A method for improving the control of inclusions in automobile beam steel by adding rare earth elements

Abstract

The application discloses a method for improving automobile beam steel inclusions by adding rare earth elements, comprising the following steps: increasing the number of rare earth killed steel continuous casting furnaces in LF process and double process from 10 to 21; controlling the end point oxygen content of the converter within 900 ppm; using hollow argon blowing stopper as the whole process protection technology means for rare earth steel casting; adopting protective casting in the casting process to ensure that the nitrogen increase of the casting machine is within 5 ppm; reducing the oxygen content in the slag in the refining process; adding calcium carbide or modifier in the LF furnace treatment of the rare earth steel to quickly form white slag, the total iron content in the slag is within 1.0%, the consumption of the added rare earth alloy is reduced, and the yield of the rare earth element is improved. The application improves the size and morphology of the product inclusions by adding rare earth elements, improves the quality of the rare earth steel product, jointly creates high value-added rare earth steel characteristic products, gradually improves the influence of Baotou Steel in the rare earth product industry, and continuously expands the market share.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgy steelmaking process, and particularly relates to a method for improving automobile beam steel inclusions by adding rare earth elements. BACKGROUND

[0002] In the actual production process in 2020, after adding rare earth in molten steel, because the rare earth elements are extremely easy to react with oxygen, large particle rare earth oxides are generated, the rare earth oxide has a high melting point, and is gathered to the inner wall of the caster nozzle in the casting process, causing serious cotton steel in the casting process of the caster, restricting the continuous casting and continuous casting furnace number, and batch production cannot be realized.

[0003] In order to solve the above problems, various comparative studies are carried out for products with different performance characteristics, a development work network progress chart and a specific experimental scheme are formulated for different steel grades, and a series of work such as sampling, entrusting inspection, test analysis, mechanism research and product application tracking at the user end are carried out on the production process of rare earth products, and finally a breakthrough is made in the control of rare earth steel inclusions.

[0004] By adding rare earth elements to the product, the size and morphology of the product inclusions are improved, the product quality is improved, the high value-added rare earth steel characteristic product is jointly created, the influence of Baogang in the rare earth product industry is gradually improved, the market share is continuously expanded, and at the same time of enterprise strategic cooperation with the user, the rare earth steel product is quickly converted into brand value, and the user shares the rare earth steel brand benefit. SUMMARY

[0005] The purpose of the present application is to provide a method for improving automobile beam steel inclusions by adding rare earth elements, which improves the size and morphology of product inclusions, improves the quality of rare earth steel products, jointly creates high value-added rare earth steel characteristic products, gradually improves the influence of Baogang in the rare earth product industry, continuously expands the market share, and at the same time of enterprise strategic cooperation with the user, the rare earth steel product is quickly converted into brand value, and the user shares the rare earth steel brand benefit.

[0006] To solve the above technical problems, the present application adopts the following technical scheme:

[0007] The present application provides a method for improving automobile beam steel inclusions by adding rare earth elements, which comprises the following steps:

[0008] The continuous casting furnace number of the rare earth killed steel in the LF process and the double process is increased from 10 to 21;

[0009] The oxygen content at the end of the converter is controlled within 900ppm, and the number of rare earth oxides and aluminum oxides in the steel is reduced;

[0010] The activity [O] in the molten steel is reduced during the refining process, and the cleanliness of the molten steel is improved;

[0011] The refining process is optimized for the T.Fe content of the rare earth steel slag, the oxygen content in the slag is reduced, the calcium carbide or modifier is added in the LF furnace treatment, the white slag is quickly formed, the total iron content in the slag is within 1.0%, the consumption of the added rare earth alloy is reduced, and the yield of the rare earth element is effectively improved.

[0012] The hollow argon blowing stopper is used in the whole rare earth casting process protection technology, the casting flocculation is prevented, and the protection casting is used in the casting process, and the nitrogen content in the casting machine is controlled to be within 5ppm.

[0013] Further, the number of the rare earth killed steel continuous casting furnace in the LF process and the double process is increased from 10 to 21.

[0014] Further, the sulfur content in the molten steel is controlled to be within 0.005%, and the slag basicity is controlled to be between 4.8 and 5.7.

[0015] Further, the rare earth alloy is added in the later period of the RH furnace vacuum treatment, the rare earth alloy is added after the vacuum circulation for 3min, and the pressure is increased.

[0016] Further, the ladle superheat is controlled to be between 23 DEG C and 30 DEG C in the continuous casting process.

[0017] Compared with the prior art, the beneficial technical effects of the present application are:

[0018] Because the affinity of the rare earth element and oxygen is very strong, the complex rare earth oxide inclusions are generated by reacting with the oxides of the molten steel, the harm of the inclusions to the product is reduced, and the performance indexes of the product are improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] The present application will be further described below in combination with the description of the drawings.

