Electric furnace continuous casting production method for annealed steel material for deep drawing

Abstract

Disclosed in the present invention is an electric furnace continuous casting production method for an annealed steel material for deep drawing, comprising the process steps of electric furnace smelting, LF refining, VD refining, square billet continuous casting, heating, rolling, slow cooling, and annealing. During electric furnace smelting, scrap steel and molten iron are used as raw materials, wherein the proportion of the molten iron is 60%-80%. During LF refining, the slag basicity is controlled to be 5.5-7. During VD refining, static argon blowing is performed after vacuum breaking, wherein the soft blowing time is controlled to be 8-14 min, and the argon pressure is controlled to be 0.1-0.3 MPa. During rolling, the initial rolling temperature ranges from 1100°C to 1200°C, and the finish rolling temperature ranges from 850°C to 1000°C. An annealing process curve satisfies the formula t2-t1=2-4 h. By means of the method, the castability in the steel continuous casting production can be improved, the number of continuous casting heats can reach six, the steel exhibits a low inclusion level, and after quenching and tempering, the impact toughness is greater than or equal to 200 J, the tensile strength is greater than or equal to 400 MPa, and the percent elongation is greater than or equal to 30%.

Description

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

[0001] The present application belongs to the field of metallurgy, and particularly relates to an electric furnace continuous casting production method of deep drawing steel annealing material. BACKGROUND

[0002] The S15A deep drawing steel has high strength, high toughness and excellent elastic limit performance, can withstand extremely high pressure and impact load, and has good wear resistance and corrosion resistance. The steel has a high aluminum content, and high melting point Al2O3 inclusions are easily produced during smelting and production, causing the continuous casting production to be blocked, seriously affecting the continuous casting of the steel; at the same time, the steel requires a low silicon content, which is difficult to control during smelting; and because the product withstands a large amount of energy impact under service conditions, if the inclusion content level in the steel is not well controlled, the deep drawing parts of the steel are prone to rupture failure during use; in order to facilitate subsequent production and cutting, the steel is annealed before leaving the factory.

[0003] SUMMARY

[0004] In order to solve the bottleneck problem existing in the prior art, high-quality scrap steel is selected to smelt with molten iron in an electric furnace, the refining basicity and soft blowing time after vacuum treatment are strictly controlled, the calcium-aluminum ratio is strictly controlled, the aluminum and silicon contents are accurately controlled, the crystallizer protective slag is selected as a peritectic steel protective slag, the castability of the steel continuous casting production is improved, the continuous casting furnace number can reach 6, the steel inclusion level is low, the impact toughness after quenching and 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%.

[0005] In order to achieve the above-mentioned application purposes, the present application provides an electric furnace continuous casting production method of deep drawing steel annealing material, which comprises the following process steps: electric furnace smelting, LF refining, VD refining, continuous casting billet, heating, rolling, slow cooling, and annealing; wherein,

[0006] The electric furnace smelting uses scrap steel and molten iron as raw materials, and the proportion of molten iron is 60% to 80%;

[0007] The LF refining controls the slag basicity to be 5.5 to 7;

[0008] After the VD refining breaks the vacuum, a high-Ca line is fed, the Ca / Al mass ratio is controlled to be 0.04 to 0.08, argon is blown statically, the soft blowing time is controlled to be 8 to 14 minutes, and the nitrogen gas pressure is 0.1 to 0.3MPa;

[0009] The electric furnace continuous casting production method of deep drawing steel annealing material, which comprises the following process steps: electric furnace smelting, LF refining, VD refining, continuous casting billet, heating, rolling, slow cooling, and annealing; wherein,

[0010] The open rolling temperature of the rolling is 1100-1200℃, and the finish rolling temperature is 850-1000℃.

[0011] The annealing process curve satisfies the formula t2-t1=2-4h, wherein t2 represents the time of discharging, and t1 represents the time of completing the temperature equalization of the steel; specifically, the annealing temperature is 670±10℃, the holding time after the temperature equalization of the steel is 2-4h, and the steel is discharged and air-cooled after the holding.

