Electric furnace continuous casting production method of steel annealing material for deep drawing

Abstract

The invention discloses an electric furnace continuous casting production method of a steel annealing material for deep drawing. The method comprises the process steps of electric furnace smelting, LF refining, VD refining, square billet continuous casting, heating, rolling, slow cooling, annealing and the like. Scrap steel and molten iron are adopted as raw materials for electric furnace smelting, and the proportion of the molten iron is 60-80% The alkalinity of slag is controlled to be 5.5-7 in LF refining; static argon blowing is carried out after VD refining vacuum breaking, the soft blowing time is controlled to be 8-14 min, and the nitrogen pressure is 0.1-0.3 MPa; the initial rolling temperature of rolling is 1100-1200 DEG C, and the final rolling temperature is 850-1000 DEG C; the annealing process curve meets the formula that t2-t1 is equal to 2-4 hours. According to the method, the castability of steel continuous casting production can be improved, the number of continuous casting furnaces can reach 6, the steel inclusion level is low, the impact toughness after thermal refining is larger than or equal to 200 J, the tensile strength is larger than or equal to 400 MPa, and the percentage elongation after fracture is larger than or equal to 30%.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to an electric furnace continuous casting production method for annealed steel material for deep drawing. Background Art

[0002] S15A deep drawing steel has high strength, high toughness and excellent elastic limit performance, can withstand extremely high pressure and impact loads, and has good wear resistance and corrosion resistance. This steel has a high aluminum content, and is prone to produce high-melting-point Al2O3 inclusions during smelting production, causing water in the continuous casting production, seriously affecting the continuous casting of steel continuous casting production; at the same time, this steel requires a low silicon content, and the smelting process is difficult to control; and, because the product is subject to large energy impacts under service conditions, if the level of inclusions in the steel cannot be well controlled, steel deep drawing parts are very likely to break and fail during use; in order to facilitate subsequent production and cutting, steel is often annealed before leaving the factory. Summary of the invention

[0003] In order to solve the bottleneck problems existing in the above-mentioned prior art, the present invention selects high-quality scrap steel and molten iron for electric furnace smelting, strictly controls the refining alkalinity and the soft blowing time after vacuum treatment, strictly controls the calcium-aluminum ratio, accurately controls the aluminum and silicon contents, and selects peritectic steel protective slag as the crystallizer protective slag to improve the castability of steel continuous casting production. The number of continuous casting furnaces can reach 6 furnaces, the level of steel inclusions is low, the impact toughness after tempering treatment is greater than or equal to 200J, the tensile strength is greater than or equal to 400MPa, and the elongation after fracture is greater than or equal to 30%.

[0004] In order to achieve the above-mentioned invention object, the present invention provides an electric furnace continuous casting production method for annealed steel for deep drawing, the production method comprising the following process steps: electric furnace smelting, LF refining, VD refining, continuous casting of billets, heating, rolling, slow cooling, annealing; wherein,

[0005] The electric furnace smelting uses scrap steel and molten iron as raw materials, with the proportion of molten iron being 60% to 80%;

[0006] The LF refining controls the slag basicity to be 5.5-7;

[0007] After the VD refining vacuum is broken, high Ca wire is fed to control the Ca / Al mass ratio to 0.04-0.08; argon is blown statically, the soft blowing time is controlled to be 8-14 minutes, and the nitrogen pressure is 0.1-0.3MPa;

[0008] The ladle temperature of the continuous casting head furnace is 1599°C to 1609°C, the ladle temperature of the second furnace is 1582°C to 1592°C, and the ladle temperature of the third furnace to the tail furnace is 1572°C to 1582°C, and argon gas is used for casting;

[0009] The starting rolling temperature of the rolling is 1100°C to 1200°C, and the final rolling temperature is 850°C to 1000°C;

[0010] The annealing process curve satisfies the formula t2-t1=2~4h, where t2 represents the time of taking out of the furnace, and t1 represents the time of completing the temperature equalization of the steel; specifically, the annealing temperature is 670±10℃, the steel is kept warm for 2~4h after being heated, and then taken out of the furnace and air-cooled.

