Steelmaking method of electro-galvanized bake-hardened steel with yield strength of 220MPa

Abstract

The invention discloses a steelmaking method of electro-galvanized bake-hardened steel with the yield strength of 220 MPa. The method comprises the following steps of molten iron desulphurization, converter smelting, RH vacuum treatment, continuous casting blank forming, plate blank heating, rolling, cooling, coiling, acid pickling cold rolling, continuous annealing and electrogalvanizing, and the RH vacuum treatment comprises the steps of judging whether oxygen needs to be blown into molten steel in the first stage or not and determining an oxygen blowing amount calculation formula; in the second stage, aluminum particles are added into the molten steel for deoxidation, the weight formula of the added aluminum particles is determined, in the third stage, a manganese-iron alloy, a niobium-iron alloy, a titanium-iron alloy and a ferroboron alloy are added into the molten steel, the weight formula of each alloy is determined, and the target carbon content in the molten steel is accurately controlled to be 0.0008-0.0019 weight percent when RH vacuum is finished; and the effective carbon content is accurately controlled. The range of the hardening value (BH value) of the hardened steel finished product is strictly controlled within 30-50 MPa, and high strength and excellent forming performance are both considered on the premise that the thickness of the automobile steel plate is not increased.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, in particular to a steelmaking method for electro-galvanized bake-hardened steel with a yield strength of 220 MPa. Background Art

[0002] In recent years, with the dual demands of improved automotive safety and reduced weight, increasing the strength of steel sheets without increasing their thickness has become a trend. In automotive manufacturing, body panels must possess a certain level of strength and toughness to ensure vehicle safety and durability. However, higher strength results in poorer formability. Achieving both high strength and excellent formability is inherently contradictory. The use of bake-hardened steel sheets in automotive manufacturing can address this technical challenge.

[0003] The essence of bake hardening is "static strain aging" at the baking temperature, which increases the steel's strength by more than 30 MPa at the baking temperature. This is also the result of controlling the interaction between dissolved carbon and dislocations during the aging process. During the baking process, dissolved carbon atoms redistribute and bind to dislocations, hindering dislocation movement and thereby enhancing the material's hardness and strength. Bake-hardened steel sheets exhibit low yield strength during stamping and excellent formability. After baking, the steel's strength is significantly increased, thereby enhancing the vehicle body's impact and dent resistance.

[0004] Currently, bake-hardened steel in the industry faces the following common technical issues: insufficient stamping deformation capacity and substandard bake hardening values (BH values). Specifically, the BH value for bake-hardened steel typically ranges from 30 to 120 MPa, with significant fluctuations. Excessively high BH values can cause the material to become hard and brittle, prone to cracking or breaking, and thus impacting product quality. Excessively low BH values can lead to insufficient strength, causing deformation or damage to automotive components such as doors and body panels, resulting in poor impact and dent resistance, impacting vehicle safety and service life. The primary cause of these large BH value fluctuations and unstable performance is the inaccurate and fluctuating control of the element content (especially carbon content) in the bake-hardened steel. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention proposes a steelmaking method for electro-galvanized bake-hardening steel with a yield strength of 220 MPa, so that the hardening value (BH value) of the bake-hardening steel is strictly controlled within the range of 30 to 50 MPa. This method takes into account both high strength and excellent formability without increasing the thickness of the automobile steel plate, thereby ensuring the safety and durability of the vehicle.

[0006] To achieve the above object, the present invention provides a steelmaking method for electrogalvanized bake-hardened steel with a yield strength of 220 MPa, which is particularly characterized by comprising the following steps:

[0007] S1) desulfurizing molten iron, wherein the sulfur content in the molten iron after desulfurization is ≤ 0.001 parts by weight;

[0008] S2) smelting in a converter, controlling the converter end temperature to 1670° C.-1690° C. and the end oxygen content to 0.040-0.085 parts by weight;

[0009] S3) RH vacuum treatment, through the following three stages, accurately controlling the target carbon content in the molten steel at the end of the RH vacuum to 0.0008-0.0019 weight percent, and accurately controlling the content of other trace elements;

[0010] In the first stage, the vacuum treatment time is 0, and the vacuum treatment lasts for 0 to 5 minutes. The vacuum degree is reduced from the initial 18kPa to below 0.067kPa. The flow rate of the vacuum driving gas argon is controlled in the range of 135-145m 3 / h;

[0011] The following method is used to determine whether oxygen blowing into the molten steel is necessary in the first stage:

[0012] The initial oxygen content of molten steel measured by RH at the station [O]0 and the initial carbon content of molten steel measured by RH at the station [C] 始 The difference between the two is set to [O] 剩余 =[O]0-[C] 始 , the initial temperature of molten steel measured at RH station is T0;

[0013] When[O] 剩余 =0.0200wt%, when T0=1620℃, no oxygen is blown into the molten steel;

[0014] When[O] 剩余 When it is lower than 0.0200wt%, oxygen blowing is required regardless of T0;

[0015] When[O] 剩余 When the content is higher than 0.0200wt% and T0 is lower than 1620℃, calculate [O] 剩余 *400+T0 value, if [O] 剩余 *When 400+T0 is less than 1628℃, oxygen blowing is required, otherwise oxygen blowing is not required;

[0016] The oxygen blowing amount is calculated by the following formula:

[0017] F 02 ={([C] 始 -[C] 脱碳终点 )×1.33+[O] 脱碳终点 -[O]0-[O] 渣} / ([O] 理 )×μ

[0018] Where:

[0019] F 02 is the oxygen blowing amount, Nm 3 / ts,

[0020] [C] 始 Determine the initial carbon content of molten steel at RH station, ppm,

[0021] [C] 脱碳终点 is the carbon content of molten steel at the end point of RH decarburization, ppm,

[0022] [O] 脱碳终点 is the oxygen content of molten steel at the end point of RH decarburization, ppm,

[0023] [O]0 is the initial oxygen content of molten steel measured at RH, ppm,

[0024] [O] 渣 The oxygen content transmitted from slag and refractory materials to molten steel during RH decarburization, ppm,

[0025] [O] 理 For every 1Nm blown into the molten steel 3 / tsTheoretical oxygen supply,

[0026] μ is the oxygen blowing yield;

[0027] In the second stage, the vacuum treatment time is 0, and the vacuum treatment lasts for 5 to 15 minutes. The vacuum degree is below 0.030kPa, and the flow rate of the vacuum driving gas argon is controlled in the range of 155-165m 3 / h, adding aluminum particles for deoxidation, and measuring the temperature and oxygen content of the molten steel after vacuum treatment for 15 minutes;

[0028] In the third stage, the vacuum treatment time is 0, and the vacuum treatment lasts for 15 to 30 minutes. The vacuum degree is below 0.020 kPa, and the flow rate of the vacuum driving gas argon is controlled in the range of 185-195 m 3 / h, after adding aluminum particles in vacuum, measure the temperature and oxygen content of the molten steel, circulate for 4 minutes, add manganese iron alloy, niobium iron alloy, titanium iron alloy, boron iron alloy to the molten steel, and meet the requirements of effective carbon C 有效 =C+0.02*Mn-0.1*Si-0.1*Nb-0.7*S-0.02*P, effective carbon C 有效 The content meets 0.0020 to 0.0050 weight percent;

[0029] S4) Continuous casting → slab heating → rolling → cooling → coiling → pickling and cold rolling → continuous annealing → electrogalvanizing.