[0020] Figure 1 The inclusions of the rare earth steel BT700L are shown.

[0021] Figure 2 The inclusions of the rare earth steel BT510L are shown. DETAILED DESCRIPTION

[0022] The following examples are used to specifically illustrate the content of the present application, and these examples are only a general description of the content of the present application, and do not limit the content of the present application.

[0023] Example 1:

[0024] The production trial of BT700L automobile beam steel with rare earth addition was carried out by the process route of KR-BOF-LF-RH-CC. The rare earth alloy was added during the RH vacuum treatment process, and the rare earth addition content was 25 ppm.

[0025] After the molten iron was treated by the KR deep desulphurization process, the sulfur content of the molten iron entering the furnace was required to be less than or equal to 0.005%, and the temperature of the molten iron entering the furnace was required to be higher than or equal to 1300℃, so as to meet the requirements of the molten iron entering the furnace (as shown in Table 1-1).

[0026] Table 1-1 Composition and temperature of the molten iron after KR desulphurization

[0027]

[0028] The carbon content at the end of the converter was controlled to be in the range of 0.03% to 0.05%, the oxygen content at the end of the converter was controlled to be less than or equal to 720 ppm, so as to avoid over-oxidation of the molten steel, reduce the oxidizability of the slag, and reduce the Al2O3 inclusions in the molten steel. The temperature at the end of the converter was controlled to be in the range of 1620℃ to 1640℃. The specific control of the end point of the converter is shown in Table 1-2.

[0029] Table 1-2 Control of the end point of the converter

[0030] Sample C(％) Mn(%) P(％) S(％) T(℃) [O] (ppm) 1# 0.03 0.08 0.012 0.012 1638 652 2# 0.03 0.08 0.010 0.008 1626 563 3# 0.04 0.06 0.011 0.009 1624 610 4# 0.03 0.07 0.013 0.013 1627 720 5# 0.04 0.06 0.012 0.014 1622 530

[0031] The LF furnace was used to quickly produce white slag, so as to ensure the basicity of the molten steel, reduce the oxidizability of the slag, and reduce the oxygen content in the molten steel. The oxidizability of the slag was less than or equal to 1.0%, which was beneficial to the removal of inclusions, desulphurization and deoxidization. The sulfur content in the molten steel was controlled to be less than or equal to 0.003%, and the basicity of the slag was controlled to be in the range of 4.8 to 5.7. The specific control of the LF process is shown in Table 1-3.

[0032] Table 1-3 Control parameters of the LF process

[0033] Sample S(％) R TFe(%) O (ppm) 1# 0.003 5.3 0.46 12 2# 0.002 4.8 0.32 9 3# 0.002 5.6 0.55 13 4# 0.003 4.9 0.41 8 5# 0.002 5.7 0.39 7

[0034] After the RH vacuum treatment, the oxygen content in the molten steel was reduced, which indicated that the Al2O3 inclusions in the molten steel continuously floated to the slag, and the inclusions in the molten steel were gradually reduced. The rare earth alloy was added in the later stage of the RH vacuum treatment. In order to ensure the uniformity of the rare earth in the steel, the vacuum circulation was 3 min after the addition of the rare earth alloy, and then the pressure was increased. After the RH treatment, calcium treatment was carried out, and the soft blowing time was 5 to 7 min after the calcium treatment. The specific control parameters of the RH process are shown in Table 1-4.

[0035] Table 1-4 Control parameters of the RH process

[0036]

[0037]

[0038] The whole casting process is protected casting, the nitrogen content increases within 5 ppm, the liquid level is stable during casting process, the ladle superheat is controlled at 25-30°C during continuous casting process, which is beneficial to improve the castability of molten steel, and also beneficial to the floating of inclusions in steel, to ensure the cleanliness of the product, the rare earth Ce content is 15-20 ppm, and the specific casting machine process control conditions are shown in Tables 1-5.

[0039] Table 1-5 Casting machine process control parameters

[0040]

[0041] By adding rare earth elements to the product, the size and morphology of the product inclusions are improved, and the product quality is improved, the detection results of D type fine inclusions are all 1.0 level, and the rest of the inclusions are all 0 level (as shown in Table 1-6). The spherical inclusions of the 2# sample were analyzed by scanning electron microscope, the [Ce] and [O] elements in the rare earth oxide accounted for a high proportion, and the formed inclusions were Al2O3-Re2O3 composite inclusions as shown in Figure 1 .

[0042] Table 1-6 Inclusion rating table

[0043]

[0044] Example two:

[0045] The production trial of automobile beam steel BT510L with the addition of rare earth, the rare earth content of this trial is 25-40 ppm, the process route is KR-BOF-LF-CC, and the rare earth alloy is added in the late stage of LF furnace treatment.

