Method for reducing the inclusion level of low-alloy high-strength steel Q355B for cold rolling

Abstract

The application provides a method for reducing the inclusion level of low-alloy high-strength steel Q355B for cold rolling, wherein a slag washing raw material composed of slag washing material and lime is added to molten steel after steelmaking, and the addition amount of the slag washing raw material is 500 kg per 100 tons of steel; wherein the amount X1 of slag washing material required per 100 tons of molten steel is X1=(530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2). In the formula, the weight of the slag washing material is X1; the weight percentage of Al2O3 in the slag washing material is Y1; the weight percentage of CaO in the slag washing material is Y2; the weight percentage of CaO in the lime is Y3; the weight percentage of oxygen in the converter end molten steel is Y4 (unit: %); the weight percentage of S in the converter end molten steel is Y5 (unit: %); and the desulfurization rate is Y6. The application designs a slag washing material for deoxidation, desulfurization and denitrification, accurately controls the contents of CaO, Al2O3 and FeO in the ladle top slag, makes the slag have good adsorption, and effectively promotes the floating of inclusions, so as to reduce the number and size of micro-inclusions in the molten steel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steelmaking, in particular to a method for reducing the inclusion level of low-alloy high-strength steel Q355B for cold rolling. BACKGROUND

[0002] In recent years, with the development of the construction industry, the requirements for building materials are becoming higher and higher. High-strength building materials have been recognized by people in the construction industry because of their advantages such as light weight, high strength, and flexible building forms. Therefore, the cold rolling industry needs to find a hot-rolled product with high strength and good plasticity to meet the downstream use requirements, and low-alloy high-strength steel Q355B for cold rolling has become a new research direction.

[0003] At present, titanium is generally added to steel during the production process of low-alloy high-strength steel Q355B at home and abroad. By utilizing the characteristics of TiN having good high-temperature thermal stability, the growth of austenite grains in the welding heat-affected zone is effectively inhibited, thereby improving the welding performance of the steel. However, due to different product uses, different reprocessing processes, and different technical requirements for hot-rolled products, low-alloy high-strength steel Q355B for cold rolling needs to meet the chemical composition, tensile test, bending test, impact test, surface and external size technical requirements in the “Low-alloy Structural Steel Hot-rolled Steel Plate and Steel Belt” GB / T3274, and the inclusions thereof need to be detected to meet the requirements of coating, forming, welding, etc. after cold rolling.

[0004] In order to obtain high-quality and high-purity steel, the molten steel is generally smelted by using external refining technology, i.e. reducing the oxygen, sulfur, harmful gas, and inclusions in the steel to a certain extent before casting. However, with the fierce market competition and the requirements of customers for the quality of steel, low-cost production of high-quality steel has become an inevitable trend in the development of the steel industry at home and abroad. Since the LF refining process consumes a large amount of manpower and materials, the production cost is relatively high, and the LF refining process also cannot meet the requirements of efficient and rapid production. Therefore, many steel enterprises cancel the LF refining process and adopt the post-furnace slag washing process. The conventional process is to move the refining slag to the argon blowing period after the converter and add it to replace the LF refining, thereby reducing the inclusion content and desulfurization in the steel. This process saves the cost of electricity, electrodes, etc. in the LF refining process, but the refining slag and slag-making cost of this general technology still exist in the production process, and the cost per ton of steel is between 15-25 yuan. Therefore, it is particularly important to develop a method for efficiently and low-cost production of low-alloy high-strength steel Q355B for cold rolling. SUMMARY

[0005] To solve the above problems existing in the prior art, the purpose of the present application is to provide a method for reducing the inclusion level of low-alloy high-strength steel Q355B for cold rolling.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is:

[0007] A method for reducing the inclusion level of low-alloy high-strength steel Q355B for cold rolling, comprising adding slag washing raw materials composed of slag washing materials and lime to the molten steel after the end of steelmaking, wherein the addition amount of the slag washing raw materials is 500 kg per 100 tons of steel;

[0008] Wherein, the amount X1 of slag washing materials required per 100 tons of molten steel is calculated by the following formula:

[0009] X1= (530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2)

[0010] In the formula, the weight of the slag washing materials is X1 (unit: kg);

[0011] The weight percentage of Al2O3 in the slag washing materials is Y1;

[0012] The weight percentage of CaO in the slag washing materials is Y2;

[0013] The weight percentage of CaO in the lime is Y3;

[0014] The weight percentage of oxygen in the converter end molten steel is Y4 (unit: %);

[0015] The weight percentage of S in the converter end molten steel is Y5 (unit: %);

[0016] The desulfurization rate is Y6.

[0017] The slag washing materials have a weight percentage composition of CaO: 10%-12%, SiO2: 1%-1.5%, Al2O3: 70%-73%, MgO: 1%-1.5%, solvent: 10%-13%, S: 0.009%-0.011%, P2O5: 0.010%-0.013%, and burning loss: 0.5%-0.9%;

[0018] The lime is first-grade metallurgical lime, and has a weight percentage composition of CaO: ≥90%, and SiO2: ≤2.5%.

[0019] The top slag of the ladle has a weight percentage composition of CaO: 33.5%-36.7%, SiO2: 4.5%-6.5%, Al2O3: 35.5%-39.0%, MgO: 2.5%-4.5%, TiO2: 2.5%-4.0%, FeO: ≤3%, and MnO: 5%-8%.

[0020] The further improvement of the present application is that the converter is used to smelt the hot metal, the hot metal wt% (S) added into the converter is less than or equal to 0.030%, and the end temperature of the converter smelting is controlled at 1650-1680 DEG C.

[0021] The further improvement of the present application is that the oxygen is determined in the ladle after adding the slag washing raw material, the aluminum wire is fed according to the oxygen content, and then the ferrotitanium is added, and the amount of the ferrotitanium added is 1.5-2.0 kg / ton of steel.

[0022] The further improvement of the present application is that the soft argon blowing with large gas amount is used after the aluminum wire is fed, the argon blowing with small gas amount is changed after the top slag is melted, the exposed surface of the hot metal is controlled at 30 cm, and the argon blowing time after the furnace is greater than or equal to 8 min.

[0023] The further improvement of the present application is that the temperature of the tundish in the continuous casting process is controlled at 1535-1545 DEG C, the casting speed is 1.1-1.2 m / min, and the specific water consumption of the secondary cooling is 0.8-0.9 L / kg.

[0024] The further improvement of the present application is that the yield strength of the low-alloy high-strength steel Q355B for cold rolling is greater than or equal to 400 MPa, the tensile strength is greater than or equal to 460 MPa, and the elongation is greater than or equal to 26%.

[0025] The further improvement of the present application is that the inclusions of the low-alloy high-strength steel Q355B for cold rolling include A type and D type, and no B type inclusions; the A type inclusion grade is not greater than 1.5, and the D type inclusion grade is not greater than 1.0.

[0026] Thanks to the above technical solutions, the present application has the following technical progress:

[0027] The present application provides a method for reducing the inclusion grade of the low-alloy high-strength steel Q355B for cold rolling, designs a low-oxidizing and high-alkalinity slag washing material with deoxidation, desulfurization and denitrification, accurately adds the slag washing material, accurately controls the CaO, Al2O3 and FeO contents in the top slag of the ladle, makes the top slag have good adsorption, effectively promotes the floating of the inclusions, reduces the number and size of the micro-inclusions in the hot metal, and ensures that the cast blank has the required component content and good mechanical properties, and meets the requirements of the high-quality low-alloy high-strength steel Q355B for cold rolling.

[0028] The present application limits the interval content of CaO and Al2O3 in the slag washing material in detail, and the desulfurization rate reaches 50%; through a large amount of data statistical analysis, an intelligent slag washing raw material matching formula is designed, the raw material matching amount is quickly and accurately obtained, and a method for reducing nitrogen in TiO2 component in the tundish top slag is creatively proposed. By adopting the method, the type and level of inclusions in the steel are significantly improved, the number of sulfide inclusions (class A) and calcium aluminate inclusions (class B and class D) in the steel is reduced, the level of class A inclusions in the steel is reduced to 2.0 level and below, the class B inclusions are denatured, the class B inclusions are not included in the steel, the level of class D inclusions is reduced to 1.5 level and below, the nitrogen content in the steel is significantly reduced, and the level of class D inclusions is reduced to 1.0 level and below. TiN

[0029] Through the accurate calculation of the method, the feeding amount of the slag washing material is optimized, the feeding amount is reduced compared with the general slag washing process, the production cost is reduced by about 5 yuan / ton of steel, the ton of steel cost is between 10-15 yuan, and the cost control effect is remarkable.