[0011] In the above technical scheme, further, the main components of the molten iron of the raw materials for electric furnace smelting are required to have a mass content of C ≥ 3.5%, Mn ≤ 0.80%, Si: 0.20% ~ 1.00%, P ≤ 0.070%, S ≤ 0.070%. Scrap steel is first loaded, and active lime is placed on the bottom of the furnace before loading to reduce the impact on the bottom of the furnace, form a molten pool in advance, stabilize the arc and dephosphorize in the early stage; after the well is powered on and a certain molten pool is formed, molten iron is added (iron cannot be added if the molten iron temperature is ≤ 1150°C). Decarburization, dephosphorization and temperature adjustment are carried out by means of oxygen supply, slag making and power supply. Steel can be tapped when the temperature is 1640°C ~ 1680°C, the chemical composition C: 0.03% ~ 0.06%, P ≤ 0.013% and the residual elements meet the requirements. Before tapping, 3.0 ~ 3.5 kg / t of aluminum powder is added for pre-deoxidation; when 1 / 4 of the steel is tapped, pre-deoxidizer, slag making material, alloy and carburizer are added. When tapping steel, it is necessary to pay attention to retaining steel and slag to prevent oxide slag from entering the ladle. The tapping time of the electric furnace is controlled at about 3 to 6 minutes.

[0012] Furthermore, argon blowing and stirring are carried out throughout the LF refining process, and the argon pressure is 0.2-0.4MPa, subject to the fluctuation of the slag surface and the non-exposed molten steel. After the liquid slag is formed, 1-3kg / t of diffusion deoxidizer is added for diffusion deoxidation, and the furnace door is closed for 10 minutes; the second batch of diffusion deoxidizer is added, and the total amount of diffusion deoxidizer added is 3-5kg / t. When the slag whiteness and temperature meet the requirements, sampling is carried out for full analysis, and the slag basicity should be controlled at 5.5-7. After the results of the first sample analysis are reported back, the composition is roughly adjusted according to the required lower limit. The order of alloy addition is: aluminum, manganese, and other alloys. The Al content in the steel is adjusted to above 0.040%, and Si is controlled to ≤0.07% before entering VD.

[0013] Furthermore, during VD refining, the argon pressure is controlled at 0.1-0.3MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly; when the vacuum reaches 100Pa, the timing starts and the holding time is ≥10min, at which time the argon pressure can be adjusted to 0.3-0.5MPa. After breaking the vacuum, final deoxidation is carried out, and aluminum wire is fed according to the Al content in the steel, and the target Al content of the finished product is controlled to be 0.04%-0.06%; high Ca wire is fed, and the Ca / Al mass ratio is controlled to be 0.04-0.08; after breaking the vacuum, argon is blown statically, and the soft blowing time should be controlled at 8-14min, and the nitrogen pressure is 0.1-0.3MPa, so that the molten steel is not exposed when the slag surface moves slightly. After the static nitrogen blowing is completed, 30-80kg / furnace of insulation is evenly added. It should be added when the steel liquid level still fluctuates at the end of static argon blowing in each furnace, and its uniform coverage should be ensured.

[0014] Furthermore, a 3-machine 3-stream arc continuous casting machine is used to continuously cast the steel billet, with a cross section of 235×265mm, a ladle temperature of 1599℃~1609℃ for the first furnace, a ladle temperature of 1582℃~1592℃ for the second furnace, and a ladle temperature of 1572℃~1582℃ for the third to tail furnaces, and argon protection is used for pouring; electronic stirring adopts the combined stirring of the crystallizer (M-EMS) and the solidification end (F-EMS), the electric stirring current of the crystallizer is set to 360±30A, and the water flow rate of the crystallizer is 140~160m 3 / h, secondary cooling water volume 0.3 ~ 0.4L / kg, the crystallizer protection slag is peritectic steel protection slag, the terminal electromagnetic stirring current is 250 ± 30A, the continuous casting billet is put into the pit for insulation, the pit entry temperature is ≥ 600 ℃, and the insulation time is ≥ 30h.

[0015] Furthermore, in the heating stage, the billet is heated in a step-beam heating furnace after leaving the insulation pit.