[0030] Furthermore, in S3), the preparation work before the first stage of treatment includes: sampling at the station, measuring the initial temperature T0 and initial oxygen content [O]0 of the molten steel, analyzing the initial carbon content [C] 始 .

[0031] Furthermore, in S3), whether it is necessary to add ferrophosphorus in the first stage is determined by the following method:

[0032] When the phosphorus content in molten steel meets 0.028-0.048 parts by weight, no ferrophosphorus is added;

[0033] When the phosphorus content in the molten steel is lower than 0.028 parts by weight, 0.042 kg / ts of ordinary ferrophosphorus is added for every 0.001 parts by weight increase in phosphorus content in the molten steel.

[0034] Further, in S3), the weight of the aluminum particles added in the second stage is calculated by the following formula: 铝粒 =[(1.125%[O] 脱碳终点 +[Als] 目标 %)*W 钢水量 ] / (R*η*W 钢水量 )

[0035] Where,

[0036] Q 铝粒 is the amount of aluminum particles added, unit: kg / ts,

[0037] [O] 脱碳终点 is the oxygen content of molten steel at the end point of RH decarburization, ppm,

[0038] [Als] 目标 is the target composition of Als in molten steel,

[0039] W 钢水量 is the amount of molten steel,

[0040] R is the yield of Al in aluminum particles,

[0041] η is the Al content in the aluminum particles.

[0042] Further, in S3), when adding ferromanganese alloy to molten steel, first, a trace amount of carbon is added to the molten steel to make the carbon content meet the requirements, and medium carbon ferromanganese is used. The amount of medium carbon ferromanganese added is calculated by the following formula:

[0043] Q 中碳锰铁 =([C] RH目标 -[C] 脱碳终点 )*W 钢水量 *10 / W 钢水量 *W 中碳锰铁含碳量 *100

[0044] Where,

[0045] Q 中碳锰铁 The addition amount of medium carbon ferromanganese, unit is kg / ts,

[0046] [C] RH目标 is the target carbon content in molten steel at the end of RH vacuum,

[0047] [C] 脱碳终点 is the carbon content of molten steel at the end point of RH decarburization,

[0048] W 钢水量 is the amount of molten steel,

[0049] W 中碳锰铁含碳量 is the carbon content of medium carbon ferromanganese;

[0050] Secondly, in order to increase the Mn content in the molten steel to 0.45-0.65 weight percent, low-carbon manganese metal is used. The amount of low-carbon manganese metal added is calculated by the following formula: 低碳金属锰 =(Mn 目标 -Mn 初始 -Mn 中碳锰铁增Mn量 )*W 钢水量 *10 / W 钢水量 *(100*W 低碳金属锰含Mn量 *R 低碳金属锰Mn收得率 )

[0051] Where,

[0052] Q 低碳金属锰 is the amount of low carbon manganese metal added, unit is kg / ts,

[0053] Mn 目标 is the target Mn content in molten steel at the end of RH vacuum,

[0054] Mn 初始 is the initial Mn content of RH,

[0055] Mn 中碳锰铁增Mn量 To increase the Mn content in molten steel when adding medium carbon ferromanganese,

[0056] W 钢水量 is the amount of molten steel,

[0057] W 低碳金属锰含Mn量 To increase the Mn content in molten steel when adding low-carbon metallic manganese,

[0058] R 低碳金属锰Mn收得率 is the yield of Mn in low-carbon metallic manganese.

[0059] Furthermore, in S3), when adding niobium iron alloy to the molten steel, the Nb content in the molten steel is made to meet 0.006 to 0.011 weight percent; and the effective carbon C有效 =C+0.02*Mn-0.1*Si-0.1*Nb-0.7*S-0.02*P, effective carbon C 有效 The content meets 0.0020-0.0050 weight percent; the amount of niobium iron alloy added is calculated by the following formula

[0060] Q 铌铁 =Nb 目标 *W 钢水量 *10 / W 钢水量 *(100*W 铌铁含Nb量 *R 铌铁Nb收得率 )

[0061] Where,

[0062] Q 铌铁 is the amount of ferroniobium added, in kg / ts,

[0063] Nb 目标 is the target Nb content in molten steel at the end of RH vacuum,

[0064] W 钢水量 is the amount of molten steel,

[0065] W 铌铁含Nb量 To increase the Nb content in molten steel when adding ferroniobium alloy,

[0066] R 铌铁Nb收得率 is the yield of Nb in ferroniobium alloy.

[0067] Furthermore, in S3), when adding ferrotitanium alloy to molten steel, the Ti content in the molten steel is 0.001 to 0.005 weight percent, and the amount of ferrotitanium alloy added is calculated by the following formula:

[0068] Q 钛铁 =Ti 目标 *W 钢水量 *10 / W 钢水量 *(100*W 钛铁含Ti量 *R 钛铁Ti收得率 )

[0069] Where,

[0070] Q 钛铁 is the addition amount of titanium-iron alloy, unit is kg / ts,

[0071] Ti 目标 is the target Ti content in molten steel at the end of RH vacuum,

[0072] W 钢水量 is the amount of molten steel,

[0073] W 钛铁含Ti量 To increase the Ti content in molten steel when adding ferro-titanium alloy,

[0074] R 钛铁Ti收得率 is the yield of Ti in ferrotitanium alloy.

[0075] Furthermore, in S3), when adding ferroboron alloy to molten steel, the B content in the molten steel is 0.0005 to 0.0015 weight percent, and the amount of ferroboron alloy added is calculated by the following formula:

[0076] Q 硼铁 =B 目标 *W 钢水量 *10 / W 钢水量 *(100*W 硼铁含B量 *R 硼铁B收得率 )

[0077] Where,

[0078] Q 硼铁 is the amount of ferroboron alloy added, unit: kg / ts,

[0079] B 目标 is the target B content in molten steel at the end of RH vacuum,

[0080] W 钢水量 is the amount of molten steel,

[0081] W 硼铁含B量 To increase the B content in molten steel when adding ferroboron alloy,

[0082] R 硼铁B收得率 is the yield of B in ferroboron alloy.