[0030] The method has the advantages of simple and feasible production process, low cost, deoxidation, desulfurization, denitrification, inclusion removal, improvement of steel slag fluidity and the like, can reduce the cost while improving the technical index and performance requirement of the low-alloy high-strength steel Q355B for cold rolling, does not need to modify the production equipment, and is very suitable for industrial large-scale popularization. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a metallographic morphology graph of example 1;

[0032] Figure 2 It is a metallographic morphology graph of comparative example 1;

[0033] Figure 3 It is a metallographic morphology graph of comparative example 2. DETAILED DESCRIPTION

[0034] The present application will be further described below.

[0035] A method for reducing the inclusion level of low-alloy high-strength steel Q355B for cold rolling, slag washing raw materials are added to molten steel for refining after steelmaking, the slag washing raw materials are composed of slag washing materials and lime, and the addition amount of the slag washing raw materials is 500 kg / 100 tons of steel.

[0036] Wherein, the amount X1 of slag washing material needed for every 100 tons of molten steel is calculated by the following formula:

[0037] X1= (530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2) ​

[0038] In the formula, the weight of the slag washing material is X1 (unit: kg);

[0039] The weight percentage of Al2O3 in the slag washing material is Y1;

[0040] The weight percentage of CaO in the slag washing material is Y2;

[0041] The weight percentage of CaO in the lime is Y3;

[0042] The weight percentage of oxygen at the end of the converter is Y4 (unit: %);

[0043] The weight percentage of S at the end of the converter is Y5 (unit: %);

[0044] The desulfurization rate is Y6.

[0045] The slag washing material has a composition by weight percentage of CaO: 10%-12%, SiO2: 1%-1.5%, Al2O3: 70%-73%, MgO: 1%-1.5%, solvent: 10%-13%, S: 0.009%-0.011%, P2O5: 0.010%-0.013%, and burning loss: 0.5%-0.9%.

[0046] The lime is first-grade metallurgical lime, and has a composition by weight percentage of CaO: ≥90%, and SiO2: ≤2.5%.

[0047] The low-alloy high-strength steel Q355B for cold rolling is prepared by the above method for reducing the level of inclusions, specifically including three steps of converter smelting, slag washing and argon blowing, and continuous casting into a billet; the molten iron is smelted and cast into a low-alloy high-strength steel Q355B with a low level of inclusions through the above three steps.

[0048] The above three steps are described and explained in detail as follows.

[0049] I. Converter smelting

[0050] In the converter smelting step, the converter is used to smelt the molten iron into molten steel; the wt% (S) of the molten iron added into the converter is ≤0.030%, and the temperature at the end of the converter smelting is controlled in the range of 1650℃-1680℃.

[0051] The content of S element in the molten iron directly affects the yield of sulfide inclusions in subsequent production, and in order to ensure the quality of steel products, it is necessary to control the content of harmful elements in the molten iron from the source.

[0052] The smelting end point temperature has a direct impact on the control of inclusions. If the smelting end point temperature is too high, the oxidizability of the molten steel increases, a large amount of oxidized inclusions are generated, and the purity of the molten steel is not easy to control. If the smelting end point temperature is too low, the subsequent slag melting effect is affected, the treatment time is insufficient, and the inclusions in the molten steel are not easy to remove. When the smelting end point temperature is controlled in the range of 1650℃ to 1680℃, the smelting effect of the molten steel can be ensured, and the generation amount of oxidized inclusions can be reasonably controlled.

[0053] II. Slag washing argon blowing

[0054] The slag washing argon blowing step refers to that after the converter smelting is completed, the molten steel is tapped, 30s after the converter is tapped, the slag washing raw materials (i.e. slag washing materials and lime) are sequentially added to the molten steel, and the bottom argon blowing of the ladle is performed at the same time, so as to promote the slag washing materials, lime and molten steel to fully contact, and to adsorb the inclusions in the molten steel to float to form a top slag. Oxygen is determined before the aluminum wire is fed in the ladle after the furnace, and then the aluminum wire is fed according to the oxygen content. First, soft blowing with a large amount of gas is adopted, and after the top slag is melted, small gas blowing is changed, the exposed surface of the molten steel is controlled to about 30cm, to prevent secondary oxidation of the molten steel, then titanium iron is added, the addition amount of titanium iron is 1.5kg / t steel to 2.0kg / t steel, the argon blowing time after the furnace is greater than or equal to 8min, the argon after temperature is 1580℃ to 1600℃, and the molten steel with the composition meeting the requirements of Q355B is obtained.

[0055] The addition amount of the slag washing materials and lime dynamically changes according to the components of the slag washing materials, the components of the lime, the converter end point oxygen and sulfur, and the desulfurization rate. The addition amount of the slag washing materials required for every 100 tons of molten steel is:

[0056] X1= (530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2)

[0057] In the formula, the weight of the slag washing materials is X1 (unit: kg);

[0058] The weight percentage of Al2O3 in the slag washing materials is Y1;

[0059] The weight percentage of CaO in the slag washing materials is Y2;

[0060] The weight percentage of CaO in the lime is Y3;

[0061] The weight percentage of oxygen in the converter end point molten steel is Y4 (unit: %);

[0062] The weight percentage of S in the converter end point molten steel is Y5 (unit: %);

[0063] The desulfurization rate is Y6.

[0064] Wherein, Y1, Y2 are determined according to the test results of slag washing material, Y3 is determined according to the test results of lime; generally, the components of slag washing material and lime purchased in the same batch are stable, so Y1, Y2 and Y3 are all fixed values;

[0065] The converter end-point oxygen is related to oxygen lance operation, end-point carbon content and end-point temperature, etc. The end-point oxygen of each converter is different, but the weight percentage of oxygen element Y4 in the molten steel at the end of the normal converter is in the range of 0.04% to 0.07%.

[0066] The converter end-point sulfur content varies according to the change of the sulfur content in the molten iron. In theory, the desulfurization rate of the converter is about 30%, but in recent years, a large amount of scrap steel is added to the converter, so the actual sulfur content entering the converter is higher than 0.030%. According to a large amount of collected data, the converter end-point sulfur content is basically the same as the sulfur content of the molten iron entering the converter. Therefore, the converter end-point sulfur content Y5 is equal to the sulfur content of the molten iron entering the converter, and the process specification requires that the sulfur content of the molten iron is ≤0.030%, i.e. Y5≤0.030%.

[0067] The judgment requirement for the sulfur content of Q355B steel product is ≤0.025%, and the converter end-point sulfur content Y5 is ≤0.030%. In order to meet the judgment standard of sulfur element, the desulfurization rate Y6 is calculated to be ≥17%.

[0068] III. Continuous casting

[0069] The ladle is lifted to the continuous casting machine for casting to prepare Q355B steel billets.

[0070] In the casting process control, the ladle temperature is 1535-1545℃, the pulling speed is 1.1-1.2m / min, the secondary cooling water ratio is 0.8-0.9L / kg, and the double-flow electromagnetic stirring is started.

[0071] According to the mechanical property test, the yield strength of Q355B steel billets is ≥400MPa, the tensile strength is ≥460MPa, and the elongation is ≥26%, and the mechanical properties of the product meet the performance requirements.

[0072] According to the inclusion determination, the inclusions of Q355B steel billets include A and D types, and the highest grade is A1.5 grade, and there is no B type inclusion.

[0073] The principle of slag washing, and the calculation method and derivation process of slag washing material are described in detail below.

[0074] 1. Mechanism of slag washing process

[0075] The so-called slag washing is that in the process of converter tapping, the slag washing raw material (including slag washing material and lime) is added into the ladle with the steel flow, and in the mixing process of the slag washing material and the molten steel, the slag washing material is quickly dissolved and fully contacted with the molten steel by the bottom blowing agitation of the ladle and the agitation of the steel flow, so that the liquid slag washing material droplets can immediately collide, merge, grow and float with the deoxidation products, thereby reducing the content of oxygen and sulfur elements in the steel, so as to purify the molten steel and improve the quality of the molten steel.

[0076] 2. Main components of the slag washing raw material and the functions thereof

[0077] The slag washing raw material is composed of the slag washing material and lime, wherein the main function of the slag washing material is to purify the molten steel, modify the ladle slag, deoxidize and desulfurize, and the main function of the lime is to desulfurize and form the top slag.