[0016] Furthermore, in the rolling stage, high-pressure water descaling is used before rolling, the descaling pressure is 28-30MPa, the starting rolling temperature is 1100℃-1200℃, and the final rolling temperature is 850℃-1000℃; the steel is immediately put into the pit for insulation or pile cooling after leaving the cooling bed, the steel with specification ≥Φ85mm is insulated, the exit temperature of the pit is ≤300℃, the insulation time is ≥24h, and the steel with specification <Φ85mm is pile cooled.

[0017] During the annealing stage, the annealing temperature is 670±10℃. The steel is kept at a temperature of 2 to 4 hours after being heated to a uniform temperature. After being kept at a temperature, it is taken out of the furnace and air-cooled.

[0018] Furthermore, the chemical composition mass content of the deep drawing steel includes C: 0.12% ~ 0.18%, Si ≤ 0.10%, Mn: 0.25% ~ 0.50%, P ≤ 0.020%, S ≤ 0.010%, Cr ≤ 0.20%, Ni ≤ 0.20%, Cu ≤ 0.20%, Al: 0.03% ~ 0.08%, Ca: 0.0012% ~ 0.0042%, and the rest is Fe and unavoidable impurities.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention selects high-quality scrap steel and molten iron for electric furnace smelting, strictly controls the refining basicity and the soft blowing time after vacuum treatment, strictly controls the calcium-aluminum ratio, accurately controls the aluminum and silicon contents, selects peritectic steel protective slag as the crystallizer protective slag, and improves the castability of steel continuous casting production. The number of continuous casting furnaces can reach 6 furnaces, the inclusion level of steel is low, the impact after quenching and tempering treatment is ≥200J, the tensile strength is ≥400MPa, and the elongation after fracture is ≥30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a graph showing the annealing process of S15A steel according to an embodiment of the present invention;

[0022] Figure 2 This is the microstructure diagram of the S15A annealed material obtained in Example 1. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0024] A method for producing an annealed steel material for deep drawing by continuous casting in an electric furnace, the method comprising the following process steps: electric furnace smelting, LF refining, VD refining, continuous casting of billets, heating, rolling, slow cooling, and annealing;

[0025] The electric furnace smelting uses scrap steel and molten iron as raw materials, with the proportion of molten iron being 60% to 80%;

[0026] The LF refining controls the slag basicity to be 5.5-7;

[0027] After the VD refining vacuum is broken, high Ca wire is fed to control the Ca / Al mass ratio to 0.04-0.08; argon is blown statically, the soft blowing time is controlled to be 8-14 minutes, and the nitrogen pressure is 0.1-0.3MPa;

[0028] The ladle temperature of the continuous casting head furnace is 1599°C to 1609°C, the ladle temperature of the second furnace is 1582°C to 1592°C, and the ladle temperature of the third furnace to the tail furnace is 1572°C to 1582°C, and argon gas is used for casting;

[0029] The starting rolling temperature of the rolling is 1100°C to 1200°C, and the final rolling temperature is 850°C to 1000°C;

[0030] The annealing process curve satisfies the formula t2-t1=2-4h, where t2 represents ... time, t1 represents ... time;

[0031] The chemical composition mass content of the deep drawing steel includes C: 0.12% ~ 0.18%, Si ≤ 0.10%, Mn: 0.25% ~ 0.50%, P ≤ 0.020%, S ≤ 0.010%, Cr ≤ 0.20%, Ni ≤ 0.20%, Cu ≤ 0.20%, Al: 0.03% ~ 0.08%, Ca: 0.0012% ~ 0.0042%, and the rest is Fe and unavoidable impurities.

[0032] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0033] Example

[0034] A method for producing deep drawing steel annealing material by electric furnace continuous casting, taking deep drawing steel S15A as an example, the process flow of Examples 1 to 5 is: electric furnace smelting → LF refining → VD refining → continuous casting of 235mm×265mm square billet → heating → rolling → slow cooling → annealing. The chemical composition of the deep drawing steel of Examples 1 to 5 is shown in Table 1.