[0083] Furthermore, the weight percentages of the yield strength 220 MPa grade electro-galvanized bake hardening steel product are as follows: C content 0.0011-0.0022 weight parts, Si content ≤0.030 weight parts, Mn content 0.45-0.65 weight parts, P content 0.028-0.048 weight parts, S content ≤0.010 weight parts, Als content 0.020-0.050 weight parts, Nb content 0.006-0.011 weight parts, Ti content 0.001-0.005 weight parts, B content 0.0005-0.0015 weight parts, N content ≤0.0030 weight parts, and the effective carbon C is set at ... 有效 =C+0.02*Mn-0.1*Si-0.1*Nb-0.7*S-0.02*P, and effective carbon C 有效 The content is 0.0020-0.0050 parts by weight, and the balance is Fe and inclusions;

[0084] The yield strength of the 220MPa grade electro-galvanized bake-hardened steel product is 220-270MPa, the tensile strength is 340-380MPa, the hardening value is 30-50MPa, and the elongation is ≥35%.

[0085] The advantages of the present invention are:

[0086] 1. The present invention uses the RH vacuum treatment process as a key process for accurately controlling the carbon content and effective carbon, and also as a key process for accurately controlling the content of Mn, P, Als, Nb, Ti, and B elements. The present invention divides the RH vacuum treatment process into three stages. Through the three stages, the target carbon content in the molten steel is accurately controlled to be 0.0008-0.0019% at the end of the RH vacuum treatment. The Mn content added to the molten steel is also accurately controlled to be 0.45-0.65%, the Nb content to be 0.006-0.011%, the Ti content to be 0.001-0.005%, and the B content to be 0.0005-0.0015%. Ultimately, the carbon content of the finished bake-hardened steel is between 0.0011-0.0022%.

[0087] 2. The present invention introduces the concept of effective carbon into the RH vacuum treatment process and sets the effective carbon C 有效 =C+0.02*Mn-0.1*Si-0.1*Nb-0.7*S-0.02*P, and control the effective carbon C 有效 The content is 0.0020 to 0.0050 parts by weight, wherein the Mn element makes a positive contribution to the effective C content, and the contribution coefficient is set to 0.02, while the Si, S, P, and Nb elements make negative contributions to the effective C content, and the contribution coefficients are set to -0.1, -0.7, -0.02, and -0.1, respectively. When the effective carbon content is lower than 0.0020%, the bake hardening value (BH value) is low, and the strength of the material does not meet the requirements; when the effective carbon content is higher than 0.0050%, the bake hardening value (BH value) is high, the material becomes hard and brittle, and is prone to cracks or breakage, affecting product quality;

[0088] The present invention discloses a steelmaking method for producing electrogalvanized bake-hardening steel with a yield strength of 220 MPa. The method precisely controls the carbon content of the finished bake-hardening steel to be between 0.0011% and 0.0022%. The method introduces the concept of effective carbon, combines the effective carbon content with the contents of Mn, Si, Nb, P, and S in the steel, and strictly limits their ranges. This allows the bake-hardening value (BH value) to be strictly controlled within a range of 30 to 50 MPa. This method achieves both high strength and excellent formability without increasing the thickness of the automotive steel plate, thereby ensuring the safety and durability of the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Figure 1 Flowchart of the present invention. DETAILED DESCRIPTION

[0090] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0091] like Figure 1 As shown, the present invention provides a steelmaking method for electro-galvanized bake-hardened steel with a yield strength of 220 MPa, comprising the following steps:

[0092] S1) desulfurization of molten iron, wherein the sulfur content in the molten iron after desulfurization is ≤ 0.001 parts by weight.

[0093] S2) smelting in a converter, controlling the converter end temperature to be 1670° C.-1690° C. and the end oxygen content to be 0.040-0.085 parts by weight.

[0094] The main steelmaking process parameters of Examples 1 to 10 and Comparative Examples 1 to 2 of the present invention are shown in Table 1 below.

[0095] Table 1 List of main steelmaking process parameters of each embodiment and comparative example

[0096]

[0097] S3) RH vacuum treatment: The target carbon content in the molten steel at the end of the RH vacuum treatment is precisely controlled to be 0.0008-0.0019 weight percent through the following three stages, and the contents of other trace elements are precisely controlled.

[0098] RH (vacuum recirculation degassing) vacuum treatment is a vacuum recirculation degassing process used in molten steel refining. It is primarily used to remove gases and inclusions from the molten steel while achieving uniform composition and temperature. The specific process is as follows: During vacuuming, molten steel enters the vacuum chamber through a riser pipe, while argon gas is blown in to form bubbles. As the gas is expelled, the density of the molten steel increases, and the steel then returns to the ladle through a downcomer, forming a continuous cycle.

[0099] RH vacuum treatment is a key process for accurately controlling carbon composition and effective carbon, as well as the content of Mn, P, Als, Nb, Ti, and B. The preparations before the first stage of treatment include: sampling at the station, measuring the initial temperature T0 and initial oxygen content [O]0 of the molten steel, and analyzing the initial carbon content [C] in the molten steel. 始 .

[0100] In the first stage, the vacuum treatment time is 0, and the vacuum treatment lasts for 0 to 5 minutes. The vacuum degree is reduced from the initial 18kPa to below 0.067kPa. The flow rate of the vacuum driving gas argon is controlled in the range of 135-145m 3 / h.

[0101] In addition, the phosphorus content in the molten steel is measured by sampling at the station to determine whether to add ferrophosphorus. Specifically, the following method is used to determine whether ferrophosphorus needs to be added in the first stage:

[0102] When the phosphorus content in the molten steel meets the requirements of 0.028-0.048 parts by weight, no ferrophosphorus is added; when the phosphorus content in the molten steel is lower than 0.028 parts by weight, 0.042 kg / ts of ordinary ferrophosphorus is added for every 0.001 parts by weight increase in phosphorus content in the molten steel.

[0103] If ferrophosphorus is added, it must be completed in the first stage (i.e. within 5 minutes after the vacuum treatment begins) because ordinary ferrophosphorus contains more oxygen and other impurities. Adding it to the molten steel as early as possible and utilizing the vacuum circulation principle can remove the impurities brought into the molten steel by ordinary ferrophosphorus and improve the purity of the molten steel.