[0078] The main components of the post-furnace slag washing raw material include CaO, Al2O3, SiO2 and MgO, and the four main components jointly realize the adsorption and separation of inclusions. The functions of the four components are as follows:

[0079] (1) CaO

[0080] CaO can adjust the basicity of the slag washing material and plays a role in desulfurization in the slag washing process; meanwhile, CaO reacts with Al2O3 to generate 7Al2O3·12CaO low-melting-point compound, so that the milk slag is located in the low-melting-point region (about 1300℃), and the slag quickly floats after adsorbing Al2O3.

[0081] In the present application, the weight percentage of CaO in the slag washing material is controlled to be 10%-12%, and the weight percentage of CaO in the lime is ≥90%.

[0082] (2) SiO2

[0083] SiO2 can adjust the basicity and viscosity of the slag. Since the silicon element requirement of the low-alloy high-strength steel Q355B for cold rolling is ≤0.1%, which belongs to low-silicon steel, the lower the content of SiO2 in the slag washing material and the lime is, the better, so as to reduce the introduction of silicon component.

[0084] In the present application, the weight percentage of SiO2 in the slag washing material is controlled to be 1%-1.5%, and the weight percentage of SiO2 in the lime is ≤2.5%.

[0085] (3) Al2O3

[0086] Al2O3 can react with CaO to generate 7Al2O3·12CaO low-melting-point compound, so that the milk residue is located in the low-melting-point region (about 1300 DEG C), so that the slag adsorbs Al2O3 and then quickly floats up; meanwhile, Al2O3 can also adjust the viscosity of the slag, and with the increase of the content of Al2O3, the fluidity of the slag is effectively improved, which can promote the slag-steel reaction and deoxidation diffusion, and reduce the oxidizability of the molten steel; but if the content of Al2O3 in the slag is too high, the activity of CaO will be reduced, and the desulfurization reaction will be inhibited.

[0087] In the application, the weight percentage of Al2O3 in the slag washing material is controlled at 70%-73%.

[0088] (4) MgO

[0089] MgO can maintain the saturation of MgO in the lining of the converter and the ladle, and the main role is to protect the lining.

[0090] In the application, the weight percentage of MgO in the slag washing material is controlled at 1%-1.5%.

[0091] 3, Preparation principle of slag washing raw materials

[0092] The principle of slag washing raw material configuration is to ensure that the top slag matrix component of the ladle is 7Al2O3·12CaO low-melting-point compound (about 1300 DEG C), and because of its hollow shape and low melting point, it is easy to adsorb inclusions and promote floating. Among them, Al2O3 is derived from Al2O3 formed by slag washing material and aluminum deoxidation; CaO is derived from slag washing material and lime (part of the CaO in the lime forms 7Al2O3·12CaO with Al2O3 in the slag, and part of the CaO in the lime is desulfurized).

[0093] 4, Calculation process of slag washing material addition amount formula

[0094] (1) Calculate the weight of Al2O3

[0095] The source of Al2O3 includes two parts:

[0096] ① derived from slag washing material

[0097] The weight of Al2O3 in the slag washing material is: the weight of the slag washing material × the weight percentage of Al2O3 in the slag washing material, that is, X1Y1;

[0098] ② derived from aluminum deoxidation products

[0099] The reaction equation of aluminum and oxygen is: 4Al +3O2=2Al2O3

[0100] Among them, the molecular weight of oxygen is 32, and the molecular weight of Al2O3 is 102;

[0101] According to the change of oxygen consumption, the weight of Al2O3 generated by aluminum deoxidation can be calculated as follows: 2x102x(Y4-0.005)x1000 / (32x3), i.e. 204x(Y4-0.005)x1000 / 96.

[0102] The oxygen content before argon blowing is usually about 0.005%, which is taken as 0.005% here.

[0103] Therefore, the total weight of Al2O3 is X1Y1+204x(Y4-0.005)x1000 / 96.

[0104] (2) Calculate the weight of CaO

[0105] The source of CaO includes three parts:

[0106] ① From the slag washing material

[0107] The weight of CaO in the slag washing material is X1Y2, i.e. the weight of the slag washing material x the weight percentage of CaO in the slag washing material.

[0108] ② From the desulfurization lime

[0109] The relevant chemical equation is: (CaO) + [S] = (CaS) + [O]

[0110] The weight of [S] at the end of the converter is Y5x1000 kg, the desulfurization rate is Y6, and the weight of [S] in the steel participating in the reaction is Y5Y6x1000 kg. Therefore, the weight of (CaO) participating in the reaction is 56xY5Y6x1000 / 32.

[0111] Therefore, the weight of the desulfurization lime is 56xY5Y6x1000 / 32 / Y3, i.e. 56x1000 / 32xY5Y6 / Y3=1750Y5Y6 / Y3.

[0112] ③ From the formation of 7Al2O3·12CaO by CaO in lime and Al2O3 in slag

[0113] 500-X1-desulfurization lime weight=500-X1-56x1000 / 32xY5Y6 / Y3

[0114] Therefore, the total weight of CaO is (500-X1-56x1000 / 32xY5Y6 / Y3)xY3+X1Y2.

[0115] (3) Calculate the aluminum-calcium ratio in the top slag

[0116] The relevant chemical equation is: 12CaO + 7Al2O3 = 7Al2O3·12CaO

[0117] The molecular weight of 12CaO is 672, the molecular weight of 7Al2O3 is 714, the molecular weight of 7Al2O3·12CaO is 1386, and 7Al2O3 / 12CaO=714 / 672=1.06

[0118] That is: [X1Y1+204×(Y4-0.005)×1000 / 96] / [(500-X1-56×1000 / 32×Y5Y6 / Y3)×Y3+X1Y2]=1.06

[0119] The formula is calculated as: X1=(530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2)

[0120] X1=(530Y3-1855Y5Y6-2125Y4+10.63) / (Y1+1.06Y3-1.06Y2)

[0121] That is, the slag washing material is added in weight, and according to the components of the slag washing material, the components of lime, the converter endpoint oxygen and the converter endpoint sulfur, and the change of the desulfurization rate, dynamic change is carried out.

[0122] 5. Specific requirements of slag washing raw materials

[0123] The slag washing raw material after the furnace in the application is two raw materials of slag washing material and lime.

[0124] The slag washing material is high-aluminum pre-melting, and each component is controlled in a narrow range to realize precise and stable batching, and the weight percentage composition is: CaO: 10%-12%, SiO2: 1%-1.5%, Al2O3: 70%-73%, MgO: 1%-1.5%, solvent: 10%-13%, S: 0.009%-0.011%, P2O5: 0.010%-0.013%, and burning loss: 0.5%-0.9%.

[0125] The lime is first-grade metallurgical lime, and the weight percentage composition is: CaO: ≥90%, SiO2: ≤2.5%.

[0126] 6. Feeding process of slag washing raw materials

[0127] After the converter tapping for 30s, the slag washing material and lime are added into the molten steel from the alloy bin in turn, and the slag washing material is manually bagged and thrown into the ladle at 10kg.

[0128] Take 100 tons of liquid steel as an example, combined with the actual situation on site, considering the work load and adding time of slag washing raw materials and the influence on temperature (100 tons of liquid steel needs about 3-5 minutes to be tapped, 200-300 kg of slag washing raw materials needs 1 minute to be added into the ladle, and the final temperature is reduced by 10-20℃), the total amount of slag washing raw materials is determined to be 500 kg / 100 tons, wherein the amount of slag washing materials is calculated by formula, and the remaining amount is the amount of lime added.

[0129] After the end of slag washing argon blowing, the ladle top slag is taken for composition analysis to verify the amount of slag washing materials. The calculation process of the composition of the ladle top slag is described in detail below.

[0130] The ladle top slag is composed of slag washing raw materials, deoxidation products and ladle lining erosion, etc., and the top slag matrix component is still 7Al2O3·12CaO low melting point compound, and the deoxidation products are mainly MnO, SiO2, etc. In order to ensure that the inclusions continue to float quickly during the post-furnace argon blowing process, the ladle top slag should have the characteristics of slag washing materials, i.e. high basicity (R≥4.0), low oxidizing property (FeO≤3%), and high fluidity.

[0131] According to the calculation of 100 tons of tapping, the calculation process is as follows:

[0132] ① The weight calculation process of MnO is as follows:

[0133] Assuming that the weight percentage of Mn element in the steel is Z1, the Mn element content in the product is 0.4%-0.5%, and the Mn element content in the liquid steel at the end of the converter is generally 0.1%, then the weight of silicon-manganese alloy required is: (Z1-0.1) / 65 / 0.9×1000, wherein 0.1 is the Mn element content in the liquid steel, 65 is the weight percentage of Mn element in silicon-manganese alloy, and 0.9 is the recovery rate of Mn element in the liquid steel,

[0134] Then the oxidized Mn element content is: silicon-manganese alloy weight×65%×0.1= (Z1-0.1) / 0.9.

