A method for controlling oxygen and forming slag to reduce B-type and C-type inclusions in high-sulfur free-cutting steel

Abstract

The application discloses an oxygen control and slagging method for reducing B-type and C-type inclusions in high-sulfur free-cutting steel, wherein no silicon-containing and aluminum-containing deoxidizing materials are added into molten steel in a smelting process, and silicon-iron powder and aluminum particles are floated on a slag surface in a LF refining process; a higher converter blowing end temperature and a molten steel argon blowing station temperature are controlled, carbon powder is firstly used for pre-deoxidation after the furnace, and only power is used for temperature rising in the alloying stage in the refining process, so that large molten steel temperature fluctuation and large oxygen content fluctuation in the refining process are avoided; lime and calcium carbide are used for slag washing in the converter tapping process, and non-metallic inclusions in the molten steel are preliminarily reduced; lime, silicon-iron powder and aluminum particles are added for slagging in the LF refining process, and the adsorption capacity of the B-type and C-type inclusions of the top slag of the ladle is further improved; and the method can stably control the B-type and C-type inclusions in the high-sulfur free-cutting steel to be 0 grade.

Description

Technical Field

[0001] This invention belongs to the technical field of high-sulfur free-cutting steel, specifically relating to a method for oxygen control and slag formation to reduce B-type and C-type inclusions in high-sulfur free-cutting steel. Background Technology

[0002] High-sulfur free-cutting steel is a type of steel with high oxygen content. Under high oxygen content conditions, while promoting the formation of the favorable MnS form, inappropriate oxygen control methods and slag-forming methods may also promote the formation of B and C type inclusions in the steel. This will lead to increased tool wear and lathe cutting costs during the cutting process of free-cutting steel, such as increased wear on lathes and cutting tools.

[0003] Existing patents on free-cutting steel mainly involve methods to control the morphology of sulfides in steel by adding free-cutting steel elements or by controlled rolling and cooling. For example, Chinese patent CN116640979A discloses a method for regulating the morphology of MnS in sulfur-based free-cutting steel. This patent involves adding a titanium-containing alloy to the molten steel during the smelting process, controlling the Ti content in the molten steel to be 0.007-0.20 wt% and the N content to be 0.002-0.01 wt%; and controlling the Ti / Mn mass ratio in the molten steel to be 0.01-15, the Ti / N mass ratio to be 6-20, and the Ti / S mass ratio to be 2-10, thereby regulating the morphology of MnS in sulfur-based free-cutting steel.

[0004] Chinese patent CN112404126A discloses a controlled rolling and cooling method for improving the sulfide morphology of free-cutting steel wire rod. This patent involves heating the steel billet at a temperature not exceeding 950℃ for 3 to 4 hours; rolling the roughing, finishing, pre-finishing, and finishing mills at a temperature not exceeding 850℃; then spinning the rolled wire rod into coils using a wire spinneret; and finally controlling the cooling of the wire rod using a Steyrmo controlled cooling line. This method suppresses the elongation of sulfides during the rolling process of the steel billet, thereby improving the sulfide morphology of free-cutting steel wire rod.

[0005] However, no existing technology has disclosed a method for controlling type B and type C inclusions in free-cutting steel through oxygen control and slag formation. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel. This method can stably control the level of type B and type C inclusions in high-sulfur free-cutting steel to level 0.

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

[0008] A method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel, the method comprising:

[0009] (1) Converter smelting: oxygen is blown from the top of the converter to smelt the iron to the final temperature of 1650-1700℃, and the final C content is 0.03-0.05%; carbon powder is added during the tapping process, ferrous sulfate is added for alloying, and lime and calcium carbide are added for slag washing. The oxygen at the argon blowing station after the furnace is kept at 50-80ppm.

[0010] (2) LF refining: After the molten steel enters the station, lime is added and electricity is applied. During the electricity application process, ferrosilicon powder and aluminum particles are introduced and diffused on the slag surface for deoxidation. The temperature of the molten steel is kept stable at 1595-1615℃ throughout the LF refining process, and the oxygen content of the molten steel is kept at 45-60ppm at the end of the LF refining process.

[0011] (3) Continuous casting: The tundish is covered with a double layer of covering agent, and the oxygen content of the molten steel in the tundish is stable at 45-55ppm in the early, middle and late stages of continuous casting.

[0012] In step (1), the amount of carbon powder added is 0.5-0.7 kg / t steel.

[0013] In step (1), the amount of quicklime added is 3-4 kg / t steel, and the amount of calcium carbide added is 0.4-0.5 kg / t steel.