[0104] In addition, based on the temperature measurement and oxygen value determination at the arrival station and the carbon content of the molten steel sampled and analyzed at the arrival station, a comprehensive calculation is made as to whether a vacuum oxygen lance should be used to blow oxygen into the molten steel. Specifically, the following method is used to determine whether oxygen blowing into the molten steel is necessary in the first stage:

[0105] The initial oxygen content of molten steel measured by RH at the station [O]0 and the initial carbon content of molten steel measured by RH at the station [C] 始 The difference between the two is set to [O] 剩余 =[O]0-[C] 始 , the initial temperature of molten steel measured at RH station is T0; when [O] 剩余 =0.0200wt%, T0=1620℃, no oxygen is blown into the molten steel; when [O] 剩余 When it is lower than 0.0200wt%, oxygen must be blown regardless of T0; when [O] 剩余 When the content is higher than 0.0200wt% and T0 is lower than 1620℃, calculate [O] 剩余 *400+T0 value, if [O] 剩余 *When 400+T0 is less than 1628℃, oxygen blowing is required. In other cases, oxygen blowing is not required.

[0106] If oxygen blowing is required, it should be completed in the first stage. If the oxygen blowing volume is abnormally high, it can be continued to the second stage. Oxygen blowing increases the oxygen content in the molten steel. On the one hand, it is necessary to meet the oxygen content required for the carbon-oxygen reaction during RH vacuum cycle decarburization. On the other hand, the molten steel at the end of decarburization has a certain oxygen content. By adding aluminum particles to the molten steel, the chemical reaction between aluminum and oxygen releases heat, which raises the temperature of the molten steel to meet the required pouring temperature.

[0107] Specifically, the oxygen blowing amount is calculated by the following formula,

[0108] F 02 ={([C] 始 -[C] 脱碳终点 )×1.33+[O] 脱碳终点 -[O]0-[O] 渣} / ([O] 理 )×μ

[0109] Where:

[0110] F 02 is the oxygen blowing amount, Nm 3 / ts,

[0111] [C] 始 Determine the initial carbon content of molten steel at RH station, ppm,

[0112] [C] 脱碳终点 is the carbon content of molten steel at the end point of RH decarburization, ppm,

[0113] [O] 脱碳终点 is the oxygen content of molten steel at the end point of RH decarburization, ppm,

[0114] [O]0 is the initial oxygen content of molten steel measured at RH, ppm,

[0115] [O] 渣 The oxygen content transmitted from slag and refractory materials to molten steel during RH decarburization, ppm,

[0116] [O] 理 For every 1Nm blown into the molten steel 3 / tsTheoretical oxygen supply,

[0117] μ is the oxygen blowing yield, which is related to the oxygen blowing height of the oxygen lance, the type of lance, etc.

[0118] [O] 理 Determination: Use the top gun to blow 1Nm into the molten steel 3 / ts oxygen when the theoretical oxygen supply, the amount of molten steel is Q (unit kg), if all the oxygen enters the molten steel, the oxygen content in the molten steel can be increased by: (0.032kg / mol*1*10 3 L) / (22.4L / mol*Q).

[0119] Determination of μ: Theoretically, the free oxygen in the molten steel can be increased by 5.3ppm. However, in the actual production process, it is not as high as the theoretical value. The reason is that during the oxygen blowing process of the top gun, part of the oxygen will be drawn away by the vacuum pump system and will react with the waste gas CO generated. The secondary combustion of CO will consume part of the oxygen. The different positions of the MFB top gun and the different oxygen flow rates will also result in different amounts of oxygen added. Therefore, the oxygen recovery rate during oxygen blowing must be tracked, tested, and data collected and analyzed and summarized. After a large number of experimental analyses and summaries, we calculated that the oxygen recovery rate is 56.6%. That is, the MFB top gun is used to blow 1NM into the molten steel. 3 The actual oxygenation of O2 is 3ppm, that is ([O] 理 )×μ=0.0003wt%.

[0120] [O] 渣 Determination: that is, the oxygen content transmitted from slag and refractory materials to molten steel during RH decarburization; this is related to the thickness of the ladle slag layer, the oxidizability of the molten steel, and the quality of the refractory materials. Tracking tests and data analysis revealed an average value of 0.0100wt%.

[0121] The main steelmaking process parameters of Examples 1 to 10 and Comparative Examples 1 to 2 in the first stage of RH treatment for 0 to 5 minutes are shown in Table 2 below.

[0122] Table 2 Main steelmaking process parameters of each embodiment and comparative example RH treatment first stage 0-5 minutes

[0123]

[0124]

[0125] In the second stage, the vacuum treatment time is 0, and the vacuum treatment lasts for 5 to 15 minutes. The vacuum degree is below 0.030kPa, and the flow rate of the vacuum driving gas argon is controlled in the range of 155-165m 3 / h, aluminum particles were added for deoxidation, and the temperature and oxygen content of the molten steel were measured after vacuum treatment for 15 minutes.

[0126] Specifically, the weight of the added aluminum particles is calculated by the following formula:

[0127] Q 铝粒 =[(1.125%[O] 脱碳终点 +[Als] 目标 %)*W 钢水量 ] / (R*η*W 钢水量 )

[0128] Where,

[0129] Q 铝粒 is the amount of aluminum particles added, unit: kg / ts,

[0130] [O] 脱碳终点 is the oxygen content of molten steel at the end point of RH decarburization, ppm,

[0131] [Als] 目标 is the target composition of Als in molten steel,

[0132] W 钢水量 is the amount of molten steel,

[0133] R is the yield of Al in aluminum particles,

[0134] η is the Al content in the aluminum particles.

[0135] The main steelmaking process parameters of Examples 1 to 10 and Comparative Examples 1 to 2 of the present invention during the second stage of RH treatment for 5 to 15 minutes are shown in Table 3 below.

[0136] Table 3 Main steelmaking process parameters of various embodiments of the present invention and comparative examples RH treatment second stage 5-15 minutes

[0137]

[0138]

[0139] In the third stage, the vacuum treatment time is 0, and the vacuum treatment lasts for 15 to 30 minutes. The vacuum degree is below 0.020 kPa, and the flow rate of the vacuum driving gas argon is controlled in the range of 185-195 m 3 / h, after adding aluminum particles in vacuum, measure the temperature and oxygen content of the molten steel, circulate for 4 minutes, and add alloy to the molten steel.

[0140] Specifically, the alloys added in the third stage include ferromanganese alloy, ferroniobium alloy, ferrotitanium alloy, and ferroboron alloy.

[0141] 1. When adding manganese-ferroalloy to molten steel, there are two purposes: one is to add a trace amount of carbon to the molten steel so that the carbon content meets the requirements; the other is to add Mn to the molten steel so that the Mn content meets the requirements.