[0135] The chemical equation for Mn oxidation is: 2Mn+O2=2MnO

[0136] The weight of MnO formed by Mn oxidation is: 142× (silicon-manganese alloy weight×65%×0.1)×100 / 110=142 / 99×100× (Z1-0.1), wherein 142 is the molecular weight of 2MnO, and 110 is the atomic weight of 2Mn.

[0137] ② The weight calculation process of SiO2 is as follows:

[0138] If the Si content in ferromanganese-silicon alloy is 17%, the Si recovery rate in molten steel is 85%, the oxidized Si content is: ferromanganese-silicon alloy weight × 17% × 0.15 = 85 / 195 × (Z1-0.1).

[0139] The chemical equation of Si oxidation is: Si + O2 = SiO2

[0140] The weight of SiO2 formed by Si oxidation is: 60 × (ferromanganese-silicon alloy weight × 17% × 0.15) × 100 / 28 = 85 / 91 × 100 × (Z1-0.1), where 60 is the molecular weight of SiO2, and 28 is the atomic weight of Si.

[0141] ③ The weight of Al2O3 oxide is: 204 × (Y4-0.005) × 1000 / 96;

[0142] ④ The weight increase of MgO caused by the erosion of the lining. According to a large amount of data statistical analysis, the average increase of MgO is 20 kg~30 kg.

[0143] ⑤ The calculation process of FeO weight:

[0144] The oxygen in the slag and the oxygen in the molten steel are in balance. Let the oxygen weight percentage in the molten steel after the furnace be Z2 (unit: %)

[0145] The chemical equation of Fe oxidation is: 2Fe + O2 = 2 FeO

[0146] Then the weight of FeO is: 144 × Z2 / 32 × 1000, where 144 is the molecular weight of 2 FeO, and 32 is the molecular weight of O2.

[0147] ⑥ The calculation process of TiO2 weight

[0148] Let Z3 be the weight percentage of Ti in the steel (unit: %),

[0149] The chemical equation of Ti oxidation is: Ti + O2 = TiO2

[0150] The weight of TiO2 is: 128 × 15 / 48 / 85 × 1000 × Z3 = 470Z3, where 128 is the molecular weight of TiO2, 48 is the atomic weight of Ti, 15 is the oxidation percentage value of Ti, and 85 is the recovery rate value of Ti.

[0151] ⑦ The calculation of ladle top slag weight:

[0152] Al2O3, MnO, MgO, SiO2, TiO2, and FeO all enter the slag, but due to the extremely small content of FeO, it can be ignored compared to other components, so it is omitted when calculating the total amount of ladle top slag.

[0153] The weight of the ladle top slag is:

[0154] 500+142 / 99×100×(Z1-0.1)+85 / 91×100×(Z1-0.1)+204×(Y4-0.005)×1000 / 96+20+128×15 / 48 / 85×1000×Z3

[0155] =520+236×(Z1-0.1)+2125×(Y4-0.005)+470Z3

[0156] =486+236Z1+2125Y4+470Z3

[0157] The weight of CaO in the top slag is: (500-X1-56×1000 / 32×Y5Y6 / Y3)×Y3+X1Y2

[0158] The weight of SiO2 in the top slag is: X1×0.01+(500-X1)×0.02+85 / 91×100×(Z1-0.1)

[0159] The weight of Al2O3 in the top slag is: X1Y1+204×(Y4-0.005)×1000 / 96

[0160] The weight of MnO in the top slag is: 142 / 99×100×(Z1-0.1)

[0161] The weight of FeO in the top slag is: 144×Z2 / 32×1000

[0162] The weight of TiO2 in the top slag is: 470Z3

[0163] The theoretical calculation value of the weight percentage of each component in the ladle top slag can be calculated through the total weight of the ladle top slag and the weight of each component.

[0164] Through actual production testing, the weight percentage of the main components of the top slag is: CaO: 33.5%-36.7%, SiO2: 4.5%-6.5%, Al2O3: 35.5%-39.0%, MgO: 2.5%-4.5%, TiO2: 2.5%-4.0%, FeO: ≤3%, MnO: 5%-8%.

[0165] By comparing the theoretical calculation value of the top slag components with the actual testing value of the top slag components, the conversion of the slag washing raw material components and whether the addition amount of the slag washing material is reasonable can be verified.

[0166] The influence of the addition of the slag washing material on the weight percentage of N element in the steel, the metallographic microstructure and the mechanical properties is described as follows:

[0167] The present application adds titanium iron when blowing argon after converter, so that the steel contains 0.040%-0.055% Ti element in percentage by weight. The addition of the alloy makes the ladle top slag contain a certain amount of TiO2, which is an oxide derived from the oxidation of Ti alloy, is a high melting point oxide with a melting point of 1850℃, is dispersedly distributed in the slag, does not melt at a temperature of 1580℃-1610℃, can be used as a surface active agent, increases the specific surface area of the slag liquid, increases the contact area of the slag liquid and the molten steel, and improves the effect of adsorbing inclusions and desulfurization. At the same time, due to the reduction of the oxidizability of the molten steel, the nitrogen absorption during the ladle argon blowing process is reduced, and the nitrogen content in the steel is reduced. The percentage by weight of TiO2 in the ladle top slag of the present application is 2.5%-4.0%.

[0168] A large amount of data collected from the production site shows that the effects of adding the slag washing material of the present application and not adding the slag washing material on the N content in the steel are compared and analyzed, and steel samples before and after argon blowing are sampled. The percentage by weight of N element before argon blowing without adding the slag washing material is 37ppm-41ppm, and the percentage by weight of N element after argon blowing is 36ppm-38ppm. The percentage by weight of N element before argon blowing with the addition of the slag washing material is 22ppm-27ppm, and the percentage by weight of N element after argon blowing is 20ppm-25ppm. The N content before and after argon blowing with the addition of the slag washing material is reduced by 40% and 30% respectively compared with the N content before and after argon blowing without the addition of the slag washing material. It can be seen that the addition of the slag washing material significantly reduces the nitrogen content in the molten steel. At the same time, due to the addition of titanium iron in the steel, the N content before and after argon blowing shows a downward trend.

[0169] After the implementation of the slag washing process of the present application, the microscopic inclusion content before and after the post-furnace argon blowing is significantly reduced. By comparing the slag washing process and the process without slag washing, when the process without slag washing is not used, the microscopic inclusion content in the steel before the post-furnace argon blowing is 76 / mm 2 -89 / mm 2 , and the microscopic inclusion content in the steel after the argon blowing is 52 / mm 2 -65 / mm 2 ; after the slag washing process of the present application is used, the microscopic inclusion content in the steel before and after the argon blowing is significantly reduced compared with the Q355B steel produced without the slag washing process, which is 27 / mm 2 -37 / mm 2 and 22 / mm 2 -25 / mm 2 , and the inclusion size is small, usually between 2μm-10μm, which shows that the slag washing process has obvious effect on the removal of inclusions.

[0170] The product without adopting the slag washing process and the product adopting the slag washing process are subjected to metallographic examination, and the structure is F+P, and the grain size is 10-10.5 grade; the inclusions of the product without adopting the slag washing process include A, B and D types, and the highest grade is 3.0 grade; the inclusions of the product adopting the slag washing process include A and D types, and the highest grade is A1.5 grade, and there is no B type inclusion, which proves that the slag washing process realizes effective reduction of the inclusion grade.

[0171] The application is further illustrated by examples below, and in the following examples, the molten steel quantity is 100 tons.

[0172] Example 1

[0173] Step 1, converter smelting

[0174] The molten steel is smelted by a converter. The content of sulfur element in the molten iron poured into the converter is 0.030%, and the final temperature of the converter smelting is 1680℃; at the final point of the converter smelting, the content of sulfur element in the molten steel is 0.030% by weight, the content of Mn element is 0.1% by weight, and the content of oxygen element is 0.07% by weight;

[0175] Step 2, slag washing and argon blowing

[0176] After the converter tapping for 30s, 213kg of slag washing material and 287kg of lime are sequentially added from the alloy bin, wherein the slag washing material is manually bagged and thrown into the ladle at 10kg / bag, and meanwhile, the bottom argon blowing of the ladle is performed.