[0012] In the technical solution, further, the mass content of the main components of the molten iron of the raw material of the electric furnace smelting is required to be C≥3.5%, Mn≤0.80%, Si: 0.20%-1.00%, P≤0.070%, and S≤0.070%. The scrap steel is first loaded, the active lime is laid on the bottom of the furnace before loading to reduce the impact on the bottom of the furnace, to form the molten pool in advance, to stabilize the electric arc, and to remove phosphorus in the early stage; the molten iron is poured in after the electric arc is formed to the bottom of the well and a certain molten pool is formed (the molten iron temperature ≤1150℃ cannot pour in the molten iron). The decarburization, the dephosphorization, and the temperature adjustment are performed through the oxygen supply, the slagging, and the power supply. The temperature is 1640-1680℃, the chemical composition C is 0.03%-0.06%, P≤0.013%, and the residual elements meet the requirements, and the molten steel can be discharged. The pre-deoxidizer is first added before the molten steel is discharged to perform the pre-deoxidation; the pre-deoxidizer, the slagging material, the alloy, and the carbon additive are added when the molten steel is discharged for 1 / 4. The molten steel and the slag are left during the molten steel discharge, and the oxidized slag is prevented from entering the ladle. The electric furnace molten steel discharge time is controlled to be about 3-6min.

[0013] Further, the bottom argon blowing stirring is performed during the whole LF refining process, the argon pressure is 0.2-0.4MPa, and the slag surface fluctuation and the bare molten steel are used as the criteria. The diffusion deoxidizer 1-3kg / t is added after the liquid slag is formed to perform the diffusion deoxidation, and the furnace door is closed for 10min. The second batch of diffusion deoxidizer is added, the total addition amount of the diffusion deoxidizer is 3-5kg / t, the slag white and the temperature meet the requirements, the sampling is performed for the full analysis, the slag basicity should be controlled to be 5.5-7, the composition is coarsely adjusted according to the lower limit of the requirement after the analysis result of the first sampling is reported back, and the alloy is added in the order of aluminum, manganese, and other alloys. The Al content in the steel is adjusted to be more than 0.040%, and the Si content is controlled to be less than or equal to 0.07% before entering the VD.

[0014] Further, during VD refining, the argon pressure is controlled at 0.1-0.3 MPa before the vacuum pump is started, and the slag surface is slightly moved without exposing the molten steel; when the vacuum degree reaches 100 Pa, the timing is started, and the holding time is ≥10 min, at this time, the argon pressure can be adjusted to 0.3-0.5 MPa. After breaking the vacuum, the final deoxidation is performed, the aluminum wire is fed according to the Al content in the steel, the Al content target of the finished product is controlled at 0.04%-0.06%, the high-Ca wire is fed, the Ca / Al mass ratio is controlled at 0.04-0.08, and after breaking the vacuum, argon is blown, the soft blowing time is controlled at 8-14 min, the nitrogen pressure is 0.1-0.3 MPa, and the slag surface is slightly moved without exposing the molten steel. After the static nitrogen blowing is finished, the holding agent is uniformly added at 30-80 kg / furnace, the addition should be performed when the molten steel surface still has fluctuations at the end of the static argon blowing of each furnace, and the uniform covering should be ensured.

[0015] Further, in the continuous casting, the 3-machine 3-flow arc-shaped continuous casting machine is used to cast the billets, the cross section is 235x265 mm, the furnace ladle temperature is 1599-1609 °C, the second furnace ladle temperature is 1582-1592 °C, the third furnace to the tail furnace ladle temperature is 1572-1582 °C, and argon protection is used for pouring; the electronic stirring uses the combined stirring of the crystallizer (M-EMS) and the solidification end (F-EMS), the crystallizer electric stirring current is set at 360±30 A, the crystallizer water flow is 140-160 m 3 / h, the secondary cooling specific water quantity is 0.3-0.4 L / kg, the crystallizer protective slag is selected to be the peritectic steel protective slag, the end electromagnetic stirring current is 250±30 A, the continuous casting billet is stored in the pit, the pit temperature is ≥600 °C, and the storage time is ≥30 h.