[0142] First, a small amount of carbon is added to the molten steel to make the carbon content meet the requirements. Medium carbon ferromanganese is used. Medium carbon ferromanganese contains carbon W. 中碳锰铁含碳量 1.7~2.0wt%Mn contentW 中碳锰铁含Mn量 75~78wt%,Set the target carbon content C in molten steel at the end of RH vacuum RH目标 , W 钢水量 is the amount of molten steel. Considering that the tundish increases carbon by 0.0003% during continuous casting, in order to meet the carbon content of 0.0011-0.0022% in the final molten steel, the target carbon content C in the molten steel at the end of RH vacuum is RH目标 The amount of medium carbon ferromanganese added is calculated as follows:

[0143] Q 中碳锰铁 =([C] RH目标 -[C] 脱碳终点 )*W 钢水量 *10 / W 钢水量 *W 中碳锰铁含碳量 *100

[0144] Where,

[0145] Q 中碳锰铁 The addition amount of medium carbon ferromanganese, unit is kg / ts,

[0146] [C] RH目标 is the target carbon content in molten steel at the end of RH vacuum,

[0147] [C] 脱碳终点 is the carbon content of molten steel at the end point of RH decarburization,

[0148] W 钢水量 is the amount of molten steel,

[0149] W 中碳锰铁含碳量 It is the carbon content of medium carbon ferromanganese.

[0150] Next, in order to increase the Mn content in the molten steel to 0.45-0.65 weight percent, low-carbon manganese metal is used. The low-carbon manganese metal contains 97-98 wt% Mn and 0.02-0.03 wt% C. In order to make the Mn content in the molten steel reach 0.45-0.65%, the amount of low-carbon manganese metal added is calculated. The amount of low-carbon manganese metal added is calculated by the following formula:

[0151] Q 低碳金属锰 =(Mn 目标 -Mn 初始 -Mn 中碳锰铁增Mn量 )*W 钢水量 *10 / W 钢水量 *(100*W 低碳金属锰含Mn量 *R 低碳金属锰Mn收得率 )

[0152] Where,

[0153] Q 低碳金属锰 is the amount of low carbon manganese metal added, unit is kg / ts,

[0154] Mn 目标 The target Mn content in molten steel at the end of RH vacuum can be 0.55% which is the median value of 0.45-0.65%.

[0155] Mn 初始 is the initial Mn content of RH,

[0156] Mn 中碳锰铁增Mn量 To increase the Mn content in molten steel when adding medium carbon ferromanganese, the calculation formula is Mn 中碳锰铁增Mn量 =Q 中碳锰铁 *W 中碳锰铁含Mn量 *R 中碳锰铁Mn收得率 / W 钢水量 *10,

[0157] W 钢水量 is the amount of molten steel,

[0158] W 低碳金属锰含Mn量 To increase the Mn content in molten steel when adding low-carbon metallic manganese,

[0159] R 低碳金属锰Mn收得率 is the yield of Mn in low-carbon metallic manganese.

[0160] This allows precise control of the C and Mn content in molten steel.

[0161] 2. When adding niobium iron alloy to molten steel, the Nb content in the molten steel should meet the requirements of 0.006-0.011 weight percent; at the same time, the effective carbon C 有效 =C+0.02*Mn-0.1*Si-0.1*Nb-0.7*S-0.02*P, effective carbon C 有效 The content meets 0.0020-0.0050 weight percentage; the niobium iron alloy contains Nb: 66wt%, R 铌铁Nb收得率 The addition amount of niobium iron alloy is calculated by the following formula:

[0162] Q 铌铁 =Nb 目标 *W 钢水量 *10 / W 钢水量 *(100*W 铌铁含Nb量 *R 铌铁Nb收得率 )

[0163] Where,

[0164] Q 铌铁 is the amount of ferroniobium added, in kg / ts,

[0165] Nb 目标 is the target Nb content in molten steel at the end of RH vacuum,

[0166] W 钢水量 is the amount of molten steel,

[0167] W 铌铁含Nb量 To increase the Nb content in molten steel when adding ferroniobium alloy,

[0168] R 铌铁Nb收得率 is the yield of Nb in ferroniobium alloy.

[0169] This allows precise control of the Nb content in the molten steel.

[0170] 3. When adding ferrotitanium alloy to molten steel, the Ti content in the molten steel should be 0.001-0.005 weight percent, with a target of 0.003%. Similarly, the amount of ferrotitanium alloy added can be calculated by the following formula:

[0171] Q 钛铁 =Ti 目标 *W 钢水量 *10 / W 钢水量 *(100*W 钛铁含Ti量 *R 钛铁Ti收得率 )

[0172] Where,

[0173] Q 钛铁 is the addition amount of titanium-iron alloy, unit is kg / ts,

[0174] Ti 目标 is the target Ti content in molten steel at the end of RH vacuum,

[0175] W 钢水量 is the amount of molten steel,

[0176] W 钛铁含Ti量 To increase the Ti content in molten steel when adding ferro-titanium alloy,

[0177] R 钛铁Ti收得率 is the yield of Ti in ferrotitanium alloy.

[0178] This allows precise control of the Ti content in molten steel.

[0179] 4. When adding ferroboron alloy to molten steel, the B content in the molten steel should be 0.0005-0.0015 weight percent, with a target of 0.0010%. Similarly, the amount of ferroboron alloy added is calculated by the following formula:

[0180] Q 硼铁 =B 目标 *W 钢水量 *10 / W 钢水量 *(100*W 硼铁含B量 *R 硼铁B收得率 )

[0181] Where,

[0182] Q 硼铁 is the amount of ferroboron alloy added, unit: kg / ts,

[0183] B 目标 is the target B content in molten steel at the end of RH vacuum,

[0184] W 钢水量 is the amount of molten steel,

[0185] W 硼铁含B量 To increase the B content in molten steel when adding ferroboron alloy,

[0186] R 硼铁B收得率 is the yield of B in ferroboron alloy.

[0187] This allows for precise control of the B content in molten steel.

[0188] After the alloys were added, the RH vacuum cycle was continued for 10 minutes to terminate the treatment.

[0189] In addition, in order to prevent carbon increase during the continuous casting process, the continuous casting mold protection slag uses ultra-low carbon steel protection slag with a carbon content of ≤0.5%, and the rest is continuously cast into billets according to ultra-low carbon steel grades.

[0190] The main steelmaking process parameters of Examples 1 to 10 and Comparative Examples 1 to 2 of the present invention during the third stage of RH treatment for 15 to 30 minutes are shown in Table 4 below.