[0046] After the hot metal is treated by KR deep desulfurization process, the sulfur content of the hot metal entering the furnace is required to be 0.005% or less, and the temperature of the hot metal entering the furnace is required to be 1300°C or higher, which meets the requirements of the hot metal entering the furnace (as shown in Table 2-1).

[0047] Table 2-1 Temperature of hot metal after KR desulfurization (%)

[0048]

[0049] The carbon content at the end of the converter is controlled at 0.03%-0.05%, the oxygen content at the end of the converter is within 900 ppm, the over-oxidation of the molten steel is avoided, the oxidation of the slag is reduced, the Al2O3 inclusions in the molten steel are reduced, and the converter end temperature is controlled at 1628-1643°C, and the specific converter end control conditions are shown in Table 2-2.

[0050] Table 2-2 Converter end control conditions

[0051] Sample C(％) Mn(%) P(％) S(％) T(℃) [O] (ppm) 6# 0.04 0.07 0.013 0.012 1643 871 7# 0.03 0.09 0.012 0.008 1636 748 8# 0.05 0.08 0.010 0.009 1628 597 9# 0.03 0.07 0.011 0.013 1640 488

[0052] LF furnace fast white slag, to ensure the basicity of molten steel, reduce the oxidation of the slag, the oxidation of the slag TFe < 1.0%, conducive to the removal of deoxidation, desulfurization and inclusion. Reduce the oxygen content of molten steel, the sulfur content in molten steel is controlled within 0.008%, the slag basicity is controlled between 4.8-5.3, LF furnace treatment ends with the addition of rare earth alloy, after the addition of rare earth alloy, calcium treatment, calcium treatment after the molten steel soft blowing time is 8min, see table 2-3 for specific LF furnace process control.

[0053] Table 2-3 LF process control parameters

[0054]

[0055]

[0056] The whole process of continuous casting pouring process adopts protective pouring, the nitrogen content increases within 5ppm, the liquid level is stable during pouring process, the tundish superheat is controlled at 23-29℃ in continuous casting process, which is conducive to improving the castability of molten steel, and also conducive to the floating of inclusions in steel, ensuring the cleanliness of the product, the rare earth Ce content is 21-32ppm, see table 2-4 for specific caster process control.

[0057] Table 2-4 caster process control parameters

[0058]

[0059] By adding rare earth elements to the product, the size and morphology of the product inclusions are improved, and the D class inclusions of the product BT510L are all within 1.5 level according to the detection results, the A class inclusions of 7# sample are 0.5 level, and the rest of the inclusions are 0 level (such as table 2-5). The spherical inclusions of 7# sample were analyzed by scanning electron microscope, and no large particle inclusions were found by scanning electron microscope detection of rare earth steel BT510L billet sample, and the main components of the inclusions were RE2O2S and RE2O2S-CaC2 complex inclusions (such as Figure 2 ). After adding trace rare earth elements, the strip or angular inclusions are further modified to spherical inclusions, the size of the inclusions is reduced, the harmfulness of the inclusions in the product is reduced, and the fine spherical inclusions will not cut the continuity of the strip structure, which is conducive to the forming performance of the product.

[0060] Table 2-5 inclusion rating table

[0061]

[0062]

[0063] The above described embodiments are only to illustrate the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A method for improving the control of inclusions in automotive beam steel by the addition of a rare earth element, characterized by: The rare earth killed steel continuous casting furnace number of LF process and duplex process is increased from 10 to 21; The activity of [O] in the molten steel is reduced, and the cleanliness of the molten steel is improved; the end point oxygen content of the converter is controlled within 900ppm, and the amount of rare earth oxides and aluminum oxides in the steel is reduced; The hollow argon blowing stopper is used in the whole process of rare earth steel casting to prevent the casting of flocculent steel, and the protective casting is used in the casting process, and the nitrogen content of the casting machine is controlled within 5ppm; The T.Fe content of the rare earth steel slag is optimized in the refining process, the oxygen content in the slag is reduced, the calcium carbide or modifier is added in the LF furnace treatment process, the white slag is quickly formed, the total iron content in the slag is within 1.0%, the consumption of rare earth alloy is reduced, and the recovery rate of rare earth elements is improved; The sulfur content in the molten steel is controlled within 0.008%, and the slag basicity is controlled between 4.8 and 5.7; The rare earth alloy is added in the later stage of RH furnace vacuum treatment, the rare earth alloy is added, and the vacuum cycle is 3min; The calcium treatment is carried out after the RH furnace treatment is completed, and the soft blowing time is 5-7min; The ladle superheat is controlled within 23-30℃ in the continuous casting process.

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