[0016] Further, in the heating stage, the square billet is stored in the pit after the heating furnace.

[0017] Further, in the rolling stage, the high-pressure water is used for descaling before rolling, the descaling pressure is 28-30 MPa, the rolling temperature is 1100-1200 °C, and the final rolling temperature is 850-1000 °C; the steel is immediately stored in the pit or stacked for cooling after the steel is cooled on the bed, the steel with a size ≥Φ85 mm is stored in the pit, the pit temperature is ≤300 °C, the storage time is ≥24 h, and the steel with a size <Φ85 mm is stacked for cooling.

[0018] In the annealing stage, the annealing temperature is 670±10 °C, the steel is uniformly heated, the holding time is 2-4 h, and the steel is cooled after the holding.

[0019] Further, the deep drawing steel has the following chemical composition: C: 0.12% to 0.18%, Si: 0.10% or less, Mn: 0.25% to 0.50%, P: 0.020% or less, S: 0.010% or less, Cr: 0.20% or less, Ni: 0.20% or less, Cu: 0.20% or less, Al: 0.03% to 0.08%, Ca: 0.0012% to 0.0042%, and the rest is Fe and inevitable impurities.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] The present application uses 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 content, selects peritectic steel protective slag for the crystallizer protective slag, improves the castability of the steel continuous casting production, the continuous casting furnace number can reach 6, the steel inclusion level is low, the impact after the quenching and 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%. BRIEF DESCRIPTION OF DRAWINGS

[0022] Fig. 1 is an annealing process curve diagram of S15A steel in the embodiment of the present application;

[0023] Fig. 2 is a microstructure diagram of S15A annealing material prepared in Example 1. DETAILED DESCRIPTION

[0024] The present application is further described below in combination with specific embodiments, but the present application is not limited in any way by the embodiments. To avoid redundancy, the raw materials in the following embodiments are all commercially available products if not specifically stated, and the methods used are all conventional methods if not specifically stated.

[0025] An electric furnace continuous casting production method of a deep drawing steel annealing material, the production method comprising the following process steps: electric furnace smelting, LF refining, VD refining, continuous casting billet, heating, rolling, slow cooling, annealing;

[0026] The electric furnace smelting uses scrap steel and molten iron as raw materials, and the molten iron ratio is 60% to 80%;

[0027] The LF refining controls the slag alkalinity to be 5.5 to 7;

[0028] After the VD refining breaks the vacuum, a high-Ca wire is fed, and the Ca / Al mass ratio is controlled to be 0.04 to 0.08; argon is blown statically, the soft blowing time is controlled to be 8 to 14 minutes, and the nitrogen gas pressure is 0.1 to 0.3 MPa;

[0029] The continuous casting head furnace ladle temperature is 1599°C to 1609°C, the second ladle temperature is 1582°C to 1592°C, the third ladle to the tail furnace ladle temperature is 1572°C to 1582°C, and argon protection is used for pouring;

[0030] The open rolling temperature of the rolling is 1100-1200℃, and the finish rolling temperature is 850-1000℃.

[0031] The annealing process curve satisfies the formula t2-t1=2-4h, wherein t2 represents the time, and t1 represents the time.

[0032] 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 inevitable impurities.

[0033] In the following examples, the unexplained contents are the same as the contents described in the above specific embodiment.

[0034] Embodiment

[0035] An electric furnace continuous casting production method of a deep drawing steel annealing material, taking deep drawing steel S15A as an example, the process flow of embodiment 1-5 is: electric furnace smelting→LF refining→VD refining→continuous casting 235mm×265mm square billet→heating→rolling→slow cooling→annealing. The chemical composition of the deep drawing steel of embodiment 1-5 is shown in table 1.