[0191] Table 4 Main steelmaking process parameters of each embodiment and comparative example RH treatment third stage 15-30 minutes

[0192]

[0193] The mechanism of action of various elements in the present invention is as follows:

[0194] Carbon (C): Element C is the most important element affecting the strength, hardness and toughness of steel. It is also the most important element affecting the BH value of bake-hardened steel. Bake-hardened steel maintains a low strength in the substrate state by controlling the carbon content to facilitate stamping. Subsequently, after high-temperature baking, the carbon supersaturated solid solution in the ferrite will precipitate to form fine carbides. These precipitates can increase the strength and hardness of the material. Too low a carbon content leads to insufficient strengthening effect after baking, and the BH value is lower than 30MPa, which cannot achieve the required high strength; too high a carbon content makes the material too hard, the stamping performance deteriorates, and the resistance to natural aging at room temperature also deteriorates. The more suitable carbon content is 0.0011-0.0022%.

[0195] Manganese (Mn): As a key alloying element in bake-hardenable steel, manganese (Mn) plays a vital role. Manganese stabilizes the austenite phase and promotes the formation of fine austenite grains during heating. During cooling, these grains transform into finer martensite or bainite, significantly improving the material's strength and hardness. Manganese combines with carbon or other elements in ferrite to form stable precipitates, which inhibit dislocation motion and enhance material strength. During the bake process, these precipitates dissolve and then reprecipitate, further enhancing performance. Manganese improves the steel's hardenability, achieving more uniform phase transformation under the same cooling conditions, ensuring excellent mechanical properties. Manganese combines with sulfur to form MnS inclusions, which act as crack barriers, reducing hot brittleness at high temperatures and preventing the risk of cracking during the bake process. However, excessive Mn additions can cause the material to become hard and brittle, hindering stamping. Therefore, the optimal manganese addition level is 0.45-0.65%.

[0196] Silicon (Si): The silicon content in bake-hardening steel should not be too high. Silicon is a strong carbide former and combines with carbon to form carbides such as FeSiC. This affects the diffusion of carbon atoms during the bake process, reducing the aging effect and thus weakening the strength increase. Silicon alters the austenite decomposition and martensite transformation processes, affecting the phase transformation kinetics of bake-hardening steel. High silicon content leads to Si enrichment on the steel surface after heat treatment, resulting in pitting during galvanizing, which affects the surface quality of the steel. Therefore, the Si content is required to be ≤ 0.030%.

[0197] Niobium (Nb): Niobium promotes grain refinement, improves the microstructure, and enhances the strength and toughness of steel, while also helping to inhibit crack propagation. As a strong carbide former, niobium combines with carbon in iron to form stable carbides. These fine precipitates precipitate during heat treatment, hindering dislocation motion and thereby enhancing material strength. Niobium can improve the surface quality of bake-hardened steel coatings. However, excessive niobium can form excessive fine precipitates, leading to an inhomogeneous microstructure and, in turn, anisotropic steel properties, reducing the stability of mechanical properties and lowering the steel's plasticity and toughness. The optimal niobium addition level is 0.006-0.011%.

[0198] Titanium (Ti): Titanium is the primary element for solid solution strengthening, offering excellent strengthening effects and a relatively low price. It promotes grain refinement in steel, thereby enhancing the material's strength and toughness. However, excessive titanium content can lead to poor mechanical properties. The optimal titanium addition level is 0.001-0.005%.

[0199] Boron (B): Boron promotes ferrite grain refinement, thereby increasing the steel's strength and toughness while reducing brittleness. By refining the grains, boron enhances the material's hardening ability during baking, resulting in higher strength in the final product. Boron forms stable carbides with iron, helping to maintain the steel's performance and stability at high temperatures and preventing softening. The optimal boron addition level is 0.0005-0.0015%.

[0200] Aluminum (Al): Aluminum is the primary deoxidizing element in steel, significantly reducing its oxygen content. It also combines with nitrogen to form AlN, effectively refining grain size. However, if the aluminum content exceeds 0.05%, aluminum oxide inclusions increase significantly, reducing steel cleanliness and negatively impacting deep-drawing performance. The optimal aluminum addition level is 0.020-0.050%.

[0201] Phosphorus (P): As a harmful element in traditional steel, the lower the phosphorus content is, the better. The present invention utilizes the beneficial effects of phosphorus and appropriately adds a certain amount of phosphorus. Phosphorus changes the microstructure of steel and promotes the transformation of austenite to martensite or other hardened structures, thereby improving the strength and hardness of the material at a lower cooling rate. An appropriate amount of phosphorus can enhance the corrosion resistance of steel. However, too high a phosphorus content will increase the brittleness of the material and reduce the toughness and plasticity of the material. The most suitable phosphorus addition amount is 0.028-0.048%.

[0202] Sulfur (S): Sulfur can easily cause hot brittleness; therefore, the sulfur content in steel should be minimized. Control S ≤ 0.010%.

[0203] Nitrogen (N): Nitrogen is an important indicator for measuring the purity of molten steel. Nitrogen easily forms inclusions and pores. To improve the purity of molten steel, the nitrogen content in the steel must be reduced as much as possible. Control N ≤ 0.0030%.

[0204] The reason for setting effective carbon C 有效 =C + 0.02*Mn - 0.1*Si - 0.1*Nb - 0.7*S - 0.02*P. This is because the effective carbon content is closely related to the Mn, Si, Nb, S, and P contents. Mn contributes positively to the effective carbon content, with a contribution coefficient of 0.02. Si, S, P, and Nb, on the other hand, combine with carbon, occupying a certain amount of carbon and thus contributing negatively to the effective carbon content, with contribution coefficients set at -0.1, -0.7, -0.02, and -0.1, respectively. Nb, in particular, despite being added in trace amounts, has a significant impact. Nb is a strong carbide-forming element, combining with carbon to form stable NbC carbides. NbC pins dislocations and hinders their movement, thereby increasing the steel's base strength before baking. However, excessive base strength should not be too high, as this can affect the material's stamping properties. The material's insufficient strength after stamping requires increased strength after bake hardening. Therefore, Nb and C combine to form stable NbC carbides, which occupy a certain amount of carbon to strengthen the material's basic strength. The effective carbon content takes into account the occupied carbon. When the effective carbon content is less than 0.0020%, the bake hardening value (BH) is low, and the material's strength does not meet the required level. When the effective carbon content is greater than 0.0050%, the bake hardening value (BH) is high, making the material hard and brittle, prone to cracking or breaking, and affecting product quality.

[0205] S4) Continuous casting → slab heating → rolling → cooling → coiling → pickling and cold rolling → continuous annealing → electrogalvanizing.