[0014] In step (2), the amount of quicklime added is 1.5-2.5 kg / t.

[0015] In step (2), the amount of ferrosilicon powder added is 0.2-0.3 kg / t, and the amount of aluminum particles added is 0.4-0.7 kg / t.

[0016] In step (2), the number of power supply times is ≤3 times and the total power supply time is ≤10min. The power supply time is 5-6min during the stage of adding slag material and supplementing alloy. The temperature of molten steel is kept stable within the range of 80-100℃ from the liquidus line throughout the LF refining process.

[0017] In step (2), the composition of the LF refining top slag is: 15-18% SiO2, 13-16% Al2O3, 32-35% CaO, 4-6% FeO, 15-18% MnO, and 6-8% MgO.

[0018] In step (3), the first layer of covering agent is an acidic covering agent, and the second layer of covering agent is carbonized rice husk.

[0019] The inclusion grades B and C in the high-sulfur free-cutting steel are both grade 0.

[0020] The high-sulfur free-cutting steel comprises the following chemical composition by weight percentage: C 0.05-0.07%, Si≤0.005%, S 0.30-0.50%, Al≤0.002%.

[0021] The oxygen control and slag formation method for reducing B and C inclusions in high-sulfur free-cutting steel provided by this invention achieves deoxidation control through the following methods: no silicon- or aluminum-containing deoxidizing materials are added to the molten steel during the smelting process; ferrosilicon powder and aluminum particles are floated onto the slag surface during the LF refining process; a relatively high converter blowing endpoint temperature and the temperature of the molten steel argon blowing station are controlled; carbon powder is used for pre-deoxidation after the furnace; and the refining process only involves heating by electricity during the slag addition and alloying stages, thus avoiding large fluctuations in molten steel temperature and oxygen content during the refining process. Specifically: Converter process: tapping temperature controlled at 1650-1700℃, tapping carbon content controlled at 0.03-0.05%, carbon powder added at 0.5-0.7 kg / t during tapping, oxygen content in molten steel at the argon blowing station at 50-80 ppm, and molten steel temperature at 1610-1650℃; LF refining process: power supply ≤ 3 times, and total power supply time ≤ 10 min, power supply for 5-6 min during slag-forming material addition and alloy replenishment stages, molten steel temperature stabilized at 80-100℃ above the liquidus throughout the LF refining process, and oxygen content in molten steel stabilized at 45-60 ppm at the end of the LF refining process; Continuous casting process: double-layer covering agent used in the tundish, the first layer being an acidic covering agent and the second being carbonized rice husk, and oxygen content in molten steel stabilized at 45-55 ppm in the early, middle, and late stages of continuous casting.

[0022] Slag formation is carried out using the following methods: During the converter tapping process, quicklime and calcium carbide are used for slag washing; during the LF refining process, quicklime, ferrosilicon powder, and aluminum particles are added for slag formation. Specifically: Converter process: 3-4 kg / t of quicklime and 0.4-0.5 kg / t of calcium carbide are added during tapping; LF refining process: 1.5-2.5 kg / t of quicklime is added upon entering the slag, and 0.2-0.3 kg / t of ferrosilicon powder and 0.4-0.7 kg / t of aluminum particles are floated into the slag surface for diffusion deoxidation, while preventing ferrosilicon powder and aluminum particles from entering the molten steel. The composition of the LF refining top slag is: 15-18% SiO2, 13-16% Al2O3, 32-35% CaO, 4-6% FeO, 15-18% MnO, and 6-8% MgO.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. No silicon- or aluminum-containing deoxidizing materials were added to the molten steel during the smelting process. During the LF refining process, ferrosilicon powder and aluminum particles were floated on the slag surface to prevent them from oxidizing with the molten steel and forming silicate (C-type) and alumina (B-type) inclusions.

[0025] 2. Control the high final temperature of converter blowing and the temperature of the argon blowing station for molten steel. Carbon powder is used for pre-deoxidation after the furnace. During the refining process, electricity is only applied to raise the temperature during the slag addition and alloying stages. This avoids the risks of large fluctuations in molten steel temperature and oxygen content during the refining process, as well as the need to add silicon- or aluminum-containing deoxidizing materials.

[0026] 3. During the converter tapping process, quicklime and calcium carbide are used for slag washing to initially reduce non-metallic inclusions in the molten steel. During the LF refining process, quicklime, ferrosilicon powder, and aluminum particles are added to form slag, which further improves the adsorption capacity of ladle top slag for Class B and Class C inclusions. At the same time, it avoids the phenomenon of ladle top slag returning oxygen to the molten steel during the continuous casting process, which would lead to secondary oxidation of the molten steel and the generation of Class B and Class C inclusions.