[0177] After the tapping is completed, the temperature and oxygen content of the ladle are measured after reaching the furnace, the argon pre-temperature is 1650℃, the oxygen content is 9ppm, 90m of aluminum wire is fed, and the argon post-oxygen content is 3ppm. After the aluminum wire is fed, the ladle is soft blown in the air, and after the top slag is melted, the argon blowing is changed to small gas amount, the molten steel bare surface is controlled at about 30cm, to prevent secondary oxidation of the molten steel, and then 200kg of ferrotitanium is added, the argon blowing time after the furnace is 10min, and the argon post-temperature is 1585℃.

[0178] Taking 100 tons of molten steel as the calculation basis, the content of Al2O3 in the slag washing material Y1 is 70% by weight, the content of CaO in the slag washing material Y2 is 10% by weight, the content of CaO in the lime Y3 is 90% by weight, the content of oxygen element in the molten steel at the final point of the converter Y4 is 0.07% by weight, the content of sulfur element in the molten steel at the final point of the converter Y5 is 0.030% by weight, the desulfurization rate Y6 is 17%, the content of manganese element in the product Z1 is 0.4% by weight, the content of free oxygen in the product Z2 is 0.0015% by weight, and the content of Ti in the steel Z3 is 0.055% by weight. The above values are substituted into the formula to calculate the input amount of the slag washing material and the lime, and the composition of the top slag of the ladle.

[0179] The addition amount of the slag washing material is calculated according to the following formula,

[0180] X1= (530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2)

[0181] Substitute the numerical values of Y1, Y2, Y3, Y4, Y5 into the above formula, and the addition amount of the slag washing material can be calculated as:

[0182] X1= (530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2)

[0183] = (530x90%-1855x0.030x17%-2130x0.07+10.65) / (70%+1.06x90%-1.06x10%)

[0184] = 213 kg

[0185] The addition amount of lime is: 500-213=287 kg

[0186] The content calculation process of each component in the ladle top slag is as follows:

[0187] The weight of the ladle top slag is:

[0188] 486+236Z1+2125Y4+470Z3

[0189] = 486+236x0.4+2125x0.07+470x0.055

[0190] = 755 kg

[0191] The weight of CaO in the top slag is:

[0192] (500-X1-56x1000 / 32xY5Y6 / Y3)xY3+X1Y2=271 kg

[0193] The weight of SiO2 in the top slag is: X1x0.01+(500-X1)x0.02+85 / 91x100x(Z1-0.1)=36 kg

[0194] The weight of Al2O3 in the top slag is: X1Y1+204x(Y4-0.005)x1000 / 96=287 kg

[0195] The weight of MnO in the top slag is: 142 / 99x100x(Z1-0.1)=43 kg

[0196] The weight of TiO2 in the top slag is: 470xZ3=26 kg

[0197] The weight of FeO in the top slag is: 144 x Z3 / 32 x 1000 = 7 kg

[0198] The weight of MgO in the top slag is: 20 kg

[0199] After calculation, the weight percentage of the main components of the top slag is: CaO: 35.87%, SiO2: 4.74%, Al2O3: 38.03%, MgO: 2.65%, TiO2: 3.43%, FeO: 0.89%, MnO: 5.68%, R: 7.57. It meets the actual detection range of the components of the top slag of the ladle.

[0200] After detection, the weight percentage of N element in the steel before argon blowing is 25 ppm, and the weight percentage of N element in the steel after argon blowing is 23 ppm; the number of micro-inclusions in the liquid steel before and after argon blowing is 28 / mm 2 and 23 / mm 2 , respectively, and the size of the micro-inclusions is 2-10 μm.

[0201] Step 3, continuous casting

[0202] The ladle is lifted to the continuous casting machine for casting, and the steel billet is rolled into Q355B steel finished product. The ladle temperature in the continuous casting process control is 1540℃, the pulling speed is 1.1 m / min, the specific water consumption of the secondary cooling is 0.8 L / kg, and the double-flow electromagnetic stirring is started.

[0203] After detection, the chemical composition and mass fraction of the prepared Q355B finished product are: C: 0.17%, Mn: 0.4%, Si: 0.07%, S: 0.0249%, P: 0.015%, Al: 0.045%, Ti: 0.055%, N: 0.0025%.

[0204] Take the Q355B finished product for mechanical property test, and the test method is in accordance with GB / T 228.1-2021 Metallic Materials Tensile Test Part 1: Room Temperature Test Method. After detection, the yield strength of the product is 438 MPa, the tensile strength is 507 MPa, and the elongation is 30%, and the mechanical properties of the product meet the performance requirements.

[0205] Take the Q355B finished product for microscopic examination, and grade the inclusions in the Q355B finished product, and the grading method is referred to GB / T 10561-2005 Standard Grading Microscopic Examination Method for Determination of Non-metallic Inclusion Content in Steel. The metallographic structure is F+P, the grain size is 10 levels, and the inclusions are A1.5, D1.0, D1.0e, D TiN 1.0.

[0206] In addition, according to the cost accounting, the cost of the slag washing raw materials used in this embodiment is 11.24 yuan / ton of steel.

[0207] Example 2

[0208] Step 1, converter smelting

[0209] The converter smelting molten steel. The content of sulfur element in the molten iron poured into the converter is 0.030%, and the temperature at the end of converter smelting is 1640℃; at the end of converter smelting, the weight percentage of sulfur element in the molten steel is 0.030%, the weight percentage of Mn element is 0.1%, and the weight percentage of oxygen element is 0.04%;

[0210] Step 2, slag washing and argon blowing

[0211] After the converter tapping for 30s, 245kg of slag washing material and 255kg of lime are sequentially added from the alloy bin, wherein the slag washing material is manually thrown into the ladle in a bag of 10kg, and at the same time, the bottom argon blowing of the ladle is carried out.

[0212] After the tapping is completed, the temperature and oxygen content of the ladle are measured after reaching the furnace, the argon pre-temperature is 1630℃, the oxygen content is 9ppm, 90m of aluminum wire is fed, and the argon post-oxygen content is 3ppm. After feeding the aluminum wire, the ladle is soft blown in the atmosphere, and after the top slag is melted, the argon blowing is changed to small gas amount, and the molten steel bare surface is controlled at about 30cm to prevent secondary oxidation of the molten steel, and then 150kg of titanium iron is added, the argon blowing time after the furnace is 9min, and the argon post-temperature is 1580℃.

[0213] Taking 100 tons of molten steel as an example for calculation, the weight percentage Y1 of Al2O3 in the slag washing material is 73%, the weight percentage Y2 of CaO is 10%, the weight percentage Y3 of CaO in the lime is 90%, the weight percentage Y4 of oxygen element is 0.04%, the weight percentage Y5 of sulfur element in the molten steel at the end of the converter is 0.030%, the desulfurization rate Y6 is 30%, the weight percentage Z1 of manganese element in the product is 0.5%, the weight percentage Z2 of free oxygen in the product is 0.0015%, and the weight percentage Z3 of Ti in the steel is 0.040%. The above values are substituted into the formula to calculate the input amount of slag washing material and lime, and the composition of the top slag of the ladle.

[0214] The amount of the slag washing material is calculated according to the following formula,

[0215] Slag washing material X1=(530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2)

[0216] =(530*90%-1855*0.03*30%-2130*0.04+10.65) / (73%+1.06*90%-1.06*10%)

[0217] =245kg

[0218] The amount of lime added is: 500-245=255kg

[0219] The content of each component in the ladle top slag is calculated as follows:

[0220] The weight of the ladle top slag is: 486+236Z1+2125Y4+470Z3=708kg

[0221] The weight of CaO in the top slag is: (500-X1-56x1000 / 32xY5Y6 / Y3)xY3+X1Y2=239kg

[0222] The weight of SiO2 in the top slag is: X1x0.01+(500-X1)x0.02+85 / 91x100x(Z1-0.1)=45kg

[0223] The weight of Al2O3 in the top slag is: X1Y1+204x(Y4-0.005)x1000 / 96=253kg

[0224] The weight of MnO in the top slag is: 142 / 99x100x(Z1-0.1)=57kg

[0225] The weight of FeO in the top slag is: 144xZ2 / 32x1000=7kg

[0226] The weight of TiO2 in the top slag is: 470xZ3=19kg

[0227] The weight of MgO in the top slag is: 20kg

[0228] After calculation, the weight percentage of main components in the top slag is: CaO: 33.7%, SiO2: 6.32%, Al2O3: 35.74%, MgO: 2.83%, TiO2: 2.66%, FeO: 0.95%, MnO: 8.08%, R: 5.33. It meets the actual detection range of the components of the ladle top slag.