[0206] The weight percentages of the 220 MPa yield strength electrogalvanized bake hardening steel product prepared according to the method of the present invention are as follows: C content 0.0011-0.0022 weight parts, Si content ≤0.030 weight parts, Mn content 0.45-0.65 weight parts, P content 0.028-0.048 weight parts, S content ≤0.010 weight parts, Als content 0.020-0.050 weight parts, Nb content 0.006-0.011 weight parts, Ti content 0.001-0.005 weight parts, B content 0.0005-0.0015 weight parts, N content ≤0.0030 weight parts, and the effective carbon C 有效 =C+0.02*Mn-0.1*Si-0.1*Nb-0.7*S-0.02*P, effective carbon C 有效 The content is 0.0020 to 0.0050 weight percent, and the balance is Fe and inclusions.

[0207] The weight ratios of the hardened steel components of Examples 1 to 10 and Comparative Examples 1 to 2 of the present invention are shown in Table 5 below.

[0208] Table 5 Weight ratio of finished products prepared in each embodiment and comparative example (wt, %)

[0209]

[0210]

[0211] The 220MPa grade electro-galvanized bake-hardened steel product produced by the method of the present invention has a yield strength of 220-270MPa, a tensile strength of 340-380MPa, a hardening value of 30-50MPa, and an elongation of ≥35%.

[0212] The properties of the hardened steel products produced in Examples 1 to 10 and Comparative Examples 1 to 2 of the present invention are shown in Table 6 below.

[0213] Table 6 Performance statistics of finished products obtained from various embodiments and comparative examples

[0214] Serial number Yield strength (MPa) Tensile strength (MPa) Bake hardening (BH) value (MPa) Elongation A 1 230 350 33 40％ 2 245 360 36 38％ 3 260 375 37 36％ 4 268 380 41 41％ 5 220 340 30 42％ 6 261 375 43 39％ 7 253 370 32 37％ 8 250 365 35 43％ 9 264 380 36 40％ 10 259 375 50 36％ Comparative Example 1 190 310 10 30％ Comparative Example 2 280 410 70 25％

[0215] As can be seen from Table 6, the properties of the hardened steel products produced by the steelmaking method of the present invention in Examples 1 to 10 are as follows: yield strength of 220 to 270 MPa, tensile strength of 340 to 380 MPa, hardening value of 30 to 50 MPa, and elongation ≥ 35%. All performance indicators meet the requirements.

[0216] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A steelmaking method for electrogalvanized bake hardening steel with a yield strength of 220 MPa, characterized in that: The steps include: S1) desulfurizing molten iron, wherein the sulfur content in the molten iron after desulfurization is ≤ 0.001 parts by weight; S2) smelting in a converter, controlling the converter end temperature to 1670° C.-1690° C. and the end oxygen content to 0.040-0.085 parts by weight; S3) RH vacuum treatment, through the following three stages, accurately controlling the target carbon content in the molten steel at the end of the RH vacuum to 0.0008-0.0019 weight percent, and accurately controlling the content of other trace elements; In the first stage, the vacuum treatment time is 0, and the vacuum treatment lasts for 0 to 5 minutes. The vacuum degree is reduced from the initial 18kPa to below 0.067kPa. The flow rate of the vacuum driving gas argon is controlled in the range of 135-145m 3 / h; The following method is used to determine whether oxygen blowing into the molten steel is necessary in the first stage: The initial oxygen content of molten steel measured by RH at the station [O]0 and the initial carbon content of molten steel measured by RH at the station [C] 始 The difference between the two is set to [O] 剩余 =[O]0-[C] 始 , the initial temperature of molten steel measured at RH station is T0; When[O] 剩余 =0.0200wt%, when T0=1620℃, no oxygen is blown into the molten steel; When[O] 剩余 When it is lower than 0.0200wt%, oxygen blowing is required regardless of T0; When[O] 剩余 When the content is higher than 0.0200wt% and T0 is lower than 1620℃, calculate [O] 剩余 *400+T0 value, if [O] 剩余 *When 400+T0 is less than 1628℃, oxygen blowing is required, otherwise oxygen blowing is not required; The oxygen blowing amount is calculated by the following formula: F 02 ={([C] 始 -[C] 脱碳终点 )×1.33+[O] 脱碳终点 -[O]0-[O] 渣 } / ([O] 理 )×μ Where: F 02 is the oxygen blowing amount, Nm 3 / ts, [C] 始 Determine the initial carbon content of molten steel at RH station, ppm, [C] 脱碳终点 is the carbon content of molten steel at the end point of RH decarburization, ppm, [O] 脱碳终点 is the oxygen content of molten steel at the end point of RH decarburization, ppm, [O]0 is the initial oxygen content of molten steel measured at RH, ppm, [O] 渣 Oxygen content transmitted from slag and refractory materials to molten steel during RH decarburization, ppm, [O] 理 For every 1Nm blown into the molten steel 3 / tsTheoretical oxygen supply, μ is the oxygen blowing yield; In the second stage, the vacuum treatment time is 0, and the vacuum treatment lasts for 5 to 15 minutes. The vacuum degree is below 0.030kPa, and the flow rate of the vacuum driving gas argon is controlled in the range of 155-165m 3 / h, adding aluminum particles for deoxidation, and measuring the temperature and oxygen content of the molten steel after vacuum treatment for 15 minutes; In the third stage, the vacuum treatment time is 0, and the vacuum treatment lasts for 15 to 30 minutes. The vacuum degree is below 0.020 kPa, and the flow rate of the vacuum driving gas argon is controlled in the range of 185-195 m 3 / h, after adding aluminum particles in vacuum, measure the temperature and oxygen content of the molten steel, circulate for 4 minutes, add manganese iron alloy, niobium iron alloy, titanium iron alloy, boron iron alloy to the molten steel, and meet the requirements of effective carbon C 有效 =C+0.02*Mn-0.1*Si-0.1*Nb-0.7*S-0.02*P, effective carbon C 有效 The content meets 0.0020 to 0.0050 weight percent; S4) Continuous casting → slab heating → rolling → cooling → coiling → pickling and cold rolling → continuous annealing → electrogalvanizing.

2. The steelmaking method of electrogalvanized bake hardening steel with a yield strength of 220 MPa according to claim 1, characterized in that: In S3), the preparation work before the first stage of treatment includes: taking samples at the station, measuring the initial temperature T0 and initial oxygen content [O]0 of the molten steel, analyzing the initial carbon content [C] 始 .

3. The steelmaking method of electrogalvanized bake hardening steel with a yield strength of 220 MPa according to claim 2, characterized in that: S3) in, judge whether to need to add ferrophosphorus in the first stage by the following method: When the phosphorus content in molten steel meets 0.028-0.048 parts by weight, no ferrophosphorus is added; When the phosphorus content in the molten steel is lower than 0.028 parts by weight, 0.042 kg / ts of ordinary ferrophosphorus is added for every 0.001 parts by weight increase in phosphorus content in the molten steel.