[0036] Table 1 Chemical composition table of deep drawing steel of embodiment 1-5

[0037] An electric furnace continuous casting production method of a deep drawing steel annealing material, including the following process steps:

[0038] The electric furnace smelting uses scrap steel plus molten iron as raw material, the molten iron ratio is 60-80%, the molten iron requires C content≥3.5%, Mn≤0.80%, Si: 0.20%-1.00%, P≤0.070%, S≤0.070%. First, load the scrap steel (load the active lime at the bottom before loading to reduce the impact on the furnace bottom, form the molten pool in advance, stabilize the electric arc and early dephosphorization), and after the electric penetration to the bottom and the formation of a certain molten pool, add the molten iron (the molten iron temperature≤1150℃ cannot add iron). Through oxygen supply, slagging, and power supply means to decarburize, dephosphorize, and adjust the temperature. The temperature is 1640-1680℃, the chemical composition C: 0.03%-0.06%, P≤0.013%, and the residual elements meet the requirements, and then the steel can be tapped, and before tapping, 3.0-3.5kg / t aluminum powder is added for pre-deoxidation. The pre-deoxidizing agent, slagging material, alloy, and carbon additive are added at 1 / 4 of the tapping; the tapping needs to pay attention to the remaining steel and slag to prevent the oxidation slag from entering the ladle, and the electric furnace tapping time is about 3-6min.

[0039] LF refining process throughout the bottom blowing argon stirring argon pressure 0.2 ~ 0.4 MPa, with slag surface fluctuation, molten steel is not exposed as accurate. Liquid slag formation after adding diffusion deoxidizer 1 ~ 3 kg / t diffusion deoxidation, closed door 10 min; adding the second batch, total 3 ~ 5 kg / t, slag white, temperature to meet the requirements, take full analysis, the slag basicity should be controlled in 5.5 ~ 7, once the sample analysis results back to the required lower composition rough adjustment, alloy addition sequence: aluminum, manganese, other alloys. The steel Al adjusted to 0.040% or more, into the VD Si control ≤0.07%.

[0040] VD refining, the vacuum pump before starting argon pressure control 0.1 ~ 0. MPa, with slag surface micro moving molten steel is not exposed as appropriate. When the vacuum degree reached 100 Pa began timing, the time ≥1 min, at this time the argon pressure can be adjusted to 0.3 ~ 0.5 MPa. Breaking vacuum after the final deoxidation, according to the Al content of steel feeding aluminum wire, control of finished products target 0.05%; feeding high Ca line, control Ca / Al ratio 0.04 ~ 0.08; breaking vacuum after static argon, soft blowing time should be controlled in 8 ~ 14 min, nitrogen pressure 0.1 ~ 0.3 MPa, with slag surface micro moving molten steel is not exposed as appropriate. Static blowing nitrogen after the end, evenly adding 30 ~ 80 kg / oven heat preservation agent should be in each static argon end of the steel liquid surface still have fluctuations when added, and ensure its uniform coverage.

[0041] Continuous casting using 3 machine 3 flow arc continuous casting machine billet, cross section is 235 x 265 mm, continuous casting head furnace ladle temperature 1599 ℃ ~ 1609 ℃, the second ladle furnace temperature 1582 ℃ ~ 1592 ℃, the third furnace to the ladle furnace temperature 1572 ℃ ~ 1582 ℃, argon protection casting; electronic stirring using crystallizer (M-EMS) and solidification end (F-EMS) combined stirring, electric stirring current set to 360 A, crystallizer water flow 150 M 3 / h, two cold water 0.33 L / kg, crystallizer protective slag selection peritectic steel protective slag, continuous casting billet into the pit heat preservation, into the pit temperature ≥600 ℃, heat preservation time ≥30 h.

[0042] Heating stage, billet out of the heat preservation pit into the step heating furnace heating.

[0043] Rolling stage, before the high pressure water descaling, descaling pressure 28 ~ 30 MPa, open rolling temperature 1100 ℃ ~ 1200 ℃, finish rolling temperature 850 ℃ ~ 1000 ℃, steel specifications for Φ70 mm, after the cooling bed stack cooling.