[0229] After detection, the weight percentage of N element in the steel before argon blowing is 22ppm, and the weight percentage of N element in the steel after argon blowing is 20ppm; the number of micro-inclusions in the molten steel before and after argon blowing is 27 / mm 2 and 22 / mm 2 , respectively, with a size of 2-10μm.

[0230] Step 3, continuous casting

[0231] The ladle is lifted to the continuous casting machine for casting, and the steel billet is rolled into Q355B steel finished product. The ladle temperature in the continuous casting process control is 1550℃, the pulling speed is 1.1m / min, the secondary cooling water ratio is 0.8L / kg, and the double-flow electromagnetic stirring is started.

[0232] The chemical composition and mass fraction of the prepared Q355B finished product are: C: 0.17%, Mn: 0.5%, Si: 0.09%, S: 0.0185%, P: 0.015%, Al: 0.045%, Ti: 0.040%, and N: 0.0023%.

[0233] The Q355B finished product is taken for mechanical property testing, and the testing method is in accordance with GB / T 228.1-2021 Metal Materials Tensile Test Part 1: Room Temperature Test Method. The yield strength of the product is 424 MPa, the tensile strength is 495 MPa, and the elongation is 31%, and the mechanical properties of the product meet the performance requirements.

[0234] The Q355B finished product is taken for microscopic examination, and the inclusions in the Q355B finished product are rated, and the rating method is referred to GB / T 10561-2005 Standard Rating Diagram Microscopic Examination Method for Determination of Non-metallic Inclusion Content in Steel. The metallographic structure is F+P, the grain size is 10.5 level, and the inclusions are A1.5, D1.0, D1.0e, and D TiN 0.5.

[0235] In addition, according to the cost accounting, the cost of the slag washing raw material used in the embodiment is 12.44 yuan / ton of steel.

[0236] Example 3

[0237] Step 1, converter smelting

[0238] Converter smelting is adopted. The sulfur content in the molten iron charged into the converter is 0.030%, and the final temperature of the converter smelting is 1670℃; at the end of the converter smelting, the weight percentage of sulfur in the molten steel is 0.030%, the weight percentage of Mn element is 0.1%, and the weight percentage of oxygen element is 0.06%;

[0239] Step 2, slag washing argon blowing

[0240] After the converter tapping for 30s, 217kg of slag washing material and 283kg of lime are added from the alloy bin in turn, wherein the slag washing material is manually thrown into the ladle with a bag of 10kg, and at the same time, the bottom argon blowing of the ladle is carried out.

[0241] After the tapping is completed, the temperature and oxygen content of the ladle are measured after reaching the furnace, the argon temperature is 1625℃, the oxygen content is 9ppm, the aluminum wire is fed for 90m, and the oxygen content after argon is 3ppm. After feeding the aluminum wire, the ladle is soft blown in the air, and after the top slag is melted, it is changed to small argon blowing, and the bare surface of the molten steel is controlled at about 30cm to prevent secondary oxidation of the molten steel, and then 170kg of titanium iron is added, the argon blowing time after the furnace is 9min, and the temperature after argon is 1585℃.

[0242] Taking 100 tons of molten steel as an example, the slag washing material Al2O3 weight percentage Y1 is 72%, the slag washing material CaO weight percentage Y2 is 11%, the lime CaO weight percentage Y3 is 90%, the oxygen element weight percentage Y4 is 0.06%, the converter end-point molten steel sulfur element weight percentage Y5 is 0.030%, the desulfurization rate Y6 is 40%, the product manganese element weight percentage Z1 is 0.45%, the product free oxygen weight percentage Z2 is 0.0015%, and the steel Ti weight percentage Z3 is 0.045%. The above values are substituted into the formula to calculate the input amount of slag washing material and lime, and the composition of the ladle top slag.

[0243] The addition amount of the slag washing material is:

[0244] X1= (530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2) = 217 kg

[0245] The addition amount of lime is: 500-217 = 283 kg

[0246] The content calculation process of each component in the ladle top slag is as follows:

[0247] The weight of the ladle top slag is: 486+236Z1+2125Y4+470Z3= 741 kg

[0248] The CaO weight in the top slag is: (500-X1-56×1000 / 32×Y5Y6 / Y3)×Y3+X1Y2= 258 kg

[0249] The SiO2 weight in the top slag is: X1×0.01+(500-X1)×0.02+85 / 91×100×(Z1-0.1)= 40 kg

[0250] The Al2O3 weight in the top slag is: X1Y1+204×(Y4-0.005)×1000 / 96= 273 kg

[0251] The MnO weight in the top slag is: 142 / 99×100×(Z1-0.1)= 50 kg

[0252] The FeO weight in the top slag is: 144×Z3 / 32×1000= 7 kg

[0253] The TiO2 weight in the top slag is: 470×Z3= 21 kg

[0254] The MgO weight in the top slag is: 30 kg

[0255] The top slag mainly contains CaO: 34.77%, SiO2: 5.45%, Al2O3: 36.86%, MgO: 4.05%, TiO2: 2.86%, FeO: 0.91%, MnO: 6.76%, R: 6.38 by weight percentage. The actual detection range of the top slag component of the ladle is consistent.

[0256] The N element in the steel before argon blowing is 25ppm by weight, and the N element in the steel after argon blowing is 23ppm by weight. The micro-inclusions in the liquid steel before and after argon blowing are 27 / mm 2 and 22 / mm 2 , respectively, with a size of 2-10μm.

[0257] Step 3, continuous casting

[0258] The ladle is lifted to the continuous casting machine for casting, and the steel billet is rolled into Q355B steel product. The tundish temperature in the continuous casting process is 1545℃, the pulling speed is 1.1m / min, the secondary cooling water ratio is 0.8L / kg, and the double-flow electromagnetic stirring is started.

[0259] The chemical composition and mass fraction of the prepared Q355B product are: C: 0.17%, Mn: 0.45%, Si: 0.08%, S: 0.018%, P: 0.015%, Al: 0.045%, Ti: 0.045%, N: 0.0025%;

[0260] The Q355B product is taken for mechanical property test, and the test method is in accordance with GB / T 228.1-2021 Metallic Materials Tensile Testing Part 1: Room Temperature Test Method. The yield strength of the product is 449MPa, the tensile strength is 497MPa, and the elongation is 30.5%. The mechanical properties of the product meet the performance requirements.

[0261] The Q355B product is taken for microscopic examination, and the inclusions in the Q355B product are rated. The rating method is in accordance with GB / T 10561-2005 Standard Rating Diagram Microscopic Examination Method for Determination of Non-metallic Inclusion Content in Steel. The metallographic structure is F+P, the grain size is 10, and the inclusions are A1.5, D1.0, D1.0e, D TiN 0.5.

[0262] In addition, according to the cost calculation, the cost of the slag washing raw materials used in this embodiment is 11.32 yuan / ton of steel.

[0263] Example 4

[0264] Step 1, converter smelting

[0265] The converter smelts the molten steel. The content of sulfur element in the molten iron added into the converter is 0.030%, and the final temperature of the converter smelting is 1680℃; at the final point of the converter smelting, the content of sulfur element in the molten steel is 0.030%, the content of Mn element is 0.1%, and the content of oxygen element is 0.07%;

[0266] Step 2, slag washing argon blowing

[0267] After the converter tapping for 30s, 197kg of slag washing material and 303kg of lime are added from the alloy bin in turn, wherein the slag washing material is manually added into the ladle by 10kg of bagging, and meanwhile, the bottom argon blowing of the ladle is performed.

[0268] After the tapping is completed, the temperature and oxygen content of the ladle are measured after reaching the furnace, the argon pre-temperature is 1625℃, the oxygen content is 9ppm, 90m of aluminum wire is fed, and the argon post-oxygen content is 3ppm. After the aluminum wire is fed, the soft blowing of the ladle is performed in the air, and after the top slag is melted, the argon blowing is changed to small gas amount, the bare surface of the molten steel is controlled to be about 30cm, so as to prevent the secondary oxidation of the molten steel, and then 189kg of ferrotitanium is added, the argon blowing time after the furnace is 9min, and the argon post-temperature is 1585℃.