4. The steelmaking method of electrogalvanized bake hardening steel with a yield strength of 220 MPa according to claim 1, characterized in that: In S3), the weight of the aluminum particles added in the second stage is calculated by the following formula: Q 铝粒 =[(1.125%[O] 脱碳终点 +[Als] 目标 %)*W 钢水量 ] / (R*η*W 钢水量 ) Where, Q 铝粒 is the amount of aluminum particles added, unit: kg / ts, [O] 脱碳终点 is the oxygen content of molten steel at the end point of RH decarburization, ppm, [Als] 目标 is the target composition of Als in molten steel, W 钢水量 is the amount of molten steel, R is the yield of Al in aluminum particles, η is the Al content in the aluminum particles.

5. The steelmaking method of electro-galvanized bake-hardening steel with a yield strength of 220 MPa according to claim 1, characterized in that: In S3), when adding ferromanganese alloy to molten steel, first, a trace amount of carbon is added to the molten steel to make the carbon content meet the requirements. Medium carbon ferromanganese is used, and the amount of medium carbon ferromanganese added is calculated by the following formula: Q 中碳锰铁 =([C] RH目标 -[C] 脱碳终点 )*W 钢水量 *10 / W 钢水量 *W 中碳锰铁含碳量 *100 Where, Q 中碳锰铁 The addition amount of medium carbon ferromanganese, unit is kg / ts, [C] RH目标 is the target carbon content in molten steel at the end of RH vacuum, [C] 脱碳终点 is the carbon content of molten steel at the end point of RH decarburization, W 钢水量 is the amount of molten steel, W 中碳锰铁含碳量 is the carbon content of medium carbon ferromanganese; Secondly, in order to increase the Mn content in the molten steel to 0.45-0.65 weight percent, low-carbon manganese metal is used. The amount of low-carbon manganese metal added is calculated by the following formula: 低碳金属锰 =(Mn 目标 -Mn 初始 -Mn 中碳锰铁增Mn量 )*W 钢水量 *10 / W 钢水量 *(100*W 低碳金属锰含Mn量 *R 低碳金属锰Mn收得率 ) Where, Q 低碳金属锰 is the amount of low carbon manganese metal added, unit is kg / ts, Mn 目标 is the target Mn content in molten steel at the end of RH vacuum, Mn 初始 is the initial Mn content of RH, Mn 中碳锰铁增Mn量 To increase the Mn content in molten steel when adding medium carbon ferromanganese, W 钢水量 is the amount of molten steel, W 低碳金属锰含Mn量 To increase the Mn content in molten steel when adding low-carbon metallic manganese, R 低碳金属锰Mn收得率 is the yield of Mn in low-carbon metallic manganese.

6. The steelmaking method of electrogalvanized bake hardening steel with a yield strength of 220 MPa according to claim 5, characterized in that: In S3), when adding niobium iron alloy to the molten steel, the Nb content in the molten steel is 0.006 to 0.011 weight percent; and the effective carbon C is 有效 =C+0.02*Mn-0.1*Si-0.1*Nb-0.7*S-0.02*P, effective carbon C 有效 The content meets 0.0020-0.0050 weight percent; the amount of niobium iron alloy added is calculated by the following formula Q 铌铁 =Nb 目标 *W 钢水量 *10 / W 钢水量 *(100*W 铌铁含Nb量 *R 铌铁Nb收得率 ) Where, Q 铌铁 is the amount of ferroniobium added, in kg / ts, Nb 目标 is the target Nb content in molten steel at the end of RH vacuum, W 钢水量 is the amount of molten steel, W 铌铁含Nb量 To increase the Nb content in molten steel when adding ferroniobium alloy, R 铌铁Nb收得率 is the yield of Nb in ferroniobium alloy.

7. The steelmaking method of electrogalvanized bake hardening steel with a yield strength of 220 MPa according to claim 6, characterized in that: In S3), when adding ferrotitanium alloy to molten steel, the Ti content in the molten steel is 0.001 to 0.005 weight percent, and the amount of ferrotitanium alloy added is calculated by the following formula: Q 钛铁 =Ti 目标 *W 钢水量 *10 / W 钢水量 *(100*W 钛铁含Ti量 *R 钛铁Ti收得率 ) Where, Q 钛铁 is the addition amount of titanium-iron alloy, unit is kg / ts, Ti 目标 is the target Ti content in molten steel at the end of RH vacuum, W 钢水量 is the amount of molten steel, W 钛铁含Ti量 To increase the Ti content in molten steel when adding ferro-titanium alloy, R 钛铁Ti收得率 is the yield of Ti in ferrotitanium alloy.

8. The steelmaking method for electrogalvanized bake hardening steel with a yield strength of 220 MPa according to claim 7, characterized in that: In S3), when adding ferroboron alloy to molten steel, the B content in the molten steel is 0.0005 to 0.0015 weight percent, and the amount of ferroboron alloy added is calculated by the following formula: Q 硼铁 =B 目标 *W 钢水量 *10 / W 钢水量 *(100*W 硼铁含B量 *R 硼铁B收得率 ) Where, Q 硼铁 is the amount of ferroboron alloy added, unit: kg / ts, B 目标 is the target B content in molten steel at the end of RH vacuum, W 钢水量 is the amount of molten steel, W 硼铁含B量 To increase the B content in molten steel when adding ferroboron alloy, R 硼铁B收得率 is the yield of B in ferroboron alloy.

9. The steelmaking method of electro-galvanized bake hardening steel with a yield strength of 220 MPa according to claim 1, characterized in that: The weight percentages of the yield strength 220 MPa grade electro-galvanized bake hardening steel product are as follows: C content 0.0011-0.0022 weight parts, Si content ≤0.030 weight parts, Mn content 0.45-0.65 weight parts, P content 0.028-0.048 weight parts, S content ≤0.010 weight parts, Als content 0.020-0.050 weight parts, Nb content 0.006-0.011 weight parts, Ti content 0.001-0.005 weight parts, B content 0.0005-0.0015 weight parts, N content ≤0.0030 weight parts, and the effective carbon C is set at ...≤0.0011-0.0022 weight parts, Mn content ≤0.030 weight parts, 有效 =C+0.02*Mn-0.1*Si-0.1*Nb-0.7*S-0.02*P, and effective carbon C 有效 The content is 0.0020-0.0050 parts by weight, and the balance is Fe and inclusions; The yield strength of the 220MPa grade electro-galvanized bake-hardened steel product is 220-270MPa, the tensile strength is 340-380MPa, the hardening value is 30-50MPa, and the elongation is ≥35%.

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