blowing is carried out. In the converter or electric furnace smelting process, the tapping temperature is 1630-1660℃, and the tapping carbon content is controlled within the range of 0.03≤[C]≤0.05%; In the converter or electric furnace smelting process, when the tapped carbon is controlled at 0.03 ≤ [C] ≤ 0.04%, 0.8-1.0 kg / t silicon carbide and 2.5-3.5 kg / t quicklime are added during the tapping process for deoxidation and slag washing; when the tapped carbon is controlled at 0.04 < [C] ≤ 0.05%, 0.6-0.8 kg / t silicon carbide and 2.0-2.5 kg / t quicklime are added during the tapping process for deoxidation and slag washing. In the LF refining process, after the molten steel enters the station, it is heated to above 1560℃ to determine its oxygen content. When the free oxygen content of the molten steel is 65ppm < [O] ≤ 85ppm, 0.3-0.4 kg / t silicon carbide, 2.0-3.0 kg / t quicklime, and 0.3-0.5 kg / t fluorite are added for slag formation and diffusion deoxidation. When the free oxygen content of the molten steel is 40 ppm ≤ [O] ≤ 65 ppm, 0.2-0.3 kg / t silicon carbide and 1.0-2.0 kg / t quicklime are added for slag formation and diffusion deoxidation. At the end of LF refining, the molten steel is subjected to oxygen determination. When the free oxygen content of the molten steel is 60 ppm < [O] ≤ 80 ppm, the soft argon blowing time is 15-20 min; when the free oxygen content of the molten steel is 40 ppm ≤ [O] ≤ 60 ppm, the soft argon blowing time is 10-15 min.

2. The smelting method according to claim 1, characterized in that, The high-sulfur, high-oxygen free-cutting steel contains ≤0.01% silicon by mass, 0.30-0.40% sulfur by mass, ≤0.002% aluminum by mass, and 120-160 ppm total oxygen.

3. High-sulfur, high-oxygen free-cutting steel obtained by the smelting method described in claim 1 or 2.

4. The high-sulfur, high-oxygen free-cutting steel according to claim 3, characterized in that, The high-sulfur, high-oxygen, free-cutting steel billet, after rolling, exhibits spindle-shaped MnS inclusions, and the oxide inclusion level in the steel is controlled at 0-0.5.

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