[0035] Table 1 Chemical composition of deep drawing steels of Examples 1 to 5

[0036]

[0037]

[0038] A method for producing an annealed steel material for deep drawing by continuous casting in an electric furnace comprises the following process steps:

[0039] Electric furnace smelting uses scrap steel and molten iron as raw materials, with a molten iron ratio of 60-80%, and the molten iron requires C content ≥3.5%, Mn≤0.80%, Si: 0.20%-1.00%, P≤0.070%, S≤0.070%. First load scrap steel (active lime is placed on the bottom of the furnace before loading to reduce the impact on the bottom of the furnace, form a molten pool in advance, stabilize the arc and dephosphorize in the early stage), and then add molten iron after the well is drilled to the bottom and a certain molten pool is formed (iron cannot be added when the molten iron temperature is ≤1150℃). Decarburization, dephosphorization and temperature adjustment are carried out by means of oxygen supply, slag making and power supply. Steel can be tapped when the temperature is 1640℃~1680℃, the chemical composition C: 0.03%~0.06%, P≤0.013% and the residual elements meet the requirements. Before tapping, 3.0~3.5kg / t aluminum powder is added for pre-deoxidation. When 1 / 4 of the steel is tapped, pre-deoxidizer, slag-forming materials, alloys and carburizers are added; when tapping, attention should be paid to retaining steel and slag to prevent oxide slag from entering the ladle. The tapping time of the electric furnace is about 3 to 6 minutes.

[0040] During the LF refining process, the bottom blowing argon is stirred at an argon pressure of 0.2-0.4MPa, and the slag surface fluctuates and the molten steel is not exposed. After the liquid slag is formed, 1-3kg / t of diffusion deoxidizer is added for diffusion deoxidation, and the furnace door is closed for 10 minutes; the second batch is added, and a total of 3-5kg / t is added. When the slag whiteness and temperature meet the requirements, a full analysis is taken, and the slag basicity should be controlled at 5.5-7. After the results of the first sample analysis are reported back, the composition is roughly adjusted according to the required lower limit. The order of alloy addition is: aluminum, manganese, and other alloys. Adjust the Al in the steel to more than 0.040%, and control Si to ≤0.07% before entering VD.

[0041] During VD refining, the argon pressure is controlled at 0.1-0.MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 100Pa, the timing starts and the holding time is ≥1min. At this time, the argon pressure can be adjusted to 0.3-0.5MPa. After breaking the vacuum, final deoxidation is carried out, and aluminum wire is fed according to the Al content in the steel to control the finished product target of 0.05%; high Ca wire is fed to control the Ca / Al ratio of 0.04-0.08; after breaking the vacuum, argon is blown statically, and the soft blowing time should be controlled at 8-14min, and the nitrogen pressure is 0.1-0.3MPa, so that the molten steel is not exposed when the slag surface moves slightly. After the static nitrogen blowing is completed, 30-80kg / furnace of insulation is evenly added. It should be added when the steel liquid level still fluctuates at the end of static argon blowing in each furnace, and ensure its uniform coverage.

[0042] The continuous casting process uses a 3-machine 3-stream arc continuous casting machine to continuously cast steel billets with a cross section of 235×265mm. The temperature of the first furnace is 1599℃~1609℃, the temperature of the second furnace is 1582℃~1592℃, and the temperature of the third to tail furnaces is 1572℃~1582℃. Argon protection is used for pouring. The electronic stirring uses the crystallizer (M-EMS) and the solidification end (F-EMS) to stir together. The electric stirring current is set to 360A, and the crystallizer water flow is 150M 3 / h, secondary cooling water volume 0.33L / kg, crystallizer protection slag selects peritectic steel protection slag, continuous casting billet enters the pit for insulation, the pit entry temperature ≥600℃, and the insulation time ≥30h.

[0043] During the heating stage, the billet is heated in a step-beam heating furnace after leaving the insulation pit.

[0044] During the rolling stage, high-pressure water is used for descaling before rolling, the descaling pressure is 28-30MPa, the starting rolling temperature is 1100℃-1200℃, the final rolling temperature is 850℃-1000℃, the steel specification is Φ70mm, and it is pile cooled after being placed on the cooling bed.

[0045] Annealing stage, S15A annealing process curve is shown in Figure 1 , the whole furnace time is 22h.

[0046] Matters not detailed in the examples are all conventional settings in the art. The mechanical properties of the annealed steel for deep drawing obtained in Examples 1 to 5 are shown in Table 2; the test results of non-metallic inclusions in the products obtained in Examples 1 to 5 are shown in Table 3; the annealing process curve of Example S15A is shown in Table Figure 1 Example 1 The microstructure of the S15A annealed material is as follows Figure 2 shown.