[0027] 4. The high-sulfur free-cutting steel produced by this process has low levels of B and C inclusions, the process is simple and easy to operate, and the production cost is low. Detailed Implementation

[0028] This invention provides a method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel, the method comprising:

[0029] (1) Converter smelting: oxygen is blown from the top of the converter to smelt the iron to the final temperature of 1650-1700℃, and the final C content is 0.03-0.05%; carbon powder is added during the tapping process, ferrous sulfate is added for alloying, and lime and calcium carbide are added for slag washing. The oxygen at the argon blowing station after the furnace is kept at 50-80ppm.

[0030] (2) LF refining: After the molten steel enters the station, lime is added and electricity is applied. During the electricity application process, ferrosilicon powder and aluminum particles are introduced and diffused on the slag surface for deoxidation. The temperature of the molten steel is kept stable at 1595-1615℃ throughout the LF refining process, and the oxygen content of the molten steel is kept at 45-60ppm at the end of the LF refining process.

[0031] (3) Continuous casting: The tundish is covered with a double layer of covering agent, and the oxygen content of the molten steel in the tundish is stable at 45-55ppm in the early, middle and late stages of continuous casting.

[0032] In step (1), the amount of carbon powder added is 0.5-0.7 kg / t steel.

[0033] In step (1), the amount of quicklime added is 3-4 kg / t steel, and the amount of calcium carbide added is 0.4-0.5 kg / t steel.

[0034] In step (2), the amount of quicklime added is 1.5-2.5 kg / t.

[0035] In step (2), the amount of ferrosilicon powder added is 0.2-0.3 kg / t, and the amount of aluminum particles added is 0.4-0.7 kg / t.

[0036] In step (2), the number of power supply times is ≤3 times and the total power supply time is ≤10min. The power supply time is 5-6min during the stage of adding slag material and supplementing alloy. The temperature of molten steel is kept stable within the range of 80-100℃ from the liquidus line throughout the LF refining process.

[0037] In step (2), the composition of the LF refining top slag is: 15-18% SiO2, 13-16% Al2O3, 32-35% CaO, 4-6% FeO, 15-18% MnO, and 6-8% MgO.

[0038] In step (3), the first layer of covering agent is an acidic covering agent, and the second layer of covering agent is carbonized rice husk.

[0039] The high-sulfur free-cutting steel comprises the following chemical composition by weight percentage: C 0.05-0.07%, Si≤0.005%, S 0.30-0.50%, Al≤0.002%.

[0040] The present invention will now be described in detail with reference to the embodiments.

[0041] Example 1

[0042] A method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel, wherein the chemical composition of the high-sulfur free-cutting steel, calculated by weight percentage, is: C 0.062%, Si 0.002%, S 0.40%, Al 0.001%. The method includes the following steps: 120t converter smelting—120t LF refining—billet continuous casting, the specific steps of which are as follows:

[0043] (1) Converter process: The top oxygen of the converter is blown to the molten iron to the final temperature of 1680℃, and the final C content is 0.032%; 75kg carbon powder is added during the tapping process, ferrous sulfate is added for alloying, and 400kg quicklime and 50kg calcium carbide are added for slag washing. The oxygen level at the argon blowing station after the furnace is set at 70ppm and the temperature is measured at 1635℃.

[0044] (2) LF refining process: After the molten steel enters the station, 200 kg of quicklime is added and the slag is energized for 5 minutes. During the energizing process, 30 kg of ferrosilicon powder and 60 kg of aluminum particles are floated into the slag surface for diffusion deoxidation. The composition of the top slag in LF refining is: 16% SiO2, 15% Al2O3, 33% CaO, 4% FeO, 16% MnO, and 7% MgO. The temperature of the molten steel is kept stable in the range of 1595-1615℃ throughout the LF refining process. The oxygen content of the molten steel is 52 ppm at the end of LF refining.

[0045] (3) Continuous casting process: The tundish is covered with a double layer of covering agent. The first layer is an acidic covering agent and the second layer is carbonized rice husk. The oxygen content of the molten steel in the tundish is 50, 50 and 49 ppm in the early, middle and late stages of continuous casting.

[0046] Example 2

[0047] A method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel, wherein the chemical composition of the high-sulfur free-cutting steel, calculated by weight percentage, is: C 0.065%, Si 0.003%, S 0.38%, Al 0.001%. The method includes the following steps: 120t converter smelting—120t LF refining—billet continuous casting, the specific steps of which are as follows:

[0048] (1) Converter process: oxygen is blown from the top of the converter to smelt the iron to the final temperature of 1650℃, and the final C content is 0.038%; 80kg of carbon powder is added during the tapping process, ferrous sulfate is added for alloying, and 420kg of quicklime and 54kg of calcium carbide are added for slag washing. The oxygen level at the argon blowing station after the furnace is set at 50ppm and the temperature is measured at 1640℃.

[0049] (2) LF refining process: After the molten steel enters the station, 240 kg of quicklime is added and the slag is energized for 6 minutes. During the energizing process, 26 kg of ferrosilicon powder and 50 kg of aluminum particles are floated into the slag surface for diffusion deoxidation. The composition of the top slag in LF refining is: 15% SiO2, 13% Al2O3, 34% CaO, 5% FeO, 16% MnO, and 6% MgO. The temperature of the molten steel is kept stable in the range of 1595-1615℃ throughout the LF refining process. The oxygen content of the molten steel is 50 ppm at the end of the LF refining process.

[0050] (3) Continuous casting process: The tundish is covered with a double layer of covering agent. The first layer is an acidic covering agent and the second layer is carbonized rice husk. The oxygen content of the molten steel in the tundish is 48, 49 and 51 ppm in the early, middle and late stages of continuous casting.

[0051] Example 3

[0052] A method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel, wherein the chemical composition of the high-sulfur free-cutting steel, calculated by weight percentage, is: C: 0.068%, Si: 0.003%, S: 0.49%, Al: 0.002%. The method includes the following steps: 120t converter smelting—120t LF refining—billet continuous casting, the specific steps of which are as follows:

[0053] (1) Converter process: oxygen is blown from the top of the converter to smelt the iron to the final temperature of 1675℃, and the final C content is 0.041%; 80kg of carbon powder is added during the tapping process, ferrous sulfate is added for alloying, and 480kg of quicklime and 45kg of calcium carbide are added for slag washing. The oxygen at the argon station after the furnace is kept at 64ppm and the temperature is measured at 1645℃.

[0054] (2) LF refining process: After the molten steel enters the station, 300 kg of quicklime is added and the slag is energized for 7 minutes. During the energizing process, 35 kg of ferrosilicon powder and 80 kg of aluminum particles are floated into the slag surface for diffusion deoxidation. The composition of the top slag in LF refining is: 18% SiO2, 13% Al2O3, 35% CaO, 6% FeO, 15% MnO, and 6% MgO. The temperature of the molten steel is kept stable in the range of 1595-1615℃ throughout the LF refining process. The oxygen content of the molten steel is 48 ppm at the end of LF refining.

[0055] (3) Continuous casting process: The tundish is covered with a double layer of covering agent. The first layer is an acidic covering agent and the second layer is carbonized rice husk. The oxygen content of the molten steel in the tundish is 51, 50 and 48 ppm in the early, middle and late stages of continuous casting.

[0056] Comparative Example 1

[0057] A method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel, wherein the chemical composition of the high-sulfur free-cutting steel, calculated by weight percentage, is: C 0.05%, Si 0.025%, S 0.36%, Al 0.002%. The method includes the following steps: 120t converter smelting—120t LF refining—billet continuous casting, the specific steps of which are as follows:

[0058] (1) Converter process: Oxygen is blown from the top of the converter to refine the molten iron to the final temperature of 1660℃, with a final carbon content of 0.025%; 600 kg of oxygen is added during the tapping process. silicon manganese Iron sulfide was added for alloying, and 300 kg of quicklime was added for slag washing. The oxygen level at the argon blowing station after the furnace was set at 55 ppm, and the temperature was measured at 1610℃.

[0059] (2) LF refining process: After the molten steel enters the station, 100 kg of quicklime is added and the slag is energized for 5 minutes. During the energizing process, 40 kg of ferrosilicon powder and 30 kg of aluminum particles are floated into the slag surface for diffusion deoxidation. The composition of the top slag in LF refining is: 20% SiO2, 13% Al2O3, 30% CaO, 5% FeO, 18% MnO, and 8% MgO. The oxygen content of the molten steel is 42 ppm at the end of LF refining.

[0060] (3) Continuous casting process: The tundish is covered with a double layer of covering agent. The first layer is an acidic covering agent and the second layer is carbonized rice husk. The oxygen content of the molten steel in the tundish is 43, 45 and 45 ppm in the early, middle and late stages of continuous casting.

[0061] Comparative Example 2

[0062] A method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel, wherein the chemical composition of the high-sulfur free-cutting steel, calculated by weight percentage, is: C 0.056%, Si 0.01%, S 0.38%, Al 0.005%. The method includes the following steps: 120t converter smelting—120t LF refining—billet continuous casting, the specific steps of which are as follows:

[0063] (1) Converter process: oxygen is blown from the top of the converter to heat the molten iron to the final temperature of 1665℃, and the final C content is 0.030%; 450Kg of aluminum iron is added during the tapping process, ferrous sulfate is added for alloying, and 300kg of quicklime is added for slag washing. The oxygen level at the argon station after the furnace is set at 45PPm and the temperature is measured at 1610℃.

[0064] (2) LF refining process: After the molten steel enters the station, 150 kg of quicklime is added and the molten steel is energized for 5 minutes. During the energizing process, 30 kg of ferrosilicon powder is floated in for diffusion deoxidation. During the refining process, 40-80 kg of ferroaluminum is added to the molten steel for deoxidation. The composition of the top slag in LF refining is: 15% SiO2, 19% Al2O3, 30% CaO, 4% FeO, 15% MnO, and 9% MgO. The oxygen content of the molten steel is 40 ppm at the end of LF refining.

[0065] (3) Continuous casting process: The tundish is covered with a double layer of covering agent. The first layer is an acidic covering agent and the second layer is carbonized rice husk. The oxygen content of the molten steel in the tundish is 40, 42 and 42 ppm in the early, middle and late stages of continuous casting.

[0066] The inclusion levels of Class B and Class C in the high-sulfur free-cutting steels in the above embodiments and comparative examples are shown in Table 1.

[0067] Table 1 Non-metallic inclusion levels

[0068] B (rough) B Fine C coarse C fine Example 1 0 0 0 0 Example 2 0 0 0 0 Example 3 0 0 0 0 Comparative Example 1 0.5 0 1.5 1.0 Comparative Example 2 1.0 0.5 0.5 0.5

[0069] The above detailed description of a method for reducing type B and type C inclusions in high-sulfur free-cutting steel by referring to the embodiments is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, changes 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 method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel, characterized in that, The method includes: (1) Converter smelting: oxygen is blown from the top of the converter to smelt the iron to the final temperature of 1650-1700℃, and the final C content is 0.03-0.05%; carbon powder is added during the tapping process, ferrous sulfate is added for alloying, and lime and calcium carbide are added for slag washing. The oxygen at the argon blowing station after the furnace is kept at 50-80ppm. (2) LF refining: After the molten steel enters the station, lime is added and electricity is applied. During the electricity application process, ferrosilicon powder and aluminum particles are introduced and diffused on the slag surface for deoxidation. The temperature of the molten steel is kept stable at 1595-1615℃ throughout the LF refining process, and the oxygen content of the molten steel is kept at 45-60ppm at the end of the LF refining process. (3) Continuous casting: The tundish is covered with a double layer of covering agent, and the oxygen content of the molten steel in the tundish is stable at 45-55 ppm in the early, middle and late stages of continuous casting. In step (2), the number of power supply times is ≤3 times and the total power supply time is ≤10min. The power supply time is 5-6min during the stage of adding slag-forming materials and supplementing alloys. The temperature of molten steel is kept stable within the range of 80-100℃ from the liquidus line throughout the LF refining process. In step (2), the composition of the LF refining top slag is: 15-18% SiO2, 13-16% Al2O3, 32-35% CaO, 4-6% FeO, 15-18% MnO, and 6-8% MgO; In step (3), the first layer of covering agent is an acidic covering agent, and the second layer of covering agent is carbonized rice husk; The inclusion grades B and C in the high-sulfur free-cutting steel are both grade 0.

2. The method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel according to claim 1, characterized in that, In step (1), the amount of carbon powder added is 0.5-0.7 kg / t steel.

3. The method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel according to claim 1, characterized in that, In step (1), the amount of quicklime added is 3-4 kg / t steel, and the amount of calcium carbide added is 0.4-0.5 kg / t steel.

4. The method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel according to claim 1, characterized in that, In step (2), the amount of quicklime added is 1.5-2.5 kg / t.

5. The method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel according to claim 1, characterized in that, In step (2), the amount of ferrosilicon powder added is 0.2-0.3 kg / t, and the amount of aluminum particles added is 0.4-0.7 kg / t.

6. The method for oxygen control and slag formation to reduce type B and type C inclusions in high-sulfur free-cutting steel according to claim 1, characterized in that, The high-sulfur free-cutting steel comprises the following chemical composition by weight percentage: C 0.05-0.07%, Si≤0.005%, S0.30-0.50%, Al≤0.002%.