[0269] Taking 100 tons of molten steel as an example for calculation, the content of Al2O3 in the slag washing material Y1 is 73%, the content of CaO in the slag washing material Y2 is 10%, the content of CaO in the lime Y3 is 90%, the content of oxygen element Y4 is 0.07%, the content of sulfur element in the molten steel at the final point of the converter Y5 is 0.030%, the desulfurization rate Y6 is 50%, the content of Mn element in the product Z1 is 0.50%, the content of free oxygen in the product Z2 is 0.0015%, and the content of Ti in the steel Z3 is 0.050%. The above values are substituted into the formula to calculate the input amount of the slag washing material and the lime, and the composition of the top slag of the ladle.

[0270] The addition amount of the slag washing material is calculated according to the following formula,

[0271] Slag washing material X1= (530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2)=197kg

[0272] The addition amount of the lime is: 500-197=303kg

[0273] The content calculation process of each component in the top slag of the ladle is as follows:

[0274] The weight of the top slag of the ladle is: 486+236Z1+2125Y4+470Z3=776kg

[0275] The weight of CaO in the top slag is: (500-X1-56×1000 / 32×Y5Y6 / Y3)×Y3+X1Y2=266kg

[0276] The weight of SiO2 in the top slag is: X1*0.01+(500-X1)*0.02+85 / 91*100*(Z1-0.1)=45 kg

[0277] The weight of Al2O3 in the top slag is: X1*Y1+204*(Y4-0.005)*1000 / 96=282 kg

[0278] The weight of MnO in the top slag is: 142 / 99*100*(Z1-0.1)=57 kg

[0279] The weight of FeO in the top slag is: 144*Z3 / 32*1000=7 kg

[0280] The weight of TiO2 in the top slag is: 470*Z3=24 kg

[0281] The weight of MgO in the top slag is: 30 kg

[0282] According to the calculation, the weight percentage of the main components of the top slag is: CaO: 34.27%, SiO2: 5.83%, Al2O3: 36.33%, MgO: 3.86%, TiO2: 3.03%, FeO: 0.87%, MnO: 7.37%, and R: 5.88. It meets the actual detection range of the components of the top slag of the ladle.

[0283] The weight percentage of N element in the steel before argon blowing is 25 ppm, and the weight percentage of N element in the steel after argon blowing is 23 ppm; the number of micro-inclusions in the molten steel before and after argon blowing is 27 / mm 2 and 22 / mm 2 , respectively, with a size of 2-10 μm.

[0284] Step 3, continuous casting

[0285] The ladle is lifted to the continuous casting machine for casting, and the steel billet is rolled into Q355B steel finished product. The ladle temperature in the continuous casting process control is 1545℃, the pulling speed is 1.1 m / min, the secondary cooling specific water quantity is 0.8 L / kg, and the double-flow electromagnetic stirring is started.

[0286] According to the detection, the chemical composition and mass fraction of the prepared Q355B finished product are: C: 0.17%, Mn: 0.50%, Si: 0.09%, S: 0.015%, P: 0.015%, Al: 0.045%, Ti: 0.050%, and N: 0.0025%.

[0287] The Q355B finished product is taken for mechanical property test, and the test method is referred to GB / T 228.1-2021 Metallic Materials-Tensile Testing-Part 1: Method of Test at Room Temperature. Through detection, the yield strength of the product is 456 MPa, the tensile strength is 517 MPa, and the elongation is 30%, and the mechanical properties of the product meet the performance requirements.

[0288] The Q355B finished product is taken for microscopic examination, and the inclusions in the Q355B finished product are rated, and the rating method is referred to GB / T 10561-2005 Determination of Non-metallic Inclusion Content in Steel-Standard Rating Diagram Microscopic Examination Method. The detection shows that the metallographic structure is F+P, the grain size is 10 levels, the inclusions are A1.5, D1.0, D1.0e, and D TiN 0.5.

[0289] In addition, through cost accounting, the cost of the slag washing raw material used in the embodiment is 10.51 yuan / ton of steel.

[0290] Comparative Example 1

[0291] In the present comparative example, only lime is added after the converter tapping, and no slag washing material is added.

[0292] The specific preparation process is as follows:

[0293] Step 1, converter smelting

[0294] The converter smelting molten steel. The sulfur content in the molten iron charged into the converter is 0.030%, and the converter smelting end temperature is 1660℃; at the converter smelting end, the weight percentage of sulfur in the molten steel is 0.030%, the weight percentage of Mn element is 0.1%, and the weight percentage of oxygen element is 0.07%;

[0295] Step 2, slag washing argon blowing

[0296] After the converter tapping for 30s, 500kg of lime is added from the alloy bin in turn.

[0297] After tapping, the ladle reaches the furnace to measure the temperature and oxygen, the argon temperature is 1650℃, the oxygen is 9ppm, the aluminum wire is fed for 90m, and the argon oxygen is 3ppm. After feeding the aluminum wire, the ladle is blown with soft air, and after the top slag is melted, it is changed to small air blowing, and the molten steel bare surface is controlled at about 30cm to prevent secondary oxidation of the molten steel, and then 189kg of titanium iron is added, and the argon blowing time after the furnace is 10min, and the argon temperature is 1585℃.

[0298] Through composition detection, the weight percentage of CaO in lime Y3 is 90%, the weight percentage of oxygen element in converter end molten steel Y4 is 0.07%, the weight percentage of manganese element in product is 0.50%, and the weight percentage of free oxygen in product is 0.0015%.

[0299] The main components of the top slag are calculated as follows: CaO: 46.12%, SiO2: 15.48%, Al2O3: 23.74%, MgO: 6.74%, TiO2: 3.13%, FeO: 3.03%, MnO: 1.76%, R: 2.98%. The components of the top slag are not within the actual detection range.

[0300] The weight percentage of N element in the steel before argon blowing is 40 ppm, and the weight percentage of N element in the steel after argon blowing is 37 ppm; the number of micro-inclusions in the liquid steel before and after argon blowing is 85 / mm 2 and 60 / mm 2 , respectively, and the size is 50-1000 μm. It can be seen that, compared with Example 1, the number and size of inclusions in the liquid steel of Comparative Example 1 are significantly increased.

[0301] Step 3, continuous casting

[0302] The ladle is lifted to the continuous casting machine for casting, and the steel billet is rolled into Q355B steel product. The temperature of the ladle in the continuous casting process is 1545℃, the pulling speed is 1.1 m / min, the specific water consumption of the secondary cooling is 0.8 L / kg, and the double-flow electromagnetic stirring is started.

[0303] The chemical composition and mass fraction of the prepared Q355B product are detected as follows: C: 0.17%, Mn: 0.50%, Si: 0.09%, S: 0.024%, P: 0.015%, Al: 0.045%, Ti: 0.050%, N: 0.0045%. It can be seen that the content of N element in the steel is >0.0035%, which does not meet the chemical composition requirement of Q335B steel grade that the content of N element is ≤0.0035%.

[0304] The Q355B product is taken for mechanical property test, and the test method is in accordance with GB / T 228.1-2021 Metallic Materials-Tensile Testing-Part 1: Method of Test at Room Temperature. The yield strength of the product is 450 MPa, the tensile strength is 515 MPa, and the elongation is 25.5%. The elongation of the product is low, and the mechanical properties of the product do not meet the performance requirements.

[0305] The Q355B product is taken for microscopic examination, and the inclusions in the Q355B product are rated. The rating method is in accordance with GB / T 10561-2005 Standard Rating Diagram Microscopic Examination Method for Determination of Non-metallic Inclusion Content in Steel. The metallographic structure is F+P, the grain size is 10, and the inclusions are A3.0, B2.0, D1.0, D1.0e, D TiN 1.5.

[0306] In addition, the cost of lime used in the comparative example is 3 yuan / ton of steel after cost accounting, although the cost is low, the product is unqualified, and the cost loss is greater.

[0307] Comparative Example 2

[0308] In the comparative example, only slag washing material is added after the converter tapping, and the weight percentage of the components of the slag washing material is: CaO: 45%, SiO2: 2%, Al2O3: 15%, MgO: 1%-1.5%, solvent: 15%, S: 0.01%, P2O5: 0.01%, and burning loss 0.9%.

[0309] The specific preparation process is:

[0310] Step 1, converter smelting

[0311] The converter smelting molten steel. The sulfur content in the molten iron charged into the converter is 0.030%, and the converter smelting end temperature is 1680℃; at the end of converter smelting, the weight percentage of sulfur in the molten steel is 0.030%, the weight percentage of Mn element is 0.1%, and the weight percentage of oxygen element is 0.07%;

[0312] Step 2, slag washing argon blowing

[0313] After the converter tapping for 30s, 500kg of ordinary slag washing material is added from the alloy bin in turn, and the ordinary slag washing material is manually thrown into the ladle with a bag of 10kg, while the ladle is bottom argon blowing.