[0044] Annealing stage, S15A annealing process curve as shown in figure 1, the whole furnace time 22 h.

[0045] The details not described in the examples are conventional settings in the art. The mechanical properties of the annealed material of the deep drawing steel produced in Examples 1-5 are shown in Table 2; the results of the non-metallic inclusion test of the products produced in Examples 1-5 are shown in Table 3; the annealing process curve of Example S15A is shown in Figure 1; the microstructure of the S15A annealed material produced in Example 1 is shown in Figure 2.

[0046] Table 2 Mechanical properties of the quenched and tempered state of the examples

[0047] Table 3 Results of the non-metallic inclusion test of the examples

[0048] For any person skilled in the art, many possible variations and modifications, or equivalent embodiments of the technical solution of the present application can be made to the technical content disclosed above without departing from the scope of the technical solution of the present application. Therefore, any simple modification, equivalent change and modification made to the above examples according to the technical essence of the present application, which does not depart from the content of the technical solution of the present application, should still belong to the scope of protection of the technical solution of the present application.

Claims

1. An electric furnace continuous casting production method of an annealed material of a deep drawing steel, characterized by, The production method comprises the following process steps: electric furnace smelting, LF refining, VD refining, continuous casting billet, heating, rolling, slow cooling and annealing, wherein, The electric furnace smelting adopts scrap steel and molten iron as raw materials, and the proportion of molten iron is 60% to 80%; The LF refining controls the slag basicity to be 5.5 to 7; After the VD refining is broken, high Ca wire is fed, the mass ratio of Ca / Al is controlled to be 0.04 to 0.08, argon is blown, the soft blowing time is controlled to be 8 to 14 minutes, and the nitrogen pressure is 0.1 to 0.3 MPa; The rolling temperature is 1100 to 1200 DEG C, and the final rolling temperature is 850 to 1000 DEG C. The annealing process curve satisfies the formula t2-t1=2 to 4h, wherein t2 represents the furnace discharge time, and t1 represents the steel material completion temperature equalization time. The chemical composition of the deep drawing steel includes C: 0.12% to 0.18%, Si≤0.10%, Mn: 0.25% to 0.50%, P≤0.020%, S≤0.010%, Cr≤0.20%, Ni≤0.20%, Cu≤0.20%, Al: 0.03% to 0.08%, Ca: 0.0012% to 0.0042%, and the rest is Fe and inevitable impurities. The main component mass content requirements of the molten iron of the electric furnace smelting raw material are C≥3.5%, Mn≤0.80%, Si: 0.20% to 1.00%, P≤0.070% and S≤0.070%.

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

3. The production method according to claim 1, characterized by, The LF refining is stirred by bottom blowing argon all the time, and the argon pressure is 0.2 to 0.4 MPa.

4. The production method according to claim 1, characterized by, During the LF refining process, the liquid slag is formed, and then 3 to 5 kg / t of diffusion deoxidizer is added in two batches; the Al content in the steel is adjusted to be more than 0.040%, and the Si content is controlled to be less than or equal to 0.07% before entering the VD.

5. The production method according to claim 1, characterized by, During the VD refining, the vacuum degree is 100 Pa, and the holding time is greater than or equal to 10 minutes; after the vacuum is broken, the final deoxidation is performed, the aluminum wire is fed according to the Al content in the steel, and the target Al content of the finished product is 0.05%.

6. The production method according to claim 1, characterized by, During the continuous casting process, the crystallizer protective slag is selected to be a peritectic steel protective slag, the continuous casting billet is stored in the pit, the pit temperature is greater than or equal to 600 DEG C, and the storage time is greater than or equal to 30 hours.

7. The production method according to claim 1, characterized by, In the continuous casting process, the electronic stirring adopts the combined stirring of the mould M-EMS and the solidification end F-EMS, the current of the mould electric stirring is set as 360±30A, the water flow of the mould is 140-160m 3 / h, and the specific water quantity of the secondary cooling is 0.3-0.4L / kg.

8. The production method according to claim 1, characterized by, ​

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