[0047] Table 2 Mechanical properties of the tempered state of the examples

[0048]

[0049] Table 3 Detection results of non-metallic inclusions in the examples

[0050] Serial number A thin A thick B thin B thick C Thin C thick D Thin D thick Example 1 0.5 1.0 0.5 0.5 0 0 0 0 Example 2 0.5 1.0 0.5 0.5 0 0 0 0 Example 3 1.0 1.0 0.5 0.5 0 0 0 0 Example 4 1.0 1.0 0.5 0.5 0 0 0 0 Example 5 1.0 1.0 0.5 0.5 0 0 0 0

[0051] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for producing annealed steel for deep drawing by continuous casting in an electric furnace, characterized in that: The production method comprises the following process steps: electric furnace smelting, LF refining, VD refining, continuous casting of billets, heating, rolling, slow cooling, and annealing; wherein, The electric furnace smelting uses scrap steel and molten iron as raw materials, with the proportion of molten iron being 60% to 80%; The LF refining controls the slag basicity to be 5.5-7; After the VD refining vacuum is broken, high Ca wire is fed to control the Ca / Al mass ratio to 0.04-0.08; argon is blown statically, the soft blowing time is controlled to be 8-14 minutes, and the nitrogen pressure is 0.1-0.3MPa; The ladle temperature of the continuous casting head furnace is 1599°C to 1609°C, the ladle temperature of the second furnace is 1582°C to 1592°C, and the ladle temperature of the third furnace to the tail furnace is 1572°C to 1582°C, and argon gas is used for casting; The starting rolling temperature of the rolling is 1100°C to 1200°C, and the final rolling temperature is 850°C to 1000°C; The annealing process curve satisfies the formula t2-t1=2-4h, where t2 represents the time of exiting the furnace, and t1 represents the time of steel material completing temperature equilibration; The chemical composition mass content of the deep drawing steel includes C: 0.12% ~ 0.18%, Si ≤ 0.10%, Mn: 0.25% ~ 0.50%, P ≤ 0.020%, S ≤ 0.010%, Cr ≤ 0.20%, Ni ≤ 0.20%, Cu ≤ 0.20%, Al: 0.03% ~ 0.08%, Ca: 0.0012% ~ 0.0042%, and the rest is Fe and unavoidable impurities.

2. The production method according to claim 1, characterized in that The main components of the molten iron of the electric furnace smelting raw material are required to have a mass content of C≥3.5%, Mn≤0.80%, Si: 0.20%-1.00%, P≤0.070%, and S≤0.070%.

3. The production method according to claim 1, characterized in that The tapping temperature of the electric furnace smelting is 1640°C to 1680°C, the chemical composition C is controlled to be 0.03% to 0.06%, P is ≤ 0.013%, and the tapping time is 3 to 6 minutes.

4. The production method according to claim 1, characterized in that The LF refining is performed with bottom blowing of argon and stirring throughout the whole process, and the argon pressure is 0.2-0.4 MPa.

5. The production method according to claim 1, characterized in that: During the LF refining process, after the liquid slag is formed, 3-5 kg / t of diffusion deoxidizer is added in two batches; the Al content in the steel is adjusted to above 0.040%, and Si is controlled to be ≤0.07% before entering VD.

6. The production method according to claim 1, characterized in that: During the VD refining, when the vacuum degree is 100Pa, the holding time is ≥10min; after breaking the vacuum, final deoxidation is performed, and aluminum wire is fed according to the Al content in the steel, and the Al content of the finished product is controlled to be 0.05%.

7. The production method according to claim 1, characterized in that: During the continuous casting process, the electronic stirring adopts the combined stirring of the crystallizer M-EMS and the solidification end F-EMS, the crystallizer electric stirring current is set to 360±30A, and the crystallizer water flow rate is 140~160m 3 / h, secondary cooling water volume 0.3~0.4L / kg.

8. The production method according to claim 1, characterized in that: During the continuous casting process, the mold protection slag is selected from peritectic steel protection slag, and the continuous casting billet is put into the pit for insulation. The pit entry temperature is ≥600°C and the insulation time is ≥30h.

Images