Method for smelting low-phosphorus steel from full waste steel electric furnace

Abstract

The invention discloses a method for smelting low-phosphorus steel from full waste steel through an electric furnace. The method comprises the procedures of waste steel burdening, electric furnace smelting and tapping. In the electric furnace smelting process, lime and dolomite are added to the bottom of a furnace before waste steel is fed into the furnace; in the smelting process, slagging materials including lime, dolomite and magnesium balls are added into a molten pool in batches; the content of FeO is controlled to be 20-25% at the smelting end point, and the basicity of slag is controlled to be 1.8-2.2. The method is easy to operate, the problem that the molten steel phosphorus content at the smelting end point is high is solved through measures of waste steel source control, deep dephosphorization in the smelting process, rephosphorization prevention and the like, and the phosphorus content at the end point is smaller than 0.004%.

Description

Technical Field

[0001] The invention relates to an electric arc furnace smelting method, in particular to a method for smelting low-phosphorus steel in an all-scrap steel electric furnace. Background Art

[0002] Phosphorus is a harmful element in steel. It exists in the form of low-melting-point compounds. Its melting point is in the hot working temperature range of steel, which reduces the steel's ability to resist deformation and causes cracks during thermal deformation. Phosphorus is easily segregated and aggregated between dendrites, existing in the form of Fe3P or Fe2P, forming a high-phosphorus brittle zone, which greatly reduces the plasticity and low-temperature impact toughness of steel, the so-called "cold brittle" phenomenon. In corrosive media, since phosphorus is distributed along the grain boundaries, corrosion develops along the grain boundaries, accelerating the corrosion rate of steel and reducing the corrosion resistance of steel.

[0003] Compared with the converter, electric furnace steelmaking has a higher ability to control the final temperature, carbon and phosphorus of molten steel. However, as the electric furnace smelting cycle is further shortened, the bottleneck problem encountered is how to quickly dephosphorize during the smelting process. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for smelting low-phosphorus steel in an all-scrap steel electric furnace, which can achieve rapid dephosphorization and control the phosphorus content of the steel to ≤0.004%.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for smelting low-phosphorus steel in an electric furnace using all scrap steel includes the steps of scrap steel batching, electric furnace smelting and steel tapping.

[0006] Furthermore, in the scrap steel batching process of the present invention, the scrap steel entering the furnace cannot contain materials with high phosphorus content such as pig iron blocks, and the scrap steel entering the furnace includes crushed material, small scrap steel, medium scrap steel, and heavy scrap steel. The weight ratio of the four types of scrap steel is crushed material: small scrap steel: medium scrap steel: heavy scrap steel = (1-1.5): (2.5-3): (3.5-4.5): (0.5-1).

[0007] Furthermore, the electric furnace smelting process of the present invention is as follows: before the scrap steel is put into the furnace, 6-10 kg / t of molten steel and 2-4 kg / t of molten steel are added to the furnace bottom; when the power is turned on for 5-8 minutes, 8-12 kg / t of molten steel is added; when the power is turned on for 14-17 minutes, 5-8 kg / t of molten steel and 6-8 kg / t of molten steel are added; when the power is turned on for 24-27 minutes, 5-8 kg / t of magnesium balls are added; the slag basicity at the end of smelting is 1.8-2.2, and the FeO content is controlled to be 20-25%.

[0008] Furthermore, the electric furnace smelting process of the present invention comprises: in the scrap steel melting stage, i.e. within 0 to 15 minutes of power-on, a voltage of 850 to 950 V and a current of 90 to 100 KA are used to quickly melt the scrap steel in the furnace; in the initial stage of molten pool heating, i.e. within 16 to 22 minutes of power-on, a voltage of 750 to 850 V and a current of 80 to 90 KA are used to control the heating rate of the molten pool and create good thermodynamic low temperature conditions for dephosphorization; in the middle and late stages of molten pool heating, i.e. within 22 to 33 minutes of power-on, a voltage of 800 to 100 V and a current of 90 to 100 KA are used to accelerate the heating rate of the molten steel in the furnace and quickly meet the steelmaking requirements.

[0009] Furthermore, in the steel-discharging process of the present invention, an infrared slag detection system is used to control the slag amount to ≤1kg / t molten steel.