[0314] After the tapping is completed, the ladle reaches the furnace to measure the temperature and oxygen, the argon temperature is 1625℃, the oxygen is 9ppm, the aluminum wire is fed 90m, and the oxygen after argon is 3ppm. After feeding the aluminum wire, the ladle is soft blown in the air, and after the top slag is melted, it is changed to small argon blowing, and the bare surface of the molten steel is controlled at about 30cm to prevent secondary oxidation of the molten steel, and then 1.89kg / t of titanium iron is added, and the argon blowing time after the furnace is 9min, and the temperature after argon is 1585℃.

[0315] Taking 100 tons of molten steel as an example, the weight percentage of Al2O3 in the slag washing material Y1 is 33%, the weight percentage of CaO Y2 is 40%, the weight percentage of CaO in lime Y3 is 90%, the weight percentage of oxygen Y4 is 0.07%, the desulfurization rate Y6 is 50%, the weight percentage of manganese in the product Z1 is 0.50%, the weight percentage of free oxygen in the product Z2 is 0.0015%, and the weight percentage of Ti in the steel Z3 is 0.055%.

[0316] The feeding amount X1 of the ordinary slag washing material is 500kg

[0317] The weight of the ladle top slag is: 486+236Z1+2125Y4+470Z3=776kg

[0318] The weight of CaO in the top slag is: 500 × Y2 = 200 kg

[0319] The weight of SiO2 in the top slag is: X1×0.01+85 / 91×100×(Z1-0.1)=97kg

[0320] The weight of Al2O3 in the top slag is: X1Y1 + 204 × (Y4 - 0.005) × 1000 / 96 = 303 kg

[0321] The weight of MnO in the top slag is: 142 / 99 × 100 × (Z1 - 0.1) = 57 kg

[0322] The weight of FeO in the top slag is: 144 × Z3 / 32 × 1000 = 18 kg

[0323] The weight of TiO2 in the top slag is: 470 × Z3 = 24 kg

[0324] The calculated weight percentages of the main components of the top slag are as follows: CaO: 25.76%, SiO2: 12.52%, Al2O3: 39.05%, MgO: 1.29%, TiO2: 3.03%, FeO: 2.32%, MnO: 7.37%, R: 2.06%.

[0325] The nitrogen content in the steel before argon blowing was 36 ppm by weight, and after argon blowing, it was 38 ppm by weight. The micro-inclusions in the molten steel before and after argon blowing were 36 per mm, respectively. 2 and 42 / mm 2 The size ranges from 50 to 700 μm. It is evident that, compared to the examples, the number and size of inclusions in the molten steel of Comparative Example 2 are significantly increased.

[0326] Step 3: Continuous casting to form billets

[0327] The ladle is hoisted to the continuous casting machine for casting, and the steel billet is rolled into Q355B steel finished product. The continuous casting process controls the ladle temperature at 1545℃, the casting speed at 1.1 m / min, the secondary cooling water ratio at 0.8 L / kg, and the electromagnetic stirring is activated in a dual-flow configuration.

[0328] The chemical composition and mass fraction of the Q355B finished product were tested and found to be as follows: C: 0.17%, Mn: 0.50%, Si: 0.09%, S: 0.021%, P: 0.015%, Al: 0.045%, Ti: 0.050%, N: 0.0041%. However, the sulfur content did not meet the expected target of 0.015%, and the nitrogen content in the steel did not meet the chemical composition requirement of ≤0.0035%.

[0329] The Q355B finished product is taken to test the mechanical properties, and the test method is referred to GB / T 228.1-2021 Metallic Materials-Tensile Testing-Part 1: Method of Test at Room Temperature. After detection, the yield strength of the product is 436 MPa, the tensile strength is 487 MPa, and the elongation is 27.5%. The mechanical properties of the product do not meet the performance requirements, but the elongation of the product is lower than that of the low-alloy high-strength steel Q355B produced by the application due to the influence of inclusions.

[0330] The Q355B finished product is taken to test the microstructure, and the inclusions in the Q355B finished product are rated. The rating method is referred to GB / T 10561-2005 Determination of Non-metallic Inclusions in Steel-Standard Rating Diagram-Microscopic Examination Method. After detection, the metallographic structure is F+P, the grain size is 10 levels, the inclusions are A3.0, D1.0, D1.0e, D TiN 1.5, and the grades of various inclusions are relatively high.

[0331] After cost accounting, the cost of the ordinary slag washing material used in the above-mentioned comparative example is 15 yuan / ton of steel, but the content of N element in the steel does not meet the chemical composition requirements, and the cost loss is greater.

[0332] The above-mentioned is only the preferred embodiment of the application, and any change and modification made according to the application patent range should be included in the scope of the application.

Claims

1. A method for reducing the inclusion rating of a low alloy high strength steel Q355B for cold rolling, characterized in that: After the end of steelmaking, slag washing raw materials composed of slag washing materials and lime are added into the molten steel, and the addition amount of the slag washing raw materials is 500 kg / 100 tons of steel; Wherein, the amount of slag washing materials X1 needed to be added per 100 tons of molten steel is calculated by the following formula: X1=(530Y3-1855Y5Y6-2130Y4+10.65) / (Y1+1.06Y3-1.06Y2) In the formula, the weight of the slag washing materials is X1, unit: kg; The weight percentage of Al2O3 in the slag washing materials is Y1; The weight percentage of CaO in the slag washing materials is Y2; The weight percentage of CaO in the lime is Y3; The weight percentage of oxygen in the molten steel at the end of the converter is Y4, unit: %; The weight percentage of S in the molten steel at the end of the converter is Y5, unit: %; The desulfurization rate is Y6; The weight percentage composition of the slag washing materials is as follows: CaO: 10%-12%, SiO2: 1%-1.5%, Al2O3: 70%-73%, MgO: 1%-1.5%, solvent: 10%-13%, S: 0.009%-0.011%, P2O5: 0.010%-0.013%, burning loss: 0.5%-0.9%; The lime is first-grade metallurgical lime, and the weight percentage composition is as follows: CaO: ≥90%, SiO2: ≤2.5%; The weight percentage composition of the top slag of the ladle is as follows: CaO: 33.5%-36.7%, SiO2: 4.5%-6.5%, Al2O3: 35.5%-39.0%, MgO: 2.5%-4.5%, TiO2: 2.5%-4.0%, FeO: ≤3%, MnO: 5%-8%.

2. The method for reducing the inclusion level of low-alloy high-strength steel Q355B for cold rolling according to claim 1, characterized in that: The converter is used to smelt the molten iron, and the S content of the molten iron poured into the converter is ≤0.030wt%, and the temperature at the end of the converter smelting is controlled at 1650℃-1680℃.

3. The method for reducing the inclusion level of low-alloy high-strength steel Q355B for cold rolling according to claim 1, characterized in that: After the slag washing raw materials are added, the oxygen in the ladle is fixed, and the aluminum wire is fed according to the oxygen content; then the ferrotitanium is added, and the addition amount of the ferrotitanium is 1.5kg / ton of steel-2.0kg / ton of steel.

4. The method for reducing the inclusion level of low-alloy high-strength steel Q355B for cold rolling according to claim 3, characterized in that: After the aluminum wire is fed, the soft blowing with large gas amount is used first, and then the argon blowing with small gas amount is used after the top slag is melted, the bare surface of the molten steel is controlled at 30cm, and the argon blowing time after the furnace is ≥8min.

5. The method for reducing the inclusion level of low alloy high strength steel Q355B for cold rolling according to claim 1, characterized in that: In the process control of continuous casting, the temperature of the tundish is 1535℃-1545℃, the casting speed is 1.1m / min-1.2m / min, and the specific water consumption of the secondary cooling is 0.8L / kg-0.9L / kg.

6. The method for reducing the inclusion level of low alloy high strength steel Q355B for cold rolling according to claim 1, characterized in that: The yield strength of the low-alloy high-strength steel Q355B for cold rolling is ≥400MPa, the tensile strength is ≥460MPa, and the elongation is ≥26%.

7. The method for reducing the inclusion level of low alloy high strength steel Q355B for cold rolling according to claim 1, characterized in that: The inclusions of the low-alloy high-strength steel Q355B for cold rolling include A type and D type, and there is no B type inclusion; the grade of the A type inclusion is not greater than 1.5 grade, and the grade of the D type inclusion is not greater than 1.0 grade.

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