[0010] The beneficial effects of adopting the above technical solution are: The present invention optimizes the scrap steel structure, adjusts the power supply parameters, controls the phosphorus content of the scrap steel entering the furnace from the source, and utilizes the low temperature conditions in the early stage of smelting to achieve rapid dephosphorization. At the same time, the addition ratio and timing of slag-making auxiliary materials are improved, the slag composition is adjusted, dephosphorization and phosphorus fixation are achieved, and phosphorus reversion is prevented during the smelting process, and finally the steel output [P] is controlled to be ≤0.004%. DETAILED DESCRIPTION

[0011] The present invention is further described in detail below in conjunction with specific implementation modes. Example 1

[0012] Taking a 130t electric arc furnace as an example, the method of smelting low-phosphorus steel in an all-scrap electric furnace includes the processes of scrap steel batching, electric furnace smelting and steel tapping. The steps of each process are as follows: (1) Scrap steel batching process: The charge of the electric furnace is all scrap steel. The scrap steel entering the furnace includes crushed material, small scrap steel, medium scrap steel and heavy scrap steel. The weight ratio of the four types of scrap steel is crushed material: small scrap steel: medium scrap steel: heavy scrap steel = 1.5:2.5:4:1. The scrap steel entering the furnace does not contain materials with high phosphorus content such as pig iron blocks.

[0013] (2) Electric furnace smelting process: before the scrap steel is put into the furnace, 7kg / t of lime and 3kg / t of dolomite are added to the bottom of the furnace; when the power is turned on for 6 minutes, 9kg / t of lime is added; when the power is turned on for 15 minutes, 7kg / t of lime and 8kg / t of dolomite are added; when the power is turned on for 25 minutes, 6kg / t of magnesium balls are added; the slag basicity at the end of smelting is 1.9, and the FeO content is controlled at 21.5%.

[0014] During the scrap steel melting stage, i.e. within 0 to 15 minutes of power-on, a voltage of 900V and a current of 95KA are used to quickly melt the scrap steel in the furnace; during the initial stage of molten pool heating, i.e. within 16 to 22 minutes of power-on, a voltage of 800V and a current of 80KA are used; during the middle and late stages of molten pool heating, i.e. within 22 to 33 minutes of power-on, a voltage of 900V and a current of 95KA are used.

[0015] (3) Steel-making process: Using infrared slag detection system, the slag amount is 0.5kg / t molten steel.

[0016] Sampling was carried out before steel was tapped and chemical analysis showed that the final phosphorus content of the molten steel was 0.0035%. Example 2

[0017] Taking a 130t electric arc furnace as an example, the method of smelting low-phosphorus steel in an all-scrap electric furnace includes the processes of scrap steel batching, electric furnace smelting and steel tapping. The steps of each process are as follows: (1) Scrap steel batching process: The charge of the electric furnace is all scrap steel. The scrap steel entering the furnace includes crushed material, small scrap steel, medium scrap steel and heavy scrap steel. The weight ratio of the four types of scrap steel is crushed material: small scrap steel: medium scrap steel: heavy scrap steel = 1.2:2.8:4.2:0.7. The scrap steel entering the furnace does not contain materials with high phosphorus content such as pig iron blocks.

[0018] (2) Electric furnace smelting process: before the scrap steel is put into the furnace, 8.2 kg / t of lime and 3.5 kg / t of dolomite are added to the bottom of the furnace; after 5.5 min of power-on, 9.2 kg / t of lime are added; after 15 min of power-on, 6.5 kg / t of lime and 7.2 kg / t of dolomite are added; after 25 min of power-on, 6.2 kg / t of magnesium balls are added; at the end of smelting, the slag basicity is 2.0 and the FeO content is controlled to 24.1%.

[0019] During the scrap steel melting stage, i.e. within 0 to 15 minutes of power-on, a voltage of 800V and a current of 95KA are used to quickly melt the scrap steel in the furnace; during the initial stage of molten pool heating, i.e. within 16 to 22 minutes of power-on, a voltage of 750V and a current of 80KA are used; during the middle and late stages of molten pool heating, i.e. within 22 to 33 minutes of power-on, a voltage of 100V and a current of 100KA are used.

[0020] (3) Steel-making process: Using infrared slag detection system, the slag amount is 0kg / t molten steel.

[0021] Sampling was carried out before steel was tapped and chemical analysis showed that the final phosphorus content of the molten steel was 0.0032%. Example 3

[0022] Taking a 130t electric arc furnace as an example, the method of smelting low-phosphorus steel in an all-scrap electric furnace includes the processes of scrap steel batching, electric furnace smelting and steel tapping. The steps of each process are as follows: (1) Scrap steel batching process: The charge of the electric furnace is all scrap steel. The scrap steel entering the furnace includes crushed material, small scrap steel, medium scrap steel and heavy scrap steel. The weight ratio of the four types of scrap steel is crushed material: small scrap steel: medium scrap steel: heavy scrap steel = 1.4:2.7:4.5:0.9. The scrap steel entering the furnace does not contain materials with high phosphorus content such as pig iron blocks.

[0023] (2) Electric furnace smelting process: before the scrap steel is put into the furnace, 7.8 kg / t of lime and 3.1 kg / t of dolomite are added to the bottom of the furnace; 7 minutes after the power is turned on, 12 kg / t of lime are added; 15.5 minutes after the power is turned on, 5.8 kg / t of lime and 7.6 kg / t of dolomite are added; 24 minutes after the power is turned on, 8 kg / t of magnesium balls are added; the slag basicity at the end of the smelting is 2.1, and the FeO content is controlled to 23.8%.

[0024] During the scrap melting stage, i.e. within 0 to 15 minutes of power-on, a voltage of 950V and a current of 95KA are used to quickly melt the scrap in the furnace; during the initial stage of molten pool heating, i.e. within 16 to 22 minutes of power-on, a voltage of 800V is used; during the middle and late stages of molten pool heating, i.e. within 22 to 33 minutes of power-on, a voltage of 950V and a current of 950KA are used.

[0025] (3) Steel-making process: Using infrared slag detection system, the slag amount is 0kg / t molten steel.

[0026] Sampling was carried out before steel was tapped and chemical analysis showed that the final phosphorus content of the molten steel was 0.0030%. Example 4

[0027] Taking a 130t electric arc furnace as an example, the method of smelting low-phosphorus steel in an all-scrap electric furnace includes the processes of scrap steel batching, electric furnace smelting and steel tapping. The steps of each process are as follows: (1) Scrap steel batching process: The charge of the electric furnace is all scrap steel. The scrap steel entering the furnace includes crushed material, small scrap steel, medium scrap steel and heavy scrap steel. The weight ratio of the four types of scrap steel is crushed material: small scrap steel: medium scrap steel: heavy scrap steel = 1:2.6:3.8:0.7. The scrap steel entering the furnace does not contain materials with high phosphorus content such as pig iron blocks.

[0028] (2) Electric furnace smelting process: before the scrap steel is put into the furnace, 8.8 kg / t of lime and 3.6 kg / t of dolomite are added to the bottom of the furnace; when the power is turned on for 5 minutes, 10 kg / t of lime is added; when the power is turned on for 16 minutes, 7.4 kg / t of lime and 7.0 kg / t of dolomite are added; when the power is turned on for 25 minutes, 6.8 kg / t of magnesium balls are added; the slag basicity at the end of smelting is 2.0, and the FeO content is controlled to 24.8%.

[0029] During the scrap steel melting stage, i.e. within 0 to 15 minutes of power-on, a voltage of 900V and a current of 100KA are used to quickly melt the scrap steel in the furnace; during the initial stage of molten pool heating, i.e. within 16 to 22 minutes of power-on, a voltage of 750V and a current of 85KA are used; during the middle and late stages of molten pool heating, i.e. within 22 to 33 minutes of power-on, a voltage of 950V and a current of 100KA are used.

[0030] (3) Steel-making process: Using infrared slag detection system, the slag amount is 0kg / t molten steel.

[0031] Sampling was carried out before steel was tapped and chemical analysis showed that the final phosphorus content of the molten steel was 0.0036%. Example 5

[0032] Taking a 130t electric arc furnace as an example, the method of smelting low-phosphorus steel in an all-scrap electric furnace includes the processes of scrap steel batching, electric furnace smelting and steel tapping. The steps of each process are as follows: (1) Scrap steel batching process: The charge of the electric furnace is all scrap steel. The scrap steel entering the furnace includes crushed material, small scrap steel, medium scrap steel and heavy scrap steel. The weight ratio of the four types of scrap steel is crushed material: small scrap steel: medium scrap steel: heavy scrap steel = 1.5:2.5:4:1. The scrap steel entering the furnace does not contain materials with high phosphorus content such as pig iron blocks.

[0033] (2) Electric furnace smelting process: before the scrap steel is put into the furnace, 9.5 kg / t of lime and 4.0 kg / t of dolomite are added to the bottom of the furnace; 7 minutes after the power is turned on, 10.5 kg / t of lime are added; 17 minutes after the power is turned on, 7.9 kg / t of lime and 6.2 kg / t of dolomite are added; 25 minutes after the power is turned on, 7.1 kg / t of magnesium balls are added; the slag basicity at the end of the smelting is 1.8, and the FeO content is controlled to 23.4%.

[0034] During the scrap steel melting stage, i.e. within 0 to 15 minutes of power-on, a voltage of 950V and a current of 100KA are used to quickly melt the scrap steel in the furnace; during the initial stage of molten pool heating, i.e. within 16 to 22 minutes of power-on, a voltage of 800V and a current of 85KA are used; during the middle and late stages of molten pool heating, i.e. within 22 to 33 minutes of power-on, a voltage of 1000V and a current of 90KA are used.

[0035] (3) Steel-making process: Using infrared slag detection system, the slag amount is 0kg / t molten steel.

[0036] Sampling was carried out before steel was tapped and chemical analysis showed that the final phosphorus content of the molten steel was 0.0030%. Example 6

[0037] Taking a 130t electric arc furnace as an example, the method of smelting low-phosphorus steel in an all-scrap electric furnace includes the processes of scrap steel batching, electric furnace smelting and steel tapping. The steps of each process are as follows: (1) Scrap steel batching process: The charge of the electric furnace is all scrap steel. The scrap steel entering the furnace includes crushed material, small scrap steel, medium scrap steel and heavy scrap steel. The weight ratio of the four types of scrap steel is crushed material: small scrap steel: medium scrap steel: heavy scrap steel = 1.3:3:3.5:0.5. The scrap steel entering the furnace does not contain materials with high phosphorus content such as pig iron blocks.

[0038] (2) Electric furnace smelting process: before the scrap steel is put into the furnace, 6.1 kg / t of lime and 2.0 kg / t of dolomite are added to the bottom of the furnace; when the power is turned on for 8 minutes, 8 kg / t of lime is added; when the power is turned on for 14 minutes, 5 kg / t of lime and 6.8 kg / t of dolomite are added; when the power is turned on for 27 minutes, 5 kg / t of magnesium balls are added; the slag basicity at the end of smelting is 2.2, and the FeO content is controlled to 20.3%.

[0039] During the scrap steel melting stage, i.e. within 0 to 15 minutes of power-on, a voltage of 950V and a current of 100KA are used to quickly melt the scrap steel in the furnace; during the initial stage of molten pool heating, i.e. within 16 to 22 minutes of power-on, a voltage of 800V and a current of 85KA are used; during the middle and late stages of molten pool heating, i.e. within 22 to 33 minutes of power-on, a voltage of 1000V and a current of 90KA are used.

[0040] (3) Steel-making process: Using infrared slag detection system, the slag amount is 0.2kg / t molten steel.

[0041] Sampling was carried out before steel was tapped and chemical analysis showed that the final phosphorus content of the molten steel was 0.0020%.

Claims

1. A method for smelting low-phosphorus steel in an electric furnace using all scrap steel, characterized in that: The invention comprises the steps of scrap steel batching, electric furnace smelting and steel tapping; the electric furnace smelting step comprises: adding lime and dolomite to the furnace bottom before the scrap steel is put into the furnace; during the smelting process, adding slag-making materials such as lime, dolomite and magnesium balls into the molten pool in batches; at the end of smelting, the FeO content is controlled at 20-25%, and the slag basicity is controlled at 1.8-2.

2.

2. The method for smelting low-phosphorus steel with all-scrap electric furnace according to claim 1, characterized in that: The scrap steel batching process: the scrap steel entering the furnace includes crushed material, small scrap steel, medium scrap steel and heavy scrap steel, and the weight ratio of the four types of scrap steel is crushed material: small scrap steel: medium scrap steel: heavy scrap steel = (1-1.5): (2.5-3): (3.5-4.5): (0.5-1); the scrap steel entering the furnace does not contain materials with high phosphorus content.

3. The method for smelting low-phosphorus steel with all-scrap electric furnace according to claim 1, characterized in that: The electric furnace smelting process is as follows: before the scrap steel is put into the furnace, 6-10 kg / t of molten steel and 2-4 kg / t of molten steel are added to the bottom of the furnace; when the power is turned on for 5-8 minutes, 8-12 kg / t of molten steel are added; when the power is turned on for 14-17 minutes, 5-8 kg / t of molten steel and 6-8 kg / t of molten steel are added; when the power is turned on for 24-27 minutes, 5-8 kg / t of magnesium balls are added.

4. The method for smelting low-phosphorus steel with all-scrap electric furnace according to claim 1, characterized in that: The electric furnace smelting process: in the scrap steel melting stage, that is, within 0 to 15 minutes of power-on, a voltage of 850 to 950 V and a current of 90 to 100 KA are used; in the initial stage of molten pool heating, that is, within 16 to 22 minutes of power-on, a voltage of 750 to 850 V and a current of 80 to 90 KA are used; in the middle and late stages of molten pool heating, that is, within 22 to 33 minutes of power-on, a voltage of 800 to 100 V and a current of 90 to 100 KA are used.

5. The method for smelting low-phosphorus steel with all-scrap electric furnace according to claim 1, characterized in that: In the steel-discharging process, an infrared slag detection system is used to control the slag amount to be ≤1kg / t of molten steel.

6. The method for smelting low-phosphorus steel with all-scrap electric furnace according to claim 1, characterized in that: The method can control the phosphorus content of steel to be ≤